Molecule Anchoring Strategy Promotes Vertically Homogeneous Crystallization and Aligned Interfaces for Efficient Pb–Sn Perovskite Solar Cells and Tandem Device

Narrow-bandgap (NBG) Pb-Sn perovskites are ideal candidates as rear subcell in all-perovskite tandem solar cells. Because Pb-Sn perovskites contain multiple components, the rational regulation of vertical structure and both interfaces of the film is primarily crucial to achieve high-performing NBG perovskite solar cells (PSCs). Herein, a molecule anchoring strategy is developed to in situ construct Cs_0.1MA_0.3FA_0.6Pb_0.5Sn_0.5I₃ perovskite film with vertically aligned crystals and optimized interfaces. Specifically, l-alanine methyl ester is developed as an anchoring additive to induce the vertical crystal growth, while PEA₂PbI₃SCN film is introduced to promote the homogeneous crystallization at the buried interface via SCN- anchoring with cations. Further ethylenediamine dihalides (EDA(I/Cl)₂) post-treatment leads to the gradient energy level alignment on the film surface. Pb-Sn PSCs based on such film show efficient charge transport and extraction, producing a champion power conversion efficiency (PCE) of 22.3% with an impressive fill factor of 82.14%. Notably, combining with semitransparent 1.78 eV wide-bandgap PSCs, the four-terminal all-perovskite tandem device achieves a PCE of 27.1%. This work opens up a new pathway to boost the performance of Pb-Sn PSCs and their tandem devices.