Photo-stimulated charge carrier transport in a polydiacetylene single crystal (PTS)

The rise time behaviour of photocurrents in a PTS crystal excited by rectangular light pulses has been measured and the rate constant K(t) of charge carrier relaxation has been evaluated. At short times (t 10 -2 s) K(t) follows a power law characteristic of transport controlled by tunnelling barriers. At intermediate times K attains a constant value that increases with light intensity according to K opt approximately I 0.85 . The effect is explained in terms of an interaction between a delocalised optical excitation of a PTS chain and a charge carrier localised at a defect. It is concluded that photo-simulated barrier crossing is the rate-determining step for charge carrier transport in presence of a photon field.