Synthesis and Photovoltaic Properties of a Low Band Gap Polymer for Organic Solar Cell

Abstract

We synthesized a low band gap alternating copolymer containing electron-rich units (i.e. dithienosiloles and benzodithiophenes) and electron-deficient units (i.e. difluorobenzothiadiazoles) for high performance organic solar cells. The polymer was prepared by the Stille coupling reaction and characterized using H-1 NMR, GPC, TGA, UV-visible absorption spectroscopy, and cyclic voltammetry. Solar cells were fabricated in a structure of ITO/PEDOT:PSS/polymer:PC70BM/Al with five different blending ratios of polymer and PC70BM (1:1.5, 1:2, 1:3, 1:3.5 and 1:4 by weight ratio). The best efficiency was achieved from the 1:3 ratio of polymer and PC70BM in the photoactive layer, and TEM revealed that there is an optimal nanoscale phase separation between polymer and PC70BM in the 1:3 ratio blend film.