Thin film solar cells achieve new record energy conversion efficiency

January 21st, 2013 by Empa

High-efficiency flexible CIGS solar cells on polyimide film developed at Empa (click image to expand - image courtesy of Empa)

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 record efficiency of 20.4% for converting sunlight into electricity.

The cells are based on CIGS semiconducting material (copper indium gallium (di)selenide) known for its potential to provide cost-effective solar electricity. The technology is currently awaiting scale-up for industrial applications.

To make solar electricity affordable on a large scale, scientists and engineers worldwide have been trying to develop a low-cost solar cell, which is both highly efficient and easy to manufacture with high throughput.

A team at Empa’s Laboratory for Thin Film and Photovoltaics, led by Professor Ayodhya N. Tiwari, has achieved a record 20.4% energy conversion efficiency for thin film CIGS solar cells on flexible polymer substrates, a massive improvement over the previous record of 18.7% achieved by the same team in May 2011.

Tiwari’s team has been investigating and developing various thin film solar cell technologies for sometime.

Over the years the laboratory has boosted the photovoltaic conversion efficiency of flexible CIGS solar cells from 12.8% in 1999, to 14.1% in 2005, 17.6% in 2010 and 18.7% in 2011.

The team, comprising PhD students Adrian Chirila and Fabian Pianezzi, has succeeded in 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 (ISE) in Freiburg, Germany.

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

“We have now managed to close the “efficiency gap” to solar cells based on polycrystalline silicon wafers or CIGS thin film cells on glass,” Professor Ayodhya N. Tiwari said.

Thin film, lightweight and flexible high-performance solar modules are attractive for numerous applications such as solar farms, roofs and facades of buildings, vehicles and portable electronics and can be produced using continuous roll-to-roll manufacturing processes that offer further cost reductions compared to standard silicon technologies.

They have the potential to enable low-cost solar electricity in the near future.

“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.

The next step is the scale-up of the technology to cover large areas in a cost-efficient roll-to-roll manufacturing process with an industrial partner,” said Professor Gian-Luca Bona, Director of Empa.

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

The research work has been supported over the years by the Swiss National Science Foundation (SNSF), the Commission for Technology and Innovation (CTI), the Swiss Federal Office of Energy (SFOE) and the EU Framework Programmes.

 

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