Development of Cu–In–Ga–S quantum dots with a narrow emission peak for red electroluminescence
Chang Jiang, Makoto Tozawa, Kazutaka Akiyoshi, Tatsuya Kameyama, Takahisa Yamamoto, Genichi Motomura, Yoshihide Fujisaki, Taro Uematsu, Susumu Kuwabata, Tsukasa Torimoto
Abstract
Narrowing the emission peak width and adjusting the peak position play a key role in the chromaticity and color accuracy of display devices with the use of quantum dot light-emitting diodes (QD-LEDs). In this study, we developed multinary Cu-In-Ga-S (CIGS) QDs showing a narrow photoluminescence (PL) peak by controlling the Cu fraction, i.e., Cu/(In+Ga), and the ratio of In to Ga composing the QDs. The energy gap of CIGS QDs was enlarged from 1.74 to 2.77 eV with a decrease in the In/(In+Ga) ratio from 1.0 to 0. The PL intensity was remarkably dependent on the Cu fraction, and the PL peak width was dependent on the In/(In+Ga) ratio. The sharpest PL peak at 668 nm with a full width at half maximum (fwhm) of 0.23 eV was obtained for CIGS QDs prepared with ratios of Cu/(In+Ga) = 0.3 and In/(In+Ga) = 0.7, being much narrower than those previously reported with CIGS QDs, fwhm of >0.4 eV. The PL quantum yield of CIGS QDs, 8.3%, was increased to 27% and 46% without a PL peak broadening by surface coating with GaSx and Ga-Zn-S shells, respectively. Considering a large Stokes shift of >0.5 eV and the predominant PL decay component of ∼200-400 ns, the narrow PL peak was assignable to the emission from intragap states. QD-LEDs fabricated with CIGS QDs surface-coated with GaSx shells showed a red color with a narrow emission peak at 688 nm with a fwhm of 0.24 eV.