Influence of defect-state on the carrier dynamics in MAPbI3 polycrystalline films

In this paper, a transient absorption microscope with submicron resolution is used to detect the internal and grain boundary regions of the prepared polycrystalline thin film grains, and the obtained transient absorption spectra are subjected to singular value decomposition and global fitting. The contributions of hot carriers, cooled carriers, and defect-trapped carriers to the transient absorption signals and the dynamic evolution of the carriers among themselves are elucidated. By comparing the carrier dynamics taking place at the boundary and internal regions, we find that the benign shallow defect state in the grain boundary region has a positive effect on accelerating the cooling of hot carriers, while the deep energy level defects induce excited state absorption signals. This study provides a basis for further understanding the effect of grain boundary defects on the performance of polycrystal perovskite devices.