Side chain effects on photoinduced absorption and photovoltaic performance of low bandgap thienylene vinylene and phenylene vinylene copolymers^*

¹ Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University, Altenbergerstr. 69, 4040 Linz, Austria
² Hasselt University, Institute for Materials Research (IMO), Agoralaan, Building D, 3590 Diepenbeek, Belgium
³ IMEC, Division IMOMEC, Wetenschapspark 1, 3590 Diepenbeek, Belgium

Corresponding author: lehuong.nguyen@jku.at

Received: 21 July 2006
Accepted: 6 October 2006
Published online: 6 December 2006

Abstract

In this work low bandgap thienylenevinylene and phenylene vinylene copolymers, which possess either 3,4-ethylenedioxylthiophene (EDOT) groups (Polymer 1) or long alkyl side chains (Polymer 2) were investigated and compared in photoinduced electron transfer properties and photovoltaic performance. The results show that the interaction of the photoexcited polymers with an electron acceptor ([6,6]-phenyl C61 – butyric acid methyl ester (PCBM)) leads to charge generation and transfer for both polymers. We found that the long alkyl side chain in Polymer 2 instead of the EDOT group in Polymer 1 enhances the open circuit voltage ( but lowers the short circuit current (. On the other hand the long alkyl side chain in Polymer 2 significantly improves the solubility and enhances processability for solar cells fabrication. Optimization of the chemical structure of these low bandgap polymers could lead to a spectral improvement of photocurrent generation in organic solar cells.