Narrow Energy Gap Polymers with Absorptions up to 1200 nm and their Photovoltaic Properties

A series of donor/acceptor carbazole copolymers comprising alternating 6,7-diphenyl-4,9-bis-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 3,6-dimethyl-9-alkyl-9H-carbazole repeat units (Pi), or 3,6-dimethyl-9-triarylamino-9H-carbazole repeat units (P2), or 9-triarylamino-9H-carbazole repeat units (P3) has been prepared following Suzuki polymerization procedures. P3 absorbs light up to 1200 nm and has an energy gap of 1.1 eV, while P1 and P2 have energy gaps of 1.3 and 1.25 eV, respectively. Photovoltaic cells with ITO/PED-OT:PSS/P3:PCBM (1:1 w/w)/Ca showed an open-circuit voltage of 0.4 V under white light illumination, power conversion efficiency of 0.61%, and short-circuit current of 5.2 mA.cm(-2).