Interfacial seed-assisted FAPbI₃ crystallization and phase stabilization enhance the performance of all-air-processed...

Formamidinium lead triiodide (FAPbI₃) has received significant attention in the field of perovskite solar cells (PSCs) owing to its excellent optoelectronic properties and high thermal stability. However, the photoactive α-FAPbI₃ perovskites are highly susceptible to degradation into non-perovskite δ-FAPbI₃ phases, especially under humid conditions, which severely diminishes the device performance of FAPbI₃ PSCs. Here, we propose an interfacial seeding strategy for regulating crystallization and stabilizing α-FAPbI₃ perovskites in humid air. By post-treating an antisolvent-free, air-processed perovskite wet film with inorganic cesium lead triiodide (CsPbI₃) nanocrystals, a functional seed layer is formed that effectively mitigates the erosion by humid air while facilitating the conversion of intermediates to the α-FAPbI₃ phase. The interfacial seed-modified FAPbI₃ perovskite films exhibit improved crystal quality and denser morphology. As a result, the efficiency of all-air-processed carbon-based PSCs is improved from 15.90% for the control to 18.04%. In addition, the unencapsulated PSCs based on interfacial seed-modified FAPbI₃ films show improved environmental stability compared to their control counterparts, maintaining 80% of their initial efficiency after 60 days.