Belgium's Interuniversity Microelectronics Center (IMEC) reported its latest photovoltaic progress at SEMICON Europa in Munich, detailing its research in thermophotovoltaic (TPV) cells based on low-cost germanium bottom cells. As part of its SOLAR+ program, IMEC reported progress in improved open-circuit voltage, efficiency and spectral response.
TPV cells, which are optimized to convert radiation from heat sources at lower temperature than the sun, require materials with a lower bandgap than silicon, which is commonly used for solar cells. Germanium (Ge) is suited for PTV applications because of its low bandgap, but problems related to proper surface passivation have hindered the development of commercially successful Ge-based TPV cells. The significantly lower cost of germanium as compared to the low-bandgap III-V alternatives motivated IMEC to tackle the issues related to using Ge in TPV applications in collaboration with Umicore, the leading manufacturer of germanium wafers.
IMEC combined improved surface passivation and novel contacting technologies, which led recently to Ge cells with an open-circuit voltage over 270mV, an AM1.5 efficiency near 8% and a broad spectral response from 400 to 1700nm. These values exceed significantly the figures reported under the given illumination conditions.
Jef Poortmans, director of the SOLAR+ program at IMEC comments:"The process does not only result in thermophotovoltaic cells with very promising performance, but it is also based on process steps which are to a large extent compatible with silicon solar cell processing. In fact, the fast progress we made over the recent period resulted largely from the synergies with our silicon solar cell expertise. The next step in IMEC's development aims at adapting the cell for higher intensities and checking its performance stability and eventually integrating it in a demonstration system."
