Multifunction Sandwich Structure Based on Diffusible 2‑Chloroethylamine for High-Efficiency and Stable Tin–Lead Mixed Perovskite Solar Cells

Low-bandgap tin–lead mixed perovskites (PVKs) are necessary for all-perovskite tandem solar cells. This work proposes a multifunctional sandwich structure with 2-chloroethylamine (CEA) as the top and bottom interface layer and perovskite as the core layer. The sandwich structured CEA allows large ClCH₂CH₂NH₃⁺ and small Cl^– to diffuse into the crystal lattice and grain boundaries of perovskites, endowing an excellent antioxidation property by forming Sn(0), coordinating with SnI₂, and controlling the perovskite crystallization process. Moreover, the energy level alignment at the interface of the perovskite and transport layer becomes more matched. As a result, the CEA-modified champion device acquires a power conversion efficiency of 18.13% with an open-circuit voltage of 0.82 V and a short-circuit current density of 30.06 mA cm^–2. Meanwhile, the environmental stability of CEA-modified devices is substantially enhanced. This work introduces a new strategy for improving the performance and stability of tin–lead mixed perovskite solar cells.