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 ($V_{\it OC})$ but lowers the short circuit current ($I_{\it SC})$. 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.