Morphology Control In Perovskite Thin Films For Highly Efficient Planar Heterojunction Solar Cells

Film morphology played a decisive role in the final device performance of planar heterojunction perovskite solar cells （PHJ-PSCs）. In order to control the perovskite film morphology, we studied the influence of solvent-enginering time, additive ratio and annealing condition in both pure iodine and mixed-halide perovskite system. The main research contents and conclusions are as follows:（1） Through optimization of the solvent engineering time, high quality CH3NH3Pbl3 perovskite film was obtained, based on which the PHJ-PSCs with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PC6oBM/Al gained a power conversion efficiency （PCE） up to 6.44% with a good repeatability, also it showed no hysteresis under different scaning conditions.（2） Study the influence of additive 1,8-diiodooctane （DIO） on CH₃NH₃PbI₃ perovskite film morphology, crystallinity, and final device performance. Based on the optimal volume ratio of 2%, high-quality compact perovskite film was obtained with enhanced crystallinity and smaller roughness. The PHJ-PSCs gained a PCE of 9.01%. In addition, the annealing temperature will also affect the device performance.（3） Study the influence of precursor concentration on CH₃NH₃PbI₃ perovskite film morphology. Based on the optimal concentration of 550 mg/ml, pinhole-free perovskite film with suitable film thickness and grain size was obtained, based on which the final PHJ-PSCs reached a PCE up to 12.24%.（4） The compact and pinhole-free CH₃NH₃PbI₃-xClx perovskite thin film was obtained using the precursors that mixing PM2, PbO2 and CH3NH3I （MAI） at an optimized ratio of 1:1:4. The morphology and formation process of CH₃NH₃PbI₃-xClx thin film was closely related to the annealing temperature and time. Highly efficient PHJ-PSCs with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃-xClx/PCBM/C60/Ag was fabricated with good performance and excellent repeatability. The PCE up to 14.03% was achieved without obvious hysteresis under different scanning condition.（5） The morphology, crystallization process, and element analysis suggested that the chlorine gradually diffused and sublimated from the film surface while the iodine moved to the surface, together with the remove of the pinholes in the film.