Dual Buried Interface Engineering for Improving Air-Processed Inverted FAPbI 3 Perovskite Solar Cells.

Fabricating perovskite solar cells (PSCs) in an ambient environment provides low-cost preparation routes for solar cells that are suitable for large-scale production. Compared with methylammonium (MA)- based perovskite materials, formamidinium lead iodide (FAPbI 3 ) possesses a more favorable bandgap for light harvesting and better thermostability. However, the phase transition from the α-phase to the δ-phase easily occurs, making it challenging for ambient-air processing. Herein, we develop a buried interface engineering strategy via two molecules including 1,4-bis(diphenylphosphino)butane (DPPB) as well as [4-(3,6-dimethyl-9 H -carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) to optimize air-processed inverted FAPbI 3 PSCs. This strategy regulates the crystallization process of the air-fabricated FAPbI 3 perovskite film, leading to a purer α-phase with significantly enhanced crystallinity and enlarged grain sizes. Apart from improving the bulk perovskite film, the defects at the NiO x /perovskite interface are passivated, and the energy levels are better matched in the modified device, which facilitates efficient carrier extraction. Resultantly, the target device processed in the open air achieves a dramatically improved power conversion efficiency from 11.37% to 18.45%, in association with an enhanced device stability.