Planarized and Compact Light Scattering Layers Based on Disordered Titania Nanopillars for Light Extraction in Organic Light Emitting Diodes

In this work, the extraction of waveguided and substrate modes in organic light emitting diodes (OLEDs) is improved by using compact light scattering layers composed of a disordered 2D array of TiO2 nanopillars. The TiO2 nanopillars are fabricated by combining a self-assembly and a solvent-assisted lift-off process, and are further planarized by a 250 nm thin epoxy-based photoresist layer to facilitate their anode deposition and integration within the OLED stack. This fabrication route allows engineering internal light outcoupling elements with a limited amount of parasitic absorption and with easily tunable light scattering properties that are effective over a broad spectral and angular range. Taking the example of a monochromatic bottom emitting OLED (lambda peak = 520 nm), the authors demonstrate an efficiency enhancement of +22%(rel) upon the incorporation of the planarized light extraction layer as well as ameliorated angular emission characteristics. This approach can be integrated in a high-throughput fabrication routine and straightforwardly extended to other OLED layouts.