Overcoming the efficiency limitation of semiconductor quantum dot-based light-emitting diodes

ended

The colloidal quantum dots (CQDs) are an emerging class of light-emitting compounds for solution-processed optoelectronics such as the light-emitting diodes (LEDs). Compared to the state-of-the-art compound semiconductors and organic light emitting diodes (OLED), the CQD-based LEDs possess extremely high color purity and low materials cost, representing the only feasible materials solution towards realization of the newly-defined Rec. 2020 standard for the next-generation displays. However, the theoretical upper limit of the device external quantum efficiency (EQE) is only ~20%, considerably lower than those in OLEDs and InGaN LEDs. The fundamental bottleneck is that it is not yet possible to control the emission directionality perpendicular to the substrate plane in the CQD superlattices, without compromising the photoluminescence quantum yield (PLQY). As a result, a lot of photons are wasted due to the total internal reflection (TIR) at the air/glass interface, as well as exciton quenching during interparticle energy transfer. In order to overcome the efficiency limitation, my research group pioneers synthesis, physics, and LED device of layer-controlled colloidal quantum wells (CQWs) of organic-inorganic hybrid lead halide perovskites (OIHPs), the two-dimensional nanocrystals of OIHP in colloidal solution. Our results have suggested that the materials system might be the ultimate solution for the quantum-dot based LEDs. We found that the CQWs possess: (i) the aggregation-induced emission (AIE) characteristics, boosting the film PLQY up to 97%, and (ii) the emission directionality (ED) perpendicular to the substrate plane in their self-assembled superlattices. Based on the new photophysical properties that have never been found in any other CQD systems, in this proposal, we aim to optimally utilize the characteristics of the AIE and ED, in order to realize high-efficiency and long-lifetime LED technology that can fulfill 100% Rec. 2020 color gamut.