Accelerated formation and improved performance of CH3NH3PbI3-based perovskite solar cells via solvent coordination and anti-solvent extraction

Abstract

The two-step sequential deposition method is widely used in the preparation of high-performance mesoscopic perovskite solar cells. However, when the conventional sequential deposition method is applied to fabricate bilayered mesostructured and planar-structured devices, inefficient conversion of PbI₂ to perovskite has been a big challenge. In this work, we report a new solvent coordination and anti-solvent extraction (SCAE) strategy for preparing porous PbI₂ films to rapidly convert all PbI₂ into perovskite active layers in bilayered mesostructured perovskite solar cells. It is demonstrated that PbI₂·DMSO (dimethyl sulfoxide, coordinated solvent) intermediate complexes are not only capable of restricting the fast growth of PbI₂ grains, but also capable of facilitating the formation and regulation of porous PbI₂ structures during the process of anti-solvent (chlorobenzene) extraction. With the porous PbI₂ template, its complete conversion time into CH₃NH₃PbI₃ is greatly shortened to less than ten minutes from one hour for the conventional method. The best device fabricated through the SCAE process exhibits a power conversion efficiency of above 15% under AM 1.5G solar illumination of 100 mW cm⁻², appreciably outperforming the device without SCAE treatment, which can be ascribed to its uniform surface morphology and more efficient carrier transfer at the interfaces. The results highlight the tunability of the PbI₂ morphology via the SCAE process and its importance to highly efficient perovskite conversion, the final perovskite morphology and device performance in a sequential deposition process.