Electron and hole transport in poly(para-phenylene vinylene):methanofullerene bulk heterojunction solar cells

摘要

We have measured the electron and hole mobility in blends of poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) and [6,6]-phenyl C_(61)-butyric acid methyl ester (PCBM) with varying MDMO-PPV/PCBM composition. It is shown that the electron mobility in the PCBM-rich phase gradually increases up to 80 wt.% PCBM, due to an increased number of percolated pathways from bottom to top electrode. In contrast to the expectations the hole mobility in the MDMO-PPV phase shows a similar behavior as a function of fullerene concentration; Starting at 40 wt.% with the value of pristine MDMO-PPV the hole mobility strongly increases and saturates beyond 67 wt.% at a value which is more than two order of magnitude higher. The large enhancement of the hole mobility and its saturation is related to recent findings on the film morphology of this material system.