Acid-functionalized fullerenes used as interfacial layer materials in inverted polymer solar cells |
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Authors: | Hyosung Choi Junghoon Lee Wonho Lee Seo-Jin Ko Renqiang Yang Jeong Chul Lee Han Young Woo Changduk Yang Jin Young Kim |
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Affiliation: | 1. Interdisciplinary School of Green Energy and KIER-UNIST Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), Banyeon-ri 100, Ulsan 689-798, South Korea;2. Department of Cogno-Mechatronics Engineering (WCU), Pusan National University, Miryang 627-706, South Korea;3. Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences Qingdao, Shandong Province 266101, PR China;4. KIER-UNIST Advanced Center for Energy, Korea Institute of Energy Research, Ulsan 689-798, South Korea |
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Abstract: | Two types of carboxylic acid functionalized fullerence derivatives, 4-(2-ethylhexyloxy)-6,6]-phenyl C61-butyric acid (p-EHO-PCBA) and bis-4-(2-ethylhexyloxy)-6,6]-phenyl C61-butyric acid (bis-p-EHO-PCBA), were synthesized and investigated as an interfacial layer for inverted polymer solar cells (iPSCs). The –COOH groups on the PCBAs chemisorb to inorganic metal oxide (TiOX), generating fullerene-based self-assembled monolayers (FSAMs). The devices with the mono- and bis-FSAMs exhibited substantially lower series resistance (RS) values of 2.10 Ω cm2 and 1.46 Ω cm2, compared to that (4.15 Ω cm2) of the unmodified device. The TiOX films modified with mono- and bis-FSAMs showed higher contact angles of 50° and 91°, respectively, than that of the pristine TiOX film (33°). The increased contact angles were attributed to the enhanced hydrophobicity, improving the wetting properties with the organic photoactive layer. In addition, a comparison of device characteristics with electroactive FSAMs and non-electroactive benzoic acid SAMs clearly indicates that the FSAMs may suggest an additional pathway for photo-induced charge transfer and charge collection to ITO. After surface modification with FSAMs, the short-circuit current density (JSC) and fill factor (FF) values increased substantially. The iPSCs based on poly(5,6-bis(octyloxy)-4-(thiophen-2-l)benzoc]1,2,5]thiadiazole) (PTBT) and 6,6]phenyl-C61-butyric acid methyl ester (PCBM) as an active layer showed remarkably improved power conversion efficiency up to 5.13% through incorporation of the FSAMs-based interfacial layer. |
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Keywords: | Surface modification Inverted polymer solar cells Self-assembled monolayer Interfacial layer Fullerene |
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