Dr. Gerald Siefer has joined the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany as an assistant student in 1997. Since then, his work is focused on the characterization and calibration of photovoltaic devices. He finished his Ph.D. on the topic of "Analysis of the performance of multi-junction cells under realistic operating conditions" in 2008. Since 2009 he is leading the team III-V cell and module characterization. His team is working on calibration techniques for multi-junction solar cells with up to 6 p-n junctions for space and terrestrial concentrator applications and the indoor and outdoor characterization of concentrator modules. He has been participating as a member of the scientific committees of several international PV conferences. Dr. Gerald Siefer is an active member of the IEC working group 7 on developing international standards related to CPV.