Research On Electron Transport Layer And Interface Modification For Perovskite Solar Cells

Due to the excellent properties of perovskite materials,such as high absorption coefficient,excellent bipolar charge transport,large carrier diffusion length,and high tolerance to trap states,the perovskite solar cells(PSC)have rapidly been developing in recent years.However,there are still many problems to prevent them from large scale commercialization.Such as,poor stability of perovskite materials,high temperature fabrication and low charge mobility of the Ti O₂ electron transport layer,and serious J-V hysteresis.As an effort to overcome the above problems,a series of investigations have been carried out to modify the Ti O₂ electron transport layer and explore new electron transport layer for high performance hybrid and all inorganic perovskite solar cells.1.The introduction of a wide-band Ca Ti O₃ compound on the surface of Ti O₂ as an interface modification layer can effectively inhibit charge recombination at the perovskite/Ti O₂interface,which can improve the efficiency and stability of the device.The ultrathin Ca Ti O₃ modification layer shows no significant effect on the transmission of light,thus cause no evident loss to the light collection ability of perovskite.While it can improve the energy level matching,therefore facilitates the carrier transport and promotes the separation of photo-generated charge carriers.On the other hand,the interface modification layer can also effectively inhibit the recombination of photogenerated electron-hole pairs at the ETL/perovskite interface and improve device performance.It shows,the device with a Ti O₂ ETL modified with a Ca Ti O₃ ultrathin film that was prepared by using Ca(NO₃)₂solution with a concentration of 3 m M presents the best photovoltaic performance,where the short-circuit current J_sc is 23.08 m A/cm²,the open-circuit voltage V_oc is 1.09 V,and the filling factor FF value is 0.76.A photoelectric conversion efficiency of 19.12%is finally obtained and it shows low hysteresis in the J-V curve.2.Considering the relatively low electron mobility of the Ti O₂ electron transport layer,and the photocatalysis of Ti O₂ under ultraviolet light which results in device instability,Zn Se compound films have been fabricatied and employed as the electron transport layer of Cs Pb Br₃ inorganic perovskite solar cell for the first time.A high-quality Cs Pb Br₃ perovskite thin film was successfully prepared on the Zn Se electron transport layer by a two-step vacuum deposition method at room temperature,and an inorganic perovskite solar cell with excellent stability has been obtained.It shows that the device assembled with with a 90 nm Zn Se electron transport layer and the Cs Pb Br₃ perovskite thin film prepared from 200 nm Pb Br₂ and Cs Br precursors shows the best photovoltaic performance,in which the short-circuit current Jsc is 8.03 m A/cm²,the open-circuit voltage Voc is 1.45 V,the fill factor FF value is 0.72,and a photoelectric conversion efficiency of 8.38%is finally obtained.And the champion device shows good repeatability and the negligible hysteresis.