Thin-film solar cells achieve efficiency of 20.4 per cent

Scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology, have developed thin-film solar cells on flexible polymer foils with a new efficiency record for converting sunlight into electricity.

The cells are based on CIGS semiconducting material (copper indium gallium [di]selenide), which is known for its potential to provide cost-effective solar electricity.

The team at Empa’s Laboratory for Thin Film and Photovoltaics, led by Ayodhya N Tiwari, is said to have achieved a record 20.4 per cent energy conversion efficiency for thin-film CIGS solar cells on flexible polymer substrates.

According to a statement, this is an improvement over the previous record of 18.7 per cent achieved by the same team in May 2011.

The team, including PhD students Adrian Chirila and Fabian Pianezzi, achieved its latest set of results by modifying the properties of the CIGS layer, grown at low temperatures, which absorbs light and contributes to the photo-current in solar cells.

The cell-efficiency value was independently certified by the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany.

Empa’s new record efficiency for flexible solar cells now exceeds the record value of 20.3 per cent for CIGS solar cells on glass substrates, and equals the highest efficiencies for polycrystalline silicon wafer-based solar cells.

‘We have now — finally — managed to close the “efficiency gap” to solar cells based on polycrystalline silicon wafers or CIGS thin film cells on glass,’ said Tiwari.

‘The series of record efficiencies for flexible CIGS solar cells developed at Empa demonstrates that thin-film solar cells can match the excellent performance of polycrystalline silicon cells. Now it is time for the next step, the scale-up of the technology to cover large areas in a cost-efficient roll-to-roll manufacturing process with an industrial partner’, said Gian-Luca Bona, director of Empa.

For this purpose, Empa is collaborating with Flisom, a start-up company involved in industrialisation of flexible CIGS solar cells.