High color rendering index of ZCIS quantum dots-based white light-emitting diodes

Abstract

CuInS₂/ZnS quantum dots (CIS/ZnS QDs) have wide full width at half maximum (FWHM) due to the emission mechanism caused by point defect. This property make CIS/ZnS QD suitable for application in solid-state lighting (SSL). However, it was mentioned in the literature that white light-emitting diode (WLED) using CIS/ZnS QDs as the conversion material has low color rendering (CRI is less than 70), and one of the methods to increase the color rendering is increasing the range of the emission spectrum. CIS QDs belong to the point defects emission mechanism, and non-stoichiometric chemical substitution can create a large number of point defects. Therefore, in this study, CIS/ZnS QDs were first prepared by traditional thermal injection method, and (ZnCuIn)S₂ (ZCIS) QDs were prepared by adding Zn²⁺, Cu⁺ and In³⁺ ions at the same time. The results show that the emission wavelengths, relative quantum yield (QY), FWHM and surface morphology of CIS/ZnS QDs are 535 nm, 83 % and 72 nm and tetrahedron, respectively. On the other hand, those are 540 nm, 32 %, 118 nm and spherical shape for ZCIS QDs. Moreover, the diffraction peaks are between chalcopyrite and zinc blende structure meaning that the samples have alloyed structure. The CIE coordinates and color rendering index (CRI) of CIS/ZnS-based WLED are (0.35, 0.31) and 68. The CRI can be improved from 68 to 90 for ZCIS-based WLED. From the above results, it is known that ZCIS QDs with a FWHM up to 118 nm can be prepared by non-stoichiometric chemical substitution diffusion method. The wide FWHM shows positive effect to increase CRI value of ZCIS-based WLED and this advantage helps ZCIS QDs to be more widely used in solid-state lighting applications.