Enabling Ultra‐Narrow‐Band Deep‐Blue Light‐Emitting Diode Via Trapping Injected Holes by Carbon Dots

Abstract Narrow‐band deep‐blue light‐emitting diodes (LEDs) (CIE y coordinate<0.08, full width at half maximum (FWHM)<20 nm) are important for the next generation of LED‐based displays. It remains a significant challenge for the design of narrow‐band deep‐blue emitters. Herein, a new strategy is proposed for constructing narrow‐band deep‐blue LEDs that are not dependent on the narrow‐band deep‐blue emitter, but only need to dope n‐type carbon dots (n‐CDs) in the active emission layer (EML) of the wide‐band blue LEDs. The n‐CDs‐LEDs show an ultra‐narrow deep‐blue emission at 430 nm with the color coordinates of (0.15, 0.04) and the FWHM of 19 nm. Wherein the EML is constructed by doping n‐CDs in Poly(9,9‐dioctylfluorene‐co‐N‐(4‐butylphenyl) diphenylamine) (TFB), which neither changes the band structure of TFB nor produces new energy levels. Transient photovoltage (TPV) and various photoelectrochemical characterizations jointly reveal that n‐CDs can trap holes to realize the carrier injection into a single energy level of TFB and achieve ultra‐narrow deep‐blue light emission. This work provides a brand‐new and simple way to realize the narrow‐band deep‐blue LEDs.