Interface Engineering Of Electron Transport Layers For Enhanced Perovskite Solar Cells

Organic-inorganic hybrid perovskite materials have been widely applied in optoelectronic devices,typically perovskite solar cells?PSCs?,attributed to the excellent physical and chemical properties,including tunable direct band gap,high absorption coefficient,high charge mobility,long diffusion length,etc.TiO₂ nanorod arrays?NAs?have been successfully applied as electron transport scaffolds in perovskite solar cells due to the direct electron transfer channels.However,the oxygen vacancies on the surface of TiO₂ lead to larger defect states limiting the power conversion efficiency?PCE?,and the high processing temperature hinders the applicability on the flexible substrates.The interface engineering can solve the issue of the oxygen vacancies on the TiO₂ surface,and the ZnO with high electron mobility can realize low temperature process of electron transport layer?ETL?in PSCs.But the acid nonresistant of ZnO could destroy the perovskite absorber layers,resulting in poor PCE.Interface modification is critical to achieving efficient and stable PSCs.Our main works are as followings:Anatase TiO₂ modified rutile TiO₂ NAs?TCNAs?:Ultrathin anatase TiO₂ shells were in-situ deposited on rutile TiO₂ nanorod arrays by a room-temperature solution method.The formed Type-II core-shell nanorod structures with interface energy level alignment helps to accelerate the interface charge transfer and passivates the defect states to improve the quality of the perovskite films.The TCNAs-based PSCs have a significantly improved performance,which exhibited PCE of11.8%with open-circuit voltage(V_OC)of 0.97 V,short-circuit current density(J_SC)of 21.8 mA/cm²,and fill factor?FF?of 55.8%,whereas the counterparts without anatase TiO₂ nanoshells showed PCE of 10.6%with V_OCC of 0.95 V,J_SCC of 21 mA/cm²,and FF of 52.5%.Self-assembled monolayer?SAM?modified TCNAs:SAM of N-[3-?Trimethoxysilyl?propyl]ethylenediamine was grafted on the surface of TCNAs TiO₂ surface at room temperature for different times.Interestingly,the PCE of 0.5 h SAM-based PSCs was significantly improved to14.89%,compared to 11.8%of the pristine TCNAs-based devices.The results indicate that the SAM controls the TCNAs surface wettability to improve the morphology and crystallinity of the following deposited perovskite layers.Moreover,the electric dipoles from the SAM increase the Fermi level of TCNAs for further enhancing the interface energy level alignment with perovskite layers to improve the interfacial charge transfer.Nb₂O₅ modified ZnO:Magnetron sputtering as taken to prepare the Nb₂O₅/ZnO double-layer electron transport structure as the ETL of PSCs to prevent the instability caused by the direct contact of the perovskite absorber layer with ZnO.We further explored the effect of different ZnO thickness on the performance of PSCs.The results show that the optimized PCE of the planar PSCs is 13.8%.In addition,the surface modification of Nb₂O₅ leading to the formation of highly crystalline and dense perovskite films,which improves the quality of the perovskite films,more importantly,the surface modification of the Nb₂O₅ forms interface energy level alignment to improve the interfacial charge transfer.