The research team led by Associate Professor Chen Shuming from the Department of Electronic and Electrical Engineering at Southern University of Science and Technology has discovered the physical mechanism behind up-conversion electroluminescence (EL) in quantum dot light-emitting diodes (QLEDs). By precisely controlling the environmental thermal energy during QLED operation and through theoretical analysis, the team demonstrated that thermally assisted hot electron emission is the key mechanism for up-conversion EL in QLEDs. The related research, titled "Thermal assisted up-conversion electroluminescence in quantum dot light emitting diodes," was published in Nature Communications.

As an electro-optical conversion device, QLEDs convert electrons into photons. According to the law of energy conservation, the energy of injected electrons must be greater than or equal to the energy of emitted photons, satisfying the condition: Vdrive≥Ephoton/e (where  Vdrive  is the driving voltage). Therefore, the turn-on voltage of a QLED must meet this condition. However, the turn-on voltage of most QLEDs is often lower than expected. For example, a red QLED emitting 2.0 eV photons typically has a turn-on voltage below 1.6 V. This phenomenon, known as up-conversion EL or sub-bandgap turn-on, has been debated regarding its underlying physical mechanism. Over the past decade, widely discussed mechanisms have included Auger-assisted energy up-conversion, Coulomb attraction effects, and electric field-assisted hot electron emission. Building on existing research, Prof. Chen Shuming’s team concluded through novel experimental demonstrations and detailed theoretical analysis that the dominant mechanism for up-conversion EL in QLEDs is thermal energy-assisted hot electron emission.

↑ EL Characteristics of QLED Under Temperature Variation ↑

↑ Customized Probe Heating/Cooling Stage from GoGo Instruments Used for Temperature-Dependent Optoelectronic Testing ↑

↑ Customized OLED Optoelectronic Testing Heating/Cooling Stage from GoGo Instruments ↑

Paper Links:

1、Https://Www.Nature.Com/Articles/S41467-022-28037-W 

2、Https://Www.Nature.Com/Articles/S41528-021-00106-Y