Molecular Modification Strategy for Efficient NiO_x-based Tin-Lead Perovskites Solar Cells and All-perovskite Tandems

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 ─SO₃ ^- 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%.