Fluorescent carbon dots from birch leaves for sustainable electroluminescent devices

The shift from depleting petroleum compounds to regenerating biomass as the raw material for organic semiconductors is a prerequisite if organic electronics is to become truly sustainable. Here, we report on a one-pot solvothermal synthesis of a biomass-based carbon dot (bio-CD) fluorescent semiconductor, using birch leaves as the sole raw material. These bio-CDs are highly soluble in ethanol (45 g L⁻¹), and deliver deep-red and narrowband emission (peak wavelength = 675 nm, full width at half maximum, FWHM = 28 nm) at a high photoluminescence quantum yield of 26% in ethanol solution. Systematic structural characterization shows that molecular pheophytin a is the single fluorophore, and that this fluorophore is localized in the bulk of the bio-CD away from its polar surface. The functionality of the birch-leaf-derived bio-CDs in sustainable organic electronics is demonstrated by its employment as the printable emitter in a light-emitting electrochemical cell, which delivers narrowband deep-red luminance of 110 cd m⁻², with a FWHM of 29 nm, at an external quantum efficiency of 0.29%. This study thus reveals a promising avenue for the functional benign synthesis and the practical solution-based implementation of narrowband bio-CDs in sustainable optoelectronic technologies.