Aryl amine substituted low energy gap carbazole polymers: preparation and photovoltaic properties

The preparation of a series of donor/acceptor copolymers comprising alternating 2,7-linked 3,6-dimethyl-9-arylamino-carbazole units and 5,7-bis-(thiophen-2-yl)-2,3-diphenyl-thieno[3,4-b] pyrazine units is presented. The triarylamine substituents are attached to the carbazole repeat units either through the para-or meta-positions. The effect of the linkage position of triaryl amine substituents in this series of polymers as well as the effect of substitution of the phenyl groups at the 2,3-positions of 5,7-bis-(thiophen-2-yl)-2,3-diphenyl-thieno[3,4-b] pyrazine repeat units with alkoxy-substituents are investigated in this work. The polymers were characterized by NMR spectroscopy, UV-Vis absorption spectroscopy and fluorescence spectroscopy, and their molecular weights were estimated using gel permeation chromatography. Polymers P1-P4 absorb light up to 900 nm and have energy gaps ranging from 1.37 to 1.40 eV. Photovoltaic cells with ITO/PEDOT:PSS/P2:PC70BM(1/4, w/w)/Al showed an open circuit voltage of 0.60 V under white light illumination, power conversion efficiency of 0.67% and short circuit current of 3.6 mA cm(-2).