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Colloidal Quantum Dot, IR LEDs Display Highest Efficiency

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BARCELONA, Spain, Dec. 5, 2018 — A composite material that is a strong light emitter as well as an efficient charge conductor — colloidal quantum dot (CQD) LEDs — has been developed by a team at the Institute of Photonic Sciences (ICFO). The nanocomposite system comprising IR CQDs is low-cost and can be integrated with CMOS, in addition to being highly efficient.

The CQD composite structure was engineered at the supra-nanocrystalline level to achieve an extremely low electronic defect density. To suppress electronic defects in CQD solids, the researchers created a matrix in which they embedded the emitting QDs. The matrix served as a remote electronic passivant for the emitter CQDs. To achieve efficient electrical injection, the matrix was engineered to facilitate efficient charge funneling into the QD emitters.

Researcher Santanu Pradhan shows the solar cell device developed for the study. Courtesy of ICFO.
Researcher Santanu Pradhan shows the solar cell device developed for the study. Courtesy of ICFO.

The researchers used the composite devices to construct solar cells and tested their performance in the IR range. They found that the effective passivation achieved in these nanocomposites, along with the modulation of the electronic density of states, resulted in solar cells that could deliver open circuit voltage (VOC) close to the theoretical limit. The VOC, which is the maximum voltage available from a solar cell, increased from 0.4 V for a single QD configuration, up to ~0.7 V for the ternary blend configuration.

The results indicate that the engineering of QCD IR-emitting LEDs at the nanoscale could significantly improve the performance efficiency of these composite devices in the IR range. The CQD LEDs demonstrated an external quantum efficiency of 7.9 percent and a power conversion efficiency of 9.3 percent — the highest value demonstrated yet for this type of device, according to the research team.


“The most surprising finding of this study is the extremely low electronic trap density that can be achieved in a conductive QD material system that is full of chemical defects arising on the surface of the dots,” said professor Gerasimos Konstantatos. “The very high quantum efficiency of those LEDs has been the consequence of this passivation strategy we demonstrate. The other exciting outcome has been the potential to reach such high VOC values for QD solar cells. That was synergistically achieved thanks to the very low trap density and a novel engineering approach to the density of states in a semiconductor film.”

The team believes that its results could open the way to using a range of the spectra that has not been fully explored for new applications such as on-chip spectrometers for food inspection, environmental monitoring, and manufacturing process monitoring, as well as active imaging systems for biomedical or night-vision applications.

“Next we will focus on how to further exploit this reduction of electronic density of states synergistically with other means to allow for simultaneous achievement of high VOC and current production, thereby targeting record power conversion efficiencies in solar cell devices,” said researcher Santanu Pradhan.

The research was published in Nature Nanotechnology (https://doi.org/10.1038/s41565-018-0312-y).

Published: December 2018
Glossary
quantum dots
A quantum dot is a nanoscale semiconductor structure, typically composed of materials like cadmium selenide or indium arsenide, that exhibits unique quantum mechanical properties. These properties arise from the confinement of electrons within the dot, leading to discrete energy levels, or "quantization" of energy, similar to the behavior of individual atoms or molecules. Quantum dots have a size on the order of a few nanometers and can emit or absorb photons (light) with precise wavelengths,...
optoelectronics
Optoelectronics is a branch of electronics that focuses on the study and application of devices and systems that use light and its interactions with different materials. The term "optoelectronics" is a combination of "optics" and "electronics," reflecting the interdisciplinary nature of this field. Optoelectronic devices convert electrical signals into optical signals or vice versa, making them crucial in various technologies. Some key components and applications of optoelectronics include: ...
infrared
Infrared (IR) refers to the region of the electromagnetic spectrum with wavelengths longer than those of visible light, but shorter than those of microwaves. The infrared spectrum spans wavelengths roughly between 700 nanometers (nm) and 1 millimeter (mm). It is divided into three main subcategories: Near-infrared (NIR): Wavelengths from approximately 700 nm to 1.4 micrometers (µm). Near-infrared light is often used in telecommunications, as well as in various imaging and sensing...
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
Research & TechnologyEuropeeducationInstitute of Photonic SciencesICFOLEDsLight Sourcesquantum dotsqdscolloidal quantum dotsCQDsMaterialsoptoelectronicssolarsemiconductorsinorganic ledsIR wavelengthinfrarednanonanoscaleEuro News

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