High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrator Application

The High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrators project seeks to provide new photovoltaic cells for Concentrator Photovoltaics (CPV) Systems with higher cell efficiency, more favorable temperature coefficients and less sensitivity to changes in spectral distribution. Our theoretical estimate predicts that a triple junction cell with an improved middle cell current could have an efficiency exceeding 38% (one sun) and higher under concentration. The main objective of this project is to provide high efficiency III-V solar cells that will reduce the overall cost per Watt for power generation using CPV systems.

The objectives of this project will be accomplished by combining state-of-the-art solar cell design and fabrication with new functionality afforded by nanostructured materials.  The driving force behind the nanomaterials approach centers around the fact that the electrical, optical, and even thermal properties of these materials can be controlled by use of particles with dimensions in the nanometer range.  Quantum dots (QDs) and quantum wells (QWs) serve as potential wells for electrons (or holes) with dimensions on the order of a few nanometers resulting in quantized discrete energy levels for electrons and holes.  Insertion of these types of structures into a solar cell can result in increased adsorption of long-wavelength light. 

The current SOA in III-V photovoltaics is the lattice-matched triple junction solar cell.  We are proposing to use apply the nanostrucuted material concepts for near-term relative efficiency, spectral and thermal property enhancements of standard multi-junction III-V solar cells.   Specifically, the lowering of the effective bandgap of the GaAs middle cell in a lattice-matched triple junction can be achieved through the incorporation of an InAs quantum dot array into the depletion region of an GaAs cell.  The InAs quantum dots in the GaAs cell will provide sub-gap absorption and thus improve the short-circuit current of this junction. This cell could then be integrated into the three-cell stack to achieve a CPV cell whose efficiency exceeds the current SOA (>40%).    In addition, the use of quantum nanostructures may also hold ancillary benefits such as improved temperature coefficients and less spectral sensitivity to variable atmospheric conditions.

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