Interface Passivation Strategy For Efficient Inverted Perovskite Solar Cells

Inverted planar perovskite solar cells（I-PSCs）have great potential in a commercial application for their low-cost,flexibility,and low-temperature preparation.However,the low photoelectric conversion efficiency（PCE）and poor stability restricted the large-scale application and development of the I-PSCs.Therefore,it is of great significance to improve the efficiency and stability of I-PSCs for its application.In this paper,the efficient and stable I-PSCs are prepared based on the two-step spin coating method and the interface defects passivation strategy.1)A simple air-retreatment strategy is proposed to improve the performance of the I-PSCs.This air-retreatment impact on the physical properties and corresponding performance of the devices are systematically studied.The results show that the grain size of the perovskite film is enhanced by this method,and the MAPbI₃ film with higher quality is successfully prepared.The average grain size of 3.91μm and the largest grain size exceeding9μm are achieved,and the trap states are reduced from 4.05×10¹⁶ cm^-3 to 1.60×10¹⁶ cm^-3.Benefiting from the relatively larger grain size,lower trap density and higher crystallinity,a high PCE of 18.44%and negligible hysteresis are obtained.This air-retreatment strategy has great potential in the large-scale,low-temperature preparation of efficient and stable PSCs.2)Tetraoctylammonium bromide（TOAB）was introduced into I-PSCs with post-treatment to enhance the efficiency and stability of the devices.The properties of perovskite films and the performance of the corresponding device are systemically researched.The results show that TOAB molecules distribute throughout the perovskite films and thus effectively passivate the trap states at the grain boundaries and the surface.The built-in electrical field(V_bi)of the devices and the hydrophobic properties of the perovskite films are enhanced by TOAB molecular arrangement at the perovskite surface.Moreover,the light-harvesting efficiency is also improved via the redistribution of the light field in the I-PSCs.Benefiting from trap sates passivation,enhanced V_bi and light-harvesting,the champion PCE of 21.47%is achieved,which is among the reported high efficiencies for inverted PSCs.In addition,device stability has been greatly improved.The PCE of I-PSCs treated by TOAB can retain 81%of its initial value after 264 h in the air and can retain 94%of its initial value after 71 days in N₂.This work represents a novel passivation strategy by the posttreatment method without disturbing the perovskite film growth to understand the sole defect effects on the device performance of PSCs.3)The perovskite films were multifunction modified by polyvinylpyrrolidone（PVP）to enhance the performance and stability of the I-PSCs.The results show that PVP can effectively passivate the surface defects of the PVSK and correspondingly,decrease the density of trap states,which thus significantly reduce the energy loss as well as increase the efficiency of the I-PSCs.The champion PCE of 20.77%is achieved using PVP modification.Besides,the stability of I-PSCs is improved with PVP introduction.The PCE of the PVP-modified devices can retain 80%of its initial value in the air（with 27～33%RH）for 14 days,while the control devices only retain 50%of its initial value.In addition,the PCE of the PVP-modified devices can retain 90%of its initial value after exposure in N₂for 65 days,while the control devices only maintain 85%for the same exposure.