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Highly Bright Yellow-Green-Emitting CuInS2 Colloidal Quantum Dots with Core/Shell/Shell Architecture for White Light-Emitting Diodes

Park, Sang Hyun, Hong, Ara, Kim, Jong-Hoon, Yang, Heesun, Lee, Kwangyeol, Jang, Ho Seong
ACS Applied Materials & Interfaces 2015 v.7 no.12 pp. 6764-6771
X-ray diffraction, color, quantum dots, spectroscopy, temperature, transmission electron microscopy, wavelengths, white light, zinc sulfide
In this study, we report bright yellow-green-emitting CuInS₂ (CIS)-based quantum dots (QDs) and two-band white light-emitting diodes (LEDs) using them. To achieve high quantum efficiency (QE) of yellow-green-emitting CIS QDs, core/shell/shell strategy was introduced to high quality CIS cores (QE = 31.7%) synthesized by using metal–oleate precursors and 1-dodecanethiol. The CIS/ZnS/ZnS QDs showed a high QE of 80.0% and a peak wavelength of 559 nm under the excitation of 450 nm, which is well matched with dominant wavelength of blue LEDs. The formation of core/shell/shell structure was confirmed by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-optical emission spectroscopy analyses. Intense and broad yellow-green emission band of the CIS/ZnS/ZnS is beneficial for bright two-band white light. When the CIS/ZnS/ZnS was coated on the blue LEDs, the fabricated white LED showed bright natural white light (luminous efficacy (ηL) = 80.3 lm·W–¹, color rendering index (Rₐ) = 73, correlated color temperature (Tc) = 6140 K). The QD–white LED package showed a high light conversion efficiency of 72.6%. In addition, the CIS/ZnS/ZnS-converted white LED showed relatively stable white light against the variation of forward bias currents of 20–150 mA [color coordinates (x, y) = (0.3320−0.3207, 0.2997−0.2867), Rₐ = 70–72, Tc = 5497–6375 K].