| 1. |
- Chen, Mengyun, et al.
(författare)
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Kinetically Controlled Synthesis of Quasi-Square CsPbI3 Nanoplatelets with Excellent Stability
- 2023
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Ingår i: Small. - : WILEY-V C H VERLAG GMBH. - 1613-6810 .- 1613-6829.
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Tidskriftsartikel (refereegranskat)abstract
- Nanoplatelets (NPLs) share excellent luminescent properties with their symmetric quantum dots counterparts and entail special characters benefiting from the shape, like the thickness-dependent bandgap and anisotropic luminescence. However, perovskite NPLs, especially those based on iodide, suffer from poor spectral and phase stability. Here, stable CsPbI3 NPLs obtained by accelerating the crystallization process in ambient-condition synthesis are reported. By this kinetic control, the rectangular NPLs into quasi-square NPLs are tuned, where enlarged width endows the NPLs with a lower surface-area-to-volume ratio (S/V ratio), leading to lower surficial energy and thus improved endurance against NPL fusion (cause for spectral shift or phase transformation). The accelerated crystallization, denoting the fast nucleation and short period of growth in this report, is enabled by preparing a precursor with complete transformation of PbI2 into intermediates (PbI3-), through an additional iodide supplier (e.g., zinc iodide). The excellent color stability of the materials remains in the light-emitting diodes under various bias stresses.
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| 2. |
- Qian, Deping, et al.
(författare)
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Correlating the Hybridization of Local-Exciton and Charge-Transfer States with Charge Generation in Organic Solar Cells
- 2023
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- In organic solar cells with very small energetic-offset (& UDelta;ELE - CT), the charge-transfer (CT) and local-exciton (LE) states strongly interact via electronic hybridization and thermal population effects, suppressing the non-radiative recombination. Here, we investigated the impact of these effects on charge generation and recombination. In the blends of PTO2:C8IC and PTO2:Y6 with very small, ultra-fast CT state formation was observed, and assigned to direct photoexcitation resulting from strong hybridization of the LE and CT states (i.e., LE-CT intermixed states). These states in turn accelerate the recombination of both CT and charge separated (CS) states. Moreover, they can be significantly weakened by an external-electric field, which enhanced the yield of CT and CS states but attenuated the emission of the device. This study highlights that excessive LE-CT hybridization due to very low , whilst enabling direct and ultrafast charge transfer and increasing the proportion of radiative versus non-radiative recombination rates, comes at the expense of accelerating recombination losses competing with exciton-to-charge conversion process, resulting in a loss of photocurrent generation.
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| 3. |
- Li, Man, et al.
(författare)
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Advances in Tin(II)-Based Perovskite Solar Cells : From Material Physics to Device Performance
- 2022
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Ingår i: Small Structures. - : Wiley. - 2688-4062. ; 3:1
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Forskningsöversikt (refereegranskat)abstract
- During the past decade, metal halide perovskites are widely studied in the field of optoelectronic materials due to their unique optical and electrical properties. Lead-based halide perovskite solar cells (PSCs), in particular, currently achieve a record efficiency of 25.5%, thus showing strong potential in industrial application. However, toxicity of lead-based perovskite materials possesses great concerns to natural environment and human body. Therefore, the quest for nontoxic and eco-friendly elements to replace lead in perovskites is of great interest. Among all the element choices, tin(II) (Sn2+) is the most promising candidate. As a rising star of lead-free PSCs, Sn-based PSCs have drawn much attention and made promising progress during the past few years. While the rapid oxidation and decomposition of Sn-based perovskites result in poor stability and low efficiency of PSCs. In this review, structural, optoelectronic properties and the critical issues of Sn-based perovskite materials are analyzed. Then, a detailed discussion on the recent methods in solving critical issues of Sn-based perovskite devices, from optimization on materials physics to device performance, is also presented. Finally, remaining challenges and future perspective are given to advance the progression of Sn-based PSCs.
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| 4. |
- Qin, Jiajun, et al.
(författare)
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From optical pumping to electrical pumping: the threshold overestimation in metal halide perovskites
- 2023
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Ingår i: Materials Horizons. - : ROYAL SOC CHEMISTRY. - 2051-6347 .- 2051-6355. ; 10:4, s. 1446-1453
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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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| 5. |
- Wang, Heyong, 1989-, et al.
(författare)
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Impacts of the Lattice Strain on Perovskite Light-Emitting Diodes
- 2023
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Ingår i: Advanced Energy Materials. - : Wiley-V C H Verlag GMBH. - 1614-6832 .- 1614-6840. ; 13:33
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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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| 6. |
- Zhang, Jibin, et al.
(författare)
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A Multifunctional "Halide-Equivalent" Anion Enabling Efficient CsPb(Br/I)(3) Nanocrystals Pure-Red Light-Emitting Diodes with External Quantum Efficiency Exceeding 23%
- 2023
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 35:8
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Tidskriftsartikel (refereegranskat)abstract
- Pure-red perovskite LEDs (PeLEDs) based on CsPb(Br/I)(3) nanocrystals (NCs) usually suffer from a compromise in emission efficiency and spectral stability on account of the surface halide vacancies-induced nonradiative recombination loss, halide phase segregation, and self-doping effect. Herein, a "halide-equivalent" anion of benzenesulfonate (BS-) is introduced into CsPb(Br/I)(3) NCs as multifunctional additive to simultaneously address the above challenging issues. Joint experiment-theory characterizations reveal that the BS- can not only passivate the uncoordinated Pb2+-related defects at the surface of NCs, but also increase the formation energy of halide vacancies. Moreover, because of the strong electron-withdrawing property of sulfonate group, electrons are expected to transfer from the CsPb(Br/I)(3) NC to BS- for reducing the self-doping effect and altering the n-type behavior of CsPb(Br/I)(3) NCs to near ambipolarity. Eventually, synergistic boost in device performance is achieved for pure-red PeLEDs with CIE coordinates of (0.70, 0.30) and a champion external quantum efficiency of 23.5%, which is one of the best value among the ever-reported red PeLEDs approaching to the Rec. 2020 red primary color. Moreover, the BS--modified PeLED exhibits negligible wavelength shift under different operating voltages. This strategy paves an efficient way for improving the efficiency and stability of pure-red PeLEDs.
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| 7. |
- Zhang, Tiankai, et al.
(författare)
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Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells
- 2022
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Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 377:6605, s. 495-501
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Tidskriftsartikel (refereegranskat)abstract
- Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2,7,7-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4-tert-butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.
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| 8. |
- Zhou, Wencai, et al.
(författare)
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The Role of Grain Boundaries on Ion Migration and Charge Recombination in Halide Perovskites
- 2024
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Ingår i: Small. - : WILEY-V C H VERLAG GMBH. - 1613-6810 .- 1613-6829.
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Tidskriftsartikel (refereegranskat)abstract
- Grain boundaries (GBs) have a significant role in polycrystalline perovskite solar cells (PSCs). However, there is ongoing debate regarding the impact of GBs on the performance and long-term stability of PSCs. Employing the first-principles molecular dynamics for perovskites, the iodine vacancy defect migrations both in bulk and at GBs are investigated. i) The positive iodine vacancy (VI+) is found that have both lower formation energy (1.4 eV) and activation energy (0.18 eV) than those of neutral iodine vacancy (VI), statistically. It indicated the VI+ acts as the dominant migrated iodine vacancy rather than VI; ii) the iodine vacancy at GBs has approximate to 0.48 eV higher activation energy than those in bulk, which leads to the accumulation of iodine vacancy at GBs; iii) the presence of VI+ result in a 3-fold increase in charge recombination ratio at GBs, compared to pristine PSCs. Based on quantum molecular dynamics statistical results, which are consistent with experimental measurements, insights into iodine vacancy migration both at GBs and in the bulk are gained. This understanding can be valuable for defects engineering related to ion migration, in order to improve the long-term stability and promote the performance of PSCs. Understanding defects engineering related to ion migration is crucial for enhancing the long-term stability and performance of hybrid perovskite solar cells. Iodine vacancies accumulate at grain boundaries due to lower formation energy and higher migration potential barrier compared to those in the bulk, which further increase the nonradiative recombination. image
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| 9. |
- Karimipour, Masoud, et al.
(författare)
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Functionalized MXene/Halide Perovskite Heterojunctions for Perovskite Solar Cells Stable Under Real Outdoor Conditions
- 2023
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 13:44
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Tidskriftsartikel (refereegranskat)abstract
- Despite the performance improvement in perovskite solar cells (PSCs) when MXenes are employed as transport layers, device stability studies are still missing. Especially under real outdoor conditions where devices are subjected to the synergy of multiple stressors. In this work, functionalized 2D titanium carbide (Ti3C2) MXene is employed in normal PSC configuration, at the interface between the halide perovskite and the hole transport layer. The functionalization of the Ti3C2 MXene is made utilizing the same organic additive passivating the halide perovskite layer. The functionalizing strategy creates a continuous link between the MXene and the halide perovskite layer. Champion MXene-based PSCs revealed a approximate to 22% efficiency, in comparison with the control device showing 20.56%. Stability analyses under ISOS protocols under different conditions (dark, continuous light irradiation and real outdoor analysis) reveal that the enhancement of the PSCs lifespan is always observed when the MXene layer is employed. Analysis under continuous light irradaition (ISOS-L) reveal an almost 100% retention of the efficiency for the MXene-modified device, and outdoor testing (ISOS-O) carried out for > 600 h reveals a T(80 )of approximate to 600 h, while the control device degrades completely. To the best of the authors knowledge, this is the first report of the stability assesment of MXene-based PSCs carried out under real outdoor (ISOS-O) conditions.
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| 10. |
- Lin, Dongxu, et al.
(författare)
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Construction of an Iodine Diffusion Barrier Using Network Structure Silicone Resin for Stable Perovskite Solar Cells
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 13:7, s. 8138-8146
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Tidskriftsartikel (refereegranskat)abstract
- Long-term stability of organic-inorganic hybrid perovskite solar cells (PSCs) is inhibited by ion diffusion. Herein, we introduce a thermally stable and hydrophobic silicone resin layer with a network structure as an interfacial layer between the perovskite and the hole-transporting layer ( HTL). Experimental and theoretical investigations confirm that the small Si-O-Si unit in the network forms both Si-I and Pb-O bonds with the perovskite surface, which physically and chemically inhibit the diffusion and self-release of iodine. Besides, the silicone resin layer suppresses the thermal crystallization of spiro-OMeTAD and optimizes the interfacial energy level alignment for hole extraction. The power conversion efficiency (PCE) of a perovskite solar cell with a silicone resin layer is improved to 21.11%. The device maintains more than 90.1% of its original PCE after 1200 h under 85 degrees C thermal stress, 99.6% after 2000 h under RH similar to 55 +/- 5%, and 83% of its original PCE after light soaking in air for 1037 h.
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