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Reorientational dynamics of organic cations in perovskite-like coordination polymers
摘要： Here we report the dynamics of organic cations as guest molecules in a perovskite host-framework. The molecular motion of CH3NH3+ (MAFe), (CH3)2NH2+ (DMAFe) and (CH3)3NH+ (TrMAFe) in the cage formed by KFe(CN)63? units was studied using a combination of experimental methods: (i) thermal analysis, (ii) dielectric and electric studies, (iii) optical observations, (iv) EPR and 1H NMR spectroscopy and (v) quasielastic neutron scattering (QENS). In the case of MAFe and TrMAFe, the thermal analysis reveals one solid-to-solid phase transition (PT) and two PTs for the DMAFe crystal. A markedly temperature-dependent dielectric constant indicates the tunable and switchable properties of the complexes. Also, their semiconducting properties are confirmed by a dc conductivity measurement. The broadband dielectric relaxation is analyzed for the TrMAFe sample in the frequency range of 100 Hz–1 GHz. QENS shows that we deal rather with the localized motion of the cation than a diffusive one. Three models, which concern the simultaneous rotation of the CH3 and/or NH3 group, π-flips and free rotations of the organic cation, are used to fit the elastic incoherent structure factor. The 1H NMR spin–lattice relaxation time for all compounds under study, as well as the second moments, has been measured in a wide temperature range. In all studied samples, the temperature dependence of the second moment of the proton NMR line indicated the gradual evolution of the molecular movements from the rigid state up to a highly disordered one.
关键词： quasielastic neutron scattering,phase transitions,perovskite,coordination polymers,dielectric properties,NMR spectroscopy,dynamics,organic cations
更新于2025-11-14 17:28:48
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Phase control of quasi-2D perovskites and improved light-emitting performance by excess organic cations and nanoparticle intercalation
摘要： The optoelectronic properties of quasi-two-dimensional organic–inorganic hybrid perovskites can be tuned by controlling the formation of Ruddlesden–Popper type phases, which enables diverse device applications such as photovoltaics and light-emitting diodes (LEDs). Herein, the influence of excess organic cations on the phase formation of (PEA)2MAn?1PbnBr3n+1 is systematically investigated with various mixing ratios to discover the phase distribution beneficial for light-emitting diodes. It is found that PEA cations exceeding Pb ions in molar ratio are required to produce small-n phases in the films with a strong photoluminescence, while excess MA cations enable the formation of more large-n phases. Low electrical conductivity inherent to the properties of quasi-2D perovskites is further lowered by the introduction of excess organic cations. This is overcome by the intercalation of zinc oxide (ZnO) nanoparticles (NPs) into the blocking layers composed of PEA cations. Importantly, these metal oxide NPs also modulate the phase distribution, enabling the realization of bright green quasi-2D perovskites with a better stability and a maximum luminance of nearly 60 000 cd m?2, which is the highest brightness compared to the so far reported quasi-2D perovskite LEDs incorporating organic cations.
关键词： phase control,excess organic cations,nanoparticle intercalation,light-emitting diodes,quasi-2D perovskites
更新于2025-09-19 17:15:36
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Conjugated Organic Cations Enable Efficient Self-Healing FASnI3 Solar Cells
摘要： The introduction of large-volume amines (LVAs) in Sn-based perovskite films has been shown to lead to promising power conversion efficiency (PCE) in Pb-free perovskite solar cells (PSCs). However, the LVAs adopted so far (e.g., phenylethylammonium [PEA] and butylammonium [BA]) are insulating and could impede charge extraction within the perovskite film. Herein, a conjugated LVA, 3-phenyl-2-propen-1-amine (PPA), is introduced in formamidinium tin iodide (FASnI3) perovskite. Our results show that the incorporation of PPA results in enlarged grain sizes, reduced trap density, preferential orientation, efficient charge extraction, and enhanced structural stability of FASnI3 film. These positive effects help in achieving efficient PSCs with a PCE as high as 9.61% with negligible hysteresis and outstanding stability (remains 92% of its initial PCE value after 1,440 h). Furthermore, the presence of PPA enables a self-healing action of PSCs. Most importantly, we report large-area (1 × 1 cm2) Sn-based PSCs achieving PCE of 7.08%.
关键词： FASnI3 solar cells,Lead-free perovskite,Photovoltaic performance,Self-healing,Conjugated organic cations
更新于2025-09-19 17:13:59
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Effects of Organic Cations on Carrier Transport at the Interface between Perovskites and Electron Transport Layers in (FA,MA)SnI <sub/>3</sub> Solar Cells
摘要： Charge extraction at carrier transport layers adjacent to perovskites is crucial for the optimization of perovskite solar cells. In particular, Sn–perovskites with no lead elements are known to struggle from charge extraction. Here, we report the effects of organic ligands like FA and MA (FA = HC(NH2)2+; MA = CH3NH3+) on charge separation at the interface between electron transport layers and perovskites. TiO2 mesoporous covering the tin-perovskites show significant changes in electronic structure and built–in potentials according to the ratio of FA to MA. Through a local probe with potential and current mapping, charge transport has been intensively examined. The best cell in this study is obtained as 5.37% at FA : MA = 3 : 1 with only iodine at the halide sites. Even though the value itself is not comparable with lead halides but it could pave a new direction to improve lead–free perovskite solar cells.
关键词： perovskite solar cells,tin perovskites,TiO2 mesoporous,charge extraction,organic cations
更新于2025-09-11 14:15:04
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Effects of n-butyl amine incorporation on the performance of perovskite light emitting diodes
摘要： The efficiency of perovskite light emitting diodes (PeLEDs) is crucially limited by leakage current and nonradiative recombination. Here we introduce n-butyl amine (BA) to modulate the growth of perovskite films as well as improve the performance of PeLEDs, and investigate in details the effects of BA incorporation on the structural, optical, and electrical characteristics of perovskite films. The results indicate that BA would terminate the grain surface and inhibit crystal growth, leading to increased radiative recombination. However, BA overload would make the films loose and recreate shunt paths. The electrical detriment of BA overload outweighs its optical benefit. As a result, optimal PeLEDs can be obtained only with moderate BA incorporation.
关键词： optical and electrical characteristics,butyl amine,crystal growth,bulky organic cations,perovskite light emitting diodes
更新于2025-09-04 15:30:14