Impacts of MAPbBr₃ Additive on Crystallization Kinetics of FAPbI₃ Perovskite for High Performance Solar Cells

• Main Authors: Zhenhuang Su, Chenyue Wang, Guanhaojie Zheng, Xingyu Gao
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Coatings
• Subjects: perovskite solar cells; in situ GIWAXS; crystal structure
• Online Access: https://www.mdpi.com/2079-6412/11/5/545

Blending perovskite with different cations has been successful in improving performance of perovskite solar cells, but the complex pathway of perovskite crystal formation remains a mystery, hindering its further development. In this paper, the detailed crystallization process of formamidinium lead iodide (FAPbI₃) perovskite films doped by methylammonium lead bromide (MAPbBr₃) additive was investigated by in situ grazing incident wide-angle X-ray scattering measurements during both spin coating and annealing. During spin-coating, it was found that the FAPbI₃ perovskite precursor easily formed a mixture of black perovskite phase (α phase) and non-perovskite yellow phase (δ phase) after the addition of MAPbBr₃, whereas only δ phase formed without MAPbBr₃. The δ phase gradually converted to α phase during annealing and there was only α phase left in both films with and without MAPbBr₃. However, the doped films presented high film quality without PbI₂ residue in contrast to the undoped films. These findings imply that the MAPbBr₃ additive can effectively suppress the formation of the unfavorable δ phase and trigger the formation of the optically active α phase even during spin-coating, which enhances the film quality possibly by removing the energy barriers from δ phase to α phase at room temperature. Finally, PSCs based on MAPbBr₃-doped FAPbI₃ were fabricated with a champion efficiency as high as 19.4% from 14.2% for the PSCs based on undoped FAPbI₃.