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

• We report the realization of charge selective CELIV for thin films.
• The presence of double CELIV peaks indicates the involvement of deep trap states.
• Photo-excited holes mainly populate shallow trap states.
• Photo-excited electrons equally populate shallow and deep trap states.
• Linear superposition does not hold when extract holes and electrons simultaneously.

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-insulator-semiconductor) structure. The experiments are performed in a typical active layer of P3HT (poly (3-hexylthiophene)):PCBM (phenyl C61-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.