Published on September 30th, 2012 | by James Ayre3
New Efficiency Record for Photovoltaic Cells Set, Jump in Efficiency Thanks to Heterojunction Technology
A new solar photovoltaic conversion efficiency record for solar cells made of amorphous and monocrystalline silicon of 21.4% was recently set, thanks to the innovations of researchers at EPFL’s Institute of Microengineering in Neuchatel. The research team, led by professor Christophe Ballif, director of the Photovoltaics Laboratory (PVlab), recently presented their work at the European Photovoltaic Solar Energy Conference and Exhibition that just happened in Frankfurt.
Thin-film solar cells are the specialization of the PVlab, and for the past few years they have been working on “hybrid technologies, better known as heterojunction technologies,” these are “hybrids” designed to enhance the performance of solar captors. “We apply an infinitesimal layer — one hundredth of a micron — of amorphous silicon on both sides of a crystalline silicon wafer,” says Christophe Ballif. The structure of this ‘sandwich’ helps to contribute to the sensors’ effectiveness.
In order for this to work efficiently, the interface that’s between the two different types of silicon needs to be optimized.
“Antoine Descoeudres managed to achieve this feat together with Stephaan DeWolf and their colleagues. They chose the commonest — and therefore cheapest — crystalline cell (called ‘p-doped silicon’), took care of its preparation and improved the process of application of amorphous silicon. They obtained a 21.4% conversion efficiency, which had never been achieved before with such type of substrates: nowadays, the best quality monocrystalline cells only attain an energy conversion efficiency of 18-19% at best. In addition, the measured open-circuit voltage was 726 mV, which constitutes a first-time accomplishment as well. Last but not least, they broke the 22% efficiency barrier on a less common substrate.”
This process, which has been validated by the Fraunhofer Institute for Solar Energy Systems (ISE) in Germany, will be published by the IEEE Journal of Photovoltaics.
According to the researchers, commercializing these innovations and bringing them to the market will still be a few years off. However, the research was financed in part by Roth & Rau Switzerland, whose parent company, Meyer Burger, is already beginning the commercialization of the machines that will be used to assemble this type of heterojunction sensors.
“Within three to five years, we expect to reach a production cost of $100 per square meter of sensors, estimates Stefaan DeWolf. In Switzerland, with the conversion efficiency achieved, such a surface will be able to produce between 200 and 300 kWh of electricity per year. “