Influence of Defects and Synthesis Conditions on the Photovoltaic Performance of Perovskite Semiconductor CsSnI3

CsSnI3 is a prototype inorganic halide perovskite that has recently been proposed as a strong candidate for photovoltaic applications because of its unique semiconductor properties. Through first-principle calculations, we show that the concentration control of intrinsic defects is critical for optimizing the photovoltaic properties of CsSnI3. Under a Sn-poor condition, a 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 with high energy. This condition is optimal for growing CsSnI3 as hole-transport material in solar cells. In contrast, when Sn becomes richer, the concentration of acceptor defects decreases; therefore, 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 CsSnI3 as the light absorber material (LAM). However, under the Sn-rich condition, the concentration of a deep-level donor defect SnI will increase, causing electron traping and non-radiative electron–hole recombination. Therefore, we propose that a moderately Sn-rich condition is optimal when CsSnI3 is used as the LAM. The defect properties of CsSnI3 are general, and the underlying chemistry is expected to be applicable to other halide perovskite semiconductors.