Methylamine-Dimer-Induced Phase Transition toward MAPbI₃ Films and High-Efficiency Perovskite Solar Modules

Abstract

Perovskite films prepared with CH₃NH₂ molecules under ambient conditions have led to rapid fabrication of perovskite solar cells (PSCs), but there remains a lack of mechanistic studies and inconsistencies with operability in their production. Here the crystal structure of CH₃NH₂-CH₃NH₃PbI₃ was analyzed to involve hydrogen bonds (CH₃NH₂···CH₃NH₃⁺) and has guided the facile, reproducible preparation of high-quality perovskite films under ambient conditions. Hydrogen bonds within CH₃NH₂···CH₃NH₃⁺ dimers were found in the CH₃NH₂-CH₃NH₃PbI₃ intermediates, accompanied by 1D-PbI₃^- chains (δ-phase). The weakly hydrogen-bonded CH₃NH₂ molecules were easily released from the CH₃NH₂-CH₃NH₃PbI₃ intermediates, contributing to rapid, spontaneous phase transition from 1D-PbI₃^- (δ-phase) to 3D-PbI₃^- (α-phase). Further introduction of CH₃NH₃Cl into the CH₃NH₂-CH₃NH₃PbI₃ intermediates led to interruption of 1D-PbI₃^- transition into 0D-Pb₂I_9-<i>x</i>Cl_<i>x</i>^5-(0 < <i>x</i> < 6), adjusting the phase transition route toward 3D-PbI₃^-. On the basis of the above understanding, CH₃NH₂ solution in ethanol and CH₃NH₃Cl were used for precursors and a best efficiency of 20.3% in PSCs was achieved. Large-scale modules (12 cm² aperture area) fabricated by a dip-coating technology exhibited an efficiency up to 16.0% and outstanding stability over 10 000 s under continuous output. The developed preparation method of perovskite precursors and insightful research into the methylamine-dimer-induced phase transition mechanism have enabled the production of high-quality perovskite films with robust operability, showing great potential for large-scale commercialization.