Soluble low band gap polymers for solar cell applications via oxidative polymerization

Abstract

Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor-acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared two low band gap conjugated polymers, with a bis-(1-cyano-2-(3,4-ethylenedioxythienyl)-vinylene)phenylene base structure and achieved an excellent solubility by the introduction of long alkoxy or oligo(oxyethylene) side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined which confirms that they indeed have a low band gap. However, as a result of their low charge carrier mobility, preliminary solar cells made of these polymers display low efficiencies.