What are Methylammonium and Solvent Fates upon Halide Perovskite Thin‐Film Preparation and Thermal Aging?

The recent remarkable achievements in terms of efficiency performance and stability hybrid organic–inorganic perovskite solar cells (PSCs) are notably obtained by optimizing the A-site cation composition formamidinium-based 3D perovskites. As methylammonium chloride is ubiquitously employed precursor solution for very high PSC, purpose present paper to unveil exact role (MA+), chloride, solvent on film growth their fate upon layer thermal annealing process. Methylammonium shown react with formamidinium form two methyl compounds while its excess eliminated along chloride. final A-sites mainly occupied formamidinium, whereas MA+ content only 2–3 mol%, below 3-N-methyl one. 1-N-methyl detected as traces. Meanwhile, homogenously throughout thickness. Upon aging stress, degraded from top formation PbI2. rapidly fully stable remain layer.