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

Abstract

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. 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 alpha-formamidinium lead triiodide (alpha-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 (RNH3Cl) in ethanol results in the stable solvation of FAPbI(3). The RNH3Cl added to the FAPbI(3) precursor solution is removed during spin-coating and high-temperature annealing via iodoplumbate complexes, such as PbI2 center dot RNH2 and PbI2 center dot HCl, coordinated with dimethylacetamide (or dimethylsulfoxide). It is possible to form very dense and uniform alpha-FAPbI(3) perovskite films with high crystallinity by combining several types of RNH3Cl. We obtain power conversion efficiencies of 24.3% using a TiO2 electrode, and of 25.1% with a SnO2 electrode.