Structural Regulation for Highly Efficient and Stable Perovskite Solar Cells via Mixed-Vapor Deposition

Because of a lack of solvent-assisted crystallization, vapor and reaction process controls are essential for structural regulation in vapor-deposited organic–inorganic hybrid perovskite thin films. In this work, we prepared a (PEA)2(MA)n−1PbnI3n mixed-dimensional perovskite thin film using mixed-vapor deposition. It was found that the surface morphology and the crystalline structure of the perovskite thin film could be effectively modulated by changing the chemical mass ratio of PEAI (C6H5CH2CH2NH3I) to MAI (CH3NH3I) powder. The carrier behavior was illustrated by transient absorption spectroscopy and conductive atomic force microscopy. A small amount of PEA+ was found to reorient the growth of perovskite grains in the [110] direction and narrow the band edge by passivating the defect states for superior local charge transport, leading to an improved power conversion efficiency (PCE) of 18.08%. Increasing the amount of PEA+ gradually caused structural transition from three-dimensional (3D) to two-dimensional (2D) perovskites, resulting in a uniform charge transport but lower total conductance; however, it significantly enhanced humidity stability. An unencapsulated sample with a 60% PEAI ratio showed little efficiency decay during the first 12 h in a humidity of 92% and maintained 87% of the initial efficiency for 1 month in a humidity of 55%. This work provides a further understanding to optimize the structural properties of vapor-deposited perovskite thin films for efficient photovoltaic devices.