Empa scientists developed thin-film solar cells on flexible plastic sheets that the conversion of sunlight into electricity reaches new record of 20.4%.

These solar cells based on semiconductor technology for CIGS (Copper indium gallium selenide), have an enormous potential for low-cost production of photovoltaic electricity. The next step is the transfer to industry for large-scale production for various applications.

A new process allows for flexible CIGS solar cells on high performance polyimide sheets (colored polymers).

To produce solar electricity cheaply scientists and engineers have long sought to develop inexpensive solar cells that have both high performance and are easy to produce in large quantities. A Empa team under the direction of Prof.Ayodhya N.Tiwari has made a new breakthrough in this direction. These researchers were able to significantly increase the rate of conversion of solar radiation into electricity solar cell CIGS thin film on flexible plastic sheets to reach a new record of 20.4% – a significant improvement over the previous record 18.7% the same team had established in May 2011.

The research team around Prof.Tiwari studies and develops long been various thin film technologies. In the years since his first world record of 12.8% in 1999, and succeeded in improving laboratory successively conversion rates, or yields, flexible CIGS solar cells to 14.1% (2005), 17.6% (2010) and 18.7 % (2011).

Performance silicon cells finally equaled

The research team was able to further optimize the properties of the CIGS light absorbing layer, optimization more successful if the layer is deposited at a relatively low temperature. The efficiency of this solar cell, verified by the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg im Breisgau, even exceeds the value record of CIGS solar cells on glass of 20.3%. Better yet: this output corresponds to the highest yields achieved with polycrystalline silicon solar cells. “We have finally been able to match the returns of polycrystalline silicon solar cells and thin film solar cells on glass CIGS”, Tiwari said.

The flexible solar modules with high efficiency thin film are particularly suitable for many applications, eg for large solar parks on roofs or facades of buildings or on portable electronic devices. They can be produced using deposition processes on rollers (“roll-to-roll”) that allow for additional cost savings compared to silicon technology. They would lower the cost of PV in the near future.

“The long series of performance records of flexible CIGS solar cells obtained at Empa shows that the performance of thin-film solar cells can quite compete with that of polycrystalline silicon cells. The time has come to move on and to upper scale with an industrial partner for industrial applications and we can also produce large-area modules, “explained the director of Empa, Gian-Luca Bona.

To achieve this, Empa is working with the firm Flisom a young company dedicated to the industrialization of the production of flexible CIGS solar cells.

This research have for years supported by the Swiss National Science Foundation (SNSF), the Commission for Technology and Innovation (CTI), the Swiss Federal Office of Energy (FOE) and the Framework EU Programmes.

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