Interfacial seed-assisted FAPbI crystallization and phase stabilization enhance the performance of all-air-processed perovskite solar cells.

Formamidinium lead triiodide (FAPbI) 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-FAPbI perovskites are highly susceptible to degradation into non-perovskite δ-FAPbI phases, especially under humid conditions, which severely diminishes the device performance of FAPbI PSCs. Here, we propose an interfacial seeding strategy for regulating crystallization and stabilizing α-FAPbI perovskites in humid air. By post-treating an antisolvent-free, air-processed perovskite wet film with inorganic cesium lead triiodide (CsPbI) nanocrystals, a functional seed layer is formed that effectively mitigates the erosion by humid air while facilitating the conversion of intermediates to the α-FAPbI phase. The interfacial seed-modified FAPbI 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 FAPbI films show improved environmental stability compared to their control counterparts, maintaining 80% of their initial efficiency after 60 days.