Two‐Step Inverted Perovskite Solar Cells with > 25% Efficiency Fabricated in Ambient Air

Abstract The two‐step method for perovskite solar cells (PSCs) offers a promising technology for scalable manufacturing, particularly under ambient air conditions, due to its inherent simplicity, high reproducibility, and operational convenience. With this approach, achieving high‐quality of lead iodide (PbI 2 ) films during the initial stage is paramount to ensuring the overall performance and stability of the devices. However, during the ambient fabrication of PbI 2 , the residual high boiling point and hygroscopic dimethyl sulfoxide (DMSO) solvent significantly compromises the resulting film quality. Here, L‐Homoarginine hydrochloride (HargCl) is introduced into the PbI 2 precursor solution, which greatly reduced the residual amount of PbI 2 ·xDMSO and passivated the internal defects of perovskite (PVK) films. By leveraging this strategy, inverted perovskite solar cells entirely in the air are successfully prepared, achieving an impressive power conversion efficiency (PCE) of 25.05% — the highest reported efficiency to date for two‐step fully air‐processed inverted PSCs. In addition, these unencapsulated devices maintained 96% of their initial power conversion efficiency after 500 h storage in the air with 20–40% RH.