Study On Interfacial Passivation And Charge Transfer Mechanism Of Perovskite Solar Cells

With the rapid development in the past ten years,the photoelectric conversion efficiency(PCE)of single organic-inorganic hybrid perovskite solar cells(PSCs)has reached 25.7%,which is very close to crystal silicon solar cells.However,a large number of defects in the phase and interfaces of perovskite film limit the further improvement of its photoelectric performance and stability.Therefore,it is of great significance to develop suitable interface defect passivation materials and study the mechanism of passivation and charge transfer.Most of the previous studies focused on defect passivation mechanism,and less on the effect of passivation layer on interface charge transfer mechanism.This research systematically elucidated how the passivation interplanar spacing affected the hole transport at HTL/perovskite interface.And on this basis,this research achieved a breakthrough in passivation layer thickness by the ammonium salts with smaller interplanar spacing.At the same time,it obtained better defect passivation effect than traditional passivation materials and improved photoelectric conversion efficiency and stability of the device.The specific research contents are as follows:Firstly,based on the relationship between the molecular chain length of ammonium salts and the interplanar spacing of passivation layers,this research realized the precise regulation of the interplanar spacing of passivation layers.The results showed that when the thicknesses of passivation layers were similar,the PCE decreased gradually with the increase of interplanar spacing.Secondly,the influence mechanism of how the passivation interplanar spacing affected the hole transport at HTL/perovskite interface was systematically illustrated.By analyzing the energy level relationship and comparing the defect passivation effect and charge transfer of films or devices passivated by different ammonium salts,it was determined that the increase of interplanar spacing would decrease the hole tunneling efficiency at perovskite/HTL interface and then reduce the PCE of devices.Finally,the passivation layer with minimal interplanar spacing(2-chlorbenzylamine iodine,2-CBAI)significantly improved device efficiency and stability.By optimizing the passivation concentration of different ammonium salts,it was found that 2-CBAI can break through the restriction of passivation layer thickness due to its better hole tunneling characteristics.By increasing the thickness,2-CBAI achieved better defect passivation effect,and the PCE of perovskite solar cells was increased from 20.24% to 23.10%,which was better than that(22.47%)of traditional device passivated by phenylethyl ammonium iodide(PEAI).In addition,the 2-CBAI passivation layer also significantly improved the illumination stability of the device.