Solvent mediating hydrogen bonding in oriented FAPbI₃ enables efficient air-processed perovskite solar cells

Air-processed cubic-phase formamidinium lead iodide (α-FAPbI₃) perovskite solar cells are promising for advanced photovoltaics but are challenged by their sensitivity to moisture. Present work explores a unique solvent of sulfolane (TMSO₂) with the capability of forming hydrogen bonding with FA⁺ ions to maintain the stability of wet film as well as initiating the oriented nucleation of α-FAPbI₃ perovskite in air environment. Different from traditional growth process, hybrid TMSO₂-FA⁺ attracts [PbI₆]⁴⁻ chains for self-assembly, density functional theory (DFT) calculations show that this approach reduces the formation energy of α-phase FAPbI₃. This method of improving film crystallization is applicable to different substrates and large-area devices. Consequently, small-area FAPbI₃ PSCs yielded a notable power conversion efficiency (PCE) of 25.09% and a high open circuit voltage (V_OC) of 1.19 V. The PSCs maintained >85% of its original value after 500 h of maximum power point tracking under illumination and demonstrate remarkable thermal stability, retaining 85% of its initial PCE after 1100 h at 65 °C in nitrogen. Moreover, the TMSO₂-regulated 36 cm² minimodules with a high PCE of 20.03% for the aperture area of 26.78 cm² manifested the great application potential of this strategy in the perovskite photovoltaics.