Highly Efficient and Stable Perovskite Solar Cells Incorporating Chlorinated-Tin Oxide Electron Transport Layers Prepared via Coordination of Diacyl-Metal Cations

Abstract

The surface passivation of metal oxide electron-transportlayers(ETLs) is a powerful strategy for realizing high-performance perovskitesolar cells. The surface properties of ETLs strongly influence carrierinjection and transfer dynamics; therefore, control of the carriertrap density is crucial. Semiconducting small molecules are consideredsuitable materials for surface passivation. However, they are expensiveand vulnerable to humid atmospheres. Ultrathin polymer layers canhave poor surface coverage owing to their spinodal dewetting. In thisstudy, we employ adipoyl chloride as an organic ligand for the chemicallyrobust and efficient surface passivation of SnO2 ETLs.Through the strong coordination of diacyl-metal cations, acyl groupsare adsorbed onto the SnO2 surfaces, and the density ofoxygen vacancies is significantly reduced. Furthermore, the changingsurface properties of the SnO2 ETLs also contribute tothe improvement of perovskite morphologies. The deeper energy levelsand reduced defect density of the ETLs promote electron injectionand transfer at the perovskite and ETL interface. The enlarged perovskitegrains are accompanied by improved electron mobility and reduced grain-boundarydensity. The resulting power conversion efficiency (PCE) increasesfrom 19.36 to 21.41%. The normalized PCE is retained at 90.4% of theinitial value for 720 h under 1 sun illumination without the encapsulationof the devices.