Bismuth incorporation has been shown to significantly decrease the performance of perovskite solar cells, which has led to the common belief that Bi_Pb is a strong nonradiative recombination center in hybrid perovskites. Using rigorous first-principles calculations, we demonstrate that Bi_Pb is not an efficient recombination center. However, Bi acts as a donor, and pushes the Fermi level closer to the conduction band; this shift promotes the formation of iodine interstitials, which are the actual nonradiative recombination centers. These insights explain why Bi incorporation is detrimental for the photovoltaic performance. More generally, it draws attention to the detrimental role unintentionally incorporated impurities can play, not by acting as nonradiative recombination centers themselves, but by shifting the Fermi level and thereby promoting the formation of efficiency-killing defects.

中文翻译：

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Bi掺入在甲基铵碘化铅中的非辐射复合中的隐藏作用

铋的掺入已显示会显着降低钙钛矿太阳能电池的性能，这导致人们普遍认为Bi _Pb是杂化钙钛矿中的强非辐射复合中心。使用严格的第一性原理计算，我们证明了Bi _Pb不是有效的重组中心。然而，Bi用作施主，将费米能级推至更接近导带。这种转变促进了碘填隙的形成，这些填隙是实际的非辐射复合中心。这些见解解释了为什么Bi掺入对光伏性能有害。更一般地，它引起人们对有害掺入的有害作用的注意，而不是通过自身充当非辐射复合中心，而是通过改变费米能级并由此促进效率杀灭缺陷的形成而无意识地掺入杂质。