Cation substitution-induced band gap and stability engineering of formamidinium-based perovskite films prepared in ambient conditions

An intermediate complex approach coupled with a preheating strategy are used to grow mixed-cation FA1xCsxPbI3 perovskite films in ambient air. This was achieved through an effective PbI2 conversion and the elimination of the detrimental moisture effect, which was ensured by the formation of an intermediate complex along with the rapid solvent evaporation induced by the preheating of the substrate and/or precursor solutions. Moreover, it is found that the control of [CsI]/[FAI] ratio clearly influences the crystallization of the alpha-perovskite phase and could effectively inhibit the growth of non-perovskite crystallites, which stabilizes the photoactive alpha-phase. X-ray diffraction analyses indicate that a change in crystal orientation from (100) to (111) direction occurs for 35% CsI added in the perovskite precursor, inducing a decrease in the band gap energy. Moreover, the stability is significantly improved in the (111) direction, in agreement with computational results obtained in literature.

Automated summary

An intermediate complex approach and a preheating strategy are used to successfully grow mixed-cation FA1xCsxPbI3 perovskite films in ambient air. This is achieved through effective PbI2 conversion and eliminating the detrimental moisture effect, ensuring the formation of an intermediate complex and rapid solvent evaporation induced by preheating. Moreover, controlling the [CsI]/[FAI] ratio influences the crystallization of the alpha-perovskite phase and effectively inhibits the growth of non-perovskite crystallites, stabilizing the photoactive alpha-phase. X-ray diffraction analysis reveals a change in crystal orientation and a decrease in band gap energy with 35% CsI added in the perovskite precursor, and improved stability in the (111) direction.