The Quantum Efficiency Roll-off–free Red Organic Light-emitting Diode via Quantum Well Structure

Technology for fabricating red organic light-emitting diodes (OLEDs) based on a multiple quantum well (MQW) structure is considered. The study aimed to develop an OLED using the MQW structure to prevent the quantum efficiency roll-off at high operating voltages, a common issue in traditional OLEDs that use doped host-guest systems. Two OLED types were fabricated to achieve this: one with a doped host-guest system and another with an MQW structure. The electrical characteristics of both devices were compared in this research, focusing on quantum efficiency. A narrow-band orange organic emitter with thermally activated delayed fluorescence emission (TADF) 2,3,5,6-tetrakis(3,6-diphenyl-9H-carbazol-9-yl)-1,4-benzenedicarbonitrile (4CzTPN-Ph) was used for the new structure, sandwiched between two layers of wide-band semiconductor mCBP, creating a quasi-two-dimensional (2D) heterostructure. Implementing the MQW structure significantly reduced the quantum efficiency roll-off at higher voltages, offering a major advantage over traditional OLEDs, where such roll-off often leads to performance reduction and shortened device lifetimes. The results showed that the OLED with the MQW structure demonstrated a brightness exceeding 600 cd/m², and stable quantum efficiency across the entire operating voltage range. Unlike traditional OLEDs, where doped systems often face challenges with uneven charge and energy distribution, the MQW structure enables better exciton confinement and more efficient utilization, thus improving device stability. Furthermore, using the MQW structure allowed for enhancement of the colour characteristics of OLEDs, making them more saturated and accurate, which is important for commercial applications such as displays and lighting systems.