The Mobility and Decay Kinetics of Charge Carriers in Pulse-Ionized Microcrystalline PCBM Powder



The mobility and decay kinetics of charge carriers produced by nanosecond pulsed ionization of a microcrystalline powder sample of phenyl-C61-butyric acid methyl ester (PCBM) have been investigated by time-resolved microwave conductivity. The sum of the electron and hole trap-free mobilities within crystallites is between 0.04 and 0.3 cm2 V–1 s–1 at room temperature with an activation energy of 0.066 eV. The decay of the conductivity, which takes place over a timescale of milliseconds at room temperature, is controlled mainly by charge-carrier trapping with an activation energy of 0.53 eV. An upper limit of 1 × 10–18 m3 s–1 is estimated for the rate coefficient of charge recombination, which is more than four orders of magnitude lower than expected for diffusion-controlled recombination, indicating PCBM to be an “indirect bandgap” semiconductor.