Synthesis and properties of new dialkoxyphenylene quinoxaline-based donor-acceptor conjugated polymers and their applications on thin film transistors and solar cells

Synthesis, properties, and optoelectronic device applications of four new bis-[4-(2-ethyl-hexyloxy)-phenyl]quinoxaline(Qx(EHP))-based donor-acceptor conjugated copolymers are reported, in which the donors are thiophene(T), dithiophene(DT), dioctylfluorene(FO), and didecyloxyphenylene(OC10). The optical band gaps (Eg) of PThQx(EHP), PDTQ(EHP), POC10DTQ(EHP), and PFODTQ(EHP) estimated from the onset absorption are 1.57, 1.65, 1.77, and 1.92 eV, respectively. The smallest Eg of PThQx(EHP) among the four copolymers is attributed to the balanced donor/acceptor ratio and backbone coplanarity, leading to a strong intramolecular charge transfer. The hole mobilities obtained from the thin film transistor (TFT) devices of PThQx(EHP), PDTQ(EHP), POC10DTQ(EHP), and PFODTQ(EHP) are 2.52 x 10⁻⁴, 4.50 x 10⁻³, 4.72 x 10⁻⁵, and 9.31 x 10⁻⁴ cm² V⁻¹ s⁻¹, respectively, with the on-off ratios of 2.00 x 10⁴, 1.89 x 10³, 4.07 x 10³, and 2.30 x 10⁴. Polymer solar cell based on the polymer blends of PFODTQ(EHP), PThQx(EHP), POC10DTQ(EHP), and PDTQ(EHP) with [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) under illumination of AM1.5 (100 mW cm⁻²) solar simulator exhibit power conversion efficiencies of 1.75, 0.92, 0.79, and 0.43%, respectively. The donor/acceptor strength, molecular weight, miscibility, and energy level lead to the difference on the TFT or solar cell characteristics. The present study suggests that the prepared bis[4-(2-ethyl-hexyloxy)-phenyl]quinoxaline donor-acceptor conjugated copolymers would have promising applications on electronic device applications.