New solar cell technologies make solar power more economical

The researchers at the Helmholtz-Zentrum für Materialien und Energie are modest optimists. They capture the sunlight as efficiently as possible and don‘t overdo it: literally. The thinfilm solar cells that Professor Martha Lux-Steiner and her colleagues are studying form the basis for the next generation of photovoltaics. The new solar cells are much thinner than the conventional silicon solar cells, while providing almost the same efficiency. The light absorbing films measure only a few hundredths of a millimetre, meaning they are around a hundred times thinner that the conventional silicon cells. That is an advantage: less material and energy consumption, less complicated production processes, more versatile applications. And the solar power becomes cheaper as well.

A kilowatt hour of solar power currently costs 30 cents, even in sun-spoilt southern Europe. Despite record oil prices, that is still many times more than the cost of generating power from fossil fuels. If all the costs are included in the reckoning, then each watt of installed solar power capacity costs around five euros today. “This price for the so-called peak output still needs to fall markedly,” says Lux-Steiner, “that is the key challenge! In the long term, we want to reduce the costs for modules to less than half a euro per watt.” On average, the cells only convert one eighth of the sunlight into electricity. Reducing costs therefore primarily means substantially increasing the yield. However, optimising the production process and raising the output of units lowers the price for a solar kilowatt hour. To achieve this, development work has to be carried out across a broad front and then has to be transferred into industrial production as quickly as possible. A tough task. That is also reflected in the name given to the international research project that aims to achieve just this: ATHLET stands for “Advanced Thin Film Technologies for Cost Effective Photovoltaics”. Led by the Helmholtz Team under the direction of Martha Lux-Steiner, scientists from 23 institutions in the field of research and industry across the whole of Europe have joined forces. The four-year project that has received some 11 million euros from the European Union since 2006 is very successful.

“Initially, however, all those involved had to take a leap of faith,” recalls Lux-Steiner. For ATHLET unites two core technologies whose representatives previously saw themselves in healthy competition with each other. Thin-film solar cells made of chalcopyrites (CIS-films) and thin-film solar cells made of micromorphous silicon. On the one hand, the ATHLET researchers are optimising the CIS thin-film solar cells. These have films made of copper, indium and selenium or sulphur that are particularly efficient in converting light into power. The technology is already used in industrial production. Now, the “ATHLETs” are researching better materials for linking up the cells so as to once more raise the power output. Similarly, new and simpler production processes are to be developed for coating the cells. “Our vision is a factory into which substrates of several square metres in size are fed and from which solar modules emerge. These would only need to be cut to size in accordance with the required wattage,” says Dr. Volker Hinrichs, who is coordinating the project at the Helmholtz Centre together with Martha Lux-Steiner. So-called micromorphous thin-film solar cells are also highly promising in which two thin silicon films are layered on top of each other. The trick is that the “tandem cell” then absorbs two different ranges of the solar spectrum and so generates more power. “We can achieve an energy yield of up to 40 per cent,” explains Lux-Steiner.

So far, however, this has only been achieved in the lab. So, the scientists have to continue working on this flat out before they manage to achieve such output in practice as well. But they also achieve milestones on the way to their ultimate goal. For example, the researchers have already substantially improved the production process, with the result that hardly any toxic wastes are left.