Cheaper silicon means cheaper solar cells

October 22, 2014
Cheaper silicon means cheaper solar cells
By using silicon fibres coated in glass, researchers have been able to make solar cells from silicon that is 1000 times more impure, and thus cheaper, than the current industry standard. Credit: Fredrik A. Martinsen

Researchers at the Norwegian University of Science and Technology have pioneered a new approach to manufacturing solar cells that requires less silicon and can accommodate silicon with more impurities than is currently the standard. Those changes mean that solar cells can be made much more cheaply than at present.

A new method of producing solar cells could reduce the amount of per unit area by 90 per cent compared to the current standard. With the high prices of pure silicon, this will help cut the cost of solar power.

"We're using less expensive raw materials in smaller amounts, we have production fewer steps and have potentially lower total energy consumption," PhD candidate Fredrik Martinsen and Professor Ursula Gibson of the Department of Physics at NTNU explain.

They recently published their technique in Scientific Reports.

Their processing technique allows them to make solar cells from silicon that is 1000 times less pure, and thus less expensive, than the current industry standard.

Glass fibres with a silicon core

The researchers' solar cells are composed of silicon fibres coated in glass. A silicon core is inserted into a glass tube about 30 mm in diameter. This is then heated up so that the silicon melts and the glass softens. The tube is stretched out into a thin glass fibre filled with silicon. The process of heating and stretching makes the fibre up to 100 times thinner.

This is the widely accepted industrial method used to produce fibre optic cables. But researchers at the Department of Physics at NTNU, working with collaborators at Clemson University in the USA, are the first to use silicon-core fibres made this way in solar cells. The active part of these solar cells is the silicon core, which has a diameter of about 100 micrometres.

Cheaper silicon means cheaper solar cells
The active part of these solar cells is the silicon core, which has a diameter of about 100 micrometres. Credit: Fredrik A. Martinsen
Lower energy consumption

This production method also enabled them to solve another problem: traditional solar cells require very pure silicon. The process of manufacturing pure silicon wafers is laborious, energy intensive and expensive. "We can use relatively dirty silicon, and the purification occurs naturally as part of the process of melting and re-solidifying in fibre form", says Gibson. "This means that you save energy, and several steps in production."

It is estimated to take roughly one-third of the energy to produce solar cells with this method compared to the traditional approach of producing .

Gibson has worked for several years to combine purification and solar cell production. She got the idea for the project after reading an article on silicon core fibres by John Ballato at Clemson University in South Carolina, who is at the forefront of research in fibre optics materials development.

"I saw that the method he described could also be used for solar cells," she said, "and we developed a key technique at NTNU that improved the fibre quality." Gibson and her research group began to work with Ballato, who is a co-author of the article published in Scientific Reports.

Silicon rods

The new type of solar cells are based on the vertical rod radial-junction design, which is a relatively new approach. The design uses less pure silicon that a planar cell, Martinsen explains, and then launches into a crash-course on the inner workings of a solar cell: photons of different wavelengths are absorbed in different layers of the silicon wafer. They generate free charges, or charge carriers, which are then separated to provide electrical energy.

These charges need to be close to the electrodes and close to the p-n junction to be captured. The p-n junction is the active region in the device - where different types of charge carriers are separated. If the charge is not captured, the energy dissipates and goes to heating up the solar cell itself.

In a traditional solar cell, the journey from where a charge is generated to the surface can be quite long. This means that highly purified silicon is required. But with silicon fibres, there is a junction all the way around the fibre. The distance from where the charge is generated to where it is captured is quite short. Charge carriers can be captured effectively, even when using impure silicon.

"The vertical rod design still isn't common in commercial use. Currently, silicon rods are produced using advanced and expensive nano-techniques that are difficult to scale," Martinsen says. "But we're using a tried and true industrial bulk processes, which can make production a lot cheaper."


The power produced by prototype cells is not yet up to commercial standards. Contemporary solar cells have an efficiency of about 18 per cent. The prototype created by NTNU researchers has only reached about 3.6 per cent. Gibson and Martinsen still have faith in the potential of this production method, and are working to improve the design and fabrication processes.

"These are the first solar cells produced this way, using impure silicon. So it isn't surprising that the power output isn't very high," says Martinsen. "It's a little unfair to compare our method to conventional solar cells, which have had 40 years to fine-tune the entire production process. We've had a steep learning curve, but not all the steps of our process are fully developed yet. We're the first people to show that you can make this way. The results are published, and the process is set in motion."

Explore further: New solar cells serve free lunch

More information: "Silicon-core glass fibres as microwire radial-junction solar cells." F. A. Martinsen, B. K. Smeltzer, M. Nord, T. Hawkins, J. Ballato & U. J. Gibson. Scientific Reports 4, Article number: 6283; DOI: 10.1038/srep06283

Related Stories

New solar cells serve free lunch

September 24, 2014

One of the most common complaints about solar power is solar panels are still too expensive to be worth the investment. Many researchers have responded by making solar cells, the tile-like components of solar panels that ...

Towards more efficient solar cells

August 13, 2014

A layer of silicon nanocrystals and erbium ions may help solar cells to extract more energy from the ultraviolet (UV, high-energy) part of the solar spectrum. Experimental physicists from the FOM Foundation, the STW Technology ...

Solar discovery sets new record for low-grade silicon

May 6, 2013

( —Solar engineers from UNSW have developed an innovative method to dramatically improve the quality of low-grade silicon, promising to significantly improve electrical efficiency and reduce the cost of solar panels.

Recommended for you

Your (social media) votes matter

January 24, 2017

When Tim Weninger conducted two large-scale experiments on Reddit - otherwise known as "the front page of the internet" - back in 2014, the goal was to better understand the ripple effects of malicious voting behavior and ...

Protective wear inspired by fish scales

January 24, 2017

They started with striped bass. Over a two-year period the researchers went through about 50 bass, puncturing or fracturing hundreds of fish scales under the microscope, to try to understand their properties and mechanics ...

'Droneboarding' takes off in Latvia

January 22, 2017

Skirted on all sides by snow-clad pine forests, Latvia's remote Lake Ninieris would be the perfect picture of winter tranquility—were it not for the huge drone buzzing like a swarm of angry bees as it zooms above the solid ...

Singapore 2G switchoff highlights digital divide

January 22, 2017

When Singapore pulls the plug on its 2G mobile phone network this year, thousands of people could be stuck without a signal—digital have-nots left behind by the relentless march of technology.

Making AI systems that see the world as humans do

January 19, 2017

A Northwestern University team developed a new computational model that performs at human levels on a standard intelligence test. This work is an important step toward making artificial intelligence systems that see and understand ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 23, 2014
How is the charge extracted out of the wire?

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.