Beamforming OLEDs for sensing applications employing a nanostructured fluorescent waveguide layer

Abstract

Organic light-emitting diodes (OLEDs) hold great promise as light sources for miniaturized and monolithically integrated optical sensors. Their unique properties and flexible processing methods enable the realization of disposable or recyclable lab-on-a-chip systems by combining multiple light sources and detector units on a single substrate. One of the main challenges in these systems is tailoring of light emission characteristics in order to illuminate specific sensing spots without the use of external optical components. Since OLEDs typically exhibit wide-angle light emission across the device surface, we propose the implementation of a nanostructured fluorescent waveguide. This layer acts as a color conversion filter by absorbing OLED light while providing narrow-angle emission of fluorescent light propagating in the waveguide. The appropriate choice of OLED emission color, fluorescent dye and nanostructure design allows for tailoring of the emission wavelength and beam characteristics. We investigate the impact of various fabrication parameters such as the layer thickness and fluorophore concentration on the color conversion efficiency as well as the directionality of the outcoupled fluorescent light. While high absorption of the OLED excitation light is beneficial in order to suppress wide-angle background emission, we show that high fluorophore content may lead to fluorescence quenching and reabsorption of fluorescent light inside the waveguide impairing resonant outcoupling effects.