Persistent photoconductivity in single crystals of the high temperature polymorph of alpha-sexithiophene

We have found persistent photoconductivity (PPC) in alpha -sexithiophene (a lpha -6T) single crystals and its properties and the charge transport in th is material are studied in the temperature range from 100 to 340 K. PPC is observed even above room temperature and the decrease in time of the conduc tivity can be described by a stretched exponential which lasts at low tempe rature (LT) for more than 10(6) s. A thermal activation energy of 0.44 eV i s observed for the relaxation time of the decay. Moreover, the PPC can be q uenched by a strong electric field. The origin of these effects is discusse d assuming metastable defect relaxations. ((C)) 2001 Elsevier Science B.V. All rights reserved.