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