A paper recently published in the journal Materials discussed the potential of colloidal quantum dots (CQDs) for nanophotonic devices.
Study: Colloidal Quantum Dots for Nanophotonic Devices. Image Credit: Van Pympk/Shutterstock.com
Background
CQDs have emerged as a significant material class with vast potential in fields like quantum information, optoelectronics, and biological medicine. They offer distinct advantages such as low-cost solution processibility and tunable emission wavelengths from visible to infrared.
Light-emitting and photovoltaic devices based on CQDs now rival alternative state-of-the-art materials in performance. Narrow-band semiconductor CQDs, in particular, show great promise for infrared technologies.
Understanding the physical properties, growth, and chemical transformations of CQDs is crucial for both commercialization and fundamental research. This paper discusses recent advancements in CQD material chemistry, device fabrication, and processing.
Photodetectors and Microspectrometers
CQD photodetectors have become a key research area due to their low preparation costs, wide spectral tunability, and compatibility with silicon-based readout integrated circuits. Mercury and lead chalcogenide CQDs, in particular, excel in infrared detection, making them ideal for infrared photodetectors.
Lead chalcogenide CQD photodetectors have evolved from single-pixel detectors to large-array imagers. Mercury chalcogenide CQD-based infrared detectors, with their broad absorption spectra and tunable bandgaps, are particularly promising for solar cells, communication technology, and biomedical imaging.
Additionally, CQDs are advantageous for spectral filtering, making them ideal for microspectrometers. Recent advances in material nanoarchitectonics-based microspectrometers highlight the need to explore novel low-dimensional materials in this field.
Innovative Applications
Low-dimensional materials have applications in various fields, such as photovoltaic devices, where well-designed heterojunctions can enhance performance. For instance, a recent study demonstrated CH3NH3PbI3/Au/Mg0.2Zn0.8O heterojunction self-powered photodetectors with high detectivity and low dark current.
Mg0.2Zn0.8O and CH3NH3PbI3 acted as the n-type layer and p-type layer, respectively. The obtained heterojunctions showed a high 0.58 A/W responsivity, and the external quantum efficiency (EQE) of the CH3NH3PbI3/Au/Mg0.2Zn0.8O heterojunction self-powered photodetectors was 84.51 times that of the Mg0.2ZnO0.8/Au photodetectors and 10.23 times that of the CH3NH3PbI3/Au photodetectors.
In another study, flexible cadmium-free CZTSSe/ZnO solar cells were fabricated by optimizing ZnO buffer layers, achieving a maximum 5.0% power conversion efficiency. These cells showed improved light absorption and charge transfer capabilities.
The flexible CZTSSe solar cells' light absorption capacity was enhanced due to the removal of the cadmium sulfide layer. Additionally, the ZnO buffer layers' optimal thickness and the proper annealing temperature of the CZTSSe/ZnO were 100 nm and 200 °C, respectively.
Eventually, the 5.0 % achieved by the optimum flexible CZTSSe/ZnO device was the highest efficiency for flexible CZTSSe/ZnO solar cells. Moreover, systematic characterizations indicated that the flexible CZTSSe/ZnO solar cells, based on optimal conditions, realized quality heterojunction, better charge transfer capability, and low defect density.
Moreover, CQDs have also been used as a sacrificial layer in polishing single-crystal silicon carbide, enhancing surface quality through pulsed ion beam sputtering.
Improving Detection Performance and Reliability
Efficiently combining photosensitive materials with optical structures is crucial to enhance light absorption and improve photodetectors' detection performance. In photoelectric devices, light can be focused into the sub-diffractive region by engineering a metal microstructure, which enhances light absorption through the plasmon exciton resonance phenomenon.
A study examined a gallium-arsenide nanowire photodetector enhanced with gold nanoparticles fabricated via thermal evaporation. The incorporation of these nanoparticles increased the photodetector's responsivity and photocurrent due to the coupling of electron gas with the excitation light.
Similarly, a phototransistor was designed to achieve high responsivity by merging two resonances using lithium-ion glass gating on a mercury telluride nanocrystal film. Enhancing the optical material characteristics can further improve the reliability and performance of optoelectronic devices.
For instance, tuning the electric field distribution and regulating solution flow have improved the homogeneity and light utilization efficiency of large-scale nanorods. Optimized ZnO nanorods can be used in collector systems and solar cells.
Additionally, a recent study investigated spatial shifts in reflected light beams on a hexagonal boron nitride/alpha-molybdenum trioxide structure. Researchers successfully enhanced the in-plane anisotropy of hexagonal boron nitride by twisting the structure.
Conclusion
Overall, this paper highlighted the promising applications of CQDs in nanophotonic devices and provided theoretical guidance for novel optical encoders and nanophotonic devices.
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