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Sökning: WFRF:(Zhang Huotian)

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1.
  • Yuan, Jun, et al. (författare)
  • Understanding energetic disorder in electron-deficient-core-based non-fullerene solar cells
  • 2020
  • Ingår i: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 63:8, s. 1159-1168
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent advances in material design for organic solar cells (OSCs) are primarily focused on developing near-infrared non-fullerene acceptors, typically A-DA D-A type acceptors (where A abbreviates an electron-withdrawing moiety and D, an electron-donor moiety), to achieve high external quantum efficiency while maintaining low voltage loss. However, the charge transport is still constrained by unfavorable molecular conformations, resulting in high energetic disorder and limiting the device performance. Here, a facile design strategy is reported by introducing the "wing" (alkyl chains) at the terminal of the DA D central core of the A-DA D-A type acceptor to achieve a favorable and ordered molecular orientation and therefore facilitate charge carrier transport. Benefitting from the reduced disorder, the electron mobilities could be significantly enhanced for the "wing"-containing molecules. By carefully changing the length of alkyl chains, the mobility of acceptor has been tuned to match with that of donor, leading to a minimized charge imbalance factor and a high fill factor (FF). We further provide useful design strategies for highly efficient OSCs with high FF.
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2.
  • Cai, Yunhao, et al. (författare)
  • Effect of the Energy Offset on the Charge Dynamics in Nonfullerene Organic Solar Cells
  • 2020
  • Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:39, s. 43984-43991
  • Tidskriftsartikel (refereegranskat)abstract
    • The energy offset, considered as the driving force for charge transfer between organic molecules, has significant effects on both charge separation and charge recombination in organic solar cells. Herein, we designed material systems with gradually shifting energy offsets, including both positive and negative values. Time-resolved spectroscopy was used to monitor the charge dynamics within the bulk heterojunction. It is striking to find that there is still charge transfer and charge generation when the energy offset reached -0.10 eV (ultraviolet photoelectron spectroscopy data). This work not only indicates the feasibility of the free carrier generation and the following charge separation under the condition of a negative offset but also elucidates the relationship between the charge transfer and the energy offset in the case of polymer chlorination.
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3.
  • Li, Chao, et al. (författare)
  • Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells
  • 2021
  • Ingår i: Nature Energy. - : NATURE RESEARCH. - 2058-7546.
  • Tidskriftsartikel (refereegranskat)abstract
    • Molecular design of acceptor and donor molecules has enabled major progress in organic photovoltaics. Li et al. show that branched alkyl chains in non-fullerene acceptors allow favourable morphology in the active layer, enabling a certified device efficiency of 17.9%. Molecular design of non-fullerene acceptors is of vital importance for high-efficiency organic solar cells. The branched alkyl chain modification is often regarded as a counter-intuitive approach, as it may introduce an undesirable steric hindrance that reduces charge transport in non-fullerene acceptors. Here we show the design and synthesis of a highly efficient non-fullerene acceptor family by substituting the beta position of the thiophene unit on a Y6-based dithienothiophen[3,2-b]-pyrrolobenzothiadiazole core with branched alkyl chains. It was found that such a modification to a different alkyl chain length could completely change the molecular packing behaviour of non-fullerene acceptors, leading to improved structural order and charge transport in thin films. An unprecedented efficiency of 18.32% (certified value of 17.9%) with a fill factor of 81.5% is achieved for single-junction organic solar cells. This work reveals the importance of the branched alkyl chain topology in tuning the molecular packing and blend morphology, which leads to improved organic photovoltaic performance.
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4.
  • Li, Xiane, et al. (författare)
  • Mapping the energy level alignment at donor/acceptor interfaces in non-fullerene organic solar cells
  • 2022
  • Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 13:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy level alignment (ELA) at donor-acceptor heterojunctions is of vital importance yet largely undetermined in organic solar cells. Here, authors determine the heterojunction ELA with (mono) layer-by-layer precision to understand the co-existence of efficient charge. Energy level alignment (ELA) at donor (D) -acceptor (A) heterojunctions is essential for understanding the charge generation and recombination process in organic photovoltaic devices. However, the ELA at the D-A interfaces is largely underdetermined, resulting in debates on the fundamental operating mechanisms of high-efficiency non-fullerene organic solar cells. Here, we systematically investigate ELA and its depth-dependent variation of a range of donor/non-fullerene-acceptor interfaces by fabricating and characterizing D-A quasi bilayers and planar bilayers. In contrast to previous assumptions, we observe significant vacuum level (VL) shifts existing at the D-A interfaces, which are demonstrated to be abrupt, extending over only 1-2 layers at the heterojunctions, and are attributed to interface dipoles induced by D-A electrostatic potential differences. The VL shifts result in reduced interfacial energetic offsets and increased charge transfer (CT) state energies which reconcile the conflicting observations of large energy level offsets inferred from neat films and large CT energies of donor - non-fullerene-acceptor systems.
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5.
  • Ma, Qing, et al. (författare)
  • Promoting charge separation resulting in ternary organic solar cells efficiency over 17.5%
  • 2020
  • Ingår i: Nano Energy. - : ELSEVIER. - 2211-2855 .- 2211-3282. ; 78
  • Tidskriftsartikel (refereegranskat)abstract
    • Ternary blend has been an effective strategy for achieving high efficiency in organic solar cells (OSCs). Herein, a non-fullerene small molecule acceptor (C8-DTC) was synthesized and added to the PM6: Y6 system as a third component. By adding 10% of C8-DTC as the second acceptor in the PM6:Y6 system, an impressive power conversion efficiency of 17.52% was achieved with simultaneously increased open-circuit voltage, short-circuit current-density, and fill factor. The reduced voltage loss was due to the lowered non-radiative recombination loss in comparison with the binary device. It was also found that a small amount of C8-DTC in the PM6:Y6 blend resulted in enhanced charge separation and charge transport by providing possible extra channels of hole extraction. And the ternary system formed a good phase separation and favored bi-continuous transport network, which is more conducive to balance the electron and hole transport. The results indicate that the ternary system formed by C8-DTC as the third component is an effective method to improve the performance of the PM6:Y6 based OSCs.
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6.
  • Zhang, Huotian, et al. (författare)
  • Reversible air-induced optical and electrical modulation of methylammonium lead bromide (MAPbBr(3)) single crystals
  • 2017
  • Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 111:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The photoluminescence (PL) variations of organic-inorganic hybrid lead halide perovskites in different atmospheres are well documented, while the fundamental mechanism still lacks comprehensive understandings. This study reports the reversible optical and electrical properties of methylammonium lead bromide (MAPbBr(3) or CH3NH3PbBr3) single crystals caused by air infiltration. With the change in the surrounding atmosphere from air to vacuum, the PL intensity of perovskite single crystals decreases, while the conductivity increases. By means of first-principles computational studies, the shallow trap states are considered as key elements in PL and conductivity changes. These results have important implications for the characterization and application of organic-inorganic hybrid lead halide perovskites in vacuum.
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7.
  • Zhang, Liangdong, et al. (författare)
  • Bright Free Exciton Electroluminescence from Mn-Doped Two-Dimensional Layered Perovskites
  • 2019
  • Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 10:11, s. 3171-3175
  • Tidskriftsartikel (refereegranskat)abstract
    • Two-dimensional (2D) perovskites incorporating hydrophobic organic spacer cations show improved film stability and morphology compared to their three-dimensional (3D) counterparts. However, 2D perovskites usually exhibit low photoluminescence quantum efficiency (PLQE) owing to strong exciton-phonon interaction at room temperature, which limits their efficiency in light-emitting diodes (LEDs). Here, we demonstrate that the device performance of 2D perovskite LEDs can be significantly enhanced by doping Mn(2+)in (benzimidazolium)(2)PbI4 2D perovskite films to suppress the exciton-phonon interaction. The distorted [PbI6](4-) octahedra by Mn-doping and the rigid benzimidazolium (BIZ) ring without branched chains in the 2D perovskite structure lead to improved crystallinity and rigidity of the perovskites, resulting in suppressed phonon-exciton interaction and enhanced PLQE. On the basis of this strategy, for the first time, we report yellow electroluminescence from free excitons in 2D (n = 1) perovskites with a maximum brightness of 225 cd m(-2) and a peak EQE of 0.045%.
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8.
  • Zhang, Qilun, 1992-, et al. (författare)
  • Natural Product Betulin-Based Insulating Polymer Filler in Organic Solar Cells
  • 2022
  • Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 6:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Introduction of filler materials into organic solar cells (OSCs) are a promising strategy to improve device performance and thermal/mechanical stability. However, the complex interactions between the state-of-the-art OSC materials and filler require careful selection of filler materials and OSC fabrication to achieve lower cost and improved performance. In this work, the introduction of a natural product betulin-based insulating polymer as filler in various OSCs is investigated. Donor–acceptor–insulator ternary OSCs are developed with improved open-circuit voltage (Voc) due to decreased trap-assisted recombination. Furthermore, filler-induced vertical phase separation due to mismatched surface energy can strongly affect charge collection at the bottom interface and limit the filler ratio. A quasi-bilayer strategy is used in all-polymer systems to circumvent this problem. Herein, the variety of filler materials in OSCs to biomass is broadened, and the filler strategy is made a feasible and promising strategy toward highly efficient, eco, and low-cost OSCs.
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9.
  • Cui, Xiaolei, et al. (författare)
  • Temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystal
  • 2017
  • Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 111:23
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystals are investigated. The dynamic current-time measurement results at different temperatures directly demonstrate that the electrical properties of the perovskite single crystal are dependent on the work temperature. We find that the Poole-Frankel conduction mechanism fits the current-voltage curves at small bias voltage (0-1 V) under darkness, which is mainly attributed to the surface defect states. The capability of carriers de-trapping from defects varies with different work temperatures, resulting in an increased current as the temperature increases under both darkness and illumination. In addition, the different transient photocurrent responses of incident light at two wavelengths (470 nm, 550 nm) further confirm the existence of defect states on the single crystal surface. Published by AIP Publishing.
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10.
  • He, Q., et al. (författare)
  • Revealing Morphology Evolution in Highly Efficient Bulk Heterojunction and Pseudo-Planar Heterojunction Solar Cells by Additives Treatment
  • 2021
  • Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 11:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Additives treatment is as a very effective strategy to optimize bulk heterojunction (BHJ) morphology. However, the inherent working mechanism of this strategy still lacks systematical investigations in non-fullerene-acceptors-based organic solar cells (OSCs). Herein, a series of BHJ and pseudo-planar heterojunction (PPHJ) OSCs using PM6 and IT-4F as the electron donor/acceptor pair, are developed to unveil the promoting effect of solvent additive 1, 8-diiodooctane (DIO) on active layer morphologies and device performance. The study clearly demonstrates that DIO can increase the crystallinity of IT-4F significantly, while it has less impact on PM6. It is notable that a new efficiency-determining crystalline balanced factor (CCLpolymer/CCLacceptor) is put forward, indicating that the more balanced CCLpolymer/CCLacceptor results in more balanced charge mobility and much better short-circuit current densities (Jsc) and fill factors (FF) of OSCs. The PPHJ blend film of PM6/IT-4F(DIO) exhibits enhanced crystallinity with more balanced CCL and favorable hierarchical distribution morphology, contributing to a champion efficiency of 13.70% with a record Jsc of 20.98 mA cm−2 and a remarkable FF of 75.9%. This work not only reveals the underlying mechanism of DIO caused morphology evolution, but also achieves highly efficient PPHJ OSCs with superior thermal stability by elaborately controlling the morphology of PPHJ film.
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11.
  • Liu, Wei, et al. (författare)
  • The Synthesis of a Multiple D-A Conjugated Macrocycle and Its Application in Organic Photovoltaic
  • 2023
  • Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773.
  • Tidskriftsartikel (refereegranskat)abstract
    • As a novel class of materials, D-A conjugated macrocycles hold significant promise for chemical science. However, their potential in photovoltaic remains largely untapped due to the complexity of introducing multiple donor and acceptor moieties into the design and synthesis of cyclic pi-conjugated molecules. Here, we report a multiple D-A ring-like conjugated molecule (RCM) via the coupling of dimer molecule DBTP-C3 as a template and thiophenes in high yields. RCM exhibits a narrow optical gap (1.33 eV) and excellent thermal stability, and shows a remarkable photoluminescence yield (phi PL) of 11.1 % in solution, much higher than non-cyclic analogues. Organic solar cell (OSC) constructed with RCM as electron acceptor shows efficient charge separation at donor-acceptor band offsets and achieves a power conversion efficiency (PCE) of 14.2 %-approximately fourfold higher than macrocycle-based OSCs reported so far. This is partly due to low non-radiative voltage loss down to 0.20 eV and a high electroluminescence yield (phi EL) of 4x10-4. Our findings emphasize the potential of D-A cyclic conjugated molecules in advancing organic photovoltaic technology. A multiple D-A ring-like conjugated molecule, RCM was synthesized via a template-directed process. RCM inherits the superior photovoltaic properties characteristic of D-A linear molecules, including a narrow optical gap and effective charge transfer. Importantly, RCM demonstrates reduced non-radiative losses, attributable to its minimized vibration.+image
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12.
  • Wang, Yuming, et al. (författare)
  • Origins of the open-circuit voltage in ternary organic solar cells and design rules for minimized voltage losses
  • 2023
  • Ingår i: Nature Energy. - : NATURE PORTFOLIO. - 2058-7546. ; 8:9, s. 978-988
  • Tidskriftsartikel (refereegranskat)abstract
    • The power conversion efficiency of ternary organic solar cells (TOSCs), consisting of one host binary blend and one guest component, remains limited by large voltage losses. The fundamental understanding of the open-circuit voltage (V-OC) in TOSCs is controversial, limiting rational design of the guest component. In this study, we systematically investigate how the guest component affects the radiative and non-radiative related parts of V-OC of a series of TOSCs using the detailed balanced principle. We highlight that the thermal population of charge-transfer and local exciton states provided by the guest binary blend (that is, the guest-component-based binary blend) has a significant influence on the non-radiative voltage losses. Ultimately, we provide two design rules for enhancing the V-OC in TOSCs: high emission yield for the guest binary blend and similar charge-transfer-state energies for host/guest binary blends; high miscibility of the guest component with the low gap component in the host binary blend. The performance of ternary organic solar cells is limited by voltage losses. Using the detailed balance principle, Wang et al. show how the third component of the blend affects the open-circuit voltage and delineate molecular design rules.
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13.
  • Yang, Rong, et al. (författare)
  • Oriented Quasi-2D Perovskites for High Performance Optoelectronic Devices
  • 2018
  • Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 30:51
  • Tidskriftsartikel (refereegranskat)abstract
    • Quasi-2D layered organometal halide perovskites have recently emerged as promising candidates for solar cells, because of their intrinsic stability compared to 3D analogs. However, relatively low power conversion efficiency (PCE) limits the application of 2D layered perovskites in photovoltaics, due to large energy band gap, high exciton binding energy, and poor interlayer charge transport. Here, efficient and water-stable quasi-2D perovskite solar cells with a peak PCE of 18.20% by using 3-bromobenzylammonium iodide are demonstrated. The unencapsulated devices sustain over 82% of their initial efficiency after 2400 h under relative humidity of approximate to 40%, and show almost unchanged photovoltaic parameters after immersion into water for 60 s. The robust performance of perovskite solar cells results from the quasi-2D perovskite films with hydrophobic nature and a high degree of electronic order and high crystallinity, which consists of both ordered large-bandgap perovskites with the vertical growth in the bottom region and oriented small-bandgap components in the top region. Moreover, due to the suppressed nonradiative recombination, the unencapsulated photovoltaic devices can work well as light-emitting diodes (LEDs), exhibiting an external quantum efficiency of 3.85% and a long operational lifetime of approximate to 96 h at a high current density of 200 mA cm(-2) in air.
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14.
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15.
  • Yuan, Jun, et al. (författare)
  • Enabling low voltage losses and high photocurrent in fullerene-free organic photovoltaics
  • 2019
  • Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite significant development recently, improving the power conversion efficiency of organic photovoltaics (OPVs) is still an ongoing challenge to overcome. One of the prerequisites to achieving this goal is to enable efficient charge separation and small voltage losses at the same time. In this work, a facile synthetic strategy is reported, where optoelectronic properties are delicately tuned by the introduction of electron-deficient-core-based fused structure into non-fullerene acceptors. Both devices exhibited a low voltage loss of 0.57 V and high short-circuit current density of 22.0 mA cm(-2), resulting in high power conversion efficiencies of over 13.4%. These unconventional electron-deficient-core-based non-fullerene acceptors with near-infrared absorption lead to low non-radiative recombination losses in the resulting organic photovoltaics, contributing to a certified high power conversion efficiency of 12.6%.
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16.
  • Yuan, Jun, et al. (författare)
  • Reducing Voltage Losses in the A-DAD-A Acceptor-Based Organic Solar Cells
  • 2020
  • Ingår i: Chem. - : CELL PRESS. - 2451-9308 .- 2451-9294. ; 6:9, s. 2147-2161
  • Tidskriftsartikel (refereegranskat)abstract
    • Power conversion efficiencies (PCEs) of solution-processed organic solar cells (OSCs) have recently reached 17.4% (certified) for single-junction devices. Crucial to this advancement is the development of non-fullerene acceptors (NFAs) since 2015. The recent A-DAD-A NFAs have attracted widespread attention because of their ladder-type electron-deficient-core-based central fused ring with improved transport properties and optimum energy levels. With the synergistic effect of electron-deficient-core and specific molecular geometry, the A-DADA molecules could achieve low voltage losses and high current generation at the same time, reaching new regimes of device physics and photophysics. This perspective will discuss the voltage losses in state-of-the-art A-DAD-A NFA-based OSCs and propose new molecular design strategies to achieve PCEs over 20% in OSCs based on these new acceptors by further decreasing their total voltage losses.
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17.
  • Zhang, Jia, et al. (författare)
  • Transport Layer Engineering Toward Lower Threshold for Perovskite Lasers
  • 2023
  • Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 35:30
  • Tidskriftsartikel (refereegranskat)abstract
    • Charge-transport layers are essential for achieving electrically pumped perovskite lasers. However, their role in perovskite lasing is not fully understood. Here, the role of charge-transport layers on the lasing actions of perovskite films is explored by investigating the amplified spontaneous emission (ASE) thresholds. A largely reduced ASE threshold and enhanced ASE intensity is demonstrated by introducing an additional hole transport layer poly(triaryl amine) (PTAA). It is shown that the key role of the PTAA layer is to accelerate the hot-carrier cooling process by extracting holes in perovskites. With reduced hot holes, the Auger recombination loss is largely suppressed, resulting in decreased ASE threshold. This argument is further supported by the fact that the ASE threshold can be further reduced from 25.7 to 7.2 mu J cm(-2) upon switching the pumping wavelength from 400 to 500 nm to directly avoid excess hot-hole generation. This work exemplifies how to further reduce the ASE threshold with transport layer engineering through hot-hole manipulation. This is critical to maintaining the excellent gain properties of perovskites when integrating them into electrical devices, paving the way for electrically pumped perovskite lasers.
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18.
  • Zhang, Qilun, 1992-, et al. (författare)
  • Industrial Kraft Lignin Based Binary Cathode Interface Layer Enables Enhanced Stability in High Efficiency Organic Solar Cells
  • 2023
  • Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095.
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, a binary cathode interface layer (CIL) strategy based on the industrial solvent fractionated LignoBoost kraft lignin (KL) is adopted for fabrication of organic solar cells (OSCs). The uniformly distributed phenol moieties in KL enable it to easily form hydrogen bonds with commonly used CIL materials, i.e., bathocuproine (BCP) and PFN-Br, resulting in binary CILs with tunable work function (WF). This work shows that the binary CILs work well in OSCs with large KL ratio compatibility, exhibiting equivalent or even higher efficiency to the traditional CILs in state of art OSCs. In addition, the combination of KL and BCP significantly enhanced OSC stability, owing to KL blocking the reaction between BCP and nonfullerene acceptors (NFAs). This work provides a simple and effective way to achieve high-efficient OSCs with better stability and sustainability by using wood-based materials. This work introduces industrial solvent fractionated LignoBoost kraft lignin (KL) in highly efficient organic solar cells (OSCs) by binary cathode interface layer (CIL) strategy, which can significantly improve the stability of both binary and ternary photoactive layer (PAL) OSC, owing to the passivation of diffusion and reaction between bathocuproine (BCP) and nonfullerene acceptors (NFAs). The results combine sustainable wood-based material with classic interface materials in advance NFA-OSCs.image
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19.
  • Zhao, Fuwen, et al. (författare)
  • Emerging Approaches in Enhancing the Efficiency and Stability in Non-Fullerene Organic Solar Cells
  • 2020
  • Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840.
  • Forskningsöversikt (refereegranskat)abstract
    • The past three years have witnessed rapid growth in the field of organic solar cells (OSCs) based on non-fullerene acceptors (NFAs), with intensive efforts being devoted to material development, device engineering, and understanding of device physics. The power conversion efficiency of single-junction OSCs has now reached high values of over 18%. The boost in efficiency results from a combination of promising features in NFA OSCs, including efficient charge generation, good charge transport, and small voltage losses. In addition to efficiency, stability, which is another critical parameter for the commercialization of NFA OSCs, has also been investigated. This review summarizes recent advances in the field, highlights approaches for enhancing the efficiency and stability of NFA OSCs, and discusses possible strategies for further advances of NFA OSCs.
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20.
  • Cheng, Hao-Wen, et al. (författare)
  • Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component
  • 2019
  • Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 19:8, s. 5053-5061
  • Tidskriftsartikel (refereegranskat)abstract
    • Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (V-OC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and V-OC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.
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21.
  • Hart, Lucy J. F., et al. (författare)
  • Understanding the Role of Triplet-Triplet Annihilation in Non-Fullerene Acceptor Organic Solar Cells
  • 2023
  • Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 13:36
  • Tidskriftsartikel (refereegranskat)abstract
    • Non-fullerene acceptors (NFAs) have enabled power conversion efficiencies exceeding 19% in organic solar cells (OSCs). However, the open-circuit voltage of OSCs remains low relative to their optical gap due to excessive non-radiative recombination, and this now limits performance. Here, an important aspect of OSC design is considered, namely management of the triplet exciton population formed after non-geminate charge recombination. By comparing the blends PM6:Y11 and PM6:Y6, it is shown that the greater crystallinity of the NFA domains in PM6:Y11 leads to a higher rate of triplet-triplet annihilation (TTA). This is attributed to the four times larger ground state dipole moment of Y11 versus Y6, which improves the long range NFA out-of-plane ordering. Since TTA converts a fraction of the non-emissive triplet states into bright singlet states, it has the potential to reduce non-radiative voltage losses. Through a kinetic analysis of the recombination processes under 1-Sun illumination, a framework is provided for determining the conditions under which TTA may improve OSC performance. If these could be satisfied, TTA has the potential to reduce non-radiative voltage losses by up to several tens of millivolts.
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22.
  • Jasiunas, Rokas, et al. (författare)
  • From Generation to Extraction: A Time-Resolved Investigation of Photophysical Processes in Non-fullerene Organic Solar Cells
  • 2020
  • Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:39, s. 21283-21292
  • Tidskriftsartikel (refereegranskat)abstract
    • Non-fullerene organic solar cells (NFOSCs) demonstrate record efficiencies exceeding 16%. In comparison with cells with the fullerene-based acceptor, the NFOSCs benefit from a longer wavelength absorption, which leads to a small highest occupied molecular orbital (HOMO) level offset. Here, we use several advanced transient investigation techniques, covering timescale from sub-ps to mu s, to address all sequence of processes starting from photoexcitation of donors or acceptors to carrier extraction in several NFOSCs and cells with phenyl-C71-butyric acid methyl ester (PCBM). Though small offsets result in higher open-circuit voltage, we show that at the same time, it limits cell performance because of inefficient hole transfer from excited acceptors to donors and enhanced geminate recombination. We demonstrate that 100 meV HOMO level offset and proper acceptor molecule structures are sufficient for efficient hole transfer (>70%) and for reduction of the geminate recombination losses down to about 20%. Subsequent extraction of unbound charge carriers in all NFOSCs is slightly faster than in cells with PCBM, while non-geminate carrier recombination causing additional losses is slightly slower in the best performing NFOSCs than in cells with PCBM.
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23.
  • Jasiunas, Rokas, et al. (författare)
  • Interplay between charge separation and hole back transfer determines the efficiency of non-fullerene organic solar cells with low energy level offset
  • 2022
  • Ingår i: Organic electronics. - : ELSEVIER. - 1566-1199 .- 1878-5530. ; 108
  • Tidskriftsartikel (refereegranskat)abstract
    • Organic bulk heterojunction solar cells with electron acceptors based on small donor-acceptor type molecules show record efficiencies mainly due to their long wavelength absorption, which enables efficient harvesting of solar light and, thus, causes high current density. Meanwhile, relative positions of HOMO and LUMO levels of donor and acceptor materials determine the open circuit voltage. Here, we apply ultrafast transient absorption and transient luminescence techniques together with specially-designed modelling technique to address charge carrier generation and recombination dynamics in detail. We demonstrate the importance of careful adjustment of the HOMO and LUMO levels, as their positions determine formation and recombination rates of interfacial charge transfer (CT) states. An insufficient donor and acceptor LUMO level offset, lower than -300 meV, leads to slow and inefficient CT state formation, while an offset of the HOMO level below -100 meV leads to fast CT state recombination, which we attribute to the back transfer of a hole from the donor to the acceptor.
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24.
  • Jasiunas, Rokas, et al. (författare)
  • Thermally Activated Reverse Electron Transfer Limits Carrier Generation Efficiency in PM6:Y6 Non-Fullerene Organic Solar Cells
  • 2022
  • Ingår i: Solar RRL. - : WILEY-V C H VERLAG GMBH. - 2367-198X. ; 6:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Transient absorption and time-resolved fluorescence measurements in a wide temperature range are used to investigate the mechanism of charge carrier generation in efficient organic solar cells based on a PM6:Y6 donor-acceptor blend. The generation mechanisms differ significantly under excitation of a donor or acceptor. The investigations reveal a temperature-dependent interplay between the formation of interfacial charge transfer (CT) states and intra-moiety CT states of the acceptor, their separation into free charge carriers and carrier recombination. The efficient charge carrier generation is ensured by the carrier separation over a small energy barrier, which is easily surmountable at room temperature. However, the overall yield of charge carrier generation at room temperature is reduced by the recombination of charge carriers due to the thermally activated back transfer of electrons from the acceptor to the donor via the highest occupied molecular orbit (HOMO) levels, which is enabled by the small energy offset between HOMO levels of the donor and the acceptor.
  •  
25.
  • Jasiuunas, Rokas, et al. (författare)
  • Carrier Mobility Dynamics under Actual Working Conditions of Organic Solar Cells
  • 2021
  • Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 125:27, s. 14567-14575
  • Tidskriftsartikel (refereegranskat)abstract
    • Although organic photovoltaics has made significant progress since its appearance decades ago, the underlying physics of charge transport in working cells is still under debate. Carrier mobility, determining the carrier extraction and recombination, is one of the most important but complex and still poorly understood parameters. Low-energy charge carrier states acting as traps play a particularly important role in carrier transport. Occupation of these states under real operation conditions of solar cells induces additional complexity. In this study, we use several transient methods and numerical modeling to address carrier transport under actual working conditions of bulk heterojunction organic solar cells based on fullerene and nonfullerene acceptors. We show that occupation of low-energy states strongly depends on the blend materials and the effective electric field. We define conditions when such occupation increases carrier mobility, making it less time-dependent on the microsecond time scale, and when its influence is only marginal. We also show that the initial mobility, determined by carrier relaxation within the high-energy part of the distributed density of states, strongly decreases with time independently of the low-energy state population.
  •  
26.
  • Kniepert, Juliane, et al. (författare)
  • Reliability of charge carrier recombination data determined with charge extraction methods
  • 2019
  • Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 126:20
  • Tidskriftsartikel (refereegranskat)abstract
    • Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing.
  •  
27.
  • Ling, Li, et al. (författare)
  • Precisely Controlled Hydration Water for Performance Improvement of Organic-Inorganic Perovskite Solar Cells
  • 2016
  • Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlagsgesellschaft. - 1616-301X .- 1616-3028. ; 26:28, s. 5028-5034
  • Tidskriftsartikel (refereegranskat)abstract
    • Recently, intensive studies on the role of water molecule in the formation of organic-inorganic perovskite film have been reported. However, not only the contradictive phenomena but also the complex processing technique has hindered the widespread use of water molecule in perovskite preparation. Here the hydration water is introduced into the precursors instead of water. By precisely controlling the content of hydration water, a smoother and more uniform perovskite film is obtained through a simple one-step spin coating method. The improvement of perovskite film quality leads to highly efficient planar perovskite solar cells. Summing up the device studies and the investigation of morphology, crystallization, and optical properties, the impact of water molecule in the formation of perovskite crystal and consequences of device performance is understood. Due to its universal adaptability and simplified process, precise control of hydration water is therefore of great utility to high quality perovskite films fabrication and large-scale production of this upcoming photovoltaic technology.
  •  
28.
  • 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.
  •  
29.
  • Perdigon-Toro, Lorena, et al. (författare)
  • Barrierless Free Charge Generation in the High-Performance PM6:Y6 Bulk Heterojunction Non-Fullerene Solar Cell
  • 2020
  • Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 32
  • Tidskriftsartikel (refereegranskat)abstract
    • Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near-unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.
  •  
30.
  • Rech, Jeromy J., et al. (författare)
  • The crucial role of end group planarity for fused-ring electron acceptors in organic solar cells
  • 2019
  • Ingår i: Materials Chemistry Frontiers. - : Royal Society of Chemistry. - 2052-1537. ; 3:8, s. 1642-1652
  • Tidskriftsartikel (refereegranskat)abstract
    • Newly developed fused-ring electron acceptors (FREAs) have proven to be an effective class of materials for extending the absorption window and boosting the efficiency of organic photovoltaics (OPVs). While numerous acceptors have been developed, there is surprisingly little structural diversity among high performance FREAs in literature. Of the high efficiency electron acceptors reported, the vast majority utilize derivatives of 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) as the acceptor moiety. It has been postulated that the high electron mobility exhibited by FREA molecules with INCN end groups is a result of close pi-pi stacking between the neighboring planar INCN groups, forming an effective charge transport pathway between molecules. To explore this as a design rationale for electron acceptors, we synthesized a new fused-ring electron acceptor, IDTCF, which has methyl substituents out of plane to the conjugated acceptor backbone. These methyl groups hinder packing and expand the pi-pi stacking distance by similar to 1 angstrom, but have little impact on the optical or electrochemical properties of the individual FREA molecule. The extra steric hindrance from the out of plane methyl substituents restricts packing and results in large amounts of geminate recombination, thus degrading the device performance. Our results show that intermolecular interactions (especially pi-pi stacking between end groups) play a crucial role in performance of FREAs. We demonstrated that the planarity of the acceptor unit is of paramount importance as even minor deviations in end group distance are enough to disrupt crystallinity and cripple device performance.
  •  
31.
  • Tu, Li, et al. (författare)
  • Aerosol jet printed silver nanowire transparent electrode for flexible electronic application
  • 2018
  • Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 123:17
  • Tidskriftsartikel (refereegranskat)abstract
    • Aerosol jet printing technology enables fine feature deposition of electronic materials onto low-temperature, non-planar substrates without masks. In this work, silver nanowires (AgNWs) are proposed to be printed into transparent flexible electrodes using a Maskless Mesoscale Material Deposition Aerosol Jet VR printing system on a glass substrate. The influence of the most significant process parameters, including printing cycles, printing speed, and nozzle size, on the performance of AgNW electrodes was systematically studied. The morphologies of printed patterns were characterized by scanning electron microscopy, and the transmittance was evaluated using an ultraviolet-visible spectrophotometer. Under optimum conditions, high transparent AgNW electrodes with a sheet resistance of 57.68 X/sq and a linewidth of 50.9 mu m were obtained, which is an important step towards a higher performance goal for flexible electronic applications.
  •  
32.
  • Upreti, Tanvi, et al. (författare)
  • Experimentally Validated Hopping-Transport Model for Energetically Disordered Organic Semiconductors
  • 2019
  • Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 12:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Charge transport in disordered organic semiconductors occurs by hopping of charge carriers between localized sites that are randomly distributed in a strongly energy-dependent density of states. Extracting disorder and hopping parameters from experimental data, such as temperature-dependent current-voltage characteristics, typically relies on parametrized mobility functionals that are integrated in a drift-diffusion solver. Surprisingly, the functional based on the extended Gaussian disorder model (eGDM) is extremely successful at this, despite it being based on the assumption of nearest neighbor hopping (nnH) on a regular lattice. We here propose a variable-range hopping (VRH) model that is integrated in a freeware drift-diffusion solver. The mobility model is calibrated using kinetic Monte Carlo calculations and shows good agreement with the Monte Carlo calculations over the experimentally relevant part of the parameter space. The model is applied to temperature-dependent space-charge-limited current (SCLC) measurements of different systems. In contrast to the eGDM, the VRH model provides a consistent description of both p- and n-type devices. We find a critical ratio of a(NN)/alpha (mean intersite distance:localization radius) of about three, below which hopping to non-nearest neighbors becomes important around room temperature and the eGDM cannot be used for parameter extraction. Typical (Gaussian) disorder values in the range 45-120 meV are found, without any clear correlation with photovoltaic performance, when the same active layer is used in an organic solar cell.
  •  
33.
  • Upreti, Tanvi, et al. (författare)
  • Slow Relaxation of Photogenerated Charge Carriers Boosts Open-Circuit Voltage of Organic Solar Cells
  • 2021
  • Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:40, s. 9874-9881
  • Tidskriftsartikel (refereegranskat)abstract
    • Among the parameters determining the efficiency of an organic solar cell, the open-circuit voltage (V-OC) is the one with most room for improvement. Existing models for the description of V-OC assume that photogenerated charge carriers are thermalized. Here, we demonstrate that quasi-equilibrium concepts cannot fully describe V-OC of disordered organic devices. For two representative donor:acceptor blends, it is shown that V-OC is actually 0.1-0.2 V higher than it would be if the system was in thermodynamic equilibrium. Extensive numerical modeling reveals that the excess energy is mainly due to incomplete relaxation in the disorder-broadened density of states. These findings indicate that organic solar cells work as nonequilibrium devices, in which part of the photon excess energy is harvested in the form of an enhanced V-OC.
  •  
34.
  • Wang, Yuming, et al. (författare)
  • Optical Gaps of Organic Solar Cells as a Reference for Comparing Voltage Losses
  • 2018
  • Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 8:28
  • Tidskriftsartikel (refereegranskat)abstract
    • The voltage loss, determined by the difference between the optical gap (E-g) and the open-circuit voltage (V-OC), is one of the most important parameters determining the performance of organic solar cells (OSCs). However, the variety of different methods used to determine E-g makes it hard to fairly compare voltages losses among different material systems. In this paper, the authors discuss and compare various E-g determination methods and show how they affect the detailed calculation of voltage losses, as well as predictions of the maximum achievable power conversion efficiency. The aim of this paper is to make it possible for the OSC community to compare voltage losses in a consistent and reasonable way. It is found that the voltage losses for strongly absorbed photons in state-of-the-art OSCs are not much less than 0.6 V, which still must be decreased to further enhance efficiency.
  •  
35.
  • Yang, Lei, et al. (författare)
  • Sulfur vs. tellurium: the heteroatom effects on the nonfullerene acceptors
  • 2019
  • Ingår i: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 62:7, s. 897-903
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of chalcogen heteroatom variation on donor materials has been systematically investigated. However, this effect on acceptors has rarely been explored. Herein, nonfullerene acceptors BFPSP and BFPTP were reported by simply changing the chalcogen atoms from S to Te. The differences between BFPSP and BFPTP in light absorption, energy levels, excited-state lifetimes, energy loss, charge mobilities, morphology, and photovoltaic properties were systematically investigated to understand the heteroatom effects. More importantly, the electroluminescence spectra, external quantum efficiency of photovoltaics and TD-DFT calculations revealed that the triplet excited state (T-1) in energy of BFPTP equals to the charge transfer (CT) state in PBDB-T:BFPTP, which allows T-1 excitons, generated by intersystem crossing, to split into free charges to contribute to the efficiency. This contribution provides a strategy for tuning the photophysical properties of nonfullerene acceptors and designing high performance triplet materials for OSCs.
  •  
36.
  • You, Yintao, et al. (författare)
  • An organic multilevel non-volatile memory device based on multiple independent switching modes
  • 2014
  • Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 15:9, s. 1983-1989
  • Tidskriftsartikel (refereegranskat)abstract
    • The demand for higher data density memory structures is greater today than ever before. Multilevel resistive organic memory devices (OMD) provide an ideal solution, in being easily fabricated, cost-effective and at the same time promising high storage capacity. However, conventional methods for multilevel OMDs impose demanding requirements on material properties and attain only limited performance. We hereby provide an alternative design concept that combines multiple switching modes in one device to realize multilevel function. The device possesses a simple structure by using a ferroelectric phase-separated blend as the active layer. Two switching modes, the ferroelectric switching and the metallic filament switching, are realized simultaneously in this device, and enable a ternary storage function. The cross-section scanning electron microscope (SEM) images provide a strong evidence of the formation and annihilation of the metallic filament.
  •  
37.
  • Zhan, Lingling, et al. (författare)
  • A Near-Infrared Photoactive Morphology Modifier Leads to Significant Current Improvement and Energy Loss Mitigation for Ternary Organic Solar Cells
  • 2018
  • Ingår i: Advanced Science. - : WILEY. - 2198-3844. ; 5:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, efficient organic solar cells (OSCs) are realized with the ternary blend of a medium band gap donor (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b]dithiophene))-alt-(5,5-(1,3-di-2-thienyl-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c]dithiophene-4,8-dione)] (PBDB-T)) with a low band gap acceptor (2,2-((2Z,2Z)-(((2,5-difluoro-1,4-phenylene)bis(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b]dithiophene-6,2-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (HF-PCIC)) and a near-infrared acceptor (2,2-((2Z,2Z)-(((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b]dithiophene-2,7-diyl)bis(4-((2-ethylhexyl)oxy)thiophene-5,2-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IEICO-4F)). It is shown that the introduction of IEICO-4F third component into PBDB-T:HF-PCIC blend increases the short-circuit current density (J(sc)) of the ternary OSC to 23.46 mA cm(-2), with a 44% increment over those of binary devices. The significant current improvement originates from the broadened absorption range and the active layer morphology optimization through the introduction of IEICO-4F component. Furthermore, the energy loss of the ternary cells (0.59 eV) is much decreased over that of the binary cells (0.80 eV) due to the reduction of both radiative recombination from the absorption below the band gap and nonradiative recombination upon the addition of IEICO-4F. Therefore, the power conversion efficiency increases dramatically from 8.82% for the binary cells to 11.20% for the ternary cells. This work provides good examples for simultaneously achieving both significant current enhancement and energy loss mitigation in OSCs, which would lead to the further construction of highly efficient ternary OSCs.
  •  
38.
  • Zhang, Huotian (författare)
  • Loss Mechanisms In Non-Fullerene Organic Solar Cells
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Photovoltaics are one of the most important sustainable energy sources in the 21st century. Among photovoltaics, organic solar cells (OSCs) offer many advantages such as ease of processing, lightweight, the potential for flexibility, and tunable properties. Its peculiar nature and complexity present a fascinating charm, attracting many researchers. Thanks to researchers' efforts, the power conversion efficiency (PCE) of OSCs has been boosted from 1% to 19% during the last three decades. Despite the exciting PCE, some problems remain to be solved, for example, the large voltage loss and long-term stability. The aim of this thesis is to understand the fundamental physics of the state-of-the-art OSCs, especially the loss mechanism. Ultimately, properly understanding the mechanisms will sever as the basis of OSCs further improvements and commercialization. This work focuses on the loss mechanisms of OSCs, particularly the open-circuit voltage and the fill factor. The beginning of this thesis introduces basic concepts regarding semiconductors physics and donor-acceptor OSCs. This part explains how a photon is used to generate electricity and the fundamentals of organic electronics. Subsequently, the detailed balance in a solar cell is reviewed, which is the basis of voltage loss analysis. In this part, we see how the input, recombination, and output form a balance. Then, the way to determine the voltage loss is shown, and the latest understandings in reducing the loss are reviewed. The fill factor, as a measure of the quality of a solar cell, is a complex parameter, especially in OSCs.The latter part of this thesis starts from the photophysical processes in an OSC, and then relates intrinsic parameters to the fill factor. The figure of merits has been employed to express the fill factor analytically. In the end, experimental methods and basic principles for the previous analysis are introduced, including Fourier transform infrared spectroscopy, the external quantum efficiency of photovoltaics (EQEPV), spectrograph for electroluminescence or photoluminescence, transient absorption, and time-delayed collection field. Overall, the thesis combined thermal dynamics and charge dynamics to analyze voltage losses and fill factor losses. The author hopes this work can contribute to a better understanding of the loss mechanisms OSCs.
  •  
39.
  • Zhao, Fuwen, et al. (författare)
  • Highly efficient fused ring electron acceptors based on a new undecacyclic core
  • 2021
  • Ingår i: Materials Chemistry Frontiers. - : ROYAL SOC CHEMISTRY. - 2052-1537. ; 5:4, s. 2001-2006
  • Tidskriftsartikel (refereegranskat)abstract
    • Two FREAs, IUIC-O and IUIC-T, based on an undecacyclic core were developed. IUIC-T having a higher extinction coefficient affords aligned energy levels with PBDB-T, finer nanoscale morphology and more orderly molecular stacking, thus achieving more efficient exciton dissociation and charge transport. Therefore, the PBDB-T:IUIC-T based OSC gains a higher PCE of 13.05%.
  •  
40.
  • Zhu, Can, et al. (författare)
  • Tuning the electron-deficient core of a non-fullerene acceptor to achieve over 17% efficiency in a single-junction organic solar cell
  • 2020
  • Ingår i: Energy & Environmental Science. - : ROYAL SOC CHEMISTRY. - 1754-5692 .- 1754-5706. ; 13:8, s. 2459-2466
  • Tidskriftsartikel (refereegranskat)abstract
    • Finding effective molecular design strategies to enable efficient charge generation and small energy loss is among the long-standing challenges in developing high performance non-fullerene organic solar cells (OSCs). Recently, we reported Y-series non-fullerene acceptors with an electron-deficient-core-based fused structure (typically Y6), opening a new door to achieve high external quantum efficiency (∼80%) while maintaining low energy loss (∼0.57 eV). On this basis, further reducing the energy losses and ultimately improving the performance of OSCs has become a research hotspot. In this paper, we design and synthesize a new member of the Y-series acceptor family, Y18, which adopts a fused benzotriazole segment with unique luminescence properties as its electron-deficient core. Compared to Y6, the benzotriazole-based acceptor Y18 exhibits extended optical absorption and higher voltage. Consequently, the device delivers a promising power conversion efficiency of 16.52% with a very low energy loss of 0.53 eV. Further device optimization by exploiting a ternary blend strategy allowed us to achieve a high efficiency of 17.11% (certified as 16.76% by NREL). Y18 may become one of the most important candidate materials for its broader absorption spectra and higher voltage of Y18 (compared to Y6) in the OSCs field.
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