Substituting Cs for MA on the surface of MAPbI(3) perovskite: A first-principles study

Recently, mixed cation/anion perovskite solar cells (PSCs) have attracted considerable attention due to their higher stability and better photovoltage performance than pure ABX(3) perovskite solar cells. However, the fundamental mechanism of such an improvement has not yet been fully investigated. In this paper, substituting cesium cation for methylammonium cation of the (1 0 0) surface of CH3NH3PbI3 perovskites was made to study the improvement of stability and electronic properties of MAPbI(3) perovskite. The results show that the decomposition energies of perovskite increase with the increased concentration of doping Cs+, which indicates that the thermodynamic stability can be enhanced. By analyzing the Bader charge and charge density difference of the perovskite/TiO2 heterostructures, we find that the system of doping Cs+ transfers more electrons to TiO2 since the distance between I and Ti reduces. Doping Cs+ can make the PbI6 octahedral frame tilt and the tilting orientation is different for different concentration of Cs+. Meanwhile, the band gap increases with the increased concentration of Cs+, which leads to the increase in open circuit voltage V-OC. This study can give some guidance for improving stability and PCE of the perovskite solar cells.