Energetic trap distributions in organic semiconductors

The electronic trap distributions of the vapor deposited electron transport material Alq3 [tris(8-(hydroxyquinoline) aluminum] and hole transport material 1-NaphDATA [4,4′,4″-tris(N-(1-naphthyl)-N-phenylamino)-triphenylamine] have been analyzed by the fractional TSC method (thermally stimulated current) and the thermally stimulated luminescence (TL) technique. The obtained trap distributions can be described by a Gaussian distribution in case of Alq3 and two discrete trap levels in case of 1-NaphDATA. In the case of Alq3, a distinction between the trapped charge carrier polarity was possible. A correlation between the I–V curves of electron- and hole-only devices and the respective trap distributions suggests that the trap distribution is responsible for the shape of the observed current–voltage characteristics. It will be shown that the observed trap states cannot be explained by intrinsic tail states of regular HOMO and LUMO levels.