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Elevated Photovoltaic Performance in Medium Bandgap Copolymers Composed of Indacenodi-thieno[3,2-b]thiophene and Benzothiadiazole Subunits by Modulating the π-Bridge

1
Key Laboratory for Utility of Environment-Friendly Composite Materials and Biomass in University of Gansu Province, School of Chemical Engineering, Northwest Minzu University, Lanzhou 730030, China
2
School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
3
CAS Key Laboratory of Bio-Based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
*
Authors to whom correspondence should be addressed.
Polymers 2020, 12(2), 368; https://doi.org/10.3390/polym12020368 (registering DOI)
Received: 1 December 2019 / Revised: 10 January 2020 / Accepted: 13 January 2020 / Published: 7 February 2020
(This article belongs to the Section Polymer Processing and Performance)
Two random conjugated polymers (CPs), namely, PIDTT-TBT and PIDTT-TFBT, in which indacenodithieno[3,2-b]thiophene (IDTT), 3-octylthiophene, and benzothiadiazole (BT) were in turn utilized as electron-donor (D), π-bridge, and electron-acceptor (A) units, were synthesized to comprehensively analyze the impact of reducing thiophene π-bridge and further fluorination on photostability and photovoltaic performance. Meanwhile, the control polymer PIDTT-DTBT with alternating structure was also prepared for comparison. The broadened and enhanced absorption, down-shifted highest occupied molecular orbital energy level (EHOMO), more planar molecular geometry thus enhanced the aggregation in the film state, but insignificant impact on aggregation in solution and photostability were found after both reducing thiophene π-bridge in PIDTT-TBT and further fluorination in PIDTT-TFBT. Consequently, PIDTT-TBT-based device showed 185% increased PCE of 5.84% profited by synergistically elevated VOC, JSC, and FF than those of its counterpart PIDTT-DTBT, and this improvement was chiefly ascribed to the improved absorption, deepened EHOMO, raised μh and more balanced μh/μe, and optimized morphology of photoactive layer. However, the dropped PCE was observed after further fluorination in PIDTT-TFBT, which was mainly restricted by undesired morphology for photoactive layer as a result of strong aggregation even if in the condition of the upshifted VOC. Our preliminary results can demonstrate that modulating the π-bridge in polymer backbone was an effective method with the aim to enhance the performance for solar cell. View Full-Text
Keywords: indacenodithieno[3,2-b]thiophene; random conjugated polymer; modulating π-bridge; photovoltaic property indacenodithieno[3,2-b]thiophene; random conjugated polymer; modulating π-bridge; photovoltaic property
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MDPI and ACS Style

An, L.; Tong, J.; Huang, Y.; Liang, Z.; Li, J.; Yang, C.; Wang, X. Elevated Photovoltaic Performance in Medium Bandgap Copolymers Composed of Indacenodi-thieno[3,2-b]thiophene and Benzothiadiazole Subunits by Modulating the π-Bridge. Polymers 2020, 12, 368.

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