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Direct Arylation Polycondensation (DAP) Synthesis of Alternating Quaterthiophene−Benzothiadiazole Copolymers for Organic Solar Cell Applications
Author(s) -
Keller Tina,
Gahlmann Tobias,
Riedl Thomas,
Scherf Ullrich
Publication year - 2019
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201900260
Subject(s) - condensation polymer , stille reaction , copolymer , chemistry , organic solar cell , energy conversion efficiency , conjugated system , polymer chemistry , polymer , polymer solar cell , fullerene , chemical engineering , organic chemistry , materials science , optoelectronics , engineering
Poly[(2,1,3‐benzothiadiazole‐4,7‐diyl)‐ alt ‐4′,3′′‐difluoro‐3,3′′′‐di(2‐octyldodecyl)‐2,2′;5′,2′′;5′′,2′′′‐quaterthiophene‐5,5′′′‐diyl)] (PBTff4T‐2OD) and poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐ alt ‐3,3′′′‐di(2‐octyldodecyl)‐2,2′;5′,2′′;5′′,2′′′‐quaterthiophene‐5,5′′′‐diyl)] (PffBT4T‐2OD) for use as the p‐donor component of high‐efficiency fullerene‐based organic solar cells are usually synthesized in established C−C cross‐coupling reactions, preferably using the Stille procedure. This report describes how PBTff4T‐2OD and PffBT4T‐2OD are generated in a direct arylation polycondensation (DAP) approach with molecular weights up to M n =19.4 kDa and 21.1 kDa, respectively, and how structural defects in the copolymers (e. g., homocoupling defects) show a strong impact on the pre‐aggregation behavior. The optimized reaction conditions allow for a distinct reduction of the amount of such defects in the resulting copolymers. When the Stille‐type products are used in the active layer of organic solar cells (OCSs) together with fullerene acceptors, high power‐conversion efficiencies (PCEs) in the range of 8.6–10.8 % have been reported. The high PCEs are particularly related to the pre‐aggregation of the conjugated copolymers prior to film formation. Despite quite similar characterization data, non‐optimized OCSs with the DAP polymers as replacement for the Stille products afforded a relatively low power‐conversion efficiency of up to 2.4 %.