Passivation of defects in inverted perovskite solar cells by imidazolium-based ionic liquid
During perovskite film preparation, defects in the film are almost impossible to avoid because of the migration of the halide ions, which is detrimental to achieve high-quality film. In general, the introduction of additive is an effective strategy to control the film morphology and to reduce the defect density. Here, a representative and simplest ionic liquid, 1-methyl-3-propylimidazolium bromide (MPIB), is selected as an additive due to its high conductivity and lone-pair electron in its cation group. Remarkably, the adding of MPIB additive into the perovskite film improves the power conversion efficiency (PCE) from 15.9% of pristine device to 18.2%. With the help of characterization analysis of scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer, etc., two contributions of MPIB additive are addressed: (1) the major one is the passivation of the uncoordinated Pb2+ to reduce the defects in the perovskite film due to the lone-pair electron in its cation group, and (2) the secondary one is beneficial to promote crystal growth to improve the film quality. Hence, this work provides an easy approach to achieve high-performance perovskite solar cell via passivation of the uncoordinated Pb2+ in the perovskite film due to the cation group of ionic liquid .