We report detailed studies of the slow relaxation of the photoinduced excess
charge carriers in organic metal-insulator-semiconductor field effect
transistors consisting of poly(3-hexylthiophene) as the active layer. The
relaxation process cannot be physically explained by processes, which lead to a
simple or a stretched-exponential decay behavior. Models based on serial
relaxation dynamics due to a hierarchy of systems with increasing spatial
separation of the photo-generated negative and positive charges are used to
explain the results. In order to explain the observed trend, the model is
further modified by introducing a gate voltage dependent coulombic distribution
manifested by the trapped negative charge carriers.Comment: 17 pages, 3 Figure