title: Solution-Processable Ionic Liquid as an Independent or Modifying Electron Transport Layer for High-Efficiency Perovskite Solar Cells.
abstract: Inorganic metal oxide, especially TiO2, has been commonly used as an electron transport layer (ETL) in regular-structure (n-i-p) planar heterojunction perovskite solar cells (PHJ-PSCs) but generally suffers from high electron recombination rate and incompatibility with low-temperature solution processability. Herein, by applying an ionic liquid (IL, 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM]PF6)) as either a TiO2-modifying interlayer or an independent ETL, we investigated systematically IL interface engineering for PHJ-PSCs. Upon spin-coating [EMIM]PF6-IL onto TiO2ETL as a modification layer, the average power conversion efficiency (PCE) of CH3NH3PbI3PHJ-PSC devices reaches 18.42 ± 0.65%, which dramatically surpasses that based on commonly used TiO2ETL (14.20 ± 0.43%), and the highest PCE (19.59%) is almost identical to that of the record PCE for planar CH3NH3PbI3PSCs (19.62%) reported very recently. On the other hand, by applying [EMIM]PF6-IL as an independent ETL, we achieved an average PCE of 13.25 ± 0.55%, and the highest PCE (14.39%) approaches that obtained for PHJ-PSCs based on independent TiO2ETL (14.96%). Both IL interface engineering methods reveal the effective electron transport of [EMIM]PF6-IL. The effects of [EMIM]PF6-IL on the surface morphology, crystallinity, and optical absorption of the perovskite film and the interface between the perovskite layer and substrate were investigated and compared with the case of independent TiO2ETL, revealing the role of [EMIM]PF6-IL in efficient electron transport.
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Qiliang
authors.initials: Q
authors.lastname: Wu
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Weiran
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Zhou
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Chen
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Yalin
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Center for Advanced Photovoltaics, Department of Electrical Engineering and ComputerScience, South Dakota State University , Brookings, South Dakota 57007, United States.
authors.forename: Qiquan
authors.initials: Q
authors.lastname: Qiao
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China (USTC) , Hefei 230026, China.
authors.forename: Shangfeng
authors.identifier: http://orcid.org/0000-0002-6931-9613
authors.initials: S
authors.lastname: Yang
keywords: dipolar interaction; electron transport layer; interface engineering; ionic liquid; perovskite solar cells