Impact of Bi doping on nonradiative carrier recombination in CsPbI₃

Bi doping is attractive in lead halide perovskites due to the potential ability of narrowing the band gap and improving the structural stability. Nevertheless, whether Bi acts as a nonradiative recombination center is still under debate. Using first-principles calculations, here, we show that Bi-assisted recombination is very weak in CsPbI₃ even with heavy doping, in spite of the fact that Bi creates a deep level in the band gap; however, Bi as an electron donor raises the Fermi level and facilitates the formation of interstitial iodine, which is the dominant recombination center in CsPbI₃. We further suggest that Na as a shallow acceptor can counteract electrical doping of Bi and downshift the Fermi level, thus inhibiting the unwanted formation of interstitial iodine. Also, it is expected that Bi- and Na-doped CsPbI₃ has higher phase stability compared with the pure system on account of the optimized tolerance factor. This work highlights the significance of taking into account the impact of compensating intrinsic defects on nonradiative recombination in studying heterovalent doping.