Charge transport in PVCz EL using multi-layered PVCz film doped with Cz

Carrier mobility and barrier height at negative electrode have been studied by considering temperature dependence of current–voltage characteristics for the electroluminescent (EL) devices fabricated from poly(N-vinylcarbazole) (PVCz) double-layered films doped with Cz. Luminance was more than 3000 cd/m2 at 110 K and 1500 cd/m2 at 300 K without electron transport molecules. Temperature dependence of the hole mobility in Cz doped PVCz has been analyzed and the activation energy for carrier hopping has been derived; 0.02 and 0.05 eV for undoped PVCz and 0.01 eV for Cz doped PVCz. The tunneling barrier height at negative electrode has been analyzed based on the position and applied-voltage-dependent electric field derived from the combination of space charge limited current and tunneling current schemes. The barrier height for undoped PVCz:perylene was 0.46 eV and that for Cz doped PVCz:perylene was 0.38 eV. The intrinsic tunneling has been confirmed from the temperature dependence of barrier height of heavily Cz doped PVCz:perylene device for the first time. In the case of undoped or lightly PVCz:perylene devices, tunneling was observed at lower temperature and charge injection became temperature-dependent with increasing temperature.