Trap states of tris-8-(hydroxyquinoline) aluminum and naphthyl-substituted benzidine derivative using thermally stimulated luminescence

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Abstract
The bulk trap state properties of a naphthyl-substituted benzidine derivative (NPB) and tris-8-(hydroxyquinoline) aluminum ( Alq 3 ) have been measured using thermally stimulated luminescence(TSL). The TSL spectra for both organic materials show significant trap distributions over the temperature range from 8 to 300 K. Using a general order TSL expression, the four peaks in NPB were modeled with trap states centered from 0.20 to 0.05 eV. Alq 3 has three TSL peaks over the temperature range, with the peak at 156 K modeled as a distribution of trap states from 0.25 to 0.13 eV. For both materials, the trapping mechanism involves a combination of first and second order emission. NPB and Alq 3 have trap states sufficiently deep to influence the carrier transport and recombination process in bilayer organic based light emitting.