Interface Optimization Of The Perovskite Solar Cells

In the past ten years,the mixed-organic-cation perovskite solar cells（PSCs）have attracted more and more attention due to their excellent performance,low cost,simple preparation process and adjustable band gap.The power conversion efficiency of PSCs has attained more than 25%,showing enormous potential for becoming the next generation of photovoltaic materials in the commercial applications.The excellent photovoltic performance and long-term stability are necessary for the large-scale industrialization of PSCs.And efficient and stable PSCs rely on high-quality perovskite films.The topics in the paper are to prepare high-quality perovskite films and study the degradation of perovskite film on device performance.The research results is that optimized perovskite films have preferable morphology and higher phase purity.And the devices have more excellent photovoltaic performance.In the study of ultraviolet stability of perovskite film,the used SnO₂ as electron transport layer（ETL）which has catalytic property can rapidly degrade the ETL/perovskite interface under ultraviolet light.There are many pinholes at the degraded interface which can hinder the carrier extraction and transmission,therefore reducing the short-circuit current of the device.（1）The perovskite phase purity in the film is vitial to perovskite solar cells.We have developed vacuum-assisted low temperature volatilization of solvent vacuum pretreatment to eliminate the side reactions in the film during the annealing process and improve the phase purity of perovskite film.The deprotonation reaction of organic amine salts is accelerated in the high temperature environment,and the methylamine produced by the deprotonation of methylamine iodide can further undergo the addition-elimination reaction with methylamine iodide.The reaction product can induce the non-perovskite phase in perovskite film,which seriously hinders the carriers transport in perovskite film.The side reaction is particularly obvious in the presence of solvent.The vacuum pretreatment before annealing to remove part of the solvent can effectively inhibit the occurrence of side reaction,and improve the phase purity of the film and the photoelectric performance of the device.The short-circuit current of the optimized device increased from 23.22 mA/cm² to 24.12 mA/cm²,the fill factor increased from 68.45%to 76.93%,and the PCE of the optimized device reached20.91%.It indicates that the vacuum pretreatment perovskite wet film has a great effect on the preparation of high quality perovskite films by solution method.（2）The light stability of perovskite solar cells is the key to its development and commercial application in the future.We have explored the influence of the electron transport layer material on the light device stability and track the decomposition process and performance evolution of the device under high-intensity ultraviolet light.The results indicate that mesoporous TiO₂ under ultraviolet light can cause the interface degradation of ETL/perovskite,and produce Pb I₂ at the interface and separate the perovskite film from the ETL,which leads to a significant reduction in the device light stability.Compared with devices based on mp-TiO₂ ETL,the performance of devices based on mp-SnO₂ also deteriorated,showing slower degradation at the mp-SnO₂/perovskite interface than mp-TiO₂based devices.There was no obvious morphology,composition change and PCE degradation of PCBM-based devices during the same test period.Compared with the TiO₂ layer,the commonly used SnO₂ layer does have a lower photocatalytic activity,but the perovskite/SnO₂ interface is severely decomposed due to the generation of pore structure,which limits the carrier injection at the interface,so device performance drop sharply.This study analyzes the influence of the electron transport layer in the inert atmosphere on the device’s ultraviolet light stability in detail,which provides an important basis for future research on the device’s light stability.