Density-of-states in pentacene from the electrical characteristics of thin-film transistors

In this work the density-of-states in the gap of pentacene is calculated from the electrical characteristics of thin-film transistors measured at different temperatures. The density-of-states after a thermal annealing in vacuum (110 °C for 1 h) was clearly different from the as deposited state. A deep level located 0.49 eV above the valence band edge completely disappeared after the annealing. This level could be related to water molecules adsorbed onto the gate dielectric during the fabrication process. Besides, a broad Gaussian distribution centered around 0.28 eV from the valence band was resolved after the annealing. These states could be related to oxygen atoms chemically bonded to adjacent pentacene molecules. The thermal treatment also contributes to reduce structural disorder, as deduced from a thinned band tail.