Doping-Free Inverted Top-Emitting Organic Light-Emitting Diodes With High Power Efficiency and Near-Ideal Emission Characteristics

Inverted top-emitting organic light-emitting diodes (ITOLEDs) with high power efficiency and near-ideal emission characteristics are demonstrated by using the combination of the following: 1) an electron-injection layer composed of
$\hbox{Cs}_{2}\hbox{CO}_{3}$
, which lowers the turn-on voltage; 2) an electron-transporting layer with optimal electron mobility, which enhances the electron current and thus improves the carrier balance; and 3) a dielectric/metal/dielectric multilayer electrode that works as a damage-free top transparent anode optimized to achieve high efficiency and ideal emission characteristics. By this approach, ITOLEDs with power efficiency values of 3.8 and 30
$\hbox{lm W}^{-1}$
are demonstrated in fluorescent and phosphorescent types, respectively, at a luminance value of 1000
$\hbox{cd}\ \hbox{m}^{-2}$
with little distortion in spectral/angular characteristics.