OLEDs suffer from viewing angle dependent spectral shift due to microcavity effects. To address this issue, we introduce a novel top‐emitting OLED with a dielectric spacer that forms multiple cavity modes. The resulting device shows almost no color shift at different viewing angles.
Cavity effects play an important role in determining the out-coupling efficiency of an OLED. By fabricating OLEDs on corrugated substrates, the waveguide and SPP modes can be extracted by diffraction. However, corrugation does not always lead to an enhancement in out-coupling efficiency due to the reduction of the electrode reflectance and hence the cavity effects. Based on the results of our rigorous couple-wave analysis (RCWA) simulation, we found that the cavity effects can be partially recovered using a low index Teflon layer inserted between the ITO anode and the substrate due to the enhancement of the reflectance of the corrugated electrodes. To verify the simulation results, we fabricated corrugated OLEDs having a low-index Teflon interlayer with an EQE of 36%, which is 29% higher than an optimized planar OLED. By experimentally measuring the OLED air mode dispersion, we confirm the cavity emission of a corrugated OLED is enhanced by the low index layer.
A typical top-emitting organic light-emitting diode (OLED) has a strong microcavity effect because of the two reflective electrodes. The cavity effect causes a serious color shift with the viewing angles and restricts the organic layer thickness. To overcome these drawbacks, we design a multimode OLED structure with dual-dielectric spacer layers, which extend the cavity length by more than 10 times. This design completely eliminates the intrinsic cavity effect caused by the top and bottom boundaries and provides freedom for the organic layer thickness. We demonstrate these effects in a white multi-mode OLED using a white emitter, which shows a negligible angular chromaticity shift of Δuv = 0.006 from 0 to 70°and a Lambertian emission profile. The simple design and the perfect angular color profiles make the multi-mode OLED structure promising in large-area displays and solid-state lighting applications.
The light outcoupling efficiency
of a top-emitting organic light-emitting
diode (OLED) is only about 20%, and the majority of the light is trapped
in the waveguide modes and surface plasmon polariton (SPP) modes.
Extracting the trapped modes can reduce the device power consumption
and improve the operating lifetime. In this study, we demonstrate
a top-emitting OLED structure with a dielectric spacer to suppress
the SPP mode and with a patterned back mirror to extract the waveguide
modes. We examine and compare several curved mirror arrays and conclude
that a micromirror array (μMA) can efficiently extract the waveguide
modes while minimizing the absorption loss. The optimized μMA
device with a semi-transparent top electrode shows a 36% external
quantum efficiency, 2 times higher than the referenced device. This
optical design can be easily incorporated into a top-emitting device
and has a great potential for displays and lighting applications.
OLEDs suffer from viewing angle dependent spectral shift due to microcavity effects. To address this issue, we introduce a novel top‐emitting OLED with a dielectric spacer which forms multiple cavity modes. The resulting device shows almost no color shift at different viewing angles.
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