Side chain influence on electrochemical and photovoltaic properties of yne-containing poly(phenylene vinylene)s

The electrochemical behaviour of four types of (phenylene ethynylene)-alt-(phenylene vinylene) hybrid polymers, 1, 2, 3, and 4 have been investigated with respect to the influence of the grafted alkoxy side chains. In the case of the fully substituted polymers 2, 3, and 4, the strong insulating nature of longer linear octadecyl or bulky branched 2-ethylhexyl side chains lowers the HOMO levels of the polymers thereby increasing the discrepancy, Delta E-g, between the electrochemical, E-g(ec), and the optical E-g(opt), bandgap energies. Thus it is not possible to establish a direct correlation between the open circuit voltage, V-OC, of bulk heterojunction solar cell devices of the configuration glass substrate/ITO/PEDOT:PSS/polymer 3:PCBM(1:3, w/w)/LiF/Al and the HOMO energy levels of polymer 3 solely, as postulated in the literature. The photovoltaic (PV) parameters greatly depend on the grafted side chains.