Redox energy barrier management for efficient tin-lead perovskite solar cells

The performance of narrow-bandgap mixed tin-lead (Sn-Pb) perovskite solar cells (PerSCs) is still limited by high defect densities due to the facile oxidation of Sn²⁺, leading to severe p-type self-doping. Here, we report a strategy of redox energy barrier managing to construct high-quality Sn-Pb perovskite, where 1,1'-bis(diphenylphosphino)ferrocene (DPPF) with a lower reaction energy barrier can protect Sn²⁺ from oxidation, where the oxidized products of DPPF tend to anchor with the Sn vacancies, effectively depressing the trap densities of perovskite. The optimized inverted PerSC reached an impressive power conversion efficiency (PCE) of 23.5% (23.38% certified) accompanied by a high open-circuit voltage of 0.89 V and a strikingly decreased energy loss of 0.36 eV. When combined with the semi-transparent wide-bandgap PerSC, the four-terminal all-perovskite tandem solar cells achieved an outstanding PCE of 26.4%.