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III-V Multi-Junction Solar Cells Utilising Group IV SiGeSn Alloys as a 1.0 eV Component Sub-Cell
P. Pearce, T. Wilson, A.D. Johnson, N.J. Ekins-Daukes
Multijunction Solar Cell, Spectroscopy, Optical Properties
Concentrator and Space Photovoltaics
Subtopic: III-V-Based Devices for Terrestrial and Space Applications
Event: 33rd European Photovoltaic Solar Energy Conference and Exhibition
Session: 4CV.4.5
1248 - 1252
ISBN: 3-936338-47-7
Paper DOI: 10.4229/EUPVSEC20172017-4CV.4.5
0,00 EUR
Document(s): paper, poster


Four-junction solar cells can theoretically achieve over 50% efficiency under 1 sun. Optimally efficient four-junction (4J) solar cells require a sub-cell with a bandgap close to 1 eV. Current high-efficiency 4J devices use lattice-mismatched sub-cells to achieve an optimal combination of bandgaps, complicating the fabrication process; thus, novel materials which can achieve a 1 eV bandgap while remaining lattice-matched to Ge are required. Group IV alloy SiGeSn is a promising material system, with functional devices having already been demonstrated. However, further investigation of the fundamental properties of relevant SiGeSn compositions is key to fabricating an efficient 4J device. We present optical measurements (spectroscopic ellipsometry and steady-state photoluminescence) and device characterization of single and triple-junction devices containing SiGeSn sub-cells. Results indicate the desired blueshift of the lowest indirect and direct energy transitions in SiGeSn relative to Ge with the addition of Si and Sn in a composition ratio around 4 to 1. Device measurements indicate good EQE performance in both devices, while the open-circuit voltage is lower than expected based on absorption around 1 eV, indicating the lower indirect edge in SiGeSn limits the voltage.