Charge carrier mobility and lifetime versus composition of conjugated polymer/fullerene bulk-heterojunction solar cells

Charge carrier mobility (μ), recombination kinetics, and lifetime (τ) have been investigated with the photo-induced charge carrier extraction by linearly increasing voltage technique (photo-CELIV) in blends of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-C61(PCBM). Different MDMO-PPV/PCBM ratios have been studied showing that increasing the PCBM content induces an increase of the photo-CELIV mobility up to two orders of magnitude. Simultaneously, the lifetime of the charge carriers decreases in such a way that the product μ × τ appears almost constant independently of the blend composition. Recombination kinetics close to the Langevin one is observed for all PCBM concentrations studied.