Dry‑Contact Trimming for All‑Perovskite Tandem Solar Cells via Solid‑Solution Homogenization

ABSTRACT All‐perovskite tandem solar cells leverage the solid‐solution nature of metal halide perovskites to tune the band gaps of wide‐ and narrow‐bandgap subcells for current matching and high photovoltage. Sn–Pb mixed perovskites with band gaps of approximately 1.2–1.3 eV are attractive bottom absorbers, but Sn‐rich surface regions, depth‐dependent compositional inhomogeneity, and associated band‐alignment issues limit both photocurrent and photovoltage. Here, we introduce a layered‐perovskite‐assisted dry‐contact trimming (LDT) strategy to reconfigure Sn–Pb narrow‐bandgap perovskites after film formation. A Dion–Jacobson‐phase ethylenediammonium lead iodide (EDAPbI 4 ) film is brought into transient solid‐state contact with the Sn–Pb perovskite and then removed after contact annealing. EDAPbI 4 functions as a temporary solid‐state contact partner that removes Sn‐rich surface species and reduces depth‐dependent lattice and compositional inhomogeneity without forming a retained 2D capping layer. This reconfiguration alleviates reverse band bending at the Sn–Pb perovskite/transport‐layer interface, suppresses nonradiative interfacial recombination, and reduces open‐circuit‐voltage losses. The improved lattice/compositional uniformity also enables thick Sn–Pb absorbers to maintain efficient charge collection and high short‐circuit current density. Consequently, single‐junction Sn–Pb devices exceed 24% efficiency, and monolithic all‐perovskite tandem devices surpass 30% with reproducible performance and operational stability. These results identify LDT as a complementary post‐crystallization strategy for engineering mixed perovskite solid‐solutions and their interfaces.