Science News: 2022 Nat. Energy, Nontoxic Production of Halide Perovskites using Ethanol-Based Green Solution Processing

　　In the mass production of perovskite solar cells, solution processing is used. In general solution processing, non-toxic or less toxic solvents are often used. However, halide perovskites have the problem of not being completely soluble in most non-toxic solutions. To solve this problem, Nat. Energy published a study of Sang Il Seok, Yonghui Lee and others at the National Institute of Ulsan National Institute of Science and Technology (UNIST) in South Korea in 2022. Here, the research team used perovskite precursor solutions soluble in ethanol-based solvent to produce the deposition of dense and uniform α-formamidinium lead triiodide (α-FAPbI₃) films. This method avoids an antisolvent dripping step.

　　The results of the study found:

1. The combination of Lewis bases, such as dimethylacetamide (or dimethylsulfoxide), and an alkylammonium chlorides (RNH₃Cl) in ethanol results in stable dissolution of FAPbI₃.
2. During spin coating and high-temperature annealing, RNH₃Cl added to the FAPbI₃ precursor solution is removed via iodoplumbate complexes, such as PbI₂·RNH₂ and PbI₂·HCl, coordinated with dimethylacetamide (or dimethylsulfoxide).
3. By combining several types of RNH₃Cl, very dense and uniform α-FAPbI3 perovskite films with high crystallinity can be formed.
4. The power conversion efficiency of 24.3% is obtained using TiO₂ electrode, and 25.1% was obtained using SnO₂ electrode.