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We study electron and hole injection in MoO3 charge generation layers (CGLs) commonly used for establishing balanced injection in multilayer stacked organic light-emitting diodes (SOLEDs). A compound CGL consisting of 100-Å-thick MoO3 and Li-doped 4,7-diphenyl-1,10-phenanthroline in a 1:1 molar ratio is demonstrated to have a high electron generation efficiency. Charge injection from the compound CGL is modeled based on a two-step process consisting of tunneling-assisted thermionic emission over an injection barrier of (1.2±0.2) eV and a trap level due to oxygen vacancies at (0.06±0.01) eV above the MoO3 valence band edge. Peak external quantum efficiencies (EQEs) of (10.5±0.2)%, (10.1±0.2)%, (8.6±0.2)%, and (8.9±0.2)% are obtained for tris-(phenylpyridine)iridium-based electrophosphorescent OLEDs with indium tin oxide (ITO) anode/CGL cathode, CGL anode/CGL cathode, CGL anode/Al cathode, and ITO anode/Al cathode contacts, respectively. Based on our analysis, a three-element green emitting electrophosphorescent SOLED is demonstrated with a peak forward-viewing EQE=(24.3±1.0)% and a power efficiency of (19±1) lm/W.

We demonstrate a white organic light-emitting device where individual red, green, and blue ͑R, G, and B͒ phosphorescent organic light-emitting devices are vertically stacked and electrically interconnected by a compound MoO 3 / Li-doped charge generation layer. For the order of B, G, and R cells positioned relative to the indium tin oxide anode, the device yields a peak total external quantum efficiency ͑EQE͒ and power efficiency ͑PE͒ of ext = ͑36Ϯ 2͒% at a current density of J =82 A / cm 2 and p =21Ϯ 1 lm/ W at J =17 A / cm 2 , respectively. The EQE and PE of the device roll off to ͑32Ϯ 2͒% and 13Ϯ 1 lm/ W at 1000 cd/ m 2 , corresponding to J =2 mA/ cm 2. At this luminance, the device shows Commission Internationale de L'Eclairage chromaticity coordinates of ͑0.45, 0.36͒ and a color rendering index of 63.

We use a general transmission matrix formalism to determine the thermal response of organic light-emitting diodes (OLEDs) under high currents normally encountered in ultra-bright illumination conditions. This approach, based on Laplace transforms, facilitates the calculation of transient coupled heat transfer in a multi-layer composite characteristic of OLEDs. Model calculations are compared with experimental data on 5 cm  5 cm green and red-emitting electrophosphorescent OLEDs under various current drive conditions. This model can be extended to study other complex optoelectronic structures under a wide variety of conditions that include heat removal via conduction, radiation, and convection. We apply the model to understand the effects of using high-thermalconductivity substrates, and the transient thermal response under pulsed-current operation.

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