The low density of deep trapping defects in metal halide perovskites (MHPs) is essential for high-performance optoelectronic devices. Shallow traps in MHPs are speculated to enhance charge recombination lifetime. However, chemical nature and distribution of these shallow traps as well as their impact on solar cell operation remain unknown. Herein, we report that shallow traps are much richer in MHPs than traditional semiconductors, and their density can be enhanced by >100 times through local surface strain, indicating that shallow traps are mainly located at the surface. The surface strain is introduced by anchoring two-amine-terminated molecules onto formamidinium cations, and the shallow traps are formed by the band edge downshifting toward defect levels. The high-density shallow traps temporarily hold one type of charge and increased the concentration of the other type of free carrier in working solar cells by keeping photogenerated charges from bimolecular recombination, resulting in a reduced open-circuit voltage loss to 317 mV.

中文翻译：

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通过表面应变将金属卤化物钙钛矿中发射电荷的浅陷阱提高 >100 倍


金属卤化物钙钛矿 （MHP） 中低密度的深捕获缺陷对于高性能光电器件至关重要。据推测，MHP 中的浅陷阱可以提高电荷复合寿命。然而，这些浅陷阱的化学性质和分布以及它们对太阳能电池运行的影响仍然未知。本文报道了浅陷阱在 MHP 中的含量远高于传统半导体，并且它们的密度可以通过局部表面应变提高 >100 倍，表明浅陷阱主要位于表面。通过将两个胺封端的分子锚定到甲脒阳离子上来引入表面应变，而浅陷阱是通过带边缘向缺陷水平下移而形成的。高密度浅陷阱暂时保持一种类型的电荷，并通过阻止光生电荷进行双分子复合，增加了工作太阳能电池中另一种自由载流子的浓度，从而将开路电压损失降低到 317 mV。