Photonic crystal material and geometry optimization for enhanced light extraction in conventional and multi-quantum well OLEDs

Organic light-emitting diodes (OLEDs) suffer from severe internal photon trapping; and therefore, conventional planar architectures extract only 20–30% of generated photons into the viewing medium. Photonic crystal (PhC) arrays embedded at the substrate interface offer a promising route to overcome this limitation through resonant Bragg scattering of in-plane guided modes into out-of-plane radiating modes. However, the dependence of light extraction efficiency (LEE) on the dielectric contrast between the PhC fill material and substrate in conventional OLEDs remains insufficiently characterized. Moreover, to the best of our knowledge, the influence of PhC on the light extraction efficiency of multi-quantum-well (MQW) OLEDs has not been previously reported. In this work, we present a systematic finite-difference time-domain investigation of PhC-enhanced light extraction across two device architectures and seven candidate PhC dielectric materials, spanning high, moderate, and low refractive index regimes: TiO 2 , yttria-stabilized zirconia [YSZ], Si 3 N 4 , HfO 2 , ZnO, Poly (methyl methacrylate) [PMMA], and air/etch. For a conventional OLED, wavelength-resolved Purcell factors, decay rate enhancements, far-field angular emission maps, and LEE enhancement factors within ±5 ∘ narrow-cone are compared. YSZ achieves the highest peak LEE enhancement factor of 3.1 at 560 nm and 4.75 at 648 nm wavelength and the highest peak Purcell factor of 1.88 among all materials, driven by its large dielectric contrast against the glass substrate. Based on this result, YSZ is selected as the PhC fill material for a blue-emitting FIrpic MQW OLED, where PhC lattice period, pillar diameter, and pillar height are independently optimized using 3D FDTD simulations. For the MQW OLED, LEE is evaluated from the ratio of the total extracted power with and without the PhC, yielding a 1.47-fold peak enhancement at the FIrpic emission maximum (∼460-470 nm), and strongly concentrated near-normal angular emission, with first-order Bragg lobes at ±10–25°. The results establish a clear hierarchy of PhC fill materials governed by dielectric contrast. Moreover, a non-monotonic dependence of the Bragg resonance on pillar height arising from higher-order mode coupling in MQW OLED provides quantitative design guidelines for integrating PhC structures into next-generation lighting devices.