Predicted Performance of High-Efficiency Photovoltaics with Energy-Selective Front Reflectors for Photon Recycling Enhancements

Energy-selective mirrors that reflect photons below a specific energy, e.g. radiatively emitted photons from the cell at the cell bandgap, back towards the solar cell enhance solar cell efficiencies via photon recycling by generating higher open-circuit voltages. The internal front reflectors are designed to admit sunlight for photogeneration at all energies above a given threshold energy above the bandgap energy, while remaining highly reflective for energies at or near the solar cell bandgap. Predicted cell performance is modeled using detailed balance and semi-empirical methods to determine optimal reflector energies for maximum cell efficiency enhancements and effects non-radiative recombination on efficiency. Improved open circuit voltages are predicted at the highest front reflectance values with energies 0.25 eV above that of the cell bandgap. For Si cells, increases of up to 2% in maximum cell efficiency corresponding to V_oc increase of 0.2 V can be achieved in single-junction solar cells approaching 33% when combined with appropriate front reflector architectures such as Bragg reflectors or dielectric stacks that restrict black body emission. For GaAs cells, up to 9% can be gained with angle emission restriction.