Enhanced Photovoltaic Performance of FASnI<sub>3</sub>‑Based Perovskite Solar Cells with Hydrazinium Chloride Coadditive KayeshMd. Emrul ChowdhuryTowhid H. MatsuishiKiyoto KanekoRyuji KazaouiSaid LeeJae-Joon NodaTakeshi IslamAshraful 2018 For the fabrication of efficient Sn-based perovskite solar cells (PSCs), deposition of uniform and pinhole-free perovskite films with low Sn<sup>4+</sup> content remains a crucial factor. In this work, we present a coadditive engineering process by introduction of hydrazinium chloride (N<sub>2</sub>H<sub>5</sub>Cl) in a single precursor solvent system to fabricate FASnI<sub>3</sub> perovskite films. The successful integration of N<sub>2</sub>H<sub>5</sub>Cl results in reduced concentration of Sn<sup>4+</sup> content by 20% in the FASnI<sub>3</sub> film leading to suppressed carrier recombination and pinhole-free uniform coverage. These remarkable improvements in the FASnI<sub>3</sub> film results in power conversion efficiency (PCE) of Sn-based PSC up to 5.4% due to a significant increase in open-circuit voltage. Moreover, the best PSC without encapsulation showed stable shelf life up to 1000 h while retaining 65% of its initial PCE.