Rakowski Rafal, Fisher William, Calbo Joaquín, Mokhtar Muhamad Z, Liang Xinxing, Ding Dong, Frost Jarvist M, Haque Saif A, Walsh Aron, Barnes Piers R F, Nelson Jenny, van Thor Jasper J
Life Science Department, Imperial College London, London SW7 2AZ, UK.
Department of Physics, Imperial College London, London SW7 2AZ, UK.
Nanomaterials (Basel). 2022 May 10;12(10):1616. doi: 10.3390/nano12101616.
Hybrid halide perovskites materials have the potential for both photovoltaic and light-emitting devices. Relatively little has been reported on the kinetics of charge relaxation upon intense excitation. In order to evaluate the illumination power density dependence on the charge recombination mechanism, we have applied a femtosecond transient mid-IR absorption spectroscopy with strong excitation to directly measure the charge kinetics via electron absorption. The irradiance-dependent relaxation processes of the excited, photo-generated charge pairs were quantified in polycrystalline MAPbI, MAPbBr, and (FAPbI)(MAPbBr) thin films that contain either methylamonium (MA) or formamidinium (FA). This report identifies the laser-generated charge species and provides the kinetics of Auger, bimolecular and excitonic decay components. The inter-band electron-hole (bimolecular) recombination was found to dominate over Auger recombination at very high pump irradiances, up to the damage threshold. The kinetic analysis further provides direct evidence for the carrier field origin of the vibrational Stark effect in a formamidinium containing perovskite material. The results suggest that radiative excitonic and bimolecular recombination in MAPbI at high excitation densities could support light-emitting applications.
混合卤化物钙钛矿材料在光伏和发光器件方面都具有潜力。关于强激发下电荷弛豫动力学的报道相对较少。为了评估光照功率密度对电荷复合机制的依赖性，我们应用了具有强激发的飞秒瞬态中红外吸收光谱，通过电子吸收直接测量电荷动力学。在含有甲基铵（MA）或甲脒（FA）的多晶MAPbI、MAPbBr和（FAPbI）（MAPbBr）薄膜中，对激发的光生电荷对的辐照度依赖性弛豫过程进行了量化。本报告确定了激光产生的电荷种类，并提供了俄歇、双分子和激子衰变成分的动力学。发现在非常高的泵浦辐照度下，直至损伤阈值，带间电子 - 空穴（双分子）复合比俄歇复合占主导。动力学分析进一步为含甲脒钙钛矿材料中振动斯塔克效应的载流子场起源提供了直接证据。结果表明，在高激发密度下，MAPbI中的辐射激子和双分子复合可支持发光应用。
