Hidden role of Bi incorporation in nonradiative recombination in methylammonium lead iodide

Abstract

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.