Interfacial seed-assisted FAPbI3 crystallization and phase stabilization enhances the performance of all-air-processed perovskite solar cells

Formamidine 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 the 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 the control counterparts, maintaining 80% of its initial efficiency after 60 days.