Influence of Defects on the Photovoltaic Properties of Perovskite Semiconductor CsSnI$_{3}$

CsSnI$_{3}$ is a prototype inorganic halide perovskite that has recently been proposed as a photovoltaic material. Through first-principles calculations, we show that the concentration control of intrinsic defects is critical for optimizing the photovoltaic properties of CsSnI$_{3}$. Under a Sn-poor condition, high concentration of acceptor defects such as Sn or Cs vacancies can form easily and produce a high p-type conductivity, and deep level defects that can become electron-hole recombination centers, all have high energy. This condition is optimal for growing CsSnI$_{3}$ as hole-transport material in solar cells. In contrast, when Sn becomes richer, the concentration of acceptor defects decreases, so the p-type conductivity may drop to a moderate level, which can increase the shunt resistance and thus the efficiency of the solar cells with CsSnI$_{3}$ as the light absorber material (LAM). However, under the Sn-rich condition, the concentration of a deep-level donor defect Sn$_{\mathrm{I}}$ will increase, causing electron traping and non-radiative electron-hole recombination. Therefore, we propose that a moderately Sn-rich condition is optimal when CsSnI$_{3}$ is used as LAM.