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Träfflista för sökning "WFRF:(Gao Feng 1981 ) "

Sökning: WFRF:(Gao Feng 1981 )

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1.
  • 2019
  • Tidskriftsartikel (refereegranskat)
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2.
  • Fan, Qunping, et al. (författare)
  • Unidirectional Sidechain Engineering to Construct Dual-Asymmetric Acceptors for 19.23 % Efficiency Organic Solar Cells with Low Energy Loss and Efficient Charge Transfer
  • 2023
  • Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 62:36
  • Tidskriftsartikel (refereegranskat)abstract
    • Achieving both high open-circuit voltage (V-oc) and short-circuit current density (J(sc)) to boost power-conversion efficiency (PCE) is a major challenge for organic solar cells (OSCs), wherein high energy loss (E-loss) and inefficient charge transfer usually take place. Here, three new Y-series acceptors of mono-asymmetric asy-YC11 and dual-asymmetric bi-asy-YC9 and bi-asy-YC12 are developed. They share the same asymmetric D(1)AD(2) (D-1=thieno[3,2-b]thiophene and D-2=selenopheno[3,2-b]thiophene) fused-core but have different unidirectional sidechain on D-1 side, allowing fine-tuned molecular properties, such as intermolecular interaction, packing pattern, and crystallinity. Among the binary blends, the PM6 : bi-asy-YC12 one has better morphology with appropriate phase separation and higher order packing than the PM6 : asy-YC9 and PM6 : bi-asy-YC11 ones. Therefore, the PM6 : bi-asy-YC12-based OSCs offer a higher PCE of 17.16 % with both high V-oc and J(sc), due to the reduced E-loss and efficient charge transfer properties. Inspired by the high V-oc and strong NIR-absorption, bi-asy-YC12 is introduced into efficient binary PM6 : L8-BO to construct ternary OSCs. Thanks to the broadened absorption, optimized morphology, and furtherly minimized E-loss, the PM6 : L8-BO : bi-asy-YC12-based OSCs achieve a champion PCE of 19.23 %, which is one of the highest efficiencies among these annealing-free devices. Our developed unidirectional sidechain engineering for constructing bi-asymmetric Y-series acceptors provides an approach to boost PCE of OSCs.
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3.
  • Ji, Fuxiang, 1991- (författare)
  • Bandgap Engineering of Lead-Free Halide Double Perovskites
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lead-free halide double perovskites (HDPs, A2BIBIIIX6) with attractive optical and electronic features are regarded as one of the most promising alternatives to overcome the toxicity and stability issues of lead halide perovskites. They provide a wide range of possible combinations and rich substitutional chemistry with interesting properties for various optoelectronic devices. However, the performance of state-of-the-art lead-free HDPs is not yet comparable to that of lead halide perovskites, especially in the photovoltaic field. One of the main reasons for this is that HDPs usually have large and/or indirect bandgaps, which limit their optical and optoelectronic properties in the visible and infrared region. In this thesis, we attempt to modify the bandgap and optical properties of HDPs using metal doping/alloying and crystallization control, as well as provide detailed understanding of the alloying at the atomic level. We also observe significant changes of the bandgap of HDPs at different temperatures (i.e., thermochromism) and uncover the reasons behind it. We first adopt the metal doping/alloying strategy to alter the absorption properties of benchmark HDPs Cs2AgBiBr6. By introducing Cu as the dopant in Cs2AgBiBr6, we significantly broaden the absorption edge from around 610 nm to around 860 nm. Systematic characterizations indicate that Cu doping introduces defect states (sub-bandgap states) in the bandgap, without changing the bandgap of Cs2AgBiBr6. Interestingly, these sub-bandgaps can generate considerable amount of band carriers upon optical excitation, making these double perovskites promising for near-infrared light detection. In parallel with the material modification using the metal doping/alloying strategy, the fundamental understanding of these doped/alloyed double perovskite is also of critical importance. In the second paper, we reveal the atomic-level structure of alloyed double perovskites by presenting a series of double perovskite alloys with the chemical formula Cs2AgIn1-xFexCl6 (x = 0-1) showing tunable bandgaps in the range of 2.8-1.6 eV. Our results show that Fe3+ substitutes In3+ in the lattice with the formation of [FeCl6]3−·[AgCl6]5− domains, which grow larger gradually as the Fe3+ concentration increases. It is noted that these domains could be further connected to form microscopically segregated Fe3+-rich phases in the double perovskite alloys. To narrow the bandgap of Cs2AgBiBr6, we also develop a crystallization control approach, where high temperature is employed to assist the single crystal growth. By simply increasing the crystal growth temperature from 60 oC to 150 oC, the bandgap of Cs2AgBiBr6 crystals can be reduced from 1.98 eV to 1.72 eV, which is the lowest reported bandgap for Cs2AgBiBr6 at ambient conditions. The underlying reason is hypothesized to be related to the increased level of Ag–Bi disorder in the crystal structure. Lastly, we observe an interesting reversible thermochromic behavior in HDPs Cs2NaFeCl6. Specifically, the optical bandgap of Cs2NaFeCl6 is reduced from 2.06 eV to 1.86 eV when the temperature increases from RT to 150 oC and turns back to its original value after cooling. Meanwhile, we observe lattice expansion during the heating/ cooling process without phase transition. Our first-principles calculation indicates that the underlying mechanism for the thermochromic phenomenon in Cs2NaFeCl6 is mainly related to the electron-phonon coupling. Although the development of HDPs is in its early stages, we believe that HDPs with impressive optical and electronic properties and rich substitutional chemistry have a bright future in optoelectronic and multifunctional applications. Our findings shed new light to the absorption and bandgap modulation of HDPs and provide new insights into the atomic-level structures of DPAs, which can help to develop efficient optoelectronic devices. 
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4.
  • Ji, Fuxiang, 1991-, et al. (författare)
  • Challenges and Progress in Lead-Free Halide Double Perovskite Solar Cells
  • 2023
  • Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 7:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Lead-free halide double perovskites (HDPs) with a chemical formula of A(2)B(+)B(3+)X(6) are booming as attractive alternatives to solve the toxicity issue of lead-based halide perovskites (APbX(3)). HDPs show excellent stability, a wide range of possible combinations, and attractive optoelectronic features. Although a number of novel HDPs have been studied, the power conversion efficiency of the state-of-the-art double perovskite solar cell is still far inferior to that of the dominant Pb-based ones. Understanding the fundamental challenges is essential for further increasing device efficiency. In this review, HDPs with attractive electronic and optical properties are focused on, and current challenges in material properties and device fabrication that limit high-efficiency photovoltaics are analyzed. Finally, the promising approaches and views to overcome these bottlenecks are highlighted.
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5.
  • Ji, Fuxiang, 1991-, et al. (författare)
  • Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl6
  • 2023
  • Ingår i: Advanced Optical Materials. - : Wiley-Blackwell. - 2162-7568 .- 2195-1071.
  • Tidskriftsartikel (refereegranskat)abstract
    • Lead-free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light-yellow to black over a temperature range of 10 to 423 K is investigated. First-principles, density functional theory (DFT)-based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron–phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK−1 based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group-IV, III–V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials.
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6.
  • Ji, Fuxiang, 1991-, et al. (författare)
  • Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl6
  • 2024
  • Ingår i: Advanced Optical Materials. - : John Wiley & Sons. - 2162-7568 .- 2195-1071. ; 12:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Lead-free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light-yellow to black over a temperature range of 10 to 423 K is investigated. First-principles, density functional theory (DFT)-based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron-phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK(-1) based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group-IV, III-V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials.
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7.
  • Ma, Ruijie, et al. (författare)
  • All-polymer solar cells with over 16% efficiency and enhanced stability enabled by compatible solvent and polymer additives
  • 2022
  • Ingår i: Aggregate. - : Wiley. - 2692-4560 .- 2766-8541. ; 3:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Considering the robust and stable nature of the active layers, advancing the power conversion efficiency (PCE) has long been the priority for all-polymer solar cells (all-PSCs). Despite the recent surge of PCE, the photovoltaic parameters of the state-of-the-art all-PSC still lag those of the polymer:small molecule-based devices. To compete with the counterparts, judicious modulation of the morphology and thus the device electrical properties are needed. It is difficult to improve all the parameters concurrently for the all-PSCs with advanced efficiency, and one increase is typically accompanied by the drop of the other(s). In this work, with the aids of the solvent additive (1-chloronaphthalene) and the n-type polymer additive (N2200), we can fine-tune the morphology of the active layer and demonstrate a 16.04% efficient all-PSC based on the PM6:PY-IT active layer. The grazing incidence wide-angle X-ray scattering measurements show that the shape of the crystallites can be altered, and the reshaped crystallites lead to enhanced and more balanced charge transport, reduced recombination, and suppressed energy loss, which lead to concurrently improved and device efficiency and stability.
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8.
  • Wang, Feng, et al. (författare)
  • Defects engineering for high-performance perovskite solar cells
  • 2018
  • Ingår i: npj Flexible Electronics. - : Nature Publishing Group. - 2397-4621. ; 2:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Metal halide perovskites have achieved great success in photovoltaic applications during the last few years. The solar to electrical power conversion efficiency (PCE) of perovskite solar cells has been rapidly improved from 3.9% to certified 22.7% due to the extensive efforts on film deposition methods, composition and device engineering. Further investigation on eliminating the defect states in perovskite absorbers is necessary to push forward the PCE of perovskite solar cells approaching the Shockley-Queisser limit. In this review, we summarize the defect properties in perovskite films and present methodologies to control the defects density, including the growth of large size crystals, photo-curing method, grain boundary and surface passivation, and modification of the substrates. We also discuss the defects-related stability and hysteresis issues and highlight the current challenges and opportunities in defects control of perovskite films.
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9.
  • Wang, Feng, 1983-, et al. (författare)
  • Fundamentals of solar cells and light-emitting diodes
  • 2019
  • Ingår i: Advanced nanomaterials for solar cells and light emitting diodes. - Amsterdam : Elsevier. - 9780128136478 ; , s. 1-35
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • This chapter focuses on introducing basic concepts in solar cell and light-emitting diode (LED) devices. First, the fundamental knowledge about semiconductors and several important materials related to solar cells and LEDs is introduced to help the reader understand the working principle of devices. Second, we describe the working principle and basic terms involving solar cells, the energy loss processes, and several strategies for high-efficiency solar cell devices. Finally, we present the basic terms and the device structure of LEDs, as well as some approaches for high-efficiency white LEDs.
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10.
  • Wang, Heyong, 1989-, et al. (författare)
  • Impacts of the Lattice Strain on Perovskite Light-Emitting Diodes
  • 2023
  • Ingår i: Advanced Energy Materials. - : Wiley-V C H Verlag GMBH. - 1614-6832 .- 1614-6840. ; 13:33
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of perovskite light-emitting diodes (PeLEDs) with both high efficiency and excellent stability remains challenging. Herein, a strong correlation between the lattice strain in perovskite films and the stability of resulting PeLEDs is revealed. Based on high-efficiency PeLEDs, the device lifetime is optimized by rationally tailoring the lattice strain in perovskite films. A PeLED with a high peak external quantum efficiency of 18.2% and a long lifetime of 151 h (T-70, under a current density of 20 mA cm(-2)) is realized with a minimized lattice strain in the perovskite film. In addition, an increase in the lattice strain is found during the long-time device stability test, indicating that the degradation of the local perovskite lattice structure could be one of the degradation mechanisms for long-term stable PeLEDs.
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11.
  • Argillander, Joakim, et al. (författare)
  • Quantum random number generation based on a perovskite light emitting diode
  • 2023
  • Ingår i: Communications Physics. - : NATURE PORTFOLIO. - 2399-3650. ; 6:1
  • Tidskriftsartikel (refereegranskat)abstract
    • True random number generation is not thought to be possible using a classical approach but by instead exploiting quantum mechanics genuine randomness can be achieved. Here, the authors demonstrate a certified quantum random number generation using a metal-halide perovskite light emitting diode as a source of weak coherent polarisation states randomly producing an output of either 0 or 1. The recent development of perovskite light emitting diodes (PeLEDs) has the potential to revolutionize the fields of optical communication and lighting devices, due to their simplicity of fabrication and outstanding optical properties. Here we demonstrate that PeLEDs can also be used in the field of quantum technologies by implementing a highly-secure quantum random number generator (QRNG). Modern QRNGs that certify their privacy are posed to replace classical random number generators in applications such as encryption and gambling, and therefore need to be cheap, fast and with integration capabilities. Using a compact metal-halide PeLED source, we generate random numbers, which are certified to be secure against an eavesdropper, following the quantum measurement-device-independent scenario. The obtained generation rate of more than 10 Mbit s(-1), which is already comparable to commercial devices, shows that PeLEDs can work as high-quality light sources for quantum information tasks, thus opening up future applications in quantum technologies.
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12.
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13.
  • Bao, Qinye, et al. (författare)
  • Regular Energetics at Conjugated Electrolyte/Electrode Modifier for Organic Electronics and Their Implications of Design Rules
  • 2015
  • Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 2:12, s. 1-6
  • Tidskriftsartikel (refereegranskat)abstract
    • Regular energetics at a conjugated electrolyte/electrode modifier are found and controlled by equilibration of the Fermi level and an additional interface double dipole step induced by ionic functionality. Based on the results, design rules for conjugated electrolyte/electrode modifiers to achieve the smallest charge injection/exaction barrier and break through the current thickness limitation are proposed.
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14.
  • Bian, Qingzhen, 1988- (författare)
  • Excitonic and charge carrier transport in organic materials and device applications
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • With the potential for future commercial use, organic electronics have been intensively studied for the last few decades. To exploit the next generation of high-performance devices, detailed study of the underlying physics is essential. Excitonic and charge carrier transport plays a critical role in device performance and related studies have attracted a lot of attention in recent decades. This thesis particularly focused on excitonic and charge carrier transport in organic materials and related device applications.In natural light harvesting systems, such as the reaction centers of purple bacteria, quantum coherence has been proposed to be present as a contributor to the related charge and energy transport processes, and almost 100% charge conversion is present in these efficient biological systems. This high energy conversion efficiency inspires the idea that if a similar strategy was used in artificial energy conversion devices such as organic photovoltaics, etc., this could significantly enhance the device’s performance. In the first study, the charge separation process in some donor/acceptor blends was investigated. The contribution of quantum coherence to device performance was studied in detail using several steady state and ultrafast transient techniques. In one efficient donor/acceptor blend, a pronounced coherence of charge separation was identified, which contributed to the enhancement of the photocurrent generation, which finally resulted in efficient device performance.For the light emitting diodes, triplet excitons harvesting plays a critical role in device performance. In the thermally activated delayed fluorescence (TADF) materials, due to an efficient reverse intersystem process from triplet excitons to singlet excitons, the losses due to triplet excitons were suppressed. As a result, a desired high quantum yield has been achieved. To enhance device efficiency, the detailed study of the upconversion physics between triplet and singlet is needed. Previous studies have proposed some physical models to explain this efficient upconversion process, while the nature of this physical process is still under debate and unclear. In my second work, we studied the exciton kinetics in two different TADF materials. These TADF materials were inserted in a protein fibril host, and the resulting protein scaffold was able to modify the geometric configuration of the related TADF molecule. As a result, an enhancement of the photoluminescence quantum yield was achieved.To achieve efficient device performance in organic electronics, the physical processes at the metal/material interface and charge carrier injection/extraction, also play a critical role. Efficient charge injection can be achieved by Ohmic contact, and charge injection/extraction of metal/organic materials has been intensively studied in the last few decades. In my third study, an efficient hole transport material based on the biopolymer DNA was introduced. A hole doping process was found in the hybrid materials and contributes to the Ohmic contacts. The hybrid material can be used in different organic electronics devices, such as field effect transistors, light emitting diodes and solar cells, and thus demonstrates a general application capability.In organic photovoltaics, the loss from the open circuit photovoltages has been an Achilles’ heel for further enhancement of device performance. The voltage loss includes the radiative and non-radiative value, and intensive studies have focused on how to suppress losses from the non-radiative channel. In my fourth study, the non-radiative voltage loss was studied in a series of terpolymer blends and ternary blends. Compared to the ternary blends, a decreased nonradiative loss was found in the terpolymer blends. 
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15.
  • Cai, Weidong, 1991-, et al. (författare)
  • Chirality Induced Crystal Structural Difference in Metal Halide Composites
  • 2022
  • Ingår i: Advanced Optical Materials. - : Wiley-V C H Verlag GMBH. - 2162-7568 .- 2195-1071. ; 10:16
  • Tidskriftsartikel (refereegranskat)abstract
    • Incorporating chiral organic compounds into metal halide frames is a common and useful method to introduce chirality in metal halide composites. The structures of resulting racemic and chiral composites are usually considered to be nearly identical owing to similar chemical bonding. In this work, by incorporating chiral MBABr (bromide methylbenzylamine) into an inorganic frame, a significant crystallization difference between the resulting racemic and chiral metal halide composites is observed, as confirmed by both structural and spectroscopic measurements. In addition, the structural transformation in the chiral composites can also be induced by moisture, ascribed to the asymmetric hydrogen bonding in chiral materials. These results provide new insights for the future synthesis of chiral materials and open up new possibilities to advance the materials functionalities.
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16.
  • Cai, Weidong, 1991- (författare)
  • Tunning Multicolor Light Emission in Lead-free Materials
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Perovskites are a class of compounds with the general formula ABX3 and becoming increasingly attractive recently. Because this kind of material possesses various advantages such as abundant raw materials, easy synthesis, excellent photoelectric properties, and short production process. As one of the applications for lead-based perovskites, the perovskite solar cells have quickly enhanced their PCE from 3.8% in 2009 to over 25% within a short period. However, the problems, such as instability of the ionic crystal nature and toxicity of lead, largely hinder the lead-based perovskites towards commercialization. Therefore, it is necessary to develop new lead-free materials as alternative to lead-based perovskites, where similar structures can be formed to inherit the excellent optoelectronic properties. Moreover, new properties can be achieved due to more abundant metal candidates in lead-free materials. Based on this, we develop different kinds of perovskite-structure-like lead-free materials such as organic inorganic hybrid materials, chiral materials and double perovskites. In addition to physical and chemical properties like photoluminescence, absorption, structure, etc., we further demonstrate their potential applications according to their unique properties such as multicolor light emission.We incorporate chiral MBA (methylbenzylamine) in inorganic metal system to obtain chiral lead-free organic inorganic hybrid materials, where significant crystallization difference is observed between rac and chiral halide compounds for the first time. Such difference is confirmed by spectrum and structural results. What’s more, we find that moisture can cause the structural transfer in chiral compounds, attributed to the asymmetric hydrogen bonding of chiral compounds. Our achievements open up new chance to improve our material property and provide new horizon for synthesis of chiral materials in the future.Then, we obtained blue emission center in Mn-based organic and inorganic compounds by choosing organic molecule MBA. The method has basic difference with the emissions in Mn based compounds. The coexisting two emission centers of our Mn based samples is verified by spectral results. Because two emission centers can induce different PL excitation responses, so that the excitation wavelengths are capable of manipulating the emission color. Specifically, we achieve CIE coordinates of (0.33, 0.35) with a white emission. The potential of our materials in anti-counterfeiting and multicolor lighting technology are further demonstrated. Our accomplishments explore a new approach for multicolor emission in Mn based materials.We finally obtained Sb3+/Cu+ co-doped Cs2NaInCl6 (CNIC) double perovskite by hydrothermal reaction which exhibits tunable dual emissions with PL quantum efficiency (PLQE) of 78%. Depending on different photoluminescence excitation (PLE) spectra between two emissions, multiple emission colors can be got by manipulating excitation wavelength. Interestingly, emission color gamut can be further tuned through manipulating the feeding ratio of CuI dopant, where warm color and cool color can be achieved separately. We further illustrated the application potential of our co-doped materials in the fileds of multicolor lighting devices and anti-counterfeiting. Our achievements open up a brand-new strategy for wider spectral luminescence of double perovskites and pace up the road for a series of new applications.
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17.
  • Chen, Desui, et al. (författare)
  • Shelf-Stable Quantum-Dot Light-Emitting Diodes with High Operational Performance
  • 2020
  • Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 32
  • Tidskriftsartikel (refereegranskat)abstract
    • Quantum-dot light-emitting diodes (QLEDs) promise a new generation of high-performance, large-area, and cost-effective electroluminescent devices for both display and solid-state lighting technologies. However, a positive ageing process is generally required to improve device performance for state-of-the-art QLEDs. Here, it is revealed that the in situ reactions induced by organic acids in the commonly used encapsulation acrylic resin lead to positive ageing and, most importantly, the progression of in situ reactions inevitably results in negative ageing, i.e., deterioration of device performance after long-term shelf storage. In-depth mechanism studies focusing on the correlations between the in situ chemical reactions and the shelf-ageing behaviors of QLEDs inspire the design of an electron-transporting bilayer, which delivers both improved electrical conductivity and suppressed interfacial exciton quenching. This material innovation enables red QLEDs exhibiting neglectable changes of external quantum efficiency (>20.0%) and ultralong operational lifetime (T-95: 5500 h at 1000 nits) after storage for 180 days. This work provides design principles for oxide electron-transporting layers to realize shelf-stable and high-operational-performance QLEDs, representing a new starting point for both fundamental studies and practical applications.
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18.
  • Chen, Haoran, et al. (författare)
  • Decoupling engineering of formamidinium-cesium perovskites for efficient photovoltaics
  • 2022
  • Ingår i: National Science Review. - : Oxford University Press. - 2095-5138 .- 2053-714X. ; 9:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Sequential Cs incorporation strategy is developed to decouple crystallization of FACs perovskite with reduced electron-phonon coupling, resulting in highly stable FACs tri-iodide perovskite photovoltaics with record efficiency. Although pure formamidinium iodide perovskite (FAPbI(3)) possesses an optimal gap for photovoltaics, their poor phase stability limits the long-term operational stability of the devices. A promising approach to enhance their phase stability is to incorporate cesium into FAPbI(3). However, state-of-the-art formamidinium-cesium (FA-Cs) iodide perovskites demonstrate much worse efficiency compared with FAPbI(3), limited by the different crystallization dynamics of formamidinium and cesium, which result in poor composition homogeneity and high trap densities. We develop a novel strategy of crystallization decoupling processes of formamidinium and cesium via a sequential cesium incorporation approach. As such, we obtain highly reproducible, highly efficient and stable solar cells based on FA(1)(-)(x)Cs(x)PbI(3) (x = 0.05-0.16) films with uniform composition distribution in the nanoscale and low defect densities. We also revealed a new stabilization mechanism for Cs doping to stabilize FAPbI(3), i.e. the incorporation of Cs into FAPbI(3) significantly reduces the electron-phonon coupling strength to suppress ionic migration, thereby improving the stability of FA-Cs-based devices.
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19.
  • Chen, Zhan, et al. (författare)
  • Photoluminescence Enhancement for Efficient Mixed-Halide Blue Perovskite Light-Emitting Diodes
  • 2023
  • Ingår i: Advanced Optical Materials. - : WILEY-V C H VERLAG GMBH. - 2162-7568 .- 2195-1071. ; 11:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of highly efficient blue perovskite light-emitting diodes (PeLEDs) remains a big challenge, requiring more fundamental investigations. In this work, significant photoluminescence enhancement in mixed halide blue perovskite films is demonstrated by using a molecule, benzylphosphonic acid, which eventually doubles the external quantum efficiency to 6.3% in sky-blue PeLEDs. The photoluminescence enhancement is achieved by forming an oxide-bonded perovskite surface at grain boundaries and suppressing electron-phonon interaction, which enhances the radiative recombination rate and reduces the nonradiative recombination rate, respectively. Moreover, severe thermal quenching is observed in the blue perovskite films, which can be explained by a two-step mechanism involving exciton dissociation and electron-phonon interaction. The results suggest that enhancing the radiative recombination rate and reducing the electron-phonon interaction-induced nonradiative recombination rate are crucial for achieving blue perovskite films with strong emission at or above room temperature.
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20.
  • Cui, Yong, et al. (författare)
  • Accurate photovoltaic measurement of organic cells for indoor applications
  • 2021
  • Ingår i: Joule. - : CELL PRESS. - 2542-4351. ; 5:5, s. 1016-1023
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Photovoltaic (PV) cells offer a convenient energy source to drive micropower electronic devices for indoor applications. However, it is challenging to measure the power conversion efficiency (PCE) of PV cells under indoor lighting and the PV community lacks a feasible and accurate measurement protocol. Here, we start with the fundamental parameters which determine the PCE, and carefully design a series of experiments to examine the origins which might cause measurement errors for organic PV measurements under indoor lighting. We demonstrate the critical importance of: 1, temporal stability and spatial homogeneity of the light sources, 2, calibration of the spectral irradiance and illuminations of the light sources, 3, the area of the cells (1 cm2 or large cells are preferred), 4, the aperture of the mask (an aperture slightly smaller than the cell area is preferred), and 5, stray lights from the measurement environment. Based on these careful investigations, we suggest a feasible measurement method, by which accurate measurement of the indoor PV efficiency is made possible. Our study will promote the healthy development of indoor PV technology for practical applications.
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21.
  • Fan, Qunping, 1989, et al. (författare)
  • High-performance all-polymer solar cells enabled by a novel low bandgap non-fully conjugated polymer acceptor
  • 2021
  • Ingår i: Science in China Series B. - : Springer Nature. - 1674-7291 .- 1869-1870. ; 64, s. 1380-1388
  • Tidskriftsartikel (refereegranskat)abstract
    • Anon-fully conjugated polymer as a new class of acceptor materials has shown some advantages over its small molecular counterpart when used in photoactive layers for all-polymer solar cells (all-PSCs), despite a low power conversion efficiency (PCE) caused by its narrow absorption spectra. Herein, a novel non-fully conjugated polymer acceptor PFY-2TS with a low bandgap of similar to 1.40 eV was developed, via polymerizing a large pi-fused small molecule acceptor (SMA) building block (namely YBO) with a non-conjugated thioalkyl linkage. Compared with its precursor YBO, PFY-2TS retains a similar low bandgap but a higher LUMO level. Moreover, compared with the structural analog of YBO-based fully conjugated polymer acceptor PFY-DTC, PFY-2TS shows similar absorption spectrum and electron mobility, but significantly different molecular crystallinity and aggregation properties, which results in optimal blend morphology with a polymer donor PBDB-T and better device physical processes in all-PSCs. As a result, PFY-2TS-based all-PSCs achieved a PCE of 12.31% with a small energy loss of 0.56 eV enabled by the reduced non-radiative energy loss (0.24 eV), which is better than that of 11.08% for the PFY-DTC-based ones. Our work clearly demonstrated that non-fully conjugated polymers as a new class of acceptor materials are very promising for the development of high-performance all-PSCs.
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22.
  • Gao, Jingfang, 1966-, et al. (författare)
  • Association of NFKBIA polymorphism with colorectal cancer risk and prognosis in Swedish and Chinese populations
  • 2007
  • Ingår i: Scandinavian Journal of Gastroenterology. - : Informa UK Limited. - 0036-5521 .- 1502-7708. ; 42:3, s. 345-350
  • Tidskriftsartikel (refereegranskat)abstract
    • Objective. The inhibitory proteins, IκBs, regulate the activity of nuclear factor kappa-beta (NF-κB), which is implicated in tumorigenesis by regulating expression of a variety of genes involved in cellular transformation, proliferation, invasion, angiogenesis and metastasis. Variants in the genes encoding IκBs may be involved in cancer development through the activation of NF-κB. The objective of this study was to investigate the susceptibility of an A to G variation (rs696) in the 3′ UTR of NFKBIA (encoding IκBα) to colorectal cancer (CRC) and the association of this polymorphism with clinicopathologic variables in CRC patients. Material and methods. A case-control study was carried out on a Swedish (155 CRCs, 438 controls) and a Chinese population (199 CRCs, 577 controls). The genotype of NFKBIA was determined by PCR-restriction fragment length polymorphism. Results. The frequency of the AG genotype was increased in the Chinese patients ≥50 years of age compared with the Chinese controls (odds ratio (OR) = 3.06, 95% confidence interval (CI) = 1.55-6.02, p=0.001), even when adjusted for age (OR = 3.20, 95% CI = 1.61-6.38, p=0.001). The GG genotype of NFKBIA was related to a poorer survival rate in the Swedish patients, independent of gender, age, tumour location, Dukes' stage and differentiation (hazard ratio = 3.10, 95% Cl = 1.28-7.60, p=0.01). Conclusions. Chinese individuals ≥50 years of age carrying the AG genotype of NFKBIA may be at an increased risk of developing CRC, and the GG genotype of NFKBIA may be considered as a prognostic factor for Swedish CRC patients. © 2007 Taylor & Francis.
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23.
  • Hou, Jianhui, et al. (författare)
  • Organic solar cells based on non-fullerene acceptors
  • 2018
  • Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 17:2, s. 119-128
  • Forskningsöversikt (refereegranskat)abstract
    • Organic solar cells (OSCs) have been dominated by donor: acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.
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24.
  • Huang, Yuting, et al. (författare)
  • Host-Guest Strategy Enabling Nonhalogenated Solvent Processing for High-Performance All-Polymer Hosted Solar Cells
  • 2023
  • Ingår i: Chinese journal of chemistry. - : WILEY-V C H VERLAG GMBH. - 1001-604X .- 1614-7065. ; 41:9, s. 1066-1074
  • Tidskriftsartikel (refereegranskat)abstract
    • The power conversion efficiencies (PCEs) of all-polymer solar cells (all-PSCs), usually processed from low-boiling-point and toxic solvents, have reached high values of 18%. However, poor miscibility and uncontrollable crystallinity in polymer blends lead to a notable drop in the PCEs when using green solvents, limiting the practical development of all-PSCs. Herein, a third component (guest) BTO was employed to optimize the miscibility and enhance the crystallinity of PM6/PY2Se-F host film processed from green solvent toluene (TL), which can effectively suppress the excessive aggregation of PY2Se-F and facilitate a nano-scale interpenetrating network morphology for exciton dissociation and charge transport. As a result, TL-processed all-polymer hosted solar cells (all-PHSCs) exhibited an impressive PCE of 17.01%. Moreover, the strong molecular interaction between the host and guest molecules also enhances the thermal stability of the devices. Our host-guest strategy provides a unique approach to developing high-efficiency and stable all-PHSCs processed from green solvents, paving the way for the industrial development of all-PHSCs.
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25.
  • Joffrin, E., et al. (författare)
  • Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
  • 2019
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
  • Forskningsöversikt (refereegranskat)abstract
    • For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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26.
  • Karlsson, Max, 1990- (författare)
  • Dynamics in Blue Emitting Metal Halide Perovskites for Light Emitting Diodes
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lighting comprises a large part of the global electricity consumption as of today, and the use of lighting in illumination and displays is only projected to grow. It is therefore imperative to meet this energy demand, not only by means of greener energy production, but also with materials that are both more efficient to fabricate as well as to use. Low cost and energy efficient light sources therefore play an important role in minimizing further greenhouse emissions from the way we choose to live.Metal halide perovskites are a group of semiconductors that have received a great amount of attention during the past years due to impressive - and continuously increasing - performance as active materials implemented in solar cells and light emitting diodes. This is due to highly desirable optoelectronic properties combined with low-cost, solution-processable fabrication methods. Simple bandgap-tunability is easily achieved by compositional and dimensional engineering, allowing perovskite emission to span a broad wavelength region from ultraviolet to near infrared. As with previous technologies, attaining stable, bright, and pure blue light has proven difficult also in metal halide perovskites. This thesis investigates some of the challenges in achieving blue emission in mixed-halide and mixed-dimensional perovskites for light-emitting-diode applications.Mixed-halide alloying provides the most straightforward way of tuning the bandgap of perovskites. Unfortunately, mixed bromide/chloride-perovskites (used to achieve blue light) suffer from both spectral and temporal instabilities, as well as severe luminescence quenching at the large chloride contents necessary for blue emission. The spectral instability arises from a segregation of halides into regions of differing halide content, and hence different bandgap, resulting in a shift in emission color during operation. Although the origins of the poor temporal stability of perovskite light emitting diodes are manifold, one of the main problems are the low barriers for halide migration under the applied electric field during operation, rapidly degrading the device properties.We first find that compositional heterogeneities, stemming from rapid uncontrolled film growth, both lowers the threshold for further halide segregation as well as serves as centers for non-radiative recombination, resulting in reduced luminescence yield. We show that by carefully moderating the crystallization dynamics it is possible to achieve films with a homogeneous composition, thereby mitigating the negative effects arising from material inhomogeneities. We identify means of how growth environment, stoichiometric tuning and chelating additives can be used to favorably control film formation and provide guidelines that can be more widely applied in the fabrication of perovskite films and devices. We continue by investigating the role of Br/Cl-alloying on device efficiency and stability in green to blue emitting perovskite LEDs. We find that chloride incorporation, while having only a minor impact on efficiency at moderate levels, detrimentally affects device stability even in small amounts. We ascribe this phenomenon to an increased mobility of halogen ions in the mixed-halide lattice resulting from an increased chemically and structurally disordered landscape with reduced migration barriers. We assign this as the major obstacle towards stable blue-emitting mixed-halide perovskite light emitting diodes.In the last work we investigate blue emitting mixed-dimensional Ruddlesden-Popper perovskites (RPPs) comprising of multiple-quantum-well-structures of varying bandgap. Successful implementation in LEDs has been attributed to efficient carrier funneling from large bandgap (donor) regions to low bandgap regions (acceptors) resulting in improved luminescence yields due to trap state filling from the locally increased carrier density. However, due to the enhanced carrier concentrations in acceptor domains, Auger recombination quickly outcompetes radiative recombination mechanisms already at moderate pump fluences or carrier injection densities in RPPs. We show that by moderating the inter-well carrier transfer, while at the same time providing adequate defect passivation, high quantum yields can be maintained even at large carrier densities. We thereby show that RPPs can support a large density of carriers without compromising luminescence efficiency, paving the way for their use in high brightness applications by engineering the funneling and recombination processes in these materials.The work in this thesis provides new insights on various dynamical processes in metal halide perovskites aimed at light emitting applications. The hope is that it will contribute toward the understanding of these systems and help in bringing these materials closer to practical use.
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27.
  • Kuang, Chaoyang, 1988- (författare)
  • Interface-Assisted Perovskite Modulations for High-Performance Light-Emitting Diodes
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Metal halide perovskites have emerged as a class of promising materials for a wide range of optoelectronic devices. Compared with traditional inorganic and organic semiconductors, perovskite materials can be easily processed via solution-based techniques at low temperatures and exhibit high photo-luminescence efficiency, outstanding colour purity, and superior charge transport properties, showing great promise for cost-effective and high-performance light-emitting diodes (LEDs).Since the first demonstration of room-temperature operating perovskite-based LEDs (PeLEDs) in 2014, various useful strategies on optimizing perovskite emissive materials and device structures have been developed, leading to notably enhanced device performance of PeLEDs during the last several years. Nevertheless, despite rapid progress in improving the external quantum efficiencies (EQEs) of PeLEDs, which are now approaching those of commercialized technologies, the operational stability of state-of-the-art PeLEDs remains poor, presenting a critical challenge for their practical applications and commercialization. Besides, a majority of the optimization strategies demonstrated for PeLEDs derivate from those developed for either perovskite photovoltaics or prevailing light-emitting technologies, e.g., organic- and quantum-dot-based LEDs. Although these strategies are helpful, more comprehensive investigations and in-depth understanding of factors affecting the property of perovskite emissive layers and the device performance of ensuing PeLEDs are highly desirable to foster further advancements of this promising technology.In this thesis, we focus our study on near-infrared PeLEDs based on triiodide perovskite emissive layers processed from precursor solutions. We systematically investigate the critical effects of precursors, substrates, and additives on the film quality of perovskite emissive layers. With the indepth understanding of the perovskite crystallization process, we developed a range of effective interface-assisted strategies on modulating the perovskite emissive layers, which enable us to achieve PeLEDs with high EQEs and excellent long-term operational stability beyond the state-of-the-art.In the first study, we unveiled the synergistic effect of precursor stoichiometry and interfacial reactions for PeLEDs. We reveal that ZnO efficiently deprotonates the organic cations, which promotes the formation of highly emissive perovskites from precursor solution with excess organic components, leading to the achievement of PeLEDs with a high EQE of 19.6 %. In the second study, we presented that such ZnO deprotonation process of excess organic cations can also assist the cation exchange process between cesium-formamidinium (FA-Cs) cation exchange, enabling low-temperature fabrication of pure-phase Cs-FA mixed cation perovskite films with widely tunable emissions peaking between 715 nm and 800 nm as well as high-performance devices with peak EQEs over 15%.In spite of enhanced device efficiency realized by the perovskite crystallization modulation, this ZnO deprotonation process places a detrimental effect on the stability of the PeLEDs, which can be accelerated by Joule heating and high electric fields during the device operation. In the third study, we, therefore, demonstrated the role of ZnO in catalyzing an efficient amidation reaction between incorporated dicarboxylic acid additives and excess FAI, preventing the above-mentioned harmful interfacial reaction. With this strategy, the operational half lifetime of the resulting PeLEDs was improved to 682 hours at 20 mA/cm2 while maintaining a high device efficiency of 18.6%.In the last work, we emphasized that the rational design of molecular reactions between two additives (diamine and triacrylate) and perovskite components with the assistance of ZnO substrates can subsequently eliminate the negative effect introduced by additive, reduce the defect density and enhance the crystal orientation in the perovskite emissive layers. The rational understanding of interfacial interactions between perovskite, additives, and ZnO, enabled us to achieve PeLEDs with a device efficiency of 23.8% as well as an outstanding operational stability T70 (reduction to 70% of initial efficiency) lifetime of 290 hours at 20 mA/cm2.The study in this thesis developed effective interface-assisted modulation strategies for high-quality perovskites towards highly efficient and stable PeLEDs for commercialization. A thorough understanding of perovskite chemistry-property-performance modulation assisted by interfaces is indispensable for the future development of PeLEDs and our study took an important step.
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28.
  • Kumawat, Naresh Kumar, et al. (författare)
  • Mobile ions determine the luminescence yield of perovskite light-emitting diodes under pulsed operation
  • 2021
  • Ingår i: Nature Communications. - : NATURE PORTFOLIO. - 2041-1723. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The external quantum efficiency of perovskite light-emitting diodes (PeLEDs) has advanced quickly during the past few years. However, under pulsed operation, an operation mode which is important for display and visible light communication, the performance of PeLEDs changes a lot and requires in-depth understanding to facilitate these applications. Here, we report the response of PeLEDs under pulsed operation in the range of 10 Hz to 20 kHz. Beyond transient effects in the low frequencies, we find that for higher frequencies (>500 Hz) the transient electroluminescence intensity depends strongly on the duty cycle. This feature is much more pronounced and of different origin than that in conventional LEDs. We rationalise our experimental observations using a mathematical model and assign these features to the effect of mobile ionic charges in the perovskite. Our work also provides important implications for the operation of PeLEDs under the steady state, where accumulation of mobile ions at the interfaces could be beneficial for high electroluminescence yields but harmful for the long-term stability. 
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29.
  • Li, Yaokai, et al. (författare)
  • Mechanism study on organic ternary photovoltaics with 18.3% certified efficiency: from molecule to device
  • 2022
  • Ingår i: Energy & Environmental Science. - : ROYAL SOC CHEMISTRY. - 1754-5692 .- 1754-5706. ; 15:2, s. 855-865
  • Tidskriftsartikel (refereegranskat)abstract
    • Multi-component organic photovoltaics (OPVs), e.g., ternary blends, are effective for high performance, while the fundamental understanding from the molecular to device level is lacking. To address this issue, we here systematically study the working mechanism of ternary OPVs based on non-fullerene acceptors (NFAs). With both molecular dynamics simulations and morphology characterization, we identify that when adding another larger band gap and highly miscible NFA, namely IT-4F or BTP-S2, into the PBDB-TF:BTP-eC9 blend, the NFAs undergo molecular intermixing selectively with BTP-eC9. This causes the composition-dependent band gap and charge recombination, and hence the composition-dependent V-OC. While the charge recombination still dominantly occurs at the PBDB-TF:BTP-eC9 interface, BTP-S2 or IT-4F plays an auxiliary role in facilitating charge transfer and suppressing non-radiative decay. Interestingly, intermolecular end-group packing in the intermixed blend is improved compared to that in pristine films, leading to higher carrier mobility. These synergistic effects significantly improve the power conversion efficiency of the device to an outstanding value of 18.7% (certified value of 18.3%).
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30.
  • Liu, Wei, et al. (författare)
  • A-pi-A structured non-fullerene acceptors for stable organic solar cells with efficiency over 17%
  • 2022
  • Ingår i: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 65:7, s. 1374-1382
  • Tidskriftsartikel (refereegranskat)abstract
    • With the development of photovoltaic materials, especially the small molecule acceptors (SMAs), organic solar cells (OSCs) have made breakthroughs in power conversion efficiencies (PCEs). However, the stability of high-performance OSCs remains a critical challenge for future technological applications. To tackle the inherent instability of SMA materials under the ambient conditions, much effort has been made to improve OSCs stability, including device modification and new materials design. Here we proposed a new electron acceptor design strategy and developed a "quasi-macromolecule" (QM) with an A-pi-A structure, where the functionalized pi-bridge is used as a linker between two SMAs (A), to improve the long-term stability without deteriorating device efficiencies. Such type of QMs enables excellent synthetic flexibility to modulate their optical/electro-chemical properties, crystallization and aggregation behaviors by changing the A and pi units. Moreover, QMs possess a unique long conjugated backbone combining high molecular weight over 3.5 kDa with high purity. Compared with the corresponding SMA BTP-4F-OD (Y6-OD), the devices based on newly synthesized A-pi-A type acceptors QM1 and QM2 could exhibit better device stability and more promising PCEs of 17.05% and 16.36%, respectively. This kind of "molecular-framework" (A-pi-A) structure provides a new design strategy for developing high-efficiency and -stability photovoltaic materials.
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31.
  • Liu, Wei, et al. (författare)
  • Manipulating molecular aggregation and crystalline behavior of A-DAD-A type acceptors by side chain engineering in organic solar cells
  • 2022
  • Ingår i: Aggregate. - : Wiley. - 2692-4560. ; 3:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Alkyl chains engineering plays an important role in photovoltaic materials for organic solar cells. Herein, three A-DAD-A (acceptor-donor-acceptor-donor-acceptor) type acceptors named Y6, Y6-C4, and Y6-C5 with different branching position on the pyrrole motif are discussed and the relationship between molecular aggregation, crystalline, and device performance are systematically investigated. The distance between the branching position and the main backbone affects their optical absorption and energy levels. Y6-C4 and Y6-C5 with the branching position at the fourth and fifth carbon of the alkyl chain show blue-shifted absorption and increased electrochemical bandgaps, compared with Y6 with the branching position at the second carbon of the alkyl side chain. In addition, this distance influences the molecular aggregation and crystalline behavior of the donor/acceptor blends. Compared with Y6-C4, Y6-C5 possesses a stronger crystalline and aggregate ability in the blends with a lower non-radiative energy loss, which results in a higher open circuit voltage (V-oc) of 0.88 V. Finally, Y6-C5-based binary device achieved a high power conversion efficiency up to 16.73% with afill factor (FF) of 0.78. These results demonstrate that the side chain engineering is an effective strategy for tuning the molecular aggregation and crystalline to improve photovoltaic performance of the A-DAD-A type acceptors.
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32.
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33.
  • Mopoung, Kunpot, et al. (författare)
  • Understanding Antiferromagnetic Coupling in Lead-Free Halide Double Perovskite Semiconductors
  • 2024
  • Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 128:12, s. 5313-5320
  • Tidskriftsartikel (refereegranskat)abstract
    • Solution-processable semiconductors with antiferromagnetic (AFM) order are attractive for future spintronics and information storage technology. Halide perovskites containing magnetic ions have emerged as multifunctional materials, demonstrating a cross-link between structural, optical, electrical, and magnetic properties. However, stable optoelectronic halide perovskites that are antiferromagnetic remain sparse, and the critical design rules to optimize magnetic coupling still must be developed. Here, we combine the complementary magnetometry and electron-spin-resonance experiments, together with first-principles calculations to study the antiferromagnetic coupling in stable Cs-2(Ag:Na)FeCl6 bulk semiconductor alloys grown by the hydrothermal method. We show the importance of nonmagnetic monovalence ions at the B-I site (Na/Ag) in facilitating the superexchange interaction via orbital hybridization, offering the tunability of the Curie-Weiss parameters between -27 and -210 K, with a potential to promote magnetic frustration via alloying the nonmagnetic B-I site (Ag:Na ratio). Combining our experimental evidence with first-principles calculations, we draw a cohesive picture of the material design for B-site-ordered antiferromagnetic halide double perovskites.
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34.
  • Peng, Zuosheng, et al. (författare)
  • A dual ternary system for highly efficient ITO-free inverted polymer solar cells
  • 2015
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 3:36, s. 18365-18371
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, it has been found that a very fine nanostructure can be realized by mixing 1-chloronaphthalene (CN) - a high-boiling solvent into a binary chlorobenzene (CB) : 1,8-diiodooctane (DIO) solvent mixture to form a ternary solvent system. An improvement in energy level alignment is also obtained by doping ICBA into a binary PTB7 : PCBM[70] blend, whereby the ternary solute system provides a new pathway for charge transfer from PTB7 to the PCBM[ 70] : ICBA alloy. This is confirmed by imaging the surface morphology of the active layer using AFM and TEM, monitoring the transient film formation process and measuring the charge transfer states with Fourier transform photocurrent spectroscopy. An encouraging PCE of 7.65% is achieved from the dual ternary system, which is the highest value ever reported for an ITO-free inverted polymer solar cell with a PEDOT:PSS layer as the top semitransparent electrode - a system which is compatible with low-cost large-area roll-to-roll manufacturing.
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35.
  • Qi, Zhenyu, et al. (författare)
  • Blueshifting the Absorption of a Small -Molecule Donor and Using it as the Third Component to Achieve High-Efficiency Ternary Organic Solar Cells
  • 2022
  • Ingår i: Solar RRL. - : WILEY-V C H VERLAG GMBH. - 2367-198X. ; 6:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Adding a small-molecule donor (SMD) to state-of-the-art nonfullerene organic solar cells (OSCs) is demonstrated as a useful strategy to construct ternary organic solar cells, as SMDs typically have high crystallinity and can tune charge transport properties of OSCs. However, the absorption of most SMDs overlaps with typical donor polymers (e.g., PM6), which is against the general guidelines of adopting materials with complementary absorption in ternary OSCs. Herein, the absorption of state-of-art SMDs (BTR-CI) by linking the beta position of the outer thiophene to the alpha position of the inner thiophene unit is intentionally blueshifted. The resulting molecule beta-S1 shows a maximum absorption peak at 505 nm in the film state, which exhibits wider bandgap and shows complementary absorption with the host system (PM6:Y6). The corresponding ternary OSCs with 20%wt beta-S1 show significantly enhanced efficiency from 16.2% to 17.1% due to the increased short-circuit current (J(sc)) and improved fill factor (FF). Herein, an effective strategy to design SMDs with both wider bandgaps and higher crystallinity for high-performance ternary OSCs is presented.
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36.
  • Qian, Deping (författare)
  • Studies of Voltage Losses in Organic Solar Cells
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Organic photovoltaic (OPV) devices based on semiconducting polymers and small molecules are potential alternatives to inorganic solar cells, owing to their advantages of being inexpensive, lightweight, flexible and suitable for roll-to-roll production. The state of art organic solar cells (OSCs) performed power conversion efficiencies (PCEs) over 13%.The quantum efficiency losses in OSCs have been significantly reduced within the charge generation and extraction processes, resulting in high EQEPV (70-90%) and high FF (70-80%). Whereas, large voltage losses (Δ? = ??/? − ???) were observed in conventional fullerene based solar cells, and it has been the main limiting factor for further OPV advancement. Therefore, strategies to reduce the voltage losses are required.In this thesis, newly designed non-fullerene (NF) acceptors are used to construct novel material systems for high efficiency solar cells. In particular, we studied the hole transfer in these fullerene free systems. We also reported a NF system that exhibit ultrafast and efficient charge separation despite a negligible driving force, as ECT is nearly identical to ??. Moreover, the small driving force is found to have minimal detrimental effects on charge transfer dynamics of the OSCs. We demonstrate a NF based OSC with efficiency of 9.5% and internal quantum efficiency nearly 90% despite a low voltage loss of 0.61 V. This creates a path towards highly efficient OSCs with a low voltage loss.CT states in OSCs are also investigated, since VOC is governed by the CT energy (ECT), which is found as ???? = ??? − 0.6 in a large set of fullerene based solar cells. In order to reduce these recombination losses from CT states, we explored polymer-diPDI systems which exhibited weakened D-A coupling strength, due to the steric hindrance effect. The radiative recombination losses at D/A interface in these NF devices are all reduced to less than 0.18 eV. In particular, in some cases, the additional emission from pure material is favorable for suppressing the non-radiative CT states decay. Consequently, the recombination losses in these NF systems are reduced to 0.5 eV, while the charge generation is still efficient as confirmed by PL quenching and EQEPV.Novel material systems based on non-fullerene acceptors are investigated. The systems performed energy offsets (ΔHOMO or ΔLUMO) less than 0.15eV, resulting in the same energy of CT states and bulk excitons. In this regard, the charge transfer energy loss is minimized. We also found that the EL spectra as well as the EQEEL of the blend solar cells are similar with that of lower gap components in blends. Thus the non-radiative voltage losses are reduced to < 0.3V and small voltage loss of 0.5-0.7V are obtained. Meanwhile, the charge generation in systems are still efficient and high EQEPV of 50-70% can be achieved. It confirms that there is no intrinsic limit for the VOC and efficiency of OPVs as compared with other photovoltaic technologies.
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37.
  • Qin, Jiajun, et al. (författare)
  • From optical pumping to electrical pumping: the threshold overestimation in metal halide perovskites
  • 2023
  • Ingår i: Materials Horizons. - : ROYAL SOC CHEMISTRY. - 2051-6347 .- 2051-6355. ; 10:4, s. 1446-1453
  • Tidskriftsartikel (refereegranskat)abstract
    • The threshold carrier density, conventionally evaluated from optical pumping, is a key reference parameter towards electrically pumped lasers with the widely acknowledged assumption that optically excited charge carriers relax to the band edge through an ultrafast process. However, the characteristically slow carrier cooling in perovskites challenges this assumption. Here, we investigate the optical pumping of state-of-the-art bromide- and iodine-based perovskites. We find that the threshold decreases by one order of magnitude with decreasing excitation energy from 3.10 eV to 2.48 eV for methylammonium lead bromide perovskite (MAPbBr(3)), indicating that the low-energy photon excitation facilitates faster cooling and hence enables efficient carrier accumulation for population inversion. Our results are then interpreted due to the coupling of phonon scattering in connection with the band structure of perovskites. This effect is further verified in the two-photon pumping process, where the carriers relax to the band edge with a smaller difference in phonon momentum that speeds up the carrier cooling process. Furthermore, by extrapolating the optical pumping threshold to the band edge excitation as an analog of the electrical carrier injection to the perovskite, we obtain a critical threshold carrier density of similar to 1.9 x 10(17) cm(-3), which is one order of magnitude lower than that estimated from the conventional approach. Our work thus highlights the feasibility of metal halide perovskites for electrically pumped lasers.
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38.
  • Sun, Huiliang, et al. (författare)
  • Reducing energy loss via tuning energy levels of polymer acceptors for efficient all-polymer solar cells
  • 2020
  • Ingår i: Science China Chemistry. - : Springer Science and Business Media LLC. - 1869-1870 .- 1674-7291. ; 63:12, s. 1785-1792
  • Tidskriftsartikel (refereegranskat)abstract
    • The open-circuit voltage (Voc) of all-polymer solar cells (all-PSCs) is typically lower than 0.9 V even for the most efficient ones. Large energy loss is the main reason for limiting Voc and efficiency of all-PSCs. Herein, through materials design using electron deficient building blocks based on bithiophene imides, the lowest unoccupied molecular orbital (LUMO) energy levels of polymer acceptors can be effectively tuned, which resulted in a reduced energy loss induced by charge generation and recombination loss due to the suppressed charge-transfer (CT) state absorption. Despite a negligible driving force, all-PSC based on the polymer donor and acceptor combination with well-aligned energy levels exhibited efficient charge transfer and achieved an external quantum efficiency over 10% while maintaining a large Voc of 1.02 V, leading to a 9.21% efficiency. Through various spectroscopy approaches, this work sheds light on the mechanism of energy loss in all-PSCs, which paves an avenue to achieving efficient all-PSCs with large Voc and drives the further development of all-PSCs.
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39.
  • Upreti, Tanvi, 1987- (författare)
  • Kinetic Monte Carlo Modelling of Organic Photovoltaic Devices
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Organic photovoltaics (OPVs) is a rapidly growing low-cost PV technology sector that relies on multiple benefits of organic semiconductors viz. being environmental-friendly with a simplified processing/fabrication and tunable properties. While the performance of OPVs has gone up to over 19 % in the last 2 decades, it still lags behind the silicon-PV technology in terms of efficiency and stability. The performance of any solar cell is essentially a combination of three quantities: short circuit current density (jSC), fill- factor (FF), and open circuit voltage (VOC). Of these quantities, especially VOC still offers a scope of further improvement as it falls short of the theoretical achievable limit which requires a better understanding of the various loss channels in an actual device leading to a VOC reduction. Through this thesis, we have developed an understanding of VOC using non-equilibrium models and proposed ways leading to its enhancement.The first step in this study was to develop an understanding of the underlying charge transport mechanism, which relates to the efficiency with which the charges can be extracted at the terminals, or electrodes. Charge transport in any disordered organic semiconductor occurs by a process of hopping, in which charge carriers jump by thermally activated tunneling between localized sites that are randomly distributed in the energy dependent density of states. Thus, among other hopping parameters, the mobility of a charge carrier is crucially dependent on the disorder. We implemented a new semi-analytical hopping model that allows for a consistent extraction of these parameters from the space charge limited conductivity (SCLC) experiments. The model was calibrated against a numerical kinetic Monte Carlo (kMC) model and was used to analyze temperature-dependent SCLC curves for multiple systems used frequently as an active layer in organic solar cells. We observed that there exists a critical ratio between the inter-site distance and the localization length that decides the applicability, or not, of the much-used extended Gaussian disorder model (EGDM). The improved hopping model functions well for both fullerene and non-fullerene-based systems and can also describe the charge transport in electron-only devices, which so far have not been described successfully using EGDM.Having the charge dynamics and other hopping parameters in place, we subsequently developed and calibrated, by independent experiments, a robust and stochastic kMC model that can calculate a full j-V curve of a solar cell correctly. With the full calibration in place with respect to the morphology, recombination rate constant and injection barriers, the motivation was to have a model that can calculate both transients and steady-state j-V curves of a given device. So far, implementing kMC to analyze a full device has been a challenge, especially due to the numerical problems associated with the presence of Ohmic contacts. The calibrated model correctly predicts the device’s j-V and non-equilibrium hopping transport recombination dynamics.A crucial approximation that stems from inorganic solar cells and that is commonly made for organic solar cells as well, is the fast and complete thermalization of charge carriers in the density of states. However, the relaxation of charge carriers in case of organic semiconductors is not as straightforward as in inorganics, but rather a complex two-step process consisting of a fast on-site relaxation followed by a slower global relaxation occurring via hopping to increasingly deep sites. We have shown that the second slow thermalization does not complete within the charge carrier lifetime in the device and leads to a VOC that is 0.1 - 0.2 V higher than the equilibrium value. This is found for both fullerene and high-performing non-fullerene OPV systems.For a given OPV device, there is a significant difference between the upper limit for the efficiency set by theoretical considerations based on the assumption of near-equilibrium (the so-called Shockley-Queisser limit) and the actual measured efficiency. We numerically explored a new funnel-shaped morphology, which can lead to an impactful gain in VOC and efficiency of an organic solar cell. In contrast to the conventional blend morphology, which does not lead to a directed motion of the photogenerated charge carriers, the funnel morphology rectifies the otherwise undirected diffusive motion of ‘hot’ charges, which leads to a higher probability of extraction at the desired contact. We utilized the reciprocity analysis to calculate the gain in VOC and efficiency as compared to a hypothetical equilibrium system of the same material. We found that for an optimized funnel morphology, the efficiency can surpass the near-equilibrium limit.Mixing materials to form a high-performing ternary OPV has emerged as a possible route to improve performance. We performed a review of literature data and deduced that the relative gain in VOC is too small to contribute to a large gain in the efficiency. Instead, the major contribution to the efficiency enhancement is due to gains in the FF and/or jSC. Also, the VOC of the ternary system is found to be tunable relative to the ratio of the added species in the host system. These experimental findings were consistently described by extensive numerical simulations in which the active layer morphology was assumed to give rise to an energetic cascade for at least one of the charge carriers. In contrast, our explicit calculations show that the commonly employed parallel junction model cannot explain the experimental findings.
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40.
  • Upreti, Tanvi, 1987-, et al. (författare)
  • On the Device Physics of High-Efficiency Ternary Solar Cells
  • 2022
  • Ingår i: Solar RRL. - : Wiley-V C H Verlag GMBH. - 2367-198X. ; 6:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Mixing a third compound into the active layer of an organic bulk heterojunction solar cell to form a ternary system has become an established way to improve performance. Various models, based on different assumptions regarding the active layer morphology and the energetics, have been proposed but there is neither consensus on the applicability of the various assumptions to different experimental systems, nor on the actual device physics of these, mostly qualitative, models. Kinetic Monte Carlo simulations are used to investigate the role of morphology and relative energy levels of the constituent materials. By comparing with experimental current–voltage characteristics, a consistent picture arises when the (minority) third compound is predominantly incorporated between the other (majority) compounds and has energy levels that are intermediate to those of the binary host. Even if morphologically imperfect, the resulting energy cascade promotes charge separation and reduces recombination, leading to higher fill factors and short-circuit current densities. The open-circuit voltage sits between that of the binary extremes, in agreement with data from an extensive literature review. This leads to selection criteria for third compounds in terms of energetics and miscibility that promote the formation of a cascade morphology in real and energy space.
  •  
41.
  • Wang, Heyong, 1989- (författare)
  • High-Quality Perovskite Films for Efficient and Stable Light-Emitting Diodes
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Metal halide perovskites have attracted significant attention for light-emitting applications, because of their excellent properties, such as high photoluminescence quantum yields (PLQYs), good charge mobility, narrow emission bandwidth, readily tunable emission spectra ranging from ultraviolet to near-infrared, and solution processability. Since the first room-temperature perovskite-based light-emitting diodes (PeLEDs) reported in 2014, tremendous efforts have been made to promote the efficiencies of PeLEDs, including theoretical simulation, materials design, and device engineering. To reach the ultimate goal of commercialization, PeLEDs with both high-efficiency and long-term operational stability are desired. Achieving high-quality perovskite emissive films is key towards this goal. Centering around the high-quality perovskite films, in this thesis, we demonstrate effective synthesis strategies for the deposition of high-quality perovskite films (including both three-dimensional and mixed-dimensional perovskites) and investigate the effects of ion migration in the perovskite films on the performance of PeLEDs.Due to the fast crystallization nature of perovskites and the low formation energy of defects, controlling the crystallization processes of these films has proved to be an effective approach for achieving high-quality perovskite films. For three-dimensional (3D) perovskite films, we have controlled the formation of these films through the assistance of molecules with the amino group. Herein, we have chosen an electron-transport molecule with two amino groups, 4,4’-diaminodiphenyl sulfone (DDS), to control the crystallization process of perovskite films (Paper 1). The resulting perovskite films consists of in-situ formed high quality perovskite nanocrystals embedded in the electron-transport molecular matrix, resulting in improved PLQYs and structural stability. PeLEDs based on these perovskite films have exhibited both high efficiency and long operational stability.In addition, we have investigated the formation of mixed-dimensional perovskite films. Efficient PeLEDs based on mixed-dimensional perovskite films were fabricated with tin dioxide (SnO2) as an electron transport layer (Paper 3). We also note that the deposition methods have a significant impact on the morphology and optical properties of prepared mixed-dimensional perovskite films (Paper 4). In addition, we provide an effective method to extend the deposition of mixed-dimensional perovskite films, replacing organic ammonium halides with amines in the perovskite precursor solutions to form organic spacer cations through the in-situ protonation process of amines (Paper 2).In spite of these efforts, the performance of PeLEDs is still far from the commercialization standard, partially limited by ion migration. In Paper 5, we discuss impacts of mobile ions in the perovskite films on the performance of PeLEDs. We find that a dynamic redistribution of mobile ions can change current density of a device, leading to EQE/hysteresis during forward and reverse voltage scan and enhanced EQE under constant driving voltages. In addition, we have found that excess mobile ions in the perovskite layer can aggravate the hysteresis and shorten the operational stability of PeLEDs.In this thesis, we also discuss the remaining key challenges in the PeLED field, including the achievement of high-performance blue, white, and lead-free PeLEDs, as well as possible strategies to address these challenges. We hope that our research findings provide insights into the basic science behind the perovskite materials, and broadly benefit other optoelectronic communities, such as perovskite solar cells, flexible electronics, and so on.
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42.
  • Wang, Yuming, 1989- (författare)
  • Voltage Losses in Non-fullerene Organic Solar Cells
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Non-fullerene acceptors have significantly boosted the efficiencies of organic solar cells (OSCs) in the past few years. State-of-the-art OSCs have achieved a certificated power conversion efficiency of 17.4%. In spite of significant professes, there is still a gap between efficiencies of OSCs and those of traditional inorganic solar cells and emerging perovskite solar cells. One of the important reasons for this gap is the large voltage losses for OSCs. Understanding and reducing the voltage losses is of critical importance for further improving the performance of the OSCs. This thesis studies the voltage losses of OSCs based on non-fullerene acceptors.The charge transfer (CT) state plays a critical role in the open-circuit voltage (VOC) of the OSCs. According to the reciprocity relation between the electroluminescence (EL) and the external quantum efficiency of solar cells (EQEPV), we know that the sub-bandgap absorbance (responsible for large radiative recombination voltage losses) and the weak emission of CT states (responsible for large non-radiative voltage losses) are the reasons for large voltage losses in fullerene-based OSCs. In addition, the driving force, defined as the difference between the energy of the singlet states and CT states, was considered to be essential for efficient charge generation, especially when the OSC field was dominated by fullerene acceptors. A series of polymer: non-fullerene pairs with different driving forces were studied by spectroscopy methods e.g. Fourier-transfer photocurrent spectroscopy (FTPS) and electroluminescence spectroscopy. It was demonstrated that both radiative recombination voltage loss and the non-radiative energy loss can be suppressed by reducing driving forces, resulting in overall decreased voltage losses of the OSCs.Another question regarding the trade-off between the voltage losses and charge generation is still under debate – is the driving force essential for the efficient charge separation? A novel polymer: non-fullerene system with negligible offsets between both the lowest unoccupied molecular orbital (LUMO) and the highest unoccupied molecular orbital (HOMO) of the donor and acceptor was studied. Although the driving force for the new system is small, it works efficiently. It implies that efficient charge generation can occur with negligible driving forces for both electrons and holes, suggesting that the high VOC and efficient charge generation can be achieved at the same time for non-fullerene OSCs.In addition to binary OSCs, the voltage losses in ternary OSCs are also studied in this thesis. It was found that the VOC of the ternary organic solar cells cannot be well interpreted by the widely used alloy or parallel model. The non-radiative voltage loss, which is not paid much attention in the two models, was found to play an important role in the tunable VOC of the ternary OSCs. We demonstrate that the non-radiative voltage losses in ternary OSCs is dependent on the radiative recombination rates and the energy levels of the CT states of the two constituting binary OSCs. Furthermore, the aggregation of the individual components can be decreased by adding the third component, suppressing the aggregation caused quenching and leading to a reduced non-radiative recombination voltage loss.The non-fullerene based OSCs with small voltage losses show great potential for indoor applications. Although it might be difficult for OSCs to compete with commercial silicon solar cells for harvesting the solar energy, we demonstrate highly efficient and stable non-fullerene OSCs under indoor light, providing a unique application possibility where OSCs can out-compete other photovoltaic technologies. For the indoor application, the OSCs takes advantage of the easily tunable absorption range of the organic semiconductors, and avoids their drawbacks of the instability under strong outdoor light containing ultraviolet light.
  •  
43.
  • Xia, Yuxin, et al. (författare)
  • Inverted all-polymer solar cells based on a quinoxaline-thiophene/naphthalene-diimide polymer blend improved by annealing
  • 2016
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:10, s. 3835-3843
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the effect of thermal annealing on the photovoltaic parameters of all-polymer solar cells based on a quinoxaline-thiophene donor polymer (TQ1) and a naphthalene diimide acceptor polymer (N2200). The annealed devices show a doubled power conversion efficiency compared to nonannealed devices, due to the higher short-circuit current (J(sc)) and fill factor (FF), but with a lower open circuit voltage (V-oc). On the basis of the morphology-mobility examination by several scanning force microscopy techniques, and by grazing-incidence wide-angle X-ray scattering, we conclude that better charge transport is achieved by higher order and better interconnected networks of the bulk heterojunction in the annealed active layers. The annealing improves charge transport and extends the conjugation length of the polymers, which do help in charge generation and meanwhile reduce recombination. Photoluminescence, electroluminescence, and light intensity dependence measurements reveal how this morphological change affects charge generation and recombination. As a result, the J(sc) and FF are significantly improved. However, the smaller band gap and the higher HOMO level of TQ1 upon annealing causes a lower V-oc. The blend of an amorphous polymer TQ1, and a semi-crystalline polymer N2200, can thus be modified by thermal annealing to double the power conversion efficiency.
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44.
  • Xiong, Min, et al. (författare)
  • Tailoring Phase Purity in the 2D/3D Perovskite Heterostructures Using Lattice Mismatch
  • 2022
  • Ingår i: ACS Energy Letters. - : AMER CHEMICAL SOC. - 2380-8195. ; 7:1, s. 550-559
  • Tidskriftsartikel (refereegranskat)abstract
    • Although the fabrication of two-dimensional (2D)/three-dimensional (3D) halide perovskite heterostructures has been employed to balance the long-term stability and high efficiency of perovskite solar cells, the formation of metastable quasi-2D perovskites remains the most serious challenge. Here, we demonstrate that large lattice mismatch derived from halide and cation differences between 2D and 3D perovskites are key to avoiding the formation of unintended 2D phases in the preparation of 2D/3D bulk heterostructure because the phase transformation becomes less thermodynamically favorable. Specifically, by employing chloride 2D perovskite (PYA)(2) PbCl4 (PYA = propargylammonium) crystals into a 3D precursor solution, we achieve a phase-pure 2D/3D heterojunction with clean type-I band alignment, which exhibits greatly reduced charge recombination. Furthermore, the incorporation of alkyne perovskites is also shown to suppress iodine diffusion and formation due to their exceptional iodine capture capacity. The resultant 2D/3D heterostructured devices exhibited enhanced efficiencies and stabilities compared with their 3D counterparts.
  •  
45.
  • Xu, Weidong, 1988-, et al. (författare)
  • Rational molecular passivation for high-performance perovskite light-emitting diodes
  • 2019
  • Ingår i: Nature Photonics. - : Springer Nature Publishing AG. - 1749-4885 .- 1749-4893. ; 13:6, s. 418-424
  • Tidskriftsartikel (refereegranskat)abstract
    • A major efficiency limit for solution-processed perovskite optoelectronic devices, for example light-emitting diodes, is trap-mediated non-radiative losses. Defect passivation using organic molecules has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near-infrared perovskite light-emitting diodes with a record external quantum efficiency of 21.6%. In addition, our passivated perovskite light-emitting diodes maintain a high external quantum efficiency of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm−2, making them more attractive than the most efficient organic and quantum-dot light-emitting diodes at high excitations.
  •  
46.
  • Xu, Weidong, 1988-, et al. (författare)
  • The progress and prospects of non-fullerene acceptors in ternary blend organic solar cells
  • 2018
  • Ingår i: Materials Horizons. - : ROYAL SOC CHEMISTRY. - 2051-6347 .- 2051-6355. ; 5:2, s. 206-221
  • Forskningsöversikt (refereegranskat)abstract
    • The rapid development of organic solar cells (OSCs) based on non-fullerene acceptors has attracted increasing attention during the past few years, with a record power conversion efficiency of over 13% in a binary bulk heterojunction architecture. This exciting development also enables new possibilities for ternary OSCs to further enhance their efficiency and stability. This review summarizes very recent developments of ternary OSCs, with a focus on blends involving non-fullerene acceptors. We also highlight the challenges and perspectives for further development of ternary blend organic solar cells.
  •  
47.
  • Yang, Heyi, et al. (författare)
  • Composition-Conditioning Agent for Doped Spiro-OMeTAD to Realize Highly Efficient and Stable Perovskite Solar Cells
  • 2022
  • Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 12:44
  • Tidskriftsartikel (refereegranskat)abstract
    • The doped Spiro-OMeTAD hole transport layer (HTL) formed using the lithium bis(trifluoromethane) sulfonimide salt and 4-tert-butylpyridine with phenethylammonium iodide surface treatment on a perovskite film has continuously dominated the record power conversion efficiencies (PCEs) of perovskite solar cells (pero-SCs). However, unstable HTL compositions and iodide salts can cause severe device degradation. In this study, an HTL composition-conditioning agent (CCA), Spiro-BD-2OEG, is designed, which contains a Spiro-OMeTAD-like backbone, functional pyridine units, and oligo (ethylene glycol) chains. This finely designed CCA presents good miscibility with Spiro-OMeTAD and its dopants and acts as a conditioning agent through weak bond interactions. As a result, the CCA-regulated HTL shows a pinhole-free and smooth morphology with enhanced Spiro-OMeTAD ordering and improves dopant stability. In addition, the gradient-distributed CCA in the HTL can narrow the energy level offset with the valence band of the perovskite. The resultant pero-SCs exhibit an excellent PCE of 24.19% without any interface treatment and weak size dependence. A remarkable PCE of 22.63% is obtained even for a 1.004-cm(2) device. Importantly, the strategy shows good universality and significantly promotes the long-term stability of the pero-SCs based on the classical doped Spiro-OMeTAD.
  •  
48.
  • Yu, Hongling, 1987- (författare)
  • Color Tuning for Perovskite Light-Emitting Diodes
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Metal halide perovskites (MHPs) are recognized as promising semiconductor materials for a variety of optical and electrical device applications due to their cost-effective and outstanding optoelectronic properties. As one of the most significant applications, perovskite light-emitting diodes (PeLEDs) hold promise for future lighting and display technologies, attributed to their high photoluminescence quantum yield (PLQY), high color purity, and tunable emission color. The emission colors of PeLEDs can be tuned by mixing the halide anions, adjusting the size of perovskite nanocrystals, or changing the dimensionality of perovskites. However, in practice, all these different approaches have their own advantages and challenges. This thesis centres around the color tunability of perovskites, aiming to develop PeLEDs with different colors using different approaches.We first demonstrate red and near-infrared PeLEDs using a straightforward approach – in situ solution-processed perovskite quantum dots (PQDs). PQDs prepared from colloidal approaches are widely reported and used in LEDs. In contrast, PQDs prepared from the in situ approaches are hardly reported, although they have advantages for device applications. By employing aromatic ammonium iodide (1-naphthylmethyl ammonium iodide, NMAI) as an agent into perovskite precursor solutions, together with annealing temperature modulation, we obtain in situ grown PQDs delivering high external quantum efficiencies (EQEs) of up to 11.0% with tunable electroluminescence (EL) spectra (667 - 790 nm). Our in situ generated PQDs based on pure-halogen perovskites can be easily obtained through a simple deposition process and free of phase segregation, making them a more promising approach for tuning the emission colors of perovskite LEDs.We then move to blue PeLEDs using cesium-based mixed-Br/Cl perovskites. Although mixed halides are a straightforward strategy to tune the emission color, PeLEDs based on this approach suffer from poor color stability, which is attributed to surface defects at grain boundaries. Under the condition of optical excitations, light density over a certain value (a threshold), oxygen, and surface defects at perovskite grain boundaries are found to be key factors inducing photoluminescence (PL) spectral instability of CsPb(Br1−xClx)3 perovskites. Upon electrical bias, defects at grain boundaries provide undesirable halide migration channels, responsible for EL spectral instability issues. Through effective defect passivation, the PL spectral resistance to oxygen is enhanced; moreover, high-performance and color-stable blue PeLEDs are achieved, delivering a maximum luminance of 5351 cd m–2 and a peak EQE of 4.55% with a peak emission wavelength at 489 nm. These findings provide new insights into the color instability issue of mixed halide blue perovskites, against which we also demonstrate an effective strategy.We finally realize single-emissive-layer (EML) white PeLEDs by employing a mixed halide perovskite film as the EML. In spite of high-performance monochromatic blue, green, and red colors, the development of white PeLEDs, especially for single-EML ones, remains a very big challenge. By effective modulation of the halide salt precursors, we achieve single-EML white PeLEDs with Commission Internationale de L’Eclairage (CIE) coordinates of (0.33, 0.33), close to those (0.3128, 0.3290) of the CIE standard illuminant D65. This work not only provides a successful demonstration of a single-EML white PeLED, but also provides useful guidelines for the future development of highperformance single-EML white PeLEDs.
  •  
49.
  • Yu, Hongling, 1987-, et al. (författare)
  • Single-emissive-layer all-perovskite white light-emitting diodes employing segregated mixed halide perovskite crystals
  • 2020
  • Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 11:41, s. 11338-11343
  • Tidskriftsartikel (refereegranskat)abstract
    • Metal halide perovskites have demonstrated impressive properties for achieving efficient monochromatic light-emitting diodes. However, the development of white perovskite light-emitting diodes (PeLEDs) remains a big challenge. Here, we demonstrate a single-emissive-layer all-perovskite white PeLED using a mixed halide perovskite film as the emissive layer. The perovskite film consists of separated mixed halide perovskite phases with blue and red emissions, which are beneficial for suppressing halide anion exchange and preventing charge transfer. As a result, the white PeLED shows balanced white light emission with Commission Internationale de L'Eclairage coordinates of (0.33, 0.33). In addition, we find that the achievement of white light emission from mixed halide perovskites strongly depends on effective modulation of the halide salt precursors, especially lead bromide and benzamidine hydrochloride in our case. Our work provides very useful guidelines for realizing single-emissive-layer all-perovskite white PeLEDs based on mixed halide perovskites, which will spur the development of high-performance white PeLEDs.
  •  
50.
  • Yu, Jianwei, 1992- (författare)
  • The Influence of Energy Levels on Voltage Losses and Charge Generation in Organic Solar Cells
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Organic solar cells (OSCs) are a next-generation photovoltaic technology that convert solar energy to electrical energy. They have attracted great attention due to their advantages of low cost, ease of synthesis, light weight, mechanical flexibility, and roll-to-roll processability. In the past decades, owing to the development of the materials, device optimization and the understanding of the working mechanism, the power conversion efficiency (PCE) has been boosted to ~19%. However, the efficiency of the OSCs is still not comparable to the conventional inorganic solar cells and emerging perovskite solar cells due to the large open-circuit voltage loss (Vloss). In addition, it is also important to obtain efficient charge generation while reducing the Vloss. Thus, understanding the loss mechanisms in the OSCs is significant for achieving further improvement.In this thesis, a novel small-molecule donor named ZR1 was used to fabricate all-small-molecule OSCs (SM-OSCs), which shows efficient charge separation and transport with the optimized hierarchical morphologies, obtaining a breakthrough efficiency of 13.34% with a low Vloss (0.54 eV) in SM-OSCs. In this system, the energy offsets between the donor and acceptor (ΔHOMO or ΔLUMO) play an important role in the open-circuit voltage (VOC) of the OSCs. According to the optoelectronic reciprocity introduced in this thesis, the sub-gap absorption and emission by charge transfer (CT) states lead to large radiative and non-radiative recombination losses. The results show that the decreased HOMO offsets between donor and acceptor can effectively reduce both radiative and non-radiative recombination losses from the CT states, resulting in a suppressed Vloss.In addition to the SM-OSCs, we also study the Vloss and charge generation in the all-polymer OSCs (all- PSCs). A series of polymer acceptors were designed and applied in all-PSCs. In this work, all devices with negligible LUMO offsets show high VOCs of 1.02-1.15 V and good short-circuit currents (JSCs) of 8.87-15.16 mA cm−2 as well as small Vlosss. This study reveals that the small Vloss and the effective charge generation can also be realized simultaneously in all-PSCs with small energy offsets.Next, we found that introducing a third component can also reduce Vloss. In this work, we start with the fundamental photophysical processes which determine the VOCs of the devices and provide a universal approach framework well explaining the VOC of ternary OSCs (TOSCs) in different situations. By combining experimental investigations with theoretical simulations, we highlight the significant influence of the thermal population arising from the guest component-related CT states and local excited (LE)states on the non-radiative recombination losses in TOSCs. Firmly based on our new understanding, we provide design rules for enhancing the VOC in TOSCs: 1) high emission yield for the guest binary system; close charge-transfer energies between two binary systems; 2) high miscibility of the guest component with the low-optical-gap component in the host binary blends.In the all-PSCs work we did before, we find the small Vloss and the effective charge generation can be achieved simultaneously with small energy offsets, which can be also observed in other non-fullerene based OSCs. It was found that some of non-fullerene acceptors based OSCs can realize an efficient charge generation and a suppressed charge recombination process with small energy offsets (< 0.3 eV) between the donor and the acceptor, leading to a low Vloss, a high JSC, and a high fill factor (FF) simultaneously. Here, we investigate a series of OSCs blends with different HOMO offsets between donor and in a large range of ~ 0 to 0.50 eV. Along with decreasing HOMO offsets, the blends show reduced Vlosss. For the JSC and the FF, we observe a maximum value at an optimal energetic offset around 0.2-0.3 eV and the optimal energetic offset appears at different values for different non-fullerene acceptors. Through the analysis of the ultrafast transient absorption, we find inefficient charge generation when the HOMO offset is close to zero, which attributed to the back transfer of a hole from the donor to the acceptor. The affected charge generation at the small HOMO offsets is probably the main reason for the deceased JSC and FF. This study demonstrates the existence of optimal energy offsets for achieving high-performance OSCs.
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