Patent Application
20120145243
This invention relates to up-conversion in solar cells and more particularly, to magnetically enhanced up-conversion.
At the present time, solar cells are primarily silicon devices because of the maturity of the silicon processing art and the fact that silicon is one of the least expensive and most abundant materials available. Further, silicon based solar cells can be easily and inexpensively integrated into silicon circuits for collection and other functions. However, it is well known in the solar cell art that most silicon solar cells are able to convert only a portion of solar energy into electricity. This is primarily due to the fact that the spectral range of Si photodiodes is confined to a wavelength range of between 200 nm and approximately 1200 nm.
In attempts to overcome the conversion drawbacks of silicon solar cells, some spectral conversion materials have been developed that absorb solar energy and reemit it in a different spectral range. Most of these spectral conversion materials provide “up-conversion” phenomena, which is the absorption of higher spectral range energy and the reemission at a lower spectral range. Thus, up-conversion materials absorb spectral energy above 1200 nm (generally around 1500 nm) and reemit it at, for example, 980 nm. Up-conversion material may be placed in proximity to the back surface of the solar cell on the front surface of the solar cell or even in some combination of the two.
Additional information on up-conversion and down-conversion materials can be found in a copending United States Patent application entitled “Photovoltaic up conversion and down conversion using rare earths”, Ser. No. 12/408,297, filed Mar. 20, 2009, (also U.S. Publication 2010/0038521) and incorporated herein by reference.
Rare earth materials are poor absorbers which has been an impediment to the adoption of rare earth up-conversion technology. Absorption by a rare earth material comes with two problems: there is both a low absorption cross section and a spectrally narrow absorption range. Thus, in some solar cells a layer of material including silicon and a blend of sensitizers is deposited so as to operate in conjunction with up-conversion materials.
Sensitizers are a material with broad absorption spectrum, e.g. from 1100 nm to 1500 nm, that can be designed to emit at approximately 1530 nm. This emission is then absorbed by the rare earth up-conversion material (e.g. Er) and up-converted to wavelengths that can be absorbed by the silicon solar cell. Additional information about sensitizers, including examples, can be found in an article entitled “Broadband sensitizers for erbium-doped planar optical amplifiers:review” by A. Polman and F. Veggel, Vol. 21, No. May 5, 2004/ J. Opt. Soc. Am. B., 871-892 and an article by J. F. Suyer et al., Optical Materials, 27 (2005), 1111-1130.
While up-conversion and sensitizers add some power and spectral conversion components to the basic amount of solar energy that silicon solar cells are able to convert, there is still only a portion of solar energy converted into electricity.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
An object of the present invention is to provide magnetic enhancement of up-conversion components to improve solar cell operation. Another object of the present invention is to provide a solar cell with magnetically enhanced up-conversion material and/or sensitizers (i.e. up-conversion components) for more efficient conversion of solar energy.
Another object of the present invention is to provide a new and improved method of magnetically enhancing up-conversion components for more efficient conversion of solar energy.
Briefly, to achieve the desired objects and aspects of the instant invention in accordance with a preferred embodiment thereof provided is a solar cell with magnetically enhanced up-conversion components. The solar cell is formed of semiconductor material and includes up-conversion components. Magnetic apparatus is positioned adjacent the back surface of the solar cell to supply a magnetic field to at least the up-conversion components. The magnetic field has an intensity and direction selected to enhance operation of the up-conversion components. Preferably the selected intensity and direction of the magnetic field is determined by trial and error.
The desired objects and aspects of the instant invention are further achieved in accordance with a preferred method of magnetically enhancing up-conversion components. The method includes providing at least one of up-conversion material and sensitizer material (i.e. up-conversion components), generally in conjunction with a semiconductor solar cell, and positioning magnetic apparatus adjacent the up-conversion components to supply a magnetic field to the up-conversion components. The magnetic field has an intensity and direction selected to enhance operation of the up-conversion components.
Specific objects and advantages of the instant invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings, in which:
Turning now to the drawings, attention is first directed to
This problem can be ameliorated somewhat by including spectral conversion materials in the silicon solar cells. Spectral conversion materials have been developed that absorb solar energy and reemit it in a different spectral range. Most of these spectral conversion materials provide “up-conversion” phenomena, which is the absorption of higher spectral range energy and the reemission at a lower spectral range. Thus, up-conversion materials absorb spectral energy above 1200 nm (generally around 1500 nm) and reemit it at, for example, 980 nm. The up-conversion phenomenon is used as an example in the present invention description because it is the most commonly used material and is believed to be the most useful in the conversion of solar energy.
Referring additionally to
It is understood that in the excited state up-conversion, 2 long wavelength photons are absorbed and one short wavelength photon is emitted. For example, in erbium two ˜1530 nm photons are absorbed and one ˜980 nm photon is emitted. The up-conversion process depends upon the hyperfine structure of the ions forming the up-conversion material. Referring additionally to
Turning now to
The electrical signal from solar cell 20 was measured as a function of wavelength, both with and without the presence of the magnet, i.e. the magnetic field. The up-conversion effect of the applied magnetic field is illustrated in
It was also found that the magnitude and direction of the magnetic field relative to the crystal orientation of the up-conversion material is important. As illustrated in
As illustrated in
Referring to
If it is determined that some cooling would further enhance the operation of the solar cell an arrangement such as that illustrated in
It should be understood that a variety of silicon solar cells including up-conversion material and/or sensitizers (both defined herein generically as up-conversion components) can be provided in the disclosed method and apparatus. In some solar cells a layer of material, generally including silicon and a blend of sensitizers, is deposited so as to operate in conjunction with up-conversion material. Sensitizers are a material with broad absorption spectrum, e.g. from 1100 nm to 1500 nm, that can be designed to emit at approximately 1530 nm. This emission is then absorbed by the rare earth up-conversion material (e.g. Er) and up-converted to wavelengths that can be absorbed by the silicon solar cell. Referring to
Thus, magnetic enhancement of up-conversion components to improve solar cell operation is disclosed. A purpose of the invention is to provide magnetic enhancement of up-conversion components to improve solar cell operation. Another purpose of the present invention is to provide a solar cell with magnetically enhanced up-conversion components for more efficient conversion of solar energy. A further purpose of the present invention is to provide a new and improved method of magnetically enhancing up-conversion components for more efficient conversion of solar energy. A solar cell with magnetically enhanced spectral conversion is more efficient at converting solar energy to absorb a broader spectrum of the incident light. Also, the magnetically enhanced spectral conversion is relatively easy and inexpensive to fabricate.
Various changes and modifications to the embodiments herein chosen for purposes of illustration will readily occur to those skilled in the art. To the extent that such modifications and variations do not depart from the spirit of the invention, they are intended to be included within the scope thereof, which is assessed only by a fair interpretation of the following claims.
