Ultra-High Efficiency, High-Concentration PV System Based On Spectral Division Between GaInP/GaInAs/Ge And BPC Silicon Cells

A novel HCPV nonimaging concentrator concept with high concentration (>500×) is presented. It uses the combination of a commercial concentration GaInP∕GaInAs∕Ge 3J cell and a concentration Back‐Point‐Contact (BPC) concentration silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cell′s reflection. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free‐form RXI‐type concentrator with a band‐pass filter embedded it, both POE and SOE performing Köhler integration to produce light homogenization. The band‐pass filter sends the IR photons in the 900–1200 nm band to the silicon cell. Computer simulations predict that four‐terminal terminal designs could achieve ∼46% added cell efficiencies using commercial 39% 3J and 26% Si cells. A first proof‐of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ∼ 100× and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J with peak efficiency of 36.9%

Structural challenges in multijunction solar cells for ultra-high CPV

The paths towards high efficiency multijunction solar cells operating inside real concentrators at ultra high concentration (>1000 suns) are described. The key addressed factors comprehend: 1) the development of an optimized tunnel junction with a high peak current density (240 A/cm2) to mitigate the non-uniform light profiles created by concentrators, 2) the inclusion of highly conductive semiconductor lateral layers to minimize the effects of the non-uniform light profiles in general, and the chromatic aberration in particular; and 3) an adequate design of reliability studies to test multijunction solar cells for real operation conditions in order to determine the fragile parts in the device and improve them. These challenges are faced by means of experimental and theoretical investigation using a quasi-3D distributed circuital model.