Novel Devices ♦ news digest crystals.”
Wolfgang Skorupa, head of the research group adds: “The atoms diffuse in the liquid-silicon-phase so rapidly that within milliseconds they form flawless mono-crystals delineated from their surroundings with nearly perfect interfaces.” In the next step, the scientists want to implement different compound semiconductors into silicon nanowires and also optimise the size and distribution of the crystals.
The results are published in the journal Nano Research: ‘III-V semiconductor nanocrystal formation in silicon nanowires via liquid-phase epitaxy’ by S. Prucnal et al, DOI: 10.1007/s12274- 014-0536-6
Organic dyes have previously been used as downshifters but dye molecules have poor photon stability and narrow absorption spectrum bands. The researchers from National Chiao Tung University and the Industrial Technology Research Institute, in Hsinchu, Taiwan, used various QDs as the downshifting agents. The resultant hybrid design offers antireflective features to boost photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region.
Quantum dots boost conversion efficiency of GaAs Solar cells Dots act as luminescent downshifters
A team of scientists from Taiwan has shown that adding CdS or CdSe quantum dots (QDs) to GaAs solar cells could increase their efficiency by nearly 25 percent. The results were reported in Nature last week.
They measured and analysed several photovoltaic parameters, including short-circuit current density, open circuit voltage, and external quantum efficiency to investigate the performance of the hybrid device. The results, they say, showed that quantum dots effectively enhanced overall power conversion efficiency by as high as 24.65 percent compared with traditional GaAs-based devices. Further analysis of the quantum efficiency response showed that the luminescent downshifting effect can be as much as 6.6 percent of the entire enhancement of photogenerated current.
This is a brief overview of ‘A Highly Efficient Hybrid GaAs Solar Cell Based on Colloidal- Quantum-Dot-Sensitization’ by Hau-Vei Han et al, Nature Scientific Reports 4, Article number: 5734 doi:10.1038/srep05734
Laser sensor could lead way to handheld bomb-detectors
Tiny plasmon-based sensor detects minute traces of explosives in the air
GaAs-based single-junction solar cells already hold the photovoltaic world record for the highest power conversion efficiency (PCE) at 28.8 percent. Boosting conversion efficiency in GaAs solar cells further requires reducing surface reflection and using the full solar spectrum, especially in the ultraviolet (UV) range.
High-energy photons can be easily absorbed at short distances, but the generated electron-hole pairs are close to the semiconductor surface, where recombination loss is strong. One way of solving this is to find a way to transform high-energy photons into lower-energy photons in process called luminescent downshifting.
A team at University of California, Berkeley led by Xiang Zhang, professor of mechanical engineering, has shown that a plasmon laser sensor can be used to detect minute concentrations of explosives in the air, including a hard-to-detect plastic explosive called PETN popular among terrorists. The results were published in the journal Nature Nanotechnology.
Plasmon lasers work by coupling electromagnetic waves with the electrons that oscillate at the surface of metals to squeeze light into nanoscale spaces far past its natural diffraction limit of half a wavelength. The UC Berkeley plasmon laser is based on a
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