Controlled crystallization of CH₃NH₃PbI₃ films for perovskite solar cells by various PbI₂(X) complexes

Lead halide complexes are efficient precursors to obtain high quality perovskite films and high performance solar cells. However, how the lead halide complex affects the crystallization kinetics and thus the film quality of perovskite has not been systematically studied. Herein, two PbI₂(X) complexes with different coordination strength of ligand X in complexation with PbI₂ (PbI₂(DMF) and PbI₂(DMSO)) are synthesized. The correlation between the morphology, evolution of the perovskite formation, defects state, carrier lifetime and the subsequent photovoltaic performance are investigated in details via a two-step coating method with various PbI₂(X) complexes. We find that PbI₂(DMSO) derived perovskite film shows larger grains and vertically oriented grain boundaries as well as enhanced photoluminescence intensity and longer carrier lifetime. As a result, highly efficient inverted planar perovskite solar cells with a power conversion efficiency up to 17.0% are achieved from PbI₂(DMSO) complex under 1 sun illumination. This research could open up a new pathway to further improve the performance of perovskite solar cells through the control of perovskite crystallization kinetics by choosing proper PbI₂(X) complex precursors.