Fabrication of Large-Grained Perovskite Films Utilizing a Recrystallization Approach Involving Multiple Vapor Annealing Steps

The swift advancement in perovskite solar cell (PSC) technology has garnered considerable interest, necessitating the move toward commercial production. Vapor deposition presents notable benefits for fabricating PSCs on a large scale with high output rates. Nonetheless, perovskite films produced via this method are prone to internal imperfections, poor crystallinity, and small grain sizes. Consequently, post-treatment processes for vapor-deposited perovskite films become crucial. In this study, we explored the impact of methylammonium chloride vapor annealing on the vapor-deposited perovskite films. Our research revealed that traditional one-step vapor annealing could indeed enlarge the grain size. However, the extended duration of treatment often resulted in numerous pinholes and inconsistent grain size distribution across the film surface. Since the presence of pinhole-free films is critical for enhancing the efficiency of photovoltaic conversion, this method, which fails to improve and may even degrade film performance, is not ideal. To address these issues and fabricate high-quality perovskite films without pinholes, we implemented a multiple vapor annealing approach. This method, rooted in a vapor treatment-induced recrystallization strategy, involves repeated fine-tuning of the crystal growth direction and controlling the rate of growth. As a result, we successfully produced perovskite films with superior crystallinity, large and uniformly distributed grains, and enhanced performance, all devoid of pinholes. The grain size was augmented from an initial size of 800 nm to approximately 3 μm. In line with these improvements, the PSC devices and modules created using this refined method attained photovoltaic conversion efficiencies of 21.29% (0.1475 cm2) and 18.53% (10 cm2), respectively.