New Thiophene-Phenylene-Thiophene Acceptor Random Conjugated Copolymers for Optoelectronic Applications

Abstract

New low band gap thiophene-phenylene-thiophene (TPT)-based donor-acceptor-donor random copolymers were synthesized for optoelectronic device applications by a palladium-catalyzed Stille coupling reaction under microwave heating. The acceptors included 2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,8-bis[5'-bromo-dithien-2-yl-quinoxalines] (DTQ) and 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethyl-hexyl)-pyrrolo[3,4-c]-pyrrole-1,4-dione (DPP). The prepared random copolymers were named as PTPTDTQ(0.55), PTPTDTQ(0.34)DPP(0.14), and PTPTDTQ(0.26)DPP(0.34) depending on the copolymer ratio. The optical band gaps (Er) of PTPTDTQ(0.55), PTPTDTQ(0.34)DPP(0.14), and PTPTDTQ(0.26)DPP(0.34) were 1.74, 1.56, and 1.48 eV, respectively. The hole mobility obtained from the field-effect transistor devices prepared from PTPTDTQ(0.55), PTPTDTQ(0.34)DPP(0.14), and PTPTDTQ(0.26)DPP(0.34) were 2.2 x 10(-3), 2.4 x 10(-3), and 4.7 x 10(-3) cm(2) V s(-1), respectively, with the on-off ratios of 4.0 x 10(4), 4.0 x 10(4), and 5.3 x 10(4). It suggested that the significant intramolecular charge transfer between the TPT and acceptor led to the band gap reduction and hole mobility enhancement. Polymer solar cells of these TPT-based copolymers blended with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-71 (PC(71) BM) under illumination of AM 1.5G (100 mW cm(-2)) solar simulator exhibited a power conversion efficiency (PCE) as high as 3.71%. Besides, the near-infrared photodetector device prepared from PTPTDTQ(0.26)DPP(0.34) showed a high external quantum efficiency exceeding 32% at 700 nm (under -3 V bias) and fast-speed response. This study suggests that the prepared TPT-based donor-acceptor random copolymers exhibited promising and versatile applications on optoelectronic devices. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2351-2360, 2010