Clemens Heske, University of Nevada, Las Vegas; Karlsruhe Institute of Technology
Alternative Buffer Materials and Their Electronic and Chemical Properties in Cu(In,Ga)(S,Se)2 and CdTe Thin-Film Solar Cells
Written by Ahmad R. Kirmani
Having reached solar power conversion efficiencies (PCEs) in excess of 20%, the CIGS and CdTe solar cell technologies are amongst prime contenders for augmenting the silicon photovoltaic technology in meeting the ever-increasing global energy demands. There are, however, as Clemens Heske points out, critical fundamental questions to be answered before commercialization can become a reality.
Surfaces and interfaces play a crucial role in dictating device performance. Therefore, Heske and his group, well-known leaders in surface science, have a lot to offer to the field of photovoltaics, which has largely progressed via optimization based on “trial-and-error.” The team employs sophisticated surface characterization tools employing photoemission spectroscopy to reveal key information regarding energy band alignment and electronic band structure at device interfaces which eventually govern charge transport and hence the success of a solar cell device. An important design rule from the group, for example, is the finding that good solar cells employ a flat offset at the conduction band edges. Shining light on the interface physics and surface intermixing behaviors, the lab has suggested better alternative buffer layers for CIGS and CdTe thin film solar cells.
The success clearly highlights the crucial help fundamental surface science has to offer in developing design rules for better-performing solar cells. Smartly tackling the fundamental questions at the heart of thin film photovoltaics can help avoid the often-menial “trial-and-error”-based device optimization.