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

Abstract 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.