Synthesis And Photovoltaic Properties Of Low-bandgap Polymers Based On N-arylcarbazole

With the energy crisis becoming serious, the solar energy as a kind of renewable energy is an important solution to this problem. The research of conjugated polymer as active material in bulk heterojunction photovoltaic devices, has attracted considerable attention. Poly(2,7-carbazole) derivatives, incorporated by electron-withdrawing group in the main chain, form a new low band gap photoactive donor materials. The focus of this paper is using the variable N-substituent of carbazoles to synthesize a series of organic photovoltaic material with deep HOMO energy level, and the photovoltaic properties were studied.Low-bandgap alternating copolymers of variable N-substituent of ethyl (PEtCzBT), phenyl (PPhCzBT) and 4-diphenylaminophenyl (PTPACzBT) on the 2,7-carbazoles and benzothiadiazole-cored oligothiophene, were synthesized through Suzuki coupling reaction. The polymers show excellent solubility in organic solvents (readily soluble in chloroform, THF and toluene etc.), good thermal stability (5% weight loss temperature of more than 417 oC), and electrochemical properties (reversible redox process with narrow bandgap), and deep HOMO energy levels (~5.1 eV), allowing them promising candidates in the solar cell fabrication. Bulk heterojunction solar cells with these polymers as electron donor and (6,6)-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptor exhibit high Voc (0.91―0.95 V) and power conversion efficiency (PCE) of the solar cells was 1.69% for PEtCzTB, 2.08% for PPhCzTB, and 2.42% for PTPACzTB. Preliminary studies suggest that they are kind of potential excellent solar cell materials.