Prof Christophe BALLIF

Prof Christophe BALLIF

PV-Center within CSEM, Neuchâtel

Application of silicon solar cells with passivated contacts in high-efficiency tandem solar cells

In this presentation, we will first discuss the requirements for making efficient two- and four-terminal devices based on silicon bottom cells. C-Si solar cells with passivated contacts (such as a-Si/c-Si heterojunctions or with tunnel oxides interfaces) are shown to be ideal for such applications. We will comment first on devices based on III-V on Si [1], showing how the 30%, 1 sun, benchmark should be overcome with suitable devices. In the second part of the presentation, we will focus on the combination of perovskite on silicon in various configurations with potential for low production cost. We will show that perovskite cells with strong transparency in the near infrared can be designed for integration into both tandem and four-terminal devices. Whereas 2-terminal devices reach close to 22% efficiency, 4-terminal measurements of tandems with small-size perovskite top cells demonstrate 25.6% efficiency, measured at maximum point for several minutes [2,3 and next]. We finally discuss the limitations and possible industrial implementations of the various approaches.


Christophe Ballif received his  Ph.D. degree in physics in 1998 in Lausanne, Switzerland. After Stays at NREL, Fraunhofer ISE and EMPA, he became in 2004 Full Professor with the Institute of microengineering, University of Neuchâtel, Switzerland, directing the Photovoltaics and Thin-Film Electronics Laboratory.  In 2009, the Institute became part of EPFL. Since 2013, he has also been the Director of the PV-Center within CSEM, Neuchâtel, an RTO specialized in industrial research and technology transfer. His research interests include materials for PV, high-efficiency c-Si solar cells and silicon heterojunction cells, multi-junction solar cells, module technology, BIPV, and Energy systems. Christophe Ballif is the laureate of the 2016 Becquerel Prize.