Reductive 2D Capping Layers through Dopamine Salt Incorporation for Pb-Sn Mixed Perovskite Solar Cells

Pb-Sn mixed perovskite is a crucial component in all-perovskite tandem cells. However, it remains a challenging task to fabricate Pb-Sn perovskite solar cells (PSCs) due to the facile oxidation of Sn²⁺. In this work, we incorporate dopamine cation (DAH⁺) to create a reductive 2D capping layer on a Pb-Sn perovskite film, simultaneously enhancing the efficiency and stability of Pb-Sn PSCs. Dopamine acts as a strong reducing agent that effectively reduces Sn⁴⁺ to Sn²⁺. The 2D/3D heterojunction induces downward band bending at the perovskite top surface, facilitating carrier separation and extraction. Consequently, the champion PSC achieved a power conversion efficiency (PCE) of 22.31%. Benefiting from the protection of the reductive 2D capping layer, the device’s stability is notably enhanced with 86% of the initial PCE retaining after 1000 h operation in N₂. This work demonstrates a promising strategy of constructing a multifunctional 2D passivation layer toward high quality Pb-Sn mixed perovskite devices.