Thermally stimulated luminescence versus thermally stimulated current in organic semiconductors

A unified model of hopping thermally stimulated luminescence (TSL) and thermally stimulated current (TSC) in disordered organic semiconductors and polymers is suggested. The differences between photoinduced TSL and TSC, measured on the same sample, are explained by the fact that metastable geminate pairs of charges rather than free carriers are primarily photogenerated in these materials. Since the Coulomb interaction does not prevent carriers from recombining into excitons, the rate-limiting step in the TSL kinetics is carrier release from traps. However, the Coulomb binding energy strongly affects the dissociation of geminate pairs into free charge carriers and, therefore, it changes the apparent activation energy of TSC.