Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Making waves with lasers

26.01.2015

Laser processing produces deep ripples in silicon over a wide area — something that could enhance solar cell efficiency

A*STAR scientists have produced a uniform nanoscale ripple pattern over a wide area on a silicon surface by scanning a femtosecond laser beam across it. Given that a rippled surface is much less reflective than a smooth surface, this simple innovation could enhance the efficiency of solar cells by boosting their ability to harvest more sunlight1.


Scanning electron micrograph showing a ripple pattern formed on a silicon surface using a femtosecond laser beam. This surface absorbs more light than an unprocessed surface and could enhance solar cell efficiency.

Reproduced, with permission, from Ref. 1 © 2014 Elsevier

The use of lasers to produce periodic surface structures is currently an area of intense research. Laser processing has the important advantage that it heats only the surface of a material, leaving underlying structures unaffected. However, many laser processing methods are limited: they can process only small areas and shallow ripples.

Now, Xincai Wang and co-workers from A*STAR’s Singapore Institute of Manufacturing Technology and Nanyang Technological University have successfully addressed these limitations. They demonstrate the potential of their technique by using it to produce a uniform ripple pattern on a silicon substrate (see image) over a large area of 30 millimeters by 30 millimeters, with an average ripple depth of 300 nanometers — about three times greater than that of other techniques.

“This increase in depth can substantially reduce light reflection and improve the light-trapping ability of the ripple structure,” Wang notes. “Hence, if the structure is used in photovoltaic devices, more light will be trapped within the structure, thereby enhancing the device efficiency.”

Straightforward and inexpensive, the technique simply involves using a cylindrical lens to widen a femtosecond laser beam to a width of 50 micrometers and then scanning the beam across the surface.

As the energy of the laser’s photons exceeds the bandgap of silicon, the photons excite electrons from the valence band to the conduction band. Such electrons would usually relax by transferring their energy to the atomic lattice, thereby heating it. However, the extremely short pulse durations mean that instead they generate an electron wave on the surface. This in turn produces a light wave, which interferes with the incoming laser beam. The silicon is removed in locations where the incoming and outgoing light waves constructively interfere with each other, giving rise to the valleys in the ripple pattern.

The researchers found that on rippling the average reflectance of a silicon surface dropped from 39.7 per cent to 12.5 per cent, which meant light absorption was enhanced by 41 per cent as a result of strong scattering by the ripple structure. This effect could be exploited to manage photon behavior in solar cells and light-emitting diodes.

The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology


Reference
Hong, L., Rusli, Wang, X. C., Zheng, H. Y., Wang, H. & Yu, H. Y. Femtosecond laser fabrication of large-area periodic surface ripple structure on Si substrate. Applied Surface Science 297, 134–138 (2014). | article

A*STAR Research | ResearchSEA
Further information:
http://www.research.a-star.edu.sg/research/7124
http://www.researchsea.com

More articles from Process Engineering:

nachricht Etching Microstructures with Lasers
25.10.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Applying electron beams to 3-D objects
23.09.2016 | Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

NTU scientists build new ultrasound device using 3-D printing technology

07.12.2016 | Health and Medicine

The balancing act: An enzyme that links endocytosis to membrane recycling

07.12.2016 | Life Sciences

How to turn white fat brown

07.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>