Wavelength Dependency of Outcoupling Peak Intensities for Emission Layers with Multi-Periodic Photonic Crystals

Planar nanostructures allow for extraction of guided modes to increase the organic light-emitting diode (OLED) efficiency. In contrast to the typically employed nanostructures with one dominant space frequency, multi-periodic photonic crystals scatter a guided mode into multiple directions and thereby extend the design space for OLED outcoupling significantly. We present photoluminescence measurements of multi-periodic photonic crystals, obtained by superposition of multiple binary gratings, in an organic emitter layer. Together with transfer matrix and rigorous coupled wave analysis (RCWA) simulations, we show that the wavelength-dependent absorption in the waveguide material strongly affects the outcoupling intensity. In addition, RCWA simulations of the individual orders' intensities are shown to be in agreement with experimental data. Due to the broad spectral emission of OLEDs, RCWA can therefore be a valuable tool to design the guided mode scattering in a broad wavelength region. Potential applications include outcoupling-enhanced OLEDs with reduced angular color change.