Motti Silvia G, Patel Jay B, Oliver Robert D J, Snaith Henry J, Johnston Michael B, Herz Laura M
Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.
TUM Institute for Advanced Study, Technische Universität München, Lichtenbergstr. 2a, 85748, Garching bei München, Germany.
Nat Commun. 2021 Nov 29;12(1):6955. doi: 10.1038/s41467-021-26930-4.
Mixed halide perovskites can provide optimal bandgaps for tandem solar cells which are key to improved cost-efficiencies, but can still suffer from detrimental illumination-induced phase segregation. Here we employ optical-pump terahertz-probe spectroscopy to investigate the impact of halide segregation on the charge-carrier dynamics and transport properties of mixed halide perovskite films. We reveal that, surprisingly, halide segregation results in negligible impact to the THz charge-carrier mobilities, and that charge carriers within the I-rich phase are not strongly localised. We further demonstrate enhanced lattice anharmonicity in the segregated I-rich domains, which is likely to support ionic migration. These phonon anharmonicity effects also serve as evidence of a remarkably fast, picosecond charge funnelling into the narrow-bandgap I-rich domains. Our analysis demonstrates how minimal structural transformations during phase segregation have a dramatic effect on the charge-carrier dynamics as a result of charge funnelling. We suggest that because such enhanced recombination is radiative, performance losses may be mitigated by deployment of careful light management strategies in solar cells.
混合卤化物钙钛矿可为串联太阳能电池提供最佳带隙，这是提高成本效益的关键，但仍可能受到有害的光照诱导相分离的影响。在这里，我们采用光泵太赫兹探测光谱来研究卤化物偏析对混合卤化物钙钛矿薄膜的电荷载流子动力学和传输特性的影响。我们惊奇地发现，卤化物偏析对太赫兹电荷载流子迁移率的影响可以忽略不计，并且富碘相中的电荷载流子没有强烈的局域化。我们进一步证明了在偏析的富碘区域中晶格非谐性增强，这可能有助于离子迁移。这些声子非谐性效应也证明了电荷以极快的皮秒级速度漏斗状注入窄带隙富碘区域。我们的分析表明，相分离过程中最小的结构转变如何由于电荷漏斗效应而对电荷载流子动力学产生显著影响。我们认为，由于这种增强的复合是辐射性的，因此通过在太阳能电池中部署精心设计的光管理策略，可能会减轻性能损失。
