(Invited) Organic Dyes Derived from Molecules in Cacao Beans for Use in Lighting Applications

Abstract

LEDs are the foundation of lighting and display products surrounding us. While they have obtained great success in the commercial market, related research and development activities remain highly active aiming to enhance factors such as energy efficiency, stability, and environmental sustainability. Currently, commercial LED products are comprised of two key components: an indium gallium nitride e LED backlight with emission centered at 450 nm to cover the blue region of the visible spectrum, and powder inorganic phosphors on top converting blue light into longer wavelengths (e.g., green and red) to tune the emission of the device. A drawback of inorganic phosphors is that scattering of the emission from the micron-sized phosphor powders leads to substantial backscattering and subsequent absorption of the emission into the LED chip, and reabsorption losses in the phosphor itself, both of which reduce the overall light output of the final LED device. Organic dyes possess environmental advantages over inorganic phosphors because they are pi-conjugated molecules made from abundant elements (C, H, N, O, etc.) and are potentially bio-sourced. In this talk, I will present dyes that have been developed from theobromine, derived from cacao beans. When blended within an industrial polymer, poly(styrene-butadiene-styrene) (SBS), their enhanced solubility enables the formation of highly transparent films, crucial for reducing scattering loss in LEDs. Furthermore, resultant dye-SBS films achieved photoluminescence quantum yields (PLQYs) of around 90% under ambient conditions. Taking advantage of their transparency and solution processability, we fabricated a waveguide with this theobromine-dye-SBS composite, which was subsequentially assembled into an edge-lit LED device of no glare and enhanced aesthetics.