Highly Efficient Perovskite/Organic Tandem Solar Cells Enabled by Mixed‐Cation Surface Modulation

Abstract Perovskite/organic tandem solar cells (POTSCs) are gaining attention due to their easy fabrication, potential to surpass the S‐Q limit, and superior flexibility. However, the low power conversion efficiencies (PCEs) of wide bandgap (Eg) perovskite solar cells (PVSCs) have hindered their development. This work presents a novel and effective mixed‐cation passivation strategy (CE) to passivate various types of traps in wide‐Eg perovskite. The complementary effect of 4‐trifluoro phenethylammonium (CF₃‐PEA⁺, denoted as CA⁺) and ethylenediammonium (EDA²⁺, denoted as EA²⁺) reduces both electron/hole defect densities and non‐radiative recombination rate, resulting in a record open‐circuit voltage (V_oc) of wide‐Eg PVSCs (1.35 V) and a high fill factor (FF) of 83.29%. These improvements lead to a record PCE of 24.47% when applied to fabricated POTSCs, the highest PCE to date. Furthermore, unencapsulated POTSCs exhibit excellent photo and thermal stability, retaining over 90% of their initial PCE after maximum power point (MPP) tracking or exposure to 60 °C for 500 h. These findings imply that the synergic effect of surface passivators is a promising strategy to achieve high‐efficiency and stable wide‐Eg PVSCs and corresponding POTSCs.