May 17, 2017: A team of researchers from the US and South Korea unveiled a unique type of nanoLEDs, which has high brightness levels (in excess of 80,000 cd/m2), and is capable of functioning as light emitters and light detectors.
In the research paper, “Double-heterojunction nanorod light-responsive LEDs for display applications”, the researchers mention that the dual-mode LEDs will enable new types of interactive displays.
The all-solution-processed double-heterojunction nanorod (DHNR) light-responsive LEDs are about 50nm long and 6nm in diameter. The paper mentions quantum dots of two different types–one which can enhance radiative recombinations that are useful for LEDs, and the other type leads to efficient separation of photo-generated carriers.
The anisotropic nanorods, which have layered structures, can be tuned independently so that they can be fine-tuned in both—recombination and charge separation in a single device. This will enable a single nanorod to be electroluminescent and generate a photocurrent. When the nanorods are stacked between electrodes, they can be arranged into pixels that can function as light-emitting and light-detecting modes by simply changing a voltage bias.
The nanorods have low turn-on voltage (1.7 V), and a maximum brightness of 80,000 cd/m2. They also exhibit low bias and high efficiencies at display-relevant brightness. According to the researchers, an external quantum efficiency of 8.0% at 1000 cd/m2 under 2.5 V bias.
The researchers pointed out that DHNR-LEDs has individual pixel sensing capability, which can support direct imaging or scanning at screen level. The dual light-emitting and light-detecting feature of the DHNR-LEDs can turn LED displays (in effect large arrays of nanoLEDs) into massively parallel data communication and processing devices performing direct display-to-display data communication.
The photo-detection capability of DHNR light-responsive LEDs is akin to a photovoltaic effect, and displays could be made to harvest or scavenge energy from light sources without the need for integrating separate solar cells, making the display even more efficient.