Influence of Molecular Weight on the Performance of Organic Solar Cells Based on a Fluorene Derivative



The performance of organic photovoltaic (OPV) bulk-heterojunction blends comprising a liquid-crystalline fluorene derivative and a small-molecular fullerene is found to increase asymptotically with the degree of polymerization of the former. Similar to various thermodynamic transition temperatures as well as the light absorbance of the fluorene moiety, the photocurrent extracted from OPV devices is found to strongly vary with increasing oligomer size up to a number average molecular weight, Mn ≈ 10 kg mol−1, but is rendered less chain-length dependent for higher Mn as the fluorene derivative gradually adopts polymeric behavior.