Simple, inexpensive fabrication procedure boosts light-capturing capabilities of tiny holes carved into silicon wafers

Jul 02, 2014
A simple and inexpensive fabrication procedure boosts the light-capturing capabilities of tiny holes carved into silicon
A straightforward procedure that transforms silver nanospheres (top) into silicon nanoholes (bottom) can overcome the shortcomings of nanowire-based solar cells. Credit: American Institute of Physics

Increasing the cost-effectiveness of photovoltaic devices is critical to making these renewable energy sources competitive with traditional fossil fuels. One possibility is to use hybrid solar cells that combine silicon nanowires with low-cost, photoresponsive polymers. The high surface area and confined nature of nanowires allows them to trap significant amounts of light for solar cell operations. Unfortunately, these thin, needle-like structures are very fragile and tend to stick together when the wires become too long.

Now, findings by Xincai Wang from the A*STAR Singapore Institute of Manufacturing Technology and co-workers from Nanyang Technological University could turn the tables on by improving the manufacturing of silicon 'nanoholes'—narrow cavities carved into that have enhanced mechanical and light-harvesting capabilities.

Nanoholes are particularly effective at capturing light because photons can ricochet many times inside these openings until absorption occurs. Yet a practical understanding of how to fabricate these tiny structures is still lacking. One significant problem, notes Wang, is control of the initial stages of nanohole formation—a crucial period that can often induce defects into the solar cell.

Instead of traditional time-consuming lithography, the researchers identified a rapid, 'maskless' approach to producing nanoholes using silver nanoparticles. First, they deposited a nanometer-thin layer of silver onto a silicon wafer which they toughened by annealing it using a rapid-burst ultraviolet laser. Careful optimization of this procedure yielded regular arrays of silver nanospheres on top of the silicon surface, with sphere size and distribution controlled by the laser annealing conditions.

Next, the nanosphere–silicon complex was immersed into a solution of hydrogen peroxide and hydrofluoric acid—a mixture that eats away at directly underneath the catalytic silver nanospheres. Subsequent removal of the silver particles with acid produced the final, nanohole-infused silicon surface (see image).

The team analyzed the solar cell activity of their nanohole interfaces by coating them with a semiconducting polymer and metal electrodes. Their experiments revealed a remarkable dependence on nanohole depth: cavities deeper than one micrometer showed sharp drops in power conversion efficiency from a maximum of 8.3 per cent due to light scattering off of rougher surfaces and higher series resistance effects.

"Our simple process for making hybrid silicon nanohole devices can successfully reduce the fabrication costs which impede the solar cell industry," says Wang. "In addition, this approach can be easily transferred to silicon thin films to develop thin-film silicon–polymer hybrid with even higher efficiency."

Explore further: One step to solar-cell efficiency: Researchers' chemical process may improve manufacturing

More information: Hong, L., Wang, X., Zheng, H., He, L., Wang, H., Yu, H. & Rusli, E. "High efficiency silicon nanohole/organic heterojunction hybrid solar cell." Applied Physics Letters 104, 053104 (2014). dx.doi.org/%2010.1063/1.4863965

add to favorites email to friend print save as pdf

Related Stories

Nanocones could be key to making inexpensive solar cells

Jun 05, 2012

(Phys.org) -- One of the biggest challenges facing the silicon photovoltaic industry is making solar cells that are economically viable. To meet this goal, the module cost, which is currently about $1/watt, ...

Nanostructures improve solar cell efficiency

May 26, 2011

To make solar cells a competitive alternative to other renewable energy sources, researchers are investigating different alternatives. A step in the right direction is through new processes that change the ...

Recommended for you

Protons fuel graphene prospects

Nov 26, 2014

Graphene, impermeable to all gases and liquids, can easily allow protons to pass through it, University of Manchester researchers have found.

Cooling with the coldest matter in the world

Nov 24, 2014

Physicists at the University of Basel have developed a new cooling technique for mechanical quantum systems. Using an ultracold atomic gas, the vibrations of a membrane were cooled down to less than 1 degree ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.