The influence of the I/Cl ratio on the performance of CH3NH3PbI3−xClx-based solar cells: why is CH3NH3I : PbCl2 = 3 : 1 the “magic” ratio?

Abstract

Methylammonium lead trihalide (CH₃NH₃PbI_3−xCl_x) perovskites are usually synthesized from two precursors, CH₃NH₃I and PbCl₂ at a ratio of 3 : 1. It was found that a slight adjustment of the I/Cl ratio in the precursor mixture plays a strong effect on solar cell performance. In this study, perovskites made with different I/Cl ratios were comparatively studied. In combination with X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) measured at the Pb L₃-edge, we demonstrate that the device performance can be directly correlated to the change in the coordination environment of Pb.