New Didecyloxyphenylene−Acceptor Alternating Conjugated Copolymers: Synthesis, Properties, and Optoelectronic Device Applications

Seven donor−acceptor copolymers incorporating didecyloxyphenylene ( DP ) donor and the following acceptors—thieno[3,4- b ]pyrazine ( TP ), 2,1,3-benzothiadiazole ( BT ), quinoxaline ( Q ), pyridine ( Py ), 2,3-dimethyl-5,7-dithien-2-yl-thieno[3,4- b ]pyrazine ( DTTP ), 4,7-dithien-2-yl-2,1,3-benzothiadiazole ( DTBT ), and 2,3-dimethyl-5,7-dithien-2-yl-quinoxaline ( DTQ )—were synthesized by Suzuki coupling polymerization. The effects of the acceptor strength and backbone planarity on the optical, electrochemical, field-effect charge transport, and photovoltaic properties of the donor−acceptor copolymers were investigated. The optical band gap (eV) of the copolymers showed the trend of DP/TP (1.47) < DP/BT (2.37) < DP/Py (2.76) < DP/Q (2.78) < DP / P (3.15). The DP/TP copolymer had a field-effect hole mobility of 1.89 × 10 −3 cm 2 V −1 s −1 . The DP/DTBT and DP/DTQ copolymers showed hole mobilities of 1.92 × 10 −4 and 2.10 × 10 −3 cm 2 V −1 s −1, respectively. The strong acceptor strength of TP and coplanar backbone in the DP/TP copolymer resulted in a large intramolecular charge transfer, leading to the observed charge transport and optical properties.. These results show that the backbone planarity of the DP / BT and DP / Q copolymers was significantly improved by incorporating thiophene moieties, leading to enhanced charge transport. Photovoltaic cells fabricated from DP/DTBT and DP/DTQ polymers blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) showed power conversion efficiencies of 0.40−0.41% under AM 1.5 solar simulator illumination (100 mW/cm 2 ). The results of the present study show that the electronic and optoelectronic properties of dialkoxylphenylene-based donor−acceptor copolymers could be tuned through the acceptor structure and backbone coplanarity.