The effect of cathode buffer in small molecule organic solar cells
Xia Hao a b c, Shenghao Wang c, Takeaki Sakurai c, Katsuhiro Akimoto c
a Institute of New Energy and Low-carbon Technology, Sichuan University
b Institute of Solar Energy Materials and Devices, College of Materials Science and Engineering, Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu , 610064, China
c Institute of Applied Physics, University of Tsukuba
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics 2018 (AP-HOPV18)
Kitakyūshū-shi, Japan, 2018 January 28th - 30th
Organizers: Shuzi Hayase, Juan Bisquert and Hiroshi Segawa
Oral, Xia Hao, presentation 047
DOI: https://doi.org/10.29363/nanoge.ap-hopv.2018.047
Publication date: 27th October 2017

Small molecule organic solar cells (OSCs) are very interesting in the photovoltaic field since they are expected to open a novel field of solar cells, that is, flexible, light
weight, and potential low-cost photovoltaic cells. In this work, we fabricated inverted structured  boron subphthalocyanine chloride (SubPc)/fullerene (C60) based small molecule organic solar cells were fabricated. The effect of bathocuproine (BCP)/Ag doped BCP (Ag:BCP) in inverted organic solar cells was investigated. We demonstrated that BCP layer can be used as a buffer layer in inverted structure OSCs and the device performance was greatly improved. Unfortunately, the device exhibited an anomalous kink in the current density-voltage (J–V) characteristics, namely, an S-shaped J–V curve, leading to a low fill factor and low power conversion efficiency (PCE). To improve device performance, Ag:BCP was used to replace the BCP layer. The results showed that the Ag:BCP layer can eliminate the S-kink in the J–V curve, resulting in a large improvement of fill factor and PCE. The origin of the S-shaped J–V curve was demonstrated to originate from the charge accumulation at the C60/BCP interface. On the contrary, the C60/Ag:BCP interface has favorable electronic properties with beneficial gap states for the transport of free carriers. Together with the good conductivity of Ag:BCP layer and the smooth morphology properties, the device performance was greatly improved by Ag:BCP buffer layer. 

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