Unravelling the Effects of Cl Addition in Single Step CH₃NH₃PbI₃ Perovskite Solar Cells

The effect of film morphology on the photovoltaic performances is illustrated. Pin holes free and uniform films could be formed by slowing down the crystallization rate through additional of excess CH₃NH₃⁺. Though better film coverage is obtained, the device series resistance increases as excess CH₃NH₃I increases. Thermogravimetric analysis confirms the presence of residual excess CH₃NH₃I in the final film. When chlorine is added to the CH₃NH₃⁺ rich system, CH₃NH₃Cl is formed and can easily sublime during annealing at 100 °C. A little trace of excess CH₃NH₃Cl can be detected from thermogravic analysis, and the residual chlorine atoms match with XPS reading