Novel regiospecific MDMO-PPV copolymer with improved charge transport for bulk heterojunction solar cells

A novel regiospecific MDMO-PPV copolymer has been synthesized by the copolymerization of the mixture of 70 wt % 1-(chloromethyl)-5- [(3,7-dimethyloctyl)oxy]-2-methoxy-4- [(octyl sulfoxy)methyl] benzene (monomer A) and 30 wt % 1-(chloromethyl)-2-[(3,7-dimethyloctyl)oxy]-5-methoxy-4- [(octyl sulfoxy)methyl] benzene (monomer 13) via the sulfinyl precoursor synthetic route. The hole mobility of the new regiospecific MDMO-PPV polymer (also called OC1C10-PPV) measured with a time-of-flight setup is found to be a factor of similar to3.5 higher at all measured electric fields at room temperature as compared to regiorandom MDMO-PPV. The electric field and temperature dependence of the hole mobility is discussed in the framework of disorder formalism. The improved charge transport properties of the novel regiospecific MDMO-PPV copolymer is attributed to the better interchain interactions facilitated by the more regular PPV backbone, which is also supported by the red shifted optical absorption and photoluminescence. Finally, the improved charge transport properties have been utilized by the fabrication of bulk heterojunction photovoltaic devices with a very high (0.71) filling factor based on the blend of the novel regiospecific MDMO-PPV copolymer and the soluble fullerene derivative 1-[3-(methoxycarbonyl)propyl]-1-phenyl-(6,6)-C-61 (PCBM).