The stability improvement of wide emission Zn_0.8Cd_0.2S quantum dot for white light-emitting diodes

Recently, the investigation of quantum dots (QDs) as color converters for white light-emitting diodes (WLEDs) has attracted a significant amount of attention, because the emission wavelength and broad excitation band of QDs can be controlled by their particle sizes and compositions. However, owing to the thermal effect, the long-term stability of QDWLEDs is one of the important tasks for their application. Moreover, the commercial WLEDs have low color rendering index (CRI) and the reabsorption effect. Therefore, in order to increase the device stability and CRI, in this study, we have used easy one-pot process to synthesize the colloidal ternary Zn_0.8Cd_0.2S (ZnCdS) QDs with wide emission, a quantum yield (QY) of 42 % and a particle size of 3.2 ± 0.5 nm. Three methods have been applied to encapsulate the QDs and their average CRIs are 78. We have demonstrated that the QDs-based WLEDs can achieve color converter robust against photooxidation, thermal quenching, and scattering, and can be applied to fabricate reliable P-QD1 device with an air gap between the emission layers. This encapsulation setup can protect the color converter and maintain the best stability over 750 hours operation time, and the Commission International d'Eclairage (CIE) chromaticity coordinates and luminous efficacy can be tuned from (0.36, 0.40) to (0.32, 0.33) and 4.5 to 3.2, respectively.