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 f or the electroluminescent (EL) devices fabricated from poly(N-vinylcarbazol e) (PVCz) double-layered films doped with Ct. Luminance was more than 3000 cd/m(2) at 110 K and 1500 cd/m(2) at 300 K without electron transport molec ules. Temperature dependence of the hole mobility in Ct 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 tunneli ng barrier height at negative electrode has been analyzed based on the posi tion and applied-voltage-dependent electric field derived from the combinat ion of space charge limited current and tunneling current schemes. The barr ier height for undoped PVCz:perylene was 0.46 eV and that for Ct doped PVCz :perylene was 0.38 eV. The intrinsic tunneling has been confirmed from the temperature dependence of barrier height of heavily Ct 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 b ecame temperature-dependent with increasing temperature. (C) 2000 Elsevier Science S.A. All rights reserved.