Solution-Processable Ionic Liquid as an Independent or Modifying Electron Transport Layer for High-Efficiency Perovskite Solar Cells

Qiliang Wu; Weiran Zhou; Qing Liu; Pengcheng Zhou; Tao Chen; Yalin Lu; Qiquan Qiao; Shangfeng Yang

doi:10.1021/acsami.6b12683

Solution-Processable Ionic Liquid as an Independent or Modifying Electron Transport Layer for High-Efficiency Perovskite Solar Cells

ACS Appl Mater Interfaces. 2016 Dec 21;8(50):34464-34473. doi: 10.1021/acsami.6b12683. Epub 2016 Dec 6.

Authors

Qiliang Wu¹, Weiran Zhou¹, Qing Liu¹, Pengcheng Zhou¹, Tao Chen¹, Yalin Lu¹, Qiquan Qiao², Shangfeng Yang¹

Affiliations

¹ 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.
² Center for Advanced Photovoltaics, Department of Electrical Engineering and ComputerScience, South Dakota State University , Brookings, South Dakota 57007, United States.

PMID: 27998137
DOI: 10.1021/acsami.6b12683

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 TiO₂ ETL as a modification layer, the average power conversion efficiency (PCE) of CH₃NH₃PbI₃ PHJ-PSC devices reaches 18.42 ± 0.65%, which dramatically surpasses that based on commonly used TiO₂ ETL (14.20 ± 0.43%), and the highest PCE (19.59%) is almost identical to that of the record PCE for planar CH₃NH₃PbI₃ PSCs (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 TiO₂ ETL (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 TiO₂ ETL, revealing the role of [EMIM]PF₆-IL in efficient electron transport.

Keywords: dipolar interaction; electron transport layer; interface engineering; ionic liquid; perovskite solar cells.