New efficiency record for flexible solar cells
A new efficiency record of just under 21.4 % for CIGS solar cells on flexible polymer film has been achieved by Empa scientists. Solar cells of this type are particularly suitable for applications on roofs, transport vehicles and mobile devices.
A group of researchers at Empa has raised the efficiency of flexible solar cells to a new record. Independent measurements revealed a value of 21.4 % when this type of solar cell converts light into electricity. By comparison, the best efficiency of a conventional (non-flexible) solar cell made of crystalline silicon is 26.7 %.
The details of the research achievement will be presented by Romain Carron, group leader in Empa's Thin Films and Photovoltaics Laboratory led by Ayodhya N. Tiwari, on September 7, 2021, at the "38th European Photovoltaic Solar Energy and Conference and Exhibition (EU PVSEC)," which will be held virtually this year.
High-efficiency flexible solar cells are produced on a polymer film using a low-temperature evaporation method. On the film, the light-absorbing semiconductor material Cu(In,Ga)Se2 slowly deposits as an ultra-thin film. Empa researcher Shiro Nishiwaki optimized the composition of the film and the alkali dopants to (further) increase the efficiency. The researchers studied the effects of combined heat and light exposure after processing the solar cells and found an increase in photovoltaic performance that remains stable after several months. The solar cells' efficiency of 21.38 % was independently confirmed at the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany.
Always new records - for more than 20 years
Tiwari and his team have been researching flexible thin-film solar cells for more than 20 years. With their deep knowledge of the technology and the underlying physical processes, they have achieved several efficiency records over the years. They started with 12.8 % in 1999, reached 14.1 % (2005), 17.6 % (2010), 18.7 % (2011), 20.4% (2013), and 20.8 % in 2019.
Flexible and lightweight solar modules with this technology are particularly suitable for applications on roofs and facades of buildings, for greenhouses, transport vehicles, airships and portable electronics. Empa is working with the Swiss company Flisom, a spin-off of Empa and ETH Zurich, on roll-to-roll production of lightweight, flexible solar modules for such applications.
The research and development work was supported by the Swiss Federal Office of Energy (SFOE).
