title: Improvement of Charge Collection and Performance Reproducibility in Inverted Organic Solar Cells by Suppression of ZnO Subgap States.
abstract: Organic solar cells (OSCs) with inverted structure usually exhibit higher power conversion efficiency (PCE) and are more stable than corresponding devices with regular configuration. Indium tin oxide (ITO) surface is often modified with solution-processed low work function metal oxides, such as ZnO, serving as the transparent cathode. However, the defect-induced subgap states in the ZnO interlayer hamper the efficient charge collection and the performance reproducibility of the OSCs. In this work, we demonstrate that suppression of the ZnO subgap states by modification of its surface with an ultrathin Al layer significantly improves the charge extraction and performance reproducibility, achieving PCE of 8.0%, which is ∼15% higher than that of a structurally identical control cell made with a pristine ZnO interlayer. Light intensity-dependent current density-voltage characteristic, photothermal deflection spectroscopy, and X-ray photoelectron spectroscopy measurements point out the enhancement of charge collection efficiency at the organic/cathode interface, due to the suppression of the subgap states in the ZnO interlayer.
authors.affiliation: Department of Physics, Institute of Advanced Materials, and Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University , 224 Waterloo Road, Kowloon Tong, NT, Hong Kong.
authors.forename: Bo
authors.initials: B
authors.lastname: Wu
authors.affiliation: Department of Physics, Institute of Advanced Materials, and Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University , 224 Waterloo Road, Kowloon Tong, NT, Hong Kong.
authors.forename: Zhenghui
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Department of Physics, Institute of Advanced Materials, and Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University , 224 Waterloo Road, Kowloon Tong, NT, Hong Kong.
authors.forename: Qingyi
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Department of Physics, Institute of Advanced Materials, and Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University , 224 Waterloo Road, Kowloon Tong, NT, Hong Kong.
authors.forename: Furong
authors.initials: F
authors.lastname: Zhu
authors.affiliation: Center of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong , Tat Chee Avenue, Kowloon Tong, Hong Kong.
authors.forename: Tsz-Wai
authors.initials: TW
authors.lastname: Ng
authors.affiliation: Center of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong , Tat Chee Avenue, Kowloon Tong, Hong Kong.
authors.forename: Chun-Sing
authors.initials: CS
authors.lastname: Lee
authors.affiliation: Department of Physics, Institute of Advanced Materials, and Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University , 224 Waterloo Road, Kowloon Tong, NT, Hong Kong.
authors.forename: Sin-Hang
authors.initials: SH
authors.lastname: Cheung
authors.affiliation: Department of Physics, Institute of Advanced Materials, and Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University , 224 Waterloo Road, Kowloon Tong, NT, Hong Kong.
authors.forename: Shu-Kong
authors.initials: SK
authors.lastname: So
keywords: charge collection; organic solar cells; organic/cathode interface; oxide interlayer; subgap states