Thermal Impact of LED Chips on Quantum Dots in Remote-Chip and On-Chip Packaging Structures

Light-emitting diode (LED) chips in quantum dot (QD)-converted LEDs serve simultaneously as a heat source and a heat sink, but it remains unclear which of these is the major factor that affects the operating temperature of QDs. Here, we investigated the thermal and optical performances of QD-converted LEDs using QD-on-chip and QD-remote-chip packaging structures, to better understand the thermal effect of LED chips on QDs. Our results indicated that the QD-on-chip structure achieved the same optical performance as the QD-remote-chip structure, while the former can save QD usage up to 75.9% owing to the higher absorption probability of QDs closer to the blue source. Most importantly, the QD-on-chip structure largely reduced the maximal surface temperature from 82.7 °C to 60.2 °C at 250 mA, and had a longer operating lifetime compared with the QD-remote-chip structure. Simulations revealed that the QD-remote-chip structure could suppress the heat transfer from chips to QDs; however, the hot spot remained in QDs, owing to the heavy conversion loss and low thermal conductivity of the silicone matrix; consequently, the QD-on-chip structure had better heat dissipation (lower temperature) for QDs closer to the chip that served as heat sinks. Therefore, it is suggested to place QDs near the heat sink with high thermal conductivity, such as the LED chip, for heat dissipation; this is better than removing QDs for blocking the heat generated by the LED chip.