Molecular Modification Strategy for Efficient NiO x ‐based Tin‐Lead Perovskites Solar Cells and All‐perovskite Tandems

ABSTRACT For low‐bandgap tin‐lead (LBG Sn–Pb) devices, conventional organic hole transport materials (HTMs) fail to balance efficiency and stability, drawing attention to inorganic nickel oxide (NiO x ) as a promising alternative. However, the inferior compatibility between NiO x and Sn–Pb perovskite severely hinders the development of NiO x ‐based Sn–Pb perovskite solar cells (PSCs) due to mismatched energy levels and oxidizing active species. Here, we propose a versatile strategy by introducing ammonium 2‐hydroxyethanesulphonate (AHES) on NiO x films to fabricate efficient and stable NiO x ‐based Sn–Pb PSCs. The ─SO 3 − in AHES could react with NiO x to regulate film morphology and optimize energy level alignment. Meanwhile, the presence of ─OH in AHES acting as Lewis base provides lone pair electrons to form hydrogen bond to modulate the crystallization process and improve film uniformity, resulting in enhanced lattice strength. As a result, our NiO x ‐based Sn–Pb device yields an efficiency of 22.98% (versus 20.02% for control) and retains 80% of the initial efficiency after continuous 1‐sun illumination after 212 h (versus 90 h for control), which is among the best NiO x ‐based Sn–Pb PSCs. Finally, the champion four‐terminal (4T) all‐perovskite tandem solar cell achieves a remarkable efficiency of 30.38%.