It has been experimentally established that $\mathrm{Bi}$ doping drastically enhances the nonradiative recombination in MA$\mathrm{Pb}\mathrm{Br}$${}_3$ (where MA represents the methylammonium ion), but the microscopic mechanism underlying this experimental observation remains unclear. Here, we perform rigorous first-principles calculations to investigate the nonradiative recombination in MA$\mathrm{Pb}\mathrm{Br}$${}_3$ with $\mathrm{Bi}$ doping. We show that while $\mathrm{Bi}$${}_{\mathrm{Pb}}$ substitutional defects themselves are not a nonradiative recombination center, $\mathrm{Bi}$ doping significantly alters the Fermi level, leading to significantly reduced formation energy of bromine interstitials ($\mathrm{Br}$${}_i$). Bromine interstitials are, in fact, a strong nonradiative recombination center with a calculated total capture coefficient of ${10}^{-7}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at room temperature, agreeing well with experiment. Hence, $\mathrm{Bi}$${}_{\mathrm{Pb}}$ could indirectly enhance the nonradiative recombination in MA$\mathrm{Pb}\mathrm{Br}$${}_3$ by promoting the formation of efficiency-killing $\mathrm{Br}$${}_i$. These findings underscore a detrimental effect of heterovalent cation doping, which may inadvertently introduce nonradiative recombination centers and limit the performance of perovskite optoelectronic devices.

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• Carrier generation & recombination
• Defects
• Electron-phonon coupling
• Optoelectronics
• Organic-inorganic hybrid perovskites
• Photovoltaic absorbers
• Semiconductor compounds
• Solar cells