Synthesis and photovoltaic property of a novel low band gap conjugated donor-acceptor copolymer consisting of 2,7-carbazole and (bithiophenevinyl)-(2-pyran-4-ylidenemalononitrile)(TVIVI)

摘要

A novel soluble conjugated donor-acceptor (D-A) copolymer, poly(2-(2-((E)-2(3,4-dihexyI-5-(7-methyl-9-octyl-9H-carbazole-2-yl)thiophene-2-yl)vinyl)-6((E)-2-(3,4-dihexyl-5-methyithiophen-2yl)vinyl-4H-pyran-4-ylidene)malononitrile) (CZPM), consisting of alternating 2,7-carbazole and (bithiophenevinyl)-(2-pyran-4-ylidenemalononitrile) (TVM) was synthesized by Suzuki coupling polymerization. The photophysical and photovoltaic properties of the copolymer were investigated. The UV-vis absorption spectrum and cyclic voltammetry measurements of CZPM film showed that the copolymer has a relatively low band gap (1.81 eV) and a deep highest occupied molecular orbital (HOMO) level (-5.55 eV). Bulk heterojunction photovoltaic devices were fabricated using CZPM as donor and (6,6)-phenyl C_(61)-butyric acid methyl ester (PCBM) as acceptor with the weight blend ratio ranging from 1:1 to 1:4. The device with the blend ratio of 1:2 between CZPM and PCBM exhibited an open-circuit voltage (V_(oc)) of 0.74V and a power conversion efficiency (PCE) of 0.1% under simulated AM1.5 solar irradiation (100 mW/cm~2). The relatively low conversion efficiency of the device is attributed to the ineffective exciton dissociation at the CZPM/PCBM interface and the imperfect film-forming property of the polymer resulting from the low molecular weight.