Low band gap polymers via a new and versatile route: The dithiocarbamate precursor route

Abstract

Much interest exists in conjugated polymers for use as the active layer in photovoltaic cells. However, such plastic solar cells often suffer from a mismatch between their absorption and the terrestrial solar spectrum. The solar emission has a maximum photon flux around 1.8 eV, whereas many conjugated polymers do not absorb sufficient light at this energy level. Hence, low band gap conjugated polymers (Eg<2.0 eV) are desirable, since their application would ultimately give rise to better efficiencies. We have developed an efficient synthetic method to obtain such polymers: the dithiocarbamate precursor route. The successful application of this new route is demonstrated for poly(3,4-diphenyl-2,5-thienylene vinylene) (DP-PTV). After optimization of this route, high molecular weight DP-PTV is readily accessible. DP-PTV indeed has a low band gap (1.7 eV) and together with its suitable HOMO/LUMO energy levels, this material is an excellent candidate for application in organic solar cells.