Internal Light‐Extraction Layers with Different Refractive Indices for Organic Light‐Emitting Diodes

High‐performance organic light‐emitting diodes (OLEDs) require a light‐extraction layer either inside or outside the device. Herein, transparent metal oxides (MOs) of various refractive indices are inserted between the anode and glass as internal light‐extraction layers to improve the efficiency of the OLED device. Optical simulations are performed to reveal the optimal thicknesses for the light‐extraction layer of metal oxides of various refractive indices. Light‐extraction layers of metal oxides with optimized thickness are then used in OLED devices to evaluate the performance of devices. The device with the higher refractive index MO light‐extraction layer tends to show better device performance. Although the internal light‐extraction layer is inserted, the current flow in the device and the color coordinate variation depending on the viewing angle do not change significantly. These results are helpful in the development of optimized internal light‐extraction layers for individual colors and in the development of OLED displays with optimized light‐extraction layers for each pixel. The improvements in the efficiency of the device are analyzed by reducing the total internal reflection (TIR) to reduce the loss of light caused in the waveguide mode or by using the microcavity (MC) effect. The optimal thickness for each refractive index is calculated through optical simulations, and optical properties are evaluated by depositing each material at the corresponding thickness.