Influence of Bi doping on physical properties of lead halide perovskites: a comparative first-principles study between CsPbI3 and CsPbBr3

We study the effects of Bi doping on the physical properties of CsPbX3 (X = I or Br), promising active materials in application to the solar cell, using first-principles calculations with the hybrid functional. In both CsPbBr3 and CsPbI3, we find that excess electrons introduced by Bi replacing Pb (Bi-Pb) are mostly compensated by native acceptors such as Cs and Pb vacancies. As a result, the equilibrium Fermi level lies far below the defect level of Bi-Pb, indicating that Bi-Pb prefers the 1+ charge state over the neutral one. The band structure of Bi-doped CsPbX3 shows that the interaction between the defect and host states affects the conduction band, narrowing the bandgap of the host material. The formation energy of Bi-Pb is smaller in CsPbI3 than in CsPbBr3, implying the easier doping of Bi in CsPbI3. The computational results successfully explain distinct doping effects on absorption spectra between CsPbI3 and CsPbBr3, which was observed in recent experiments. (c) 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).