A group of researchers at Empa has raised the efficiency of flexible solar cells to a new record level. Independent measurements showed 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 %.
Highly efficient flexible solar cells are produced using a low-temperature evaporation method on a polymer film. The light-absorbing semiconductor material Cu(In,Ga)Se2 is slowly deposited on the foil as a wafer-thin film. Empa researcher Shiro Nishiwaki optimized the composition of the film and the alkali dopants in order to (further) increase the efficiency. The researchers investigated the effects of combined heat and light exposure after processing the solar cells and found an increase in photovoltaic performance that remains stable even after several months. The efficiency of the solar cells of 21.38 percent was independently confirmed by the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg.
Tiwari and his team have been researching flexible thin-film solar cells for more than 20 years and have achieved several efficiency records during this time. 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.
