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PASTA: Science Walking On Sunshine

Walking On Sunshine: PASTA System Aids Solar Cell Creation At UWC

A year-long discussion between the Universities of the Western Cape and Utrecht University in the Netherlands has culminated in the arrival of the PASTA instrument on campus. The instrument is a multi-chamber ultra-high vacuum system used to produce thin film silicon solar cells (the solar cell being the building block for a solar panel, amongst other things).

Christopher Arendse, Professor in UWC’s Department of Physics and Astronomy, and Prof Ruud Schropp of the University of Utrecht started talking about moving the machine to Cape Town while attending  the 26th International Conference on Amorphous and Nanocrystalline Semiconductors in Aachen, Germany in 2015.

Schropp’s physics department recently merged with the Energy research Center of the Netherlands (ECN) thin film branch in Eindhoven which already had similar equipment - and they didn’t simply want to scrap the instrument in Utrecht.

With UWC and Utrecht University’s long history of student exchanges and collaborations, the choice of where to send the PASTA instrument was clear.

“The main thing is that we are pursuing alternative avenues to produce efficient and stable solar cells made of thin films, which can be cheaper,” Prof Arendse notes.

Solar panels usually look like a flat glass plate with a few wafers inside. With the thin film technology solar cells can be produced on flexible plastic and cheaper substrates. They are lightweight and can be rolled up, depending on what substrates you use.

“Together we have been developing the hot wire chemical vapour deposition (HWCVD) technique, which is not only a more gentle deposition technique, but also faster,” according to Prof Schropp, one of the pioneers in HWCVD technology. “Faster is important because that saves money.”

UWC’s physics programme has long been interested in this particular technology.

Up to now, the University used has only had one chamber that could grow one layer of material at a time. But a solar cell is composed of more than one layer of material, and each of these layers needs to be deposited in a different chamber - and PASTA allows for that.

Once the instrument is operational students and researchers can take the individual layers they have been working on over the years and develop them further, incorporating them into a working device.

“We’ve never had the opportunity to demonstrate a working solar cell before. We contributed to the basic research on how to optimise them, but could never demonstrate the benefits,” says Prof Arendse.

The machine is the first of its kind at a South African university - and Prof Arendse is itching to create a solar cell from scratch as soon as the machine is operational.

The solar cell is grown from layers of gases which react within the chambers of the machine to deposit thin films. Each thin film layer is made up of a different material with a specific property and together the stacked layers make up the working electronic parts.

“It’s a bottom-up process; not like taking a tree and chopping it up to make a toothpick,” explains Prof Arendse.

This technology has huge game-changing potential.

“It is cheap to deposit a thin film when you are using a string of vacuum chambers like this has. Then it becomes possible to compete with the mainstream crystalline silicon because your product is serving a different application.”

The flexibility and light weight of this particular kind of solar cell, combined with South Africa’s natural abundance of sunlight, could be a major selling point for developing this particular stream within the local photovoltaic industry.

“We have the expertise, the bright and hardworking students, the support of UWC and the National Research Foundation, the collaborations with international leaders in the field like Prof Schropp - and now the equipment as well,” says Prof Arendse.

“With further support from industry and government, we can explore the bigger picture, beyond just what we can do in the laboratory: We can create an industry.”