Formamidinium-Based Perovskite Solar Cells with Enhanced Moisture Stability and Performance via Confined Pressure Annealing

Abstract

Formamidinium (FA)-based perovskite solar cells (PSC) show enhanced stability compared to their methylammonium (MA)-based counterparts. However, their stability needs to be further enhanced for the potential commercial applications. We demonstrate here that the high-quality thin film can be obtained for the FA-based perovskite with remarkably enhanced moisture stability using a confined-pressure annealing (CPA) processing and controlling the amount of Cs introduced into the FAPbI3 perovskite precursor solution. Without additional 2D cation additives, surface passivation, or encapsulation, no phase degradation was observed for the Cs0.1FA0.9PbI3 perovskite under a humidity of 70% RH for over 500 h. The unencapsulated device maintained over 70% performance for 500 h compared to <80 h of the conventional processed devices, which is comparable to the outstanding moisture stability of the 2D/3D perovskites. The FA-based perovskite grain size was promoted to over 1 μm with a high static water contact angle up to 112°. The surface cation composition was varied with the concentrated FA cation species at the surface while homogenized Cs/FA distribution inside the film. The trapped-state density and carrier recombination rate were also reduced with a high fill factor of 82% and an efficiency over 20.23%. This work suggests that the intrinsic stability of the 3D perovskite could be further enhanced by adjusting the surface compositions during the crystallization process.