Carrier Injection Tailoring and Electroluminescence Properties of Carbon Dots in Electroluminescent Light‐Emitting Diodes

Abstract

Fantastic carbon dots (CDs) are demonstrated as carrier injection tailoring and emitters of electroluminescent light‐emitting diodes (LEDs). Using N‐Methyl‐2‐pyrrolidone as a carbon source, CDs are facilely synthesized by hydrothermal method. Transmission electron microscopy, X‐Ray photoelectron spectroscopy, atomic force microscopy, and photoluminescence measurements confirm that the CDs show good film morphology and particular electronic properties. With CDs‐doped poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) tailoring hole injection, the 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole‐based UV organic LED (OLED) gives maximum radiance of 2.34 mW cm−2 and external quantum efficiency (EQE) of 1.51%. With CDs as electron injection layer, the inverted UV OLED shows a maximum radiance of 1.13 mW cm−2 and EQE of 0.38%. The hole/electron injection characteristics are further elucidated using current–voltage characteristics and impedance spectroscopy. Electroluminescent LEDs using pure CDs and CDs‐doped poly(9‐vinylcarbazole) (PVK) as emitters are demonstrated. The CDs‐based electroluminescent LED shows superior electro‐optical properties with a maximum luminance of 48.67 cd m−2 at 8 V, luminous efficiency of 0.022 cd A−1, power efficiency of 0.023 lm W−1, and EQE of 0.023%, owing to the energy transfer from PVK to CDs. The research paves an alternative approach for broadening CDs applications and advancing novel electroluminescent LEDs.