Synthesis and photovoltaic properties of the copolymers of 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene and 2,5-thienylene-vinylene

The random copolymers of 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene (MEH-PV) and 2,5-thienylene-vinylene (ThV) were synthesized by Gilch method [H.G. Gilch, W.L. Wheelwright, J. Polym. Sci. Part A, Polym. Chem. 4 (1996) 1337; H. Becker, H. Spreitzer, K. Ibrom, W. Kreuder, Macromolecules 32 (1999) 4925; J.A. Mikroyannidis, Chem. Mater. 15 (2003) 1865], the alternate copolymer of MEH-PV and ThV was synthesized by Hornor-Emmons reaction, and poly(3-hexyl-thienylene-vineylene) was synthesized by Stille coupling reaction. The absorption characteristics of the copolymers were modulated by changing the ratio of ThV to MEH-PV units in the copolymers. With the increase of the ThV ratio, the absorption spectra of the copolymers were broadened and red-shifted in comparison with that of MEH-PPV. Hole mobility of the random copolymer with 18% ThV is an order higher than that of MEH-PPV. The polymer photovoltaic cells based on the blend of the copolymer and C60 were fabricated and characterized by I-V and input photon to converted current efficiency (IPCE) measurements. Energy conversion efficiency under a white light (70 mW/cm2) of the photovoltaic cell based on the copolymer containing 18% ThV increased by 47% in comparison with that of the device based on MEH-PPV. The performance improvement of the polymer photovoltaic cell based on the random copolymers should benefit from the broader absorption and higher hole mobility of the copolymers.