Charge carrier mobility and lifetime of organic bulk heterojunctions analyzed by impedance spectroscopy

Charge carrier diffusion and recombination in an absorber blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) with indium tin oxide (ITO) and aluminium contacts have been analyzed in the dark by means of impedance spectroscopy. Reverse bias capacitance exhibits Mott-Schottky-like behavior indicating the formation of a Schottky junction (band bending) at the P3H:PCBM-Al contact. Impedance measurements show that minority carrier (electrons) diffuse out of the P3HT:PCBM-Al depletion zone and their accumulation contributes to the capacitive response at forward bias. A diffusion-recombination impedance model accounting for the mobility and lifetime parameters is outlined. Electron mobility results to be 2 × 10-3 cm2 V-1 s-1 and lifetime lies within the milliseconds timescale. © 2008 Elsevier B.V. All rights reserved