Dependence of electroluminescent properties on cathode metalsin PVCz double-layered organic EL devices

We have investigated cathode metal dependence of electroluminescence (EL) c haracteristics of PVCz based EL devices by using Sr, Mg and Ag. The followi ng has been clarified. First, we have obtained luminance as high as 1000 cd /m(2) for Poly(Nvinylcarbazole) (PVCz) EL devices without electron transpor t molecules but only emissive dye by using Mg and Sr metals cathode; while the device with Ag cathode showed a brightness about half as high. Secondly , threshold voltage for electroluminescence and barrier height for charge c arrier injection both showed clear dependence on metal work function. Third ly, chemical shift of core electron binding energy by X-ray photoelectron s pectroscopy showed oxidation of Sr metal electrode near PVCz surface even i f deposited under background pressure of 10(-10) Torr, while that of Me sho wed negligible shift. (C) 2000 Published by Elsevier Science S.A. All right s reserved.