Weak-conjugation linked donor–acceptor emitters for efficient near-ultraviolet organic light-emitting diodes with narrowed full width at half maximum

Abstract

High-performance near-ultraviolet organic light-emitting diodes (NUV OLEDs) are very limited due to the scarcity of short-wavelength emitters. Herein, three weak-conjugation donor–acceptor molecules are designed using carbazole and phenanthroimidazole as the donor and the acceptor, respectively. These molecules exhibit excellent thermal and morphological stability and efficient NUV photoluminescence. Using these dyes as dopants, the devices at 10 wt% doping concentration exhibit efficient UV emission with small full width at half maximum (FWHM) values of 38, 38, 56 nm and small Commission Internationale de L’Eclairage coordinate y values (CIE_y) of 0.028, 0.028, 0.045, respectively. The doped device showed a maximum external quantum efficiency of 7.97% and high exciton utility efficiency in the range of 62–93%. Using an ortho-position molecule as an emitter, the nondoped device exhibited small efficiency roll-offs (2% at 100 cd m⁻² and 18% at 1000 cd m⁻²) and excellent color purity (a FWHM of 36 nm and a CIE_y coordinate of 0.037) with the peak wavelength at 404 nm. This research provides a method for designing efficient NUV emitters for OLEDs with good color purity and small efficiency roll-off by weak-conjugation link between a donor and an acceptor.