A deconvoluted PL approach to probe the charge carrier dynamics of the grain interior and grain boundary of a perovskite film for perovskite solar cell applications

Abstract

We explore a new characterization approach capable of probing the grain interior (GI) and grain boundary (GB) of a CH₃NH₃PbI_3−xCl_x perovskite thin film. In particular, we have found that the photoluminescence (PL) spectrum observed for a CH₃NH₃PbI_3−xCl_x perovskite thin film is asymmetric, and can be deconvoluted using a bi-Gaussian function, representing the ordered and disordered phases of the perovskite film. In order to understand the origin of the ordered and disordered phases of the perovskite film, two-dimensional (2D) PL mapping was performed to resolve the PL spectra at the nanoscale level. Quantitative analysis of the local PL spectra revealed that the ordered phase originated from the GIs while the disordered phase mainly came from the GBs. In particular, power-dependent PL measurements of the deconvoluted PL spectra revealed that smaller grained perovskites showed defect-mediated recombination at GBs but exciton-like transitions at GIs. In contrast, perovskite films with large grains followed an excellent power law, showing exciton-like recombination at both GIs and GBs. As expected, perovskite solar cells fabricated with large grains showed an increased efficiency with higher light absorption and higher charge extraction efficiency.