Guanidinium chloride passivated perovskites for efficient solar cells: The role of passivating solvent

Passivating treatment using organic molecules has become one of the most efficient means to reduce electronic defects and enhance perovskite crystallinity for high-performance perovskite solar cells (PSCs). However, the solvents essentially needed to dissolve the passivating molecules are rarely concerned during the construction of high-quality perovskite layers. Here, the role of the passivating solvents in the secondary growth process and defect passivation of methylammonium lead iodide (MAPbI₃) perovskite films and their influence on the final device performance are systemically investigated. In the guanidinium chloride (GACl)-passivated MAPbI₃ films produced with different passivating solvents, we found that the passivating solvents with poor solubility toward MAPbI₃ crystals can hardly alter the film morphology and the passivation effect of GACl molecules only works on the upper surface of the photoactive layer. However, the isopropanol (IPA) capable of partially dissolving the preformed MAPbI₃ crystals contributes to the formation of excellent polycrystalline perovskite morphologies with remarkably enhanced grain size and reduced grain boundaries. Consequently, a maximum power conversion efficiency (PCE) of 18.65% has been realized for the inverted PSCs fabricated under GACl/IPA passivating treatment conditions. These results indicate that the solvent used to dissolve passivators is of great importance in manipulating the MAPbI₃ films, providing crucial understanding on the rational selection of solvents to establish the most effective passivation solutions for improving the quality of perovskite films and enhancing the PSC efficiencies.