In-depth Investigation of Methylamine Gas Post-treatment for MAPbI3 Films and its Potential for Upscaling Perovskite Solar Cells

Abstract

Scaling up perovskite solar cells (PSCs) for commercial applications requires maintaining film quality across large areas, a challenge often compounded by morphological defects and chemical heterogeneity. Methylamine gas treatment (MATM) offers a promising post-processing strategy by inducing liquefaction and recrystallization of Methylammonium-based perovskite films, thereby enhancing their uniformity and chemical homogeneity. However, how to properly conduct the MATM-particularly the influence of environmental humidity on its outcome has rarely been investigated. In this study, we report that environmental moisture critically undermines MATM efficacy by triggering side reactions that generate PbO, PbIOH, and MAPbI2OH impurities. Through systematic comparison of MAPbI3 films treated under dry and humid conditions, we elucidate the degradation mechanisms using various analyses and conclude moisture exposure during MATM drastically increases trap densities and non-radiative recombination, leading to reduced carrier lifetimes and photovoltaic performance. A PSC with an initial power conversion efficiency (PCE) of 16.67% exhibits a significant improvement to 19.48% after undergoing MATM in a dry environment. In contrast, when MATM is performed under humid conditions, although the surface smoothness of the MAPbI3 film is greatly improved, the PCE of the device declines instead of increasing. This outcome highlights the detrimental effects of side reactions induced by moisture during the MATM process. These findings underscore the importance of moisture isolation in MATM to enable the reliable upscaling of high-efficiency and stable perovskite solar modules.