Effect of Molecular Orientation of Donor Polymers on Charge Generation and Photovoltaic Properties in Bulk Heterojunction All‐Polymer Solar Cells |
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Authors: | Jea Woong Jo Hyungju Ahn Min Jae Ko Alex K.‐Y. Jen Hae Jung Son |
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Affiliation: | 1. Photoelectronic Hybrid Research Center, Korea Institute of Science and Technology, Seoul, Korea;2. Pohang Accelerator Laboratory, Kyungbuk, Pohang, Korea;3. KU‐KIST Graduate School of Converging Science and Technology Korea University, Seoul, Korea;4. Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA;5. Department of Chemistry, University of Washington, Seattle, WA, USA |
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Abstract: | All‐polymer solar cells (all‐PSCs) utilizing p‐type polymers as electron‐donors and n ‐typepolymers as electron‐acceptors have attracted a great deal of attention, and their efficiencies have been improved considerably. Here, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5‐fluoro‐2,1,3‐benzothiadiazole with different relative amounts of 2,2′‐bithiophene (2T) and dithieno[3,2‐b;2′,3′‐d]thiophene (DTT). Solar cells are prepared by blending the polymer donors with a naphthalene diimide‐based polymer acceptor (PNDI) or a [6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) acceptor and their morphologies and crystallinity as well as optoelectronic, charge‐transport and photovoltaic properties are studied. Interestingly, charge generation in the solar cells is found to show higher dependence on the crystal orientation of the donor polymer for the PNDI‐based all‐PSCs than for the conventional PC71BM‐based PSCs. As the population of face‐on‐oriented crystallites of the donor increased in PNDI‐based PSC, the short‐circuit current density (JSC) and external quantum efficiency of the devices are found to significantly improve. Consequently, device efficiency was enhanced of all‐PSC from 3.11% to 6.01%. The study reveals that producing the same crystal orientation between the polymer donor and acceptor (face‐on/face‐on) is important in all‐PSCs because they provide efficient charge transfer at the donor/acceptor interface. |
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Keywords: | conjugated polymers copolymers molecular orientation nonfullerene acceptors polymer solar cells |
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