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Highly Efficient Tandem White OLED Using a Hollow Structure

A simple fabrication method for a light extraction layer is required. In this report, an internal light extraction layer composed of a high refractive index material and an air void is fabricated in five steps. A direct printing process followed by annealing of the randomly arrayed poly(benzyl methacrylate) pillars after a planarization process using TiO2‐nanoparticle dispersed resist and sol is used. These substrates are used for light extraction in white tandem organic light emitting diodes (WOLEDs). By combining the hollow structure and hemi‐spherical lens, WOLEDs without and with the light extraction structures are found to show maximum external quantum efficiencies of 35.6% and 103%, respectively. The power efficiencies at 100 cd m−2 of the WOLEDs without and with the light extraction structures are found to be 26.5 and 93.2 lm W−1, respectively. A color rendering index of 86.4, correlated color temperature of 4860 K, and CIE of (0.353, 0.389) are achieved in the WOLEDs with light extraction structures.