Effect of extrinsic traps on thermally stimulated luminescence in molecularly doped polymers

The low-temperature thermally stimulated luminescence (TSL) technique has b een applied to study the influence of shallow and deep traps on localized s tate distribution in charge transport polymer systems. Effect of shallow tr aps is studied in molecularly doped polymer (MDP), as tri-p-tolyamine (TTA) -doped polystyrene in which a small concentration of di-p-anisyl-p-tolylami ne (DAT), acting as a weak hole trap, was added (E-t = 0.15 eV). It was fou nd that deep trap is created when DAT is doped into poly(N-epoxypropylcarba zole) (PEPC) (E-t = 0.5 eV) due to the difference in ionization potential o f these materials. The results are described in terms of the Gaussian disor der model, which provides reasonable understanding of all trends observed i n the TSL. The effect of extrinsic shallow trapping on TSL properties can b e reasonably interpreted in terms of the effective energetic disorder and t he TSL results are in good agreement with those obtained earlier by charge transport studies. The effect of percolative motion of charge carriers with in manifold of trapping states on TSL properties of deep trap-containing po lymers was found for the first time. (C) 2000 Elsevier Science S.A. All rig hts reserved.