Efficient Inverted Organic Solar Cells Based on a Fullerene Derivative-Modified Transparent Cathode

Indium tin oxide (ITO) is a transparent conductive material which is extensively used in organic solar cells (OSCs) as electrodes. In inverted OSCs, ITO is usually employed as a cathode, which should be modified by cathode buffer layers (CBLs) to achieve better contact with the active layers. In this paper, an amine group functionalized fullerene derivative (DMAPA-C-60) is used as a CBL to modify the transparent cathode ITO in inverted OSCs based on PTB7 as a donor and PC71BM as an acceptor. Compared with traditional ZnO CBL, DMAPA-C-60 exhibited comparable transmittance. OSCs based on DMAPA-C-60 show much better device performance compared with their ZnO counterparts (power conversion efficiencies (PCEs) improved from 6.24 to 7.43%). This is mainly because a better contact between the DMAPA-C-60 modified ITO and the active layer is formed, which leads to better electron transport and collection. Nanoscale morphologies also demonstrate that the surface of DMAPA-C-60-modified ITO is plainer than the ZnO counterparts, which also leads to the better device performance.National Natural Science Foundation of China [21574072, 21375069, 21675091, 21404065]; Natural Science Foundation for Distinguished Young Scientists of Shandong Province [JQ201403]; Taishan Young Scholar Program of Shandong Province [tsqn20161027]; Key Research and Development Project of Shandong Province [2016GGX102028, 2016GGX102039]; Project of Shandong Province Higher Educational Science and Technology Program [J15LC20]; Scientific Research Foundation for Returned Overseas Chinese Scholars of State Education Ministry [20111568]; People's Livelihood Science and Technology Project of Qingdao [166257nsh, 173378nsh]; Innovation Leader Project of Qingdao [168325zhc]; China Postdoctoral Science Foundation [2017M612199]; Postdoctoral Scientific Research Foundation of Qingdao; First Class Discipline Project of Shandong ProvinceSCI(E)ARTICLE91