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FOTON-OHM UMR CNRS 6082            





The aim of the ANR MENHIRS project (2011-PRGE-007-01) is to provide low-cost and high efficiency tandem cells grown on crystalline silicon (c- Si) substrates, with merging both the monocrystalline Si approach with the high-efficiency monocrystalline multijunction approach based on III-V materials. These CPV cells will be used under natural lighting and under low light concentrators (100 suns) developed by IRDEP-CNRS, and benchmarked under medium concentration by Heliotrop sas.

The PV cells efficiency is one of the most important parameters for the final cost of electricity, since it impacts directly the ratio between produced energy and production cost. With 22% efficiency modules based on c-Si, the technology seems to reach its limits. To increase further the efficiency of c-Si cells and modules, going to multijunction devices (association of two different absorbing layers in the same cell) seems to be the obvious choice. While many projects tend to focus on all silicon technology, best high bandgap cells are yet based on III-V compounds. This project proposes to demonstrate the proof-of-concept for a monolithic integration of high efficiency multijunction CPV device on a low cost monocrystalline silicon substrate upon which a III-V lattice-matched material will be grown using molecular beam Epitaxy (MBE). This Lattice-Matched heterostructure with its very low structural defect densities (Dislocations, AntiPhase Domains, point defects) will be capable of sustaining III-V high performing PV devices onto silicon with long life-time. This
novel route overcomes the problems of high cost substrates (as compared to Ge or III-V substrates used currently for this kind of CPV), the killer structural defect formation and reliability issues of lattice mismatched systems (metamorphic approach) and the low reliability and low lifetime of hybrid techniques
(such as wafer bonding). The integration of photovoltaic functions onto a single silicon substrate will also achieve a reduction in the use of III-V based semiconducting materials in high-efficiency multijunction CPVs.

contact : olivier.durand@insa-rennes.fr

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