Progress in Non-Cd Quantum Dot Development for Lighting Applications

Abstract

During the past few years there has been a significant progress in adapting the properties of non-Cd quantum dots (QDs) for lighting applications. It includes synthesis of novel materials, improvement of quantum efficiency and thermal stability, and most importantly, manufacturability on a scale large enough to meet the needs of the lighting industry. In this paper, we review the characteristics of three most mature non-Cd QD material systems, InP, CuInS2 and doped ZnS/ZnSe, from the perspective of lighting applications. Of these three systems, the InP-based QDs with core/shell structure are now available with quantum efficiency (QE) comparable to the best performing CdSe QDs, and in quantities large enough to meet the lighting needs. The CuInS2 QDs have also emerged as another non-toxic alternative to CdSe QDs but they need significant development to be comparable to InP and CdSe QDs.

Design of cadmium-free colloidal II–VI semiconductor quantum dots exhibiting RGB emission

“…42 For semiconductor materials studied in the present study, the energy band gaps of bulk materials and optical bowing parameter have already been determined experimentally. 42 The effective masses of electrons and holes, m e * /m 0 and m h * /m 0 , for the unalloyed compounds have also reported in the previous papers; 8,[43][44][45][46][47][48][49] however, the values for intermediate compositions of the alloys have not yet been reported. Therefore, in the present calculation, the effective mass of alloys was assumed to be a mole fraction weighted mean effective mass of the two unalloyed compounds as a first approximation; for the AB x C 1 x pseudobinary alloys, the effective mass of the alloy at the composition x is expressed by the following equation:…”

“…The parameters for the unalloyed bulk materials used in the present calculations are summarized in Table I. 8,29,32,43,[46][47][48][49][50][51][52][53][54] …”

“…1 Owing to these features, QDs have been developed for various applications in light emitting diodes (Q-LEDs), 2,3 electroluminescence devices (Q-ELs) 4,5 and color converters for blue-LED light to red and green light. [6][7][8] CdSe-based materials are commonly used as QD-phosphors in such applications; 2-7 however, alternative materials that do not contain toxic cadmium are strongly desired. InP is a III-V semiconductor with an energy band of 1.28 eV in the bulk material 9 and is a particularly promising as alternative, because of its energy band gap is relatively close to that of CdSe (1.74 eV).…”

“…21 The emission full width at half maximum of a typical ternary QDs is 100 nm, while that of a CdSe QD is approximately 30 nm. 8,14 Thus, suitable alternative material systems to CdSe have not yet been established.…”

Quantum Dot Light-Emitting Diode with Ligand-Exchanged ZnCuInS₂ Quantum Dot

“…InP [9], [10] and CuInS 2 [11], [12] QDs were found to exhibit high PL-QYs and luminance performance for the corresponding QLEDs by optimizing synthesis conditions, such as the synthesis temperature, the reaction time, the concentration of raw materials, and the insertion of a carrier blocking layer. Previous papers demonstrated that PL-QYs of more than 80% were achieved, and this value is high enough for practical display and biological applications [13], [14]. Furthermore, the luminance performance of QLEDs with Cd-free QDs has been improved by controlling the organic ligand [15]; however, further investigation is required due to insufficient understanding of carrier dynamics in QLEDs.…”