Open-circuit voltage exceeding the outermost HOMO-LUMO offset in cascade organic solar cells |
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| Institution: | 1. Key Laboratory of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, PR China;2. Key Laboratory of Wireless-Optical Communications, Chinese Academy of Sciences, School of Information Science and Technology, University of Science and Technology of China, Hefei, 230026, PR China;1. State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China;2. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China;3. CAS Research/Education Center for Excellence in Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China;1. Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA;2. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA;3. Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA;4. State Key Laboratory of Electronic Thin Films and Integrated Devices, Department of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, PR China |
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| Abstract: | We demonstrate a planar organic solar cell with a four-layer cascade architecture that exhibits an open-circuit voltage (Voc) greater than the offset in energy between the highest occupied molecular orbital (HOMO) of the outermost donor and the lowest unoccupied molecular orbital (LUMO) of the outermost acceptor. The device consists of a subphthalocyanine (SubPc)/fullerene (C60) heterojunction that is modified by inserting one or two additional donor layers between SubPc and the anode. We find that two-, three- and four-layer structures yield similar Voc (1.0 V, 0.91 V and 0.94 V, respectively), even though the outermost HOMO-LUMO offset decreases from 1.4 eV to 1.10 eV, and to 0.9 eV, respectively. Analysis of the turn-on voltage in dark provides further evidence that open-circuit voltage is not limited by the outermost HOMO-LUMO offset. |
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| Keywords: | Cascade Open-circuit voltage Small molecule Turn-on voltage Organic Solar cell |
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