Charge-Carrier Trapping Dynamics in Bismuth-Doped Thin Films of MAPbBr₃ Perovskite

Successful chemical doping of metal halide perovskites with small amounts of heterovalent metals has attracted recent research attention because of its potential to improve long-term material stability and tune absorption spectra. However, some additives have been observed to impact negatively on optoelectronic properties, highlighting the importance of understanding charge-carrier behavior in doped metal halide perovskites. Here, we present an investigation of charge-carrier trapping and conduction in films of MAPbBr₃ perovskite chemically doped with bismuth. We find that the addition of bismuth has no effect on either the band gap or exciton binding energy of the MAPbBr₃ host. However, we observe a substantial enhancement of electron-trapping defects upon bismuth doping, which results in an ultrafast charge-carrier decay component, enhanced infrared emission, and a notable decrease of charge-carrier mobility. We propose that such defects arise from the current approach to Bi-doping through addition of BiBr₃, which may enhance the presence of bromide interstitials.