A stress relaxation strategy for preparing high-quality organic-inorganic perovskite thin films via a vapor-solid reaction

Perovskite solar cells (PSCs) prepared through vapor-solid reactions exhibit promising potential for commercial application due to their scalability and lack of organic solvents. Unlike solution-based drying processes, the vapor-solid reaction causes the perovskite thin film to undergo volume expansion rather than shrinkage. Consequently, the residual stress within the vapor-processed perovskite thin film differs significantly from that within the solution-processed film. In this study, we investigate the characteristics of residual stress in films obtained via vapor-solid reactions. Building upon this, we develop a vapor-annealing strategy to alleviate the residual stress. Through post-treatment of the film with organic ammonium salt vapor, we successfully obtained high-quality perovskite thin films devoid of residual stress. As a result, the optimized PSCs achieve an impressive champion power conversion efficiency (PCE) of 22.06%. Furthermore, the unencapsulated device maintains 97% of its initial PCE after 3600 h storage under ambient conditions, and the encapsulated device 84% of its initial PCE after a 720 h thermal test at 85 C-degrees. These results underscore the significance of eliminating residual stress in ensuring the long-term stability of high-efficiency PSCs.