Evolution of Two-Dimensional Perovskite Films Under Atmospheric Exposure and Its Impact on Photovoltaic Performance.

Two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) have garnered significant attention due to their enhanced stability compared with their three-dimensional counterparts. However, the power conversion efficiency (PCE) of 2D perovskite solar cells (2D-PSCs) remains lower than that of 3D-PSCs. Understanding the microstructural evolution of 2D perovskite films during fabrication is essential for improving their performance. This study demonstrates that exposing bare 2D perovskite films to the atmosphere during device fabrication can significantly enhance the PCE of 2D-PSCs. The performance improvement is primarily attributed to the gradual evaporation of organic butylammonium (BA) spacer cations from the film as butylamine (BA) gas. This evaporation refines the film's composition and structure, leading to the spontaneous formation of larger- phase RPPs, which exhibit superior carrier mobility. Consequently, the PCE of 2D-PSCs is enhanced. This work offers new insights into the structural evolution of 2D RPP films under ambient conditions and provides a feasible strategy for optimizing the performance of 2D-PSCs and other optoelectronic devices.