Optical modeling of top-emitting micro-OLEDs

Top-emitting organic light-emitting diodes (OLEDs) have become essential device architectures for high-resolution micro-displays in virtual and augmented reality. Planar OLEDs are typically modeled as one-dimensional multilayer stacks having infinite lateral dimensions. While these models are sufficient to describe the optical behaviors of conventional large-area devices, they may deviate for micro-devices having smaller lateral sizes comparable to wavelengths. In this work, we investigate the optical efficiency of top-emitting micro-OLEDs by resolving the limitations of previous computational approaches. We first optimize the microcavity structure of a top-emitting OLED using the transfer-matrix formalism. We then establish reliable three-dimensional finite-difference time-domain simulation conditions by analyzing the limitations of two-dimensional calculations and the effects of domain and mesh sizes. Based on the optimized structure and simulation conditions, we systematically investigate the scaling effect of pixel size. We reveal that optical efficiency remains stable for pixels larger than 1 μm but drops sharply in the sub-micron regime. This degradation is attributed to the weakening of microcavity resonance and increased lateral light leakage at the pixel boundaries. Our findings suggest that novel optical designs, distinct from those for large-area devices, are required for future nano-pixel displays.