Energetic distribution of interface states extracted from photo-conductance of organic thin film transistors

• A new method was introduced to obtain the energy distribution of interface states.
• It was extracted from photo-conductance of OTFTs illuminated with different photon energies.
• The method was proved by exhibiting the well-known states of pentacene at 1.82 eV and 1.49 eV.
• New states at the various energy levels, possibly related to oxygen, were found by this method.

In this paper, a new method is introduced to obtain the energetic distribution of the interface states (density of states; DOS) extracted from the photo-conductance of organic thin film transistors (OTFTs) which exhibit varied transfer characteristics under illumination with different photon energies. The method was applied to pentacene OTFTs, and the results were compared with existing data. The major findings were not only the existence of the well-known peaks of DOS at 1.82 eV (free exciton of pentacene), and at 1.49 eV (extrinsic exciton due to dihydropentacene) but also new peaks were found at 1.25 eV, 1.29 eV, 1.31 eV, and 1.35 eV in the mid-gap. The new peaks were strongly enhanced under exposure to oxygen, and thus seem to be related to the defects associated with the presence of oxygen.

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