Grants and Contributions:

Grant or Award spanning more than one fiscal year (2017-2018 to 2020-2021).

The interest in III-V multi-junction solar cells is currently driven by space applications, but the largest potential market for these cells is certainly terrestrial. In this regard, terrestrial concentrator systems utilizing high-efficiency III-V multi-junction solar cells have been increasingly considered for large-scale generation of electrical power. However, this long-sought for integration of III-V multi-junction solar cells in large-scale consumer applications depends on the ability to establish new scalable technologies with higher efficiencies and significant material cost saving. The state-of-the-art multi-junction solar cells are grown on bulk gallium arsenide (GaAs) or germanium (Ge) substrates, which are prohibitively expensive. To circumvent these technological bottlenecks, this project aims at designing, developing, and optimizing a novel monolithic III-V multi-junction solar cells with an optimal 1eV subcell. The key strategy here is to introduce silicon-germanium-thin (SiGeSn) semiconductor in the fabrication of III-V solar cells. The proposed design consists of InGaP/InGaAs/SiGeSn/Ge junctions. The fact that SiGeSn bandgap can be tuned around 1eV while being lattice-matched to Ge will enable an optimal absorption of solar spectrum, which is central to further enhance the conversion efficiency. Moreover, the fact that high-crystalline quality SiGeSn and Ge layers can be grown on silicon wafers will also eliminate the need for bulk Ge and enable the integration of the proposed solar cells onto mechanically robust and inexpensive Si handle substrates. This is key to achieve the cost-effectiveness necessary for the development of large-scale, terrestrial applications of III-V solar cell technologies.