Substitution of Ethylammonium Halides Enabling Lead-Free Tin- Based Perovskite Solar Cells with Enhanced Efficiency and Stability

Tin (Sn)-based perovskite solar cells (PSCs) have attracted extensive attention due to the irlow toxicity and excellent optoelectric properties. Nonetheless, the development of Sn-based PSCs is still hampered by poor film quality due to the fast crystallization and the oxidation from Sn2+ to Sn4+. In this work, we compare and employ three ethylammonium halides, EAX (X = Cl, Br, I) to explore their roles in Sn-based perovskites and solar cells. We find that crystallinity and crystallization orientation of perovskites are optimized with the regulation of EAI. EABr leads to reduced defect density and enhanced crystallinity but also the lowest absorption and the widest band gap owing to the substitution of Br-. Notably, perovskites with EACl exhibit the best crystallinity, lowest defect density, and excellent antioxidant capacity benefiting from the partial substitution of Cl-. Consequently, the EACl-modified device achieves a champion PCE of 12.50% with an improved Voc of 0.79 V. Meanwhile, an unencapsulated EACl device shows excellent shelf stability with negligible efficiency degradation after 5400 h of storage in a N2-filled glovebox, and the encapsulated device retains its initial efficiency after continuous light illumination at the maximum power point for 100 h in air.