Electroluminescent Warm White Light‐Emitting Diodes Based on Passivation Enabled Bright Red Bandgap Emission Carbon Quantum Dots

Abstract

The development of efficient red bandgap emission carbon quantum dots (CQDs) for realizing high‐performance electroluminescent warm white light‐emitting diodes (warm‐WLEDs) represents a grand challenge. Here, the synthesis of three red‐emissive electron‐donating group passivated CQDs (R‐EGP‐CQDs): R‐EGP‐CQDs‐NMe 2 , ‐NEt 2 , and ‐NPr 2 is reported. The R‐EGP‐CQDs, well soluble in common organic solvents, display bright red bandgap emission at 637, 642, and 645 nm, respectively, reaching the highest photoluminescence quantum yield (QY) up to 86.0% in ethanol. Theoretical investigations reveal that the red bandgap emission originates from the rigid π‐conjugated skeleton structure, and the ‐NMe 2 , ‐NEt 2 , and ‐NPr 2 passivation plays a key role in inducing charge transfer excited state in the π‐conjugated structure to afford the high QY. Solution‐processed electroluminescent warm‐WLEDs based on the R‐EGP‐CQDs‐NMe 2 , ‐NEt 2 , and ‐NPr 2 display voltage‐stable warm white spectra with a maximum luminance of 5248–5909 cd m −2 and a current efficiency of 3.65–3.85 cd A −1 . The warm‐WLEDs also show good long‐term operational stability ( L / L 0 > 80% after 50 h operation, L 0 : 1000 cd m −2 ). The electron‐donating group passivation strategy opens a new avenue to realizing efficient red bandgap emission CQDs and developing high‐performance electroluminescent warm‐WLEDs.

Recent advance of carbon dots in bio-related applications

“…Further advancement is needed to improve the PL QY for high intensity or contrast image. Recently, several groups have been reported highly fluorescent red-emissive CDs with PL QY as high as 86% [16] and the emission peak was also extended NIR region (725 nm) [17]. This progress shined light of the further application of CDs in the bio-related applications [18].…”

Multifunctional p‐Type Carbon Quantum Dots: a Novel Hole Injection Layer for High‐Performance Perovskite Light‐Emitting Diodes with Significantly Enhanced Stability

“…The strong stretching vibration bands of OH, NH, and CC are observed at 3445, 3227, and 1640 cm −1 , respectively. In addition, the strong band at 1710, 1520, and 1380 cm −1 are attributed to CO, CN, and CN stretching vibrations, respectively …”

Earth abundant colloidal carbon quantum dots for luminescent solar concentrators

“…In addition, it is very important to find an efficient and rapid way to purify the as-prepared C-dots, as currently the purification process is very complicated and time-consuming, involving a post purification process using silica column chromatography or dialysis. 96,102…”

“…102 This large Stokes shift could be due to both the narrow size distribution (s o 14%) and efficient surface passivation by NR 2 groups (R = Me, Et and Pr). 102 In addition, the C-dots have a QY as high as 86%, while this type of C-dots was synthesized using very toxic and air-unstable N,N-dimethyl-, N,N-diethyl-, and N,N-dipropylparaphenylenediamine precursors, limiting their potential application in opto-electronic devices. 102 Zhou et al reported the control of the Stokes shift of C-dots through conjugated sp 2 -domain controlling and surface charge engineering.…”

“…102 In addition, the C-dots have a QY as high as 86%, while this type of C-dots was synthesized using very toxic and air-unstable N,N-dimethyl-, N,N-diethyl-, and N,N-dipropylparaphenylenediamine precursors, limiting their potential application in opto-electronic devices. 102 Zhou et al reported the control of the Stokes shift of C-dots through conjugated sp 2 -domain controlling and surface charge engineering. 3 With oleylamine (OLA) treatment, the surface of the C-dots can be effectively passivated by OLA, thereby reducing electron transitions from surface states, minimizing the absorption of the C-dots in the range of 550-700 nm, leading to a decrease of the overlap between the absorption and emission spectra.…”