Single-crystal II-VI on Si single-junction and tandem solar cells

CdTe is one of the leading materials used in solar photovoltaics. However, the maximum reported CdTe cell efficiencies are considerably lower than the theoretically expected efficiencies for the ∼1.48 eV CdTe band gap. We report a class of single crystal CdTe-based solar cells grown epitaxially on crystalline Si that show promise for enhancing the efficiency and greatly lowering the cost per watt of single-junction and multijunction solar cells. The current-voltage results for our CdZnTe on Si solar cells show open-circuit voltages significantly higher than previously reported for any II-VI cells and as close to the thermodynamic limit as the best III-V-based cells.