Measuring electron and hole mobilities in organic systems: charge selective CELIV

We report on the realization of charge selective CELIV (charge extraction by linearly increasing voltage) via the selective extraction of each charge carrier species in a SiO2 inserted MIS (metal-insulatorsemiconductor) structure. The experiments are performed in a typical active layer of P3HT (poly (3-hexylthiophene)):PCBM (phenyl C-61-butyric acid methyl ester) with a composition ratio of 1:1. The presence of double CELIV peaks indicates the involvement of deep trap states in the charge transport process. Furthermore the difference in excitation intensity dependence between photo-excited holes and electrons suggests a difference in population probabilities of electrons and holes for shallow and deep trap states. Charge selective CELIV experiments also show that the simultaneous extraction of holes and electrons is not a simple linear superposition of the cases where they are extracted separately, indicating that a fraction of photo-excited charges populating shallow trap states can escape from the device. (C) 2015 Elsevier B.V. All rights reserved.