Influence of the Electron Deficient Co‐Monomer on the Optoelectronic Properties and Photovoltaic Performance of Dithienogermole‐based Co‐Polymers |
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Authors: | Chin Pang Yau Zhuping Fei Raja Shahid Ashraf Munazza Shahid Scott E Watkins Pichaya Pattanasattayavong Thomas D Anthopoulos Vasilis G Gregoriou Christos L Chochos Martin Heeney |
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Affiliation: | 1. Department of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington, London, UK;2. CSIRO Molecular and Health Technologies, Australia;3. Department of Physics and Centre for Plastic Electronics, Imperial College London, South Kensington, London, UK;4. Advent Technologies SA, Patras Science Park, Platani‐Rio, Patra, Greece |
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Abstract: | A series of donor–acceptor (D–A) conjugated polymers utilizing 4,4‐bis(2‐ethylhexyl)‐4H‐germolo3,2‐b:4,5‐b′]dithiophene ( DTG ) as the electron rich unit and three electron withdrawing units of varying strength, namely 2‐octyl‐2H‐benzod]1,2,3]triazole ( BTz ), 5,6‐difluorobenzoc]1,2,5]thiadiazole ( DFBT ) and 1,2,5]thiadiazolo3,4‐c]pyridine ( PT ) are reported. It is demonstrated how the choice of the acceptor unit ( BTz , DFBT , PT ) influences the relative positions of the energy levels, the intramolecular transition energy (ICT), the optical band gap (Egopt), and the structural conformation of the DTG ‐based co‐polymers. Moreover, the photovoltaic performance of poly(4,4‐bis(2‐ethylhexyl)‐4H‐germolo3,2‐b:4,5‐b′]dithiophen‐2‐yl)‐(1,2,5]thiadiazolo3,4‐c]pyridine)] ( PDTG‐PT ), poly(4,4‐bis(2‐ethylhexyl)‐4H‐germolo3,2‐b:4,5‐b′]dithiophen‐2‐yl)‐(2‐octyl‐2H‐benzod]1,2,3]triazole)] ( PDTG‐BTz ), and poly(4,4‐bis(2‐ethylhexyl)‐4H‐germolo3,2‐b:4,5‐b′]dithiophen‐2‐yl)‐(5,6‐difluorobenzoc]1,2,5]thiadiazole)] ( PDTG‐DFBT ) is studied in blends with 6,6]‐phenyl‐C70‐butyric acid methyl ester ( PC70BM ). The highest power conversion efficiency (PCE) is obtained by PDTG‐PT (5.2%) in normal architecture. The PCE of PDTG‐PT is further improved to 6.6% when the device architecture is modified from normal to inverted. Therefore, PDTG‐PT is an ideal candidate for application in tandem solar cells configuration due to its high efficiency at very low band gaps (Egopt = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co‐polymers containing bridged bithiophenes with 5‐member fused rings in the central core and possessing an Egopt below 1.4 eV. |
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Keywords: | dithienogermole organic solar cells conjugated polymers |
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