Ethanol-based green-solution processing of α-formamidinium lead triiodide perovskite layers

The use of non-toxic or less-toxic solvents in the mass production of solution-processed perovskite solar cells is essential. However, halide perovskites are generally not completely soluble in most non-toxic solvents. Here we report the deposition of dense and uniform α-formamidinium lead triiodide (α-FAPbI 3 ) films using perovskite precursor solutions dissolved in ethanol-based solvent. The process does not require an antisolvent dripping step. The combination of a Lewis base, such as dimethylacetamide (or dimethylsulfoxide), and an alkylammonium chloride (RNH 3 Cl) in ethanol results in the stable solvation of FAPbI 3 . The RNH 3 Cl added to the FAPbI 3 precursor solution is removed during spin-coating and high-temperature annealing via iodoplumbate complexes, such as PbI 2 ·RNH 2 and PbI 2 ·HCl, coordinated with dimethylacetamide (or dimethylsulfoxide). It is possible to form very dense and uniform α-FAPbI 3 perovskite films with high crystallinity by combining several types of RNH 3 Cl. We obtain power conversion efficiencies of 24.3% using a TiO 2 electrode, and of 25.1% with a SnO 2 electrode. Manufacturing of perovskite solar cells would benefit from the avoidance of hazardous solvents and multistep processing. Now, Yun et al. report an ethanol-based perovskite precursor solution that does not need an antisolvent step, enabling devices with 25% efficiency.