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Salford Univ’s single-step solar cells

More efficient, cost-effective and durable thin-film solar cells could be made by adapting the sputtering technique used to create anti-reflection glass.
Siobhan Wagner, 14 January 2009
Source: The Engineer

Researchers at Salford University believe the method is ideal for the large-scale deposition of copper indium diselenide (CIS) — a thin-film photovoltaic material that is seen as a more efficient alternative to amorphous silicon.  CIS cells absorb 99 per cent of the sunlight that hits them and have the potential to convert 20 per cent of this into useful electrical power. They are also better able to withstand damage from solar radiation, so are ideal for use in space-based applications.

Prof Arthur Hill, Salford team leader, said the photovoltaic properties of CIS have been studied since the 1980s but the material is not widely used in the solar panel market because its fabrication techniques are costly and complicated.  ‘It is difficult to accurately control the ratio of the component parts — copper, indium and diselenide,’ he said. He said a traditional method for producing CIS cells involved electroplating indium and copper. The electricity-conducting component of the cell, diselenide, is added using a gaseous selenisation process.

This multi-step method causes variable results, said Hill. Seeking to improve this, he applied for, and received, a research grant from the Joule Centre for Energy Research and Development, based at Manchester University.  He and a group of researchers from Salford University’s Institute for Materials Research then began studying a single-step method, called pulse deposition magnetron sputtering (PDMS). ‘The method is already used by the glass industry for producing anti-reflection and infrared coatings,’ said Hill.

‘So we thought if we could develop this as a means of putting down the CIS material, it would be a technique that would be well-known to the manufacturing industry.’  The PDMS process takes place in a vacuum chamber. A high-voltage source shoots positively charged ions inside the chamber and the ions accelerate toward a negative electrode. These energetic particles dislodge, or sputter, atoms off the surface of the negative electrode. The atoms then recondense on a glass surface and form a thin film.

Hill said his research team will soon perfect the parameters of the PDMS but his group has already created several prototype CIS cells using the method.  ‘Right now we have thin-film CIS cells that are about one to two microns thick, but we would like to go thinner, maybe to a half micron,’ he said.

In future the team also intends to study the possibility of using flexible polymer substrates instead of glass.  The Salford University team has partnered with thin-film deposition metalisation specialist General Vacuum to help with research and possible commercialisation.

Hill predicted that PDMS-made CIS cells could be on the market in three to five years time. ‘If this technique had not been used industrially then I would see major problems in scaling this up,’ he said.  ‘But the equipment is out there and although they are not at present depositing these materials, I would hope the scaling problems would not be too severe.’