Enhancing grain growth of caesium-formamidinium-based lead halide perovskite thin films through PbI2 precursor engineering in vapor-solid reaction

Vapor-solid reaction methods are highly regarded as potential solutions for large-scale production of perovskite thin films due to their scalability, compatibility with silicon tandem technology, and lack of solvents. However, the limited penetration of organic vapor through the solid inorganic film results in a slow growth rate of perovskite, leading to poor crystallinity and small grain size. This high defect density in the grain boundaries hinders the enhancement of device performance. In this study, we used 1,3-diaminoguanidine monohydrochloride as an additive in the PbI2 precursor films, which effectively improved perovskite grain growth in the vapor-solid reaction process. After optimization, we achieved high-quality perovskite thin films with a large grain size exceeding 5 μm. Notably, solar devices based on these large-grain perovskite thin films achieved a high power conversion efficiency up to 21.13%. [Display omitted] •1,3-diaminoguanidine monohydrochloride was used to improve the growth of perovskite crystals.•Formamidinium-based perovskite thin films with large grain sizes exceeding 5 μm were obtained by vapor-solid reaction.•Perovskite solar cells with vapor-reacted perovskite thin films achieved a power conversion efficiency of 21.13%.