Coadditive Engineering with 5-Ammonium Valeric Acid Iodide for Efficient and Stable Sn Perovskite Solar Cells

Sn-based perovskite solar cells (PSCs) featuring high performance and long-term stability are very challenging because Sn²⁺ is relatively prone to oxidation. Here, we have performed coadditive engineering with 5-ammonium valeric acid iodide (5-AVAI) for FASnI₃-based perovskite films. From the morphological, structural, and elemental analyses, we observed that 5-AVAI affects the crystal growth of perovskites through its hydrogen bond with I^- of the SnI₆ ^4- octahedral. As a result, pinhole-free homogeneous and stable Sn-based perovskite films form over a large area with lower Sn⁴⁺ content. This made us able to enhance the power conversion efficiency (PCE) for Sn-based PSCs up to 7% in a 0.25 cm² aperture area. Most importantly, the 5-AVAI added PSCs showed a record stability and maintained their initial PCE under 1 sun continuous illumination at maximum power point tracking for 100 h.