Conversion efficiency of broad-band sunlight in single-junction photovoltaics (PV's) is limited due to heat dissipation to less than 32%. Overcoming this requires inventive techniques, where their viability is compared to cheap and abundant silicon photovoltaics on one hand; or the efficient and costly multi-junction cells on the other.
The recently proposed Thermally Enhanced Photoluminescence (TEPL) conversion device may take the place in-between, and potentially present high conversion efficiencies – with a single-junction solar cell. A PV cell is placed adjacent to a thermally insulated photo-luminescent (PL) absorber. The absorber is excited and heated by concentrated sun-light, consequently radiating blue-shifted PL emission toward the PV cell, resulting in higher conversion efficiencies compared to direct illumination or Thermal-PV at similar temperature. Spectral measurements based calculations show that efficiencies over 46% may be reached using a GaAs PV, and absorber working temperatures below 1500°C.
TEPL prototype faces two major design challenges: absorber material, and photon management. Broad absorption, together with high PL external quantum efficiency (EQE), must be maintained at high temperatures. Here we demonstrate our achievements toward a TEPL converter. Using Cr, Ce & Nd, co-doped in YAG, we reach over 85% EQE with full absorption of sunlight up to 1.1µm. For photon recycling, paramount to maintain high chemical potential of the solar radiation, highly reflective surfaced and dichroic mirrors surround the absorber; reflecting photons not used by the PV cell to be reabsorbed in the absorber. We demonstrate a TEPL conversion device predicted to support conversion efficiencies over 15% under these conditions.