Space-charge limited current in regioregular poly-3-hexyl-thiophene

Temperature dependent current-voltage characteristics of an organic diode based on a thin film of regioregular poly-3-hexyl-thiophene (P3HT) are compared with results of a theoretical model assuming space-charge limited currents with a density of states (DOS), nonmonotonous in energy. This DOS was deduced from experiments utilizing the method of thermally stimulated currents. Both, experiments and theory result in an almost power-law dependence of jproportional toV(m), where the exponent m increases with decreasing temperature assuming a value of m=2 at room temperature. This effect can be accounted for by filling of deep traps at lower temperatures. Transport of charge carriers in P3HT seems to be limited by hopping in disordered regions rather than by the transport via extended states within crystalline grains.