An extremely low-index photonic crystal layer for enhanced light extraction from organic light-emitting diodes

This paper reports organic light-emitting diodes (OLEDs) with improved light extraction fabricated by embedding an extremely low-index photonic crystal (LIPC) layer. The LIPC layer increases the optical efficiency through the reduced wave-guide mode between the substrate and anode both by increased light resonance and by a strengthened diffraction effect from an extremely low-refractive-index medium, specifically a line structure composed of a vacuum gap. As a result, the current efficiency and power efficiency of the LIPC-OLEDs are 1.51 and 1.93 times higher, respectively, than the reference device at 1000 cd m^-2. Because most of the light extraction is significant, especially in the forward direction, at the specific wavelengths satisfying the Bragg's diffraction equation, it is possible to calculate the anomalous spectrum of the LIPC-OLED through the finite-difference time domain (FDTD) method.