Mode Dispersion in Photonic Crystal Organic Light-Emitting Diodes

Similar to an electronic lattice determining the motion of electrons in solids, photonic crystals (PhCs) are periodic photonic nanostructures that determine the propagation of photons. By incorporating PhCs into organic light-emitting diodes (OLEDs), the device efficiency and emission spectra can be modified, which can be explained and predicted by the mode dispersion. In this work, we experimentally measure the mode dispersion of 1-D and 2-D PhC OLEDs at different azimuthal angles with angle-resolved electroluminescence spectra. The results are explained using an intuitive geometry approach, which shifts and slices the cone-shaped optical modes to obtain the mode dispersion of PhC OLEDs. We note that the weak cavity mode and a narrow photonic band gap are visible only after eliminating the intrinsic emitter spectrum in the air mode dispersion. In the end, we discuss the implication of mode dispersion on the OLED light extraction.