White-Light-Emitting Diodes from Directional Heat-Conducting Hexagonal Boron Nitride Quantum Dots

In quantum-dots-converted white-light-emitting diodes (QDs-WLEDs), red-emitting quantum dots are usually mixed with yellow-emitting phosphors in luminescent polymer layer to achieve a high color rendering index. However, the thermal stability of QDs is severely challenged by the high working temperature of the luminescent polymer layer with a low thermal conductivity. In this work, we enhanced the vertical thermal conductivity of the luminescent layer by filling vertically arranging hexagon boron nitride sheets (hBNS) inside using an ice template method. This created a relatively high thermal conductivity heat dissipation channel for luminescent particles. Sodium carboxymethylcellulose templates were created to support the vertically arranging hBNS. Using the proposed method, we fabricated a new package design of vertical-enhanced QDs-WLEDs (Ver-WLEDs) and compared its thermal performance with that of isotropic-enhanced QDs-WLEDs (Iso-WLEDs) and common QDs-WLEDs (Com-WLEDs). At the same working current, the maximal working temperature of Ver-WLEDs (116 °C) was 36 and 21 °C lower than that of Iso-WLEDs (152 °C) and Com-WLEDs (137 °C), respectively. Our novel method to enhance the vertical thermal conductivity of luminescent polymer layer could shed light on the application of QDs in high-power light-emitting diodes.