Colloidal quantum dots for nanophotonic devices

Article recently published in the magazine Materials discussed the potential of colloidal quantum dots (CQDs) in nanophotonic devices.

Background

CQDs have become an important class of materials with significant potential for a range of applications in various fields such as quantum information, optoelectronics and biological medicine due to their distinct advantages such as solution processability at low cost and wide tunability of the emission wavelength from visible light to infrared.

The performance of CQD-based light-emitting and photovoltaic devices has become comparable to state-of-the-art alternative materials (SOTA). Moreover, narrowband semiconductor CQDs have shown great potential in infrared technology.

Therefore, an in-depth and new insight into the physical properties, growth and chemical transformations of CQDs would benefit both commercialization and purely basic research. In this article, the authors discuss the latest information related to CQD, including CQD material chemistry, device fabrication, and processing.

Photodetectors and microspectrometers

In recent years, CQD photodetectors have become an active area of ​​research due to their inherent advantages such as low preparation cost, wide range of spectral persistence, and compatibility with silicon-based readout integrated circuits via solution processing. For example, mercury chalcogenide CQD and lead chalcogenide CQD have demonstrated outstanding infrared sensing performance as the main CQD materials, making them the most suitable materials for the fabrication of infrared photodetectors.

Lead chalcogenide CQD photodetectors have rapidly developed from single-pixel photodetectors to large-format cameras. Mercury chalcogenide CQD-based infrared detectors with broad absorption spectrum and tunable bandgaps have potential applications in solar cells, communications technology, and biomedical imaging.

Moreover, the use of CQDs is also beneficial in spectral filtering, which makes them promising for microspectrometers. Recent research on the advancement of microspectrometers based on material nanoarchitectonics has suggested the need to explore new low-dimensional materials in this field.

Low-dimensional materials can be used in a variety of fields, such as photovoltaic devices, where well-designed heterojunctions can improve device performance. In a recent study, CH₃NH₃PbI₃/Au/Mg_0.2Sign_0.8Self-powered heterojunction photodetectors with enhanced dark current detection and attenuation were demonstrated.

Mg_0.2Sign_0.8O and CH₃NH₃PbI₃ acted as an n-type layer and a p-type layer, respectively. The obtained heterojunctions showed a high sensitivity of 0.58 A/W, and the external quantum efficiency (EQE) of CH₃NH₃PbI₃/Au/Mg_0.2Sign_0.8O, self-powered heterojunction photodetectors were 84.51 times larger than Mg_0.2ZnO_0.8/Au photodetectors and 10.23 times more than CH₃NH₃PbI₃/Au photodetectors.

This work provided novel concepts for studying perovskite photodetectors with high detection and low dark current. The study fabricated flexible cadmium-free CZTSSe/ZnO solar cells by optimizing zinc oxide (ZnO) buffer layers to achieve a maximum energy conversion efficiency of 5.0%.

The light absorption capacity of CZTSSe flexible solar cells has been increased by removing the cadmium sulfide layer. Additionally, the optimal thickness of the ZnO buffer layers and the specific annealing temperature of CZTSSe/ZnO were 100 nm and 200 °C, respectively.

Ultimately, the 5.0% achieved by the optimally flexible CZTSSe/ZnO device was the highest efficiency for flexible CZTSSe/ZnO solar cells. Moreover, systematic characterizations demonstrated that flexible CZTSSe/ZnO solar cells, operated under optimal conditions, provide high-quality heterojunction, improved charge transfer capacity, and low defect density.

Another recent study showed that the introduction of CQDs as a sacrificial layer is possible when polishing single-crystalline silicon carbide by using pulsed ion beam sputtering to improve surface quality. This provided a novel approach to high-precision, ultra-smooth surface fabrication from single-crystalline silicon carbide.

Improving detection performance and reliability

Photosensitive materials and optical structures must be effectively combined to improve light absorption and improve the detection efficiency of photodetectors. In photoelectric devices, light can be forced into the subdiffractive region by designing a metal microstructure. Then, the phenomenon of plasmon exciton resonance enhances the light absorption.

This study investigated a gallium arsenide nanowire photodetector with improved performance by introducing gold nanoparticles produced by thermal evaporation. The sensitivity and photocurrent of the proposed photodetector were increased by coupling electron gas with excitation light in gold nanoparticles.

Similarly, a phototransistor was designed that coupled the two resonances using lithium-ion glass gating made of a mercury nanocrystalline layer and a nanocrystal to achieve high sensitivity. Moreover, the reliability and performance of optoelectronics can be improved by optimizing and studying the properties of the optical material.

For example, tuning the electric field distribution and controlling the solution flow increased the uniformity of large-scale nanorods. This approach also increased the light-use efficiency of the nanorods. Optimized ZnO nanorods can be used in collector systems and solar cells.

Similarly, a recent study investigated the spatial shifts of the reflected light beam in a hexagonal boron nitride/alpha-molybdenum trioxide structure. The researchers in this study managed to improve the in-plane anisotropy of hexagonal boron nitride through twisting. Overall, the paper highlights the promising applications of CQD in nanophotonic devices and provides theoretical guidance for novel optical encoders and nanophotonic devices.

Disclaimer: The views expressed here are those of the author expressed in his personal capacity and do not necessarily reflect the views of AZoM.com Limited T/A AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms of Use of this website.