Lead iodide growth regulation included by N-formylmorpholine with strong electron-withdrawing groups for all-air-processed perovskite solar cells

Two-step sequential deposition represents a promising approach for attaining high-performance perovskite solar cells (PSCs). Nevertheless, a crucial challenge, especially under ambient conditions, lies in effectively enhancing the conversion efficiency of PbI₂ and improving the crystallization quality of perovskite. Herein, N-formylmorpholine (NFM) is used as an additive to prepare high crystallinity and large particle size of the perovskite film by generating a porous large-grain PbI₂ layer with two-step method. The theoretical calculations and characterization analysis reveal that NFM with end group C=O possesses both lone pair electrons and exhibits the highest electron cloud density in NFM, which governs the formation of covalent bonds between NFM and Pb²⁺, resulting in PbI₂ arrangement and reducing the chance of forming two-dimensional (2D) perovskite. Furthermore, highly (001)-oriented perovskite film with reduced trap density is obtained. Consequently, the NFM-based PSCs fabricated in air without control conditions achieve a champion photoelectric conversion efficiency of 21.88% and enhanced device stability. Our study highlights the electron-withdrawing group effect of organic molecule in improving the performance of all-air-processed PSCs.