Sub-Bandgap-Voltage Electroluminescence of Light-Emitting Diodes

Sub-bandgap-voltage electroluminescence (EL) has been frequently reported in quantum dot, organic, and perovskite light-emitting diodes. Due to the complex physical process across devices, the underlying mechanism is still under intensive debate. Here, based on thermodynamics, we offer an orthodox explanation of sub-bandgap-voltage EL and discuss the applicability of the previously proposed models.