Bilayer-structure white organic light-emitting diode based on [Alq 3 :rubrene] and the electron transporting characteristics investigation using impedance spectroscopy

A bilayer-structure white organic light-emitting diode (WOLED) using 5,6,11,12-tetraphenylnaphthacene (rubrene) doped tris(8-hydroxy-quinolinato)aluminum (Alq3), [Alq3:rubrene], as electron-transport and yellow-green emitting layer and 2-methyl-9,10-bis(naphthalen-2-yl)anthracene as hole-transport and blue emitting layer is demonstrated. The device shows Commission Internationale de L׳Eclairage color coordinates of (0.34, 0.40) and a maximum luminance of 1132cd/m2 at 8V. the electron transporting characteristics of [Alq3:rubrene] and Alq3 are comparatively investigated by using current versus voltage characteristics and impedance spectroscopy measurements such as impedance, phase, and capacitance as a function of bias voltage. Our results indicate that rubrene doping slightly impedes electron transporting of Alq3. This, to a certain extent, counteracts the promotion of device luminance.