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Improving the efficiency of intermediate band quantum dot solar cells

Conventional single junction (e.g. silica GaAs) solar cells absorb photons only from a limited range of spectra (i.e. above the band-gap photons) missing almost 60% of the energy that can potentially be obtained from the entire solar spectrum. Intermediate band (IB) solar cells with Quantum Dots (QD) tuned to absorb photons from a wider range of wavelengths offer a solution to this problem. However the current models for IB solar cells come with disadvantages of current leakage low efficiency and low open circuit voltage. The inventors have overcome these limitations by developing a new model for a Gallium Arsenide (GaAs) based IB solar cell where the QDs are placed outside the depletion region enabling the capture of photons from a wider range of spectra (including sub-band-gap photons) and raising the efficiency of energy conversion from 28% to 42%. Current leakage is associated with recombination of charge carriers inside of QDs . The inventors have developed a novel strategy to avoid this problem by eliminating recombination in QDs and consequent current leakage. The solar cell is composed of three layers. The bottom layer is an n-doped GaAs substrate layer; covered by a second thin p-doped buffer layer which is finally topped by an absorber stack-layer. QDs enable additive adsorption of two lower energy (sub-band-gap) photons resulting in generation of additional photocurrent. The invention provides an excellent approach to solve the pressing problem of manufacturing high efficiency solar cells. The theoretical calculations show that the under a 500-sun concentration the efficiency limit of the Gallium Arsenide (GaAs) based solar cell described here can be as high as 50%. The researchers are currently investigating how to optimize the process for manufacture of the solar cells.

Benefits:

1) Convert energy from a wide range of the solar spectrum into electrical energy 2) Quantum dot absorber spatially separated from the depletion region 3) No leakage current generated

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