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) < DPIP (3.15). The DP/TP copolymer had a field-effect hole mobility of 1.89 x 10(-3) cm(2) V-1 s(-1). The DP/DTBT and DP/DTQ copolymers showed hole mobilities of 1.92 x 10(-4) and 2.10 x 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.