Efficient synthesis of multinary Zn-Cu-Ga-Se1−xSx quantum dots as full visible-covering emitters and their tricolored white electroluminescence

Abstract

Metal chalcogenide I-III-VI quantum dots (QDs) have been regarded as promising emitters for optoelectronic applications such as color conversion and electroluminescence devices owing to the beneficial attributes including environmentally friendly composition, high fluorescence, and high degree of compositional flexibility. In this work, we explore the efficient synthesis of widely emission-tunable (blue-to-deep red) multinary Zn–Cu–Ga–Se1−xSx (ZCGSe1−xSx) QDs enabled by use of highly reactive anionic sources of Se-diphenylphosphine (DPP) and S-DPP and the fabrication of high-performance white lighting non-Cd QD-light-emitting diode (QLED). Upon gradually varying nominal x values from 0 to 1, ZCGSeS QDs exhibit a systematic blue-shift in photoluminescence (PL) from yellow to green due to Se/S ratio-dependent band gap engineering and possess high PL quantum yields (QYs) of >73% after appropriate ZnS shell is applied. To further extend PL coverage, off-stoichiometric Cu/Ga molar ratios are additionally varied in synthesis of ZCGS and ZCGSe cores, by which blue PL from the former and deep-red PL from the latter ones are secured after ZnS shelling. Among a series of full visible-covering ZCGSe1−xSx/ZnS QDs, three emitters of blue, green, and red QDs are chosen for the fabrication of all solution-processed tricolored white QLED, whose emitting layer is composed of a mixture of such three primary color QDs. This white QLED, the first demonstration of non-Cd QD-based tricolored lighting device, shows a high peak luminance of 2135 cd/m2, external quantum efficiency of 3.8% and exceptional color rendering index up to 90.