WO2008132445A2 - Solar cell - Google Patents

Solar cell Download PDF

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Publication number
WO2008132445A2
WO2008132445A2 PCT/GB2008/001436 GB2008001436W WO2008132445A2 WO 2008132445 A2 WO2008132445 A2 WO 2008132445A2 GB 2008001436 W GB2008001436 W GB 2008001436W WO 2008132445 A2 WO2008132445 A2 WO 2008132445A2
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WO
WIPO (PCT)
Prior art keywords
previous
thermovoltaic
electromagnetic radiation
current
photovoltaic
Prior art date
Application number
PCT/GB2008/001436
Other languages
French (fr)
Other versions
WO2008132445A3 (en
Inventor
Mazhar Ali Bari
Original Assignee
Science Technology Research Partners Limited
Sands, Howard, Simon
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Science Technology Research Partners Limited, Sands, Howard, Simon filed Critical Science Technology Research Partners Limited
Priority to EP08737091A priority Critical patent/EP2150990A2/en
Publication of WO2008132445A2 publication Critical patent/WO2008132445A2/en
Publication of WO2008132445A3 publication Critical patent/WO2008132445A3/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/052—Cooling means directly associated or integrated with the PV cell, e.g. integrated Peltier elements for active cooling or heat sinks directly associated with the PV cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/052—Cooling means directly associated or integrated with the PV cell, e.g. integrated Peltier elements for active cooling or heat sinks directly associated with the PV cells
    • H01L31/0521—Cooling means directly associated or integrated with the PV cell, e.g. integrated Peltier elements for active cooling or heat sinks directly associated with the PV cells using a gaseous or a liquid coolant, e.g. air flow ventilation, water circulation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S10/00—PV power plants; Combinations of PV energy systems with other systems for the generation of electric power
    • H02S10/10—PV power plants; Combinations of PV energy systems with other systems for the generation of electric power including a supplementary source of electric power, e.g. hybrid diesel-PV energy systems
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/10—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects
    • H10N10/13—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects characterised by the heat-exchanging means at the junction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to a solar cell for generating electricity.
  • Solar cells are used to convert solar radiation into electrical energy.
  • the solar spectrum can be approximated to a satisfactory degree by a black-body spectrum with a corresponding temperature of about 6500 K as shown in figure 1.
  • Absorption and scattering by the ozone and water vapour in the Earth's atmosphere leads to substantial decreases in the ultra violet (UV) and infrared (IR) parts of the spectrum reaching sea level .
  • UV ultra violet
  • IR infrared
  • PV cells are typically at best 20% to 25% efficient (with respect to the total amount of available energy) but this may decrease as the operating temperature of the PV cell increases.
  • PV elements typically utilise the visible and near-UV spectrum dependent on the particular material used in their construction. However, this part of the spectrum comprises only about 43% of the energy present in the entire solar spectrum shown in figure 1. Roughly 49% of the solar spectrum is made up from the near infrared (NIR) region for which PV elements are not generally optimised. The effect of NIR and IR radiation on a PV element that cannot use these wavelengths is usually to simply heat it up, which further reduces electrical conversion efficiency as PV elements are more efficient at cooler temperatures.
  • Thermovoltaic (TV) elements also known as thermoelectric or Seebeck elements) use a temperature gradient to generate a current. Solar radiation may be used to develop this temperature gradient. However, TV elements are not very efficient when low temperature gradients are used.
  • PV element i.e. cool enough to maintain a useable efficiency
  • an apparatus for converting electromagnetic radiation into an electrical current comprises a photovoltaic element and a thermovoltaic element arranged to absorb a portion of the incident radiation before the incident radiation reaches the photovoltaic element.
  • the PV element utilises predominantly the visible and near-UV band of the incident radiation and the TV element utilises predominantly the IR and NIR region with the added benefit that because the IR and NIR wavelengths may be effectively filtered from the incident radiation before reaching the PV element, the PV element may be kept cooler (and therefore run more efficiently) than if it were exposed directly to the full wavelength range.
  • the TV element hot junction side can be kept at a much higher temperature without affecting the efficiency of the PV element. This also improves thermal management of the apparatus.
  • thermovoltaic element may be separated from the photovoltaic element. This further keeps the PV element cooler.
  • thermovoltaic element may comprise a hot junction.
  • thermovoltaic element may further comprise a cold junction.
  • thermovoltaic element may further comprise a heat sink for cooling the cold junction.
  • the heat sink or heat radiator enables a higher temperature gradient by keeping the cold junction closer to ambient temperature .
  • thermovoltaic element may further comprise an infrared absorber. This further increases the temperature of the TV element and further filters out IR and
  • the infrared absorber may be selected from the group consisting of CuY 1 - X Ca x O 2 , Al x O, LiNbO 3 ,
  • thermovoltaic element may be substantially transparent in the visual and/or UV wavelength regions. This allows more of the shorter wavelengths (or higher energies) to reach the PV element.
  • thermovoltaic element may further comprise one or more substantially transparent electrodes.
  • the electrodes may be transparent at least in the visible and/or UV wavelength range so that they do not block useful radiation from reaching the PV element.
  • the one or more substantially transparent electrodes may be indium tin oxide (ITO) .
  • ITO is a suitable transparent conductor but other transparent conductors may be used within the TV or PV elements to provide electrical contacts.
  • Transparent electrodes may be applied across the face of layers in the solar cell rather than around the periphery leading to a simpler construction.
  • the solar cell may further comprise a thermal insulating layer between the thermovoltaic element and the photovoltaic element.
  • the thermal insulating layer may be a vacuum or an airgap.
  • the photovoltaic element may further comprise a heat sink. This heat sink or heat radiator may be used to further cool the PV element.
  • the solar cell may further comprise a protective layer. This protective layer may be used to protect the solar cell from environmental damage or other physical damage.
  • the protective layer may be a transparent or semi-transparent material such as glass or a plastics material and may also be coloured or otherwise filter out particular wavelengths.
  • the solar cell may further comprise an insulating layer between the protective layer and the thermovoltaic layer.
  • the first current may be arranged in parallel or in series with the second current.
  • a higher output current may be achieved and in series a higher voltage may be achieved.
  • the thermovoltaic element comprises a p-n junction.
  • the PV element may also comprise one or more p-n junctions .
  • thermovoltaic element may comprise an array of quantum dots, nanowires and/or quantum wells. These structures may combine the required semiconductor properties and IR absorption.
  • the apparatus may be a solar cell.
  • the photovoltaic element may comprise one or more materials selected from the group consisting of: single-crystalline silicon, poly-crystalline silicon, thin film silicon, amorphous silicon, gallium arsenide, ceramic- based semiconductors, polymeric materials, polymeric hybrid materials, organic material, carbon nanotubes, graphite, Highly ordered pyrolytic graphite, HOPG, graphene and carbon nanofibers and inorganic material.
  • the complete apparatus may be made flexible as well making it suitable for many "building integrated photovoltaic" (BIPV) applications.
  • the portion of the incident radiation absorbed by the thermovoltaic element has a longer wavelength than a substantial part of the incident radiation not absorbed. At least some of the higher wavelengths may be filtered out by the TV element.
  • thermovoltaic element generating a first current such that a portion of the electromagnetic radiation is absorbed by the thermovoltaic element; and directing the remainder of the flux of electromagnetic radiation on to a photovoltaic element generating a second current.
  • the portion of the electromagnetic radiation absorbed by the thermovoltaic element has a longer wavelength than a substantial part of the electromagnetic radiation not absorbed. The portion that is not absorbed may then be absorbed by the photovoltaic element to generated the second current.
  • the photovoltaic element may be maintained at a lower temperature than the thermovoltaic element .
  • Various techniques to maintain this temperature difference may be used including for instance, insulation and direct cooling.
  • the electromagnetic radiation may be solar radiation.
  • other sources of electromagnetic radiation may be utilised.
  • an electrical distribution system comprising the apparatus described above together with any one or more of: temperature sensor or sensors, a thermal control system and an electrical storage system.
  • FIG. 1 shows a graph of an approximated solar spectrum
  • FIG. 2 shows a schematic diagram of a cross section through a solar cell according an embodiment of the present invention, given by way of example only.
  • FIG. 2 shows a solar cell 10 according to one embodiment.
  • the solar cell 10 is formed as a stacked arrangement and shall now be described layerwise starting with the first layer that is encountered by incident solar radiation falling on the solar cell 10 from above (as shown in figure 2), in use.
  • a transparent protective cover 30 is formed over the surface of the solar cell 10.
  • the next layer is a vacuum layer 40, which provides thermal insulation between the transparent protective cover 30 and the electrically active components beneath. Vacuum seals (not shown in figure 2) are used to maintain the vacuum.
  • Under the vacuum layer 40 is a thermovoltaic (TV) element comprising a p-type semiconductor layer 50, an n- type semiconductor layer 60 and a single crystalline substrate 70.
  • TV thermovoltaic
  • the TV element is preferably transparent to the visible, near-UV and/or UV portion of the solar spectrum.
  • the interface between the p-type and n-type semiconductor layers acts as a hot junction 55 of the TV element.
  • the interface between the n-type semiconductor layer 60 and the single crystalline substrate 70 acts as a cold junction 65 of the TV element.
  • the p- type semiconductor layer 50 may be dyed with an IR absorber such as for instance: organic dyes, this may include but not limited to Solvent Soluble Near Infrared Dyes, Water Soluble Near
  • This IR absorber may coat the p-type (or n-type) semiconductor layer 50 or be incorporated throughout it.
  • Each element of the TV layer may preferably be manufactured from a semiconductor material that is substantially transparent at least to visible or near-UV radiation. Suitable transparent materials include n-ZnO, p- CuAlO, CuYi- X Ca x O 2 , YZn 1 - X Al x O, LiNbO 3 , Ga 2 O 3 , CuInTe 2 or CuInGaSe 2 but others may be used.
  • the single crystalline substrate 70 is kept cold by a heat sink 80 (or heat radiator) .
  • the heat sink 80 extends sideways beyond the solar cell 10 stack and may be bonded to the single crystalline substrate 70 by In solder 90, or any other method that provides high thermal conductivity of the joint.
  • a second vacuum layer 100 provides additional optional thermal insulation between the TV element and a photovoltaic (PV) element below.
  • PV photovoltaic
  • vacuum seals may be used to maintain the vacuum.
  • the PV element may be of any suitable type and may preferably be efficient when exposed to the visible, near-UV and/or UV wavelengths of incident solar radiation.
  • Semiconductor p-type layer 110 and n-type layer 120 form the PV element and operate in a way known in the art of PV cells.
  • the lower layer 120 of the PV element may optionally be kept cool by a further heat sink 130 or heat radiator.
  • the heat sink 103 may extend across the entire back surface of the solar cell 10 as this layer does not need to be transparent.
  • the PV element may be bonded to heat sink 130 in any suitable way such as, for instance, by In soldering or bonded with high thermal conductivity resin. From the point of view of electrical efficiency the two elements (TV and PV) represent two different voltage/current sources. They can thus have different source parameters, namely open-loop voltages, short-circuit currents and internal resistances among others.
  • Several solar cells 10 may be connected together in a battery arrangement in order to increase the source voltage and/or current .
  • the solar cell 10 may be used to generate electricity where an efficient source of power is required.
  • Space vehicle and satellite applications particularly benefit from the combined high efficiency nature of the device and its high power to weight or size ratio. In space applications a requirement of maintaining sealed vacuum chambers may also be removed leading to further weight reductions. Other vehicle or portable device applications may also benefit from this device.
  • the TV and PV elements may be of any suitable type.
  • the TV element layers do not necessarily have to be semiconductors.
  • Metals, oxides, conductive polymers, organic materials and/or other conductors may be used.
  • the hot junction should preferably be at the top (as shown in figure 2) , i.e. towards the incident solar radiation, and the cold junction at the bottom. Placing the cold junction between the hot junction and PV element has a benefit of reducing the effect of radiation heating the PV element, which may unnecessarily occur if the hot junction is facing or adjacent the PV element .
  • the TV and PV elements may abut without any insulation or separation.
  • the TV element may instead be formed from a single oxide layer. Areas of different type (p for n-type substrate and n for p-type substrate) may be formed by, but not exclusively, with the help of diffusion, ion beam implantation.
  • a TV element may be located on the backside of the solar cell .
  • the TV element may comprise one or more thermoelectric devices, such as thermoelectric modules for example.
  • thermoelectric devices such as thermoelectric modules for example.
  • suitable thermoelectric devices may comprise thermoelectric materials such as filled skutterdites, chlathrate structured compounds, fine grain sized thermoelectric materials, and film shaped thermoelectric materials, ZnO, Carbon nanotube composites, for example.
  • the thermoelectric devices may comprise single stage devices, or multistage cascade structures, for example.
  • the thermoelectric devices may also comprise thin-film thermoelectric materials, or may be thermoelectric devices comprising organic or polymer thermoelectric materials.
  • the PV element may comprise one or more photovoltaic devices. Any suitable type of photovoltaic device may be used, and suitable photovoltaic devices may comprise materials such as conventional crystalline silicon, thin film silicon, amorphous silicon, gallium arsenide and other semiconductor materials. Suitable photovoltaic devices also include single junction or multi-junction solar cells, and dye-doped solar cells based on titanium dioxide using any carbon based materials such as, but not restricted, to carbon nanotubes, graphite, Highly ordered pyrolytic graphite (HOPG), graphene and carbon nanofibers. Suitable photovoltaic devices also include photovoltaic materials such as ceramic-based semiconductors, polymeric or polymeric hybrid materials.
  • the photovoltaic devices may also include optics such as concentrator lenses and mirrors, antireflective coatings, textured cell surfaces, metamaterials and back reflectors.
  • optics such as concentrator lenses and mirrors, antireflective coatings, textured cell surfaces, metamaterials and back reflectors.
  • the PV and TV elements may be manufactured by a variety of methods including vacuum deposition, screen printing and spaying onto a substrate, for example.
  • the PV and/or TV elements may be formed from inorganic (e.g. Si, Ge or AlGas) or organic (e.g. polyaniline, tetrathiotetracene (TTT) iodides) materials.
  • inorganic e.g. Si, Ge or AlGas
  • organic e.g. polyaniline, tetrathiotetracene (TTT) iodides
  • the PV and TV elements may be formed as separate or a single layer.
  • the origin of electromagnetic radiation is not restricted to the sun but other emitters of electromagnetic radiation such as thermal emitters and atomic batteries, for example.
  • the wavelength of the electromagnetic radiation is not limited to the visible spectrum but may for instance extend into the ultraviolet or infrared spectrum.

Abstract

Apparatus (10) and method for converting electromagnetic radiation into an electrical current, whereby a photovoltaic element generates a first current from incident radiation (20), and a thermovoltaic element generates a second current and absorbs a portion of the incident radiation (20) before the incident radiation (20) reaches the photovoltaic element.

Description

SOLAR CELL
Field of the Invention
The present invention relates to a solar cell for generating electricity.
Background of the Invention
Solar cells are used to convert solar radiation into electrical energy. The solar spectrum can be approximated to a satisfactory degree by a black-body spectrum with a corresponding temperature of about 6500 K as shown in figure 1. Absorption and scattering by the ozone and water vapour in the Earth's atmosphere leads to substantial decreases in the ultra violet (UV) and infrared (IR) parts of the spectrum reaching sea level .
Conventional semiconductor photovoltaic (PV) cells are typically at best 20% to 25% efficient (with respect to the total amount of available energy) but this may decrease as the operating temperature of the PV cell increases. PV elements typically utilise the visible and near-UV spectrum dependent on the particular material used in their construction. However, this part of the spectrum comprises only about 43% of the energy present in the entire solar spectrum shown in figure 1. Roughly 49% of the solar spectrum is made up from the near infrared (NIR) region for which PV elements are not generally optimised. The effect of NIR and IR radiation on a PV element that cannot use these wavelengths is usually to simply heat it up, which further reduces electrical conversion efficiency as PV elements are more efficient at cooler temperatures. Thermovoltaic (TV) elements (also known as thermoelectric or Seebeck elements) use a temperature gradient to generate a current. Solar radiation may be used to develop this temperature gradient. However, TV elements are not very efficient when low temperature gradients are used.
"Thermoelectrics : Direct Solar Thermal Energy Conversion" Terry M. Tritt, Harald Bόttner, and Lidong Chen; MRS BULLETIN VOLUME 33, pp. 366-368, APRIL 2008 (http: //www. mrs.org/s_mrs/bin.asp?CID=12527&DID=20864IS-DOC=F ILE. PDF), at figure 2 also shows the proportion and wavelengths of solar radiation suitable for conventional photovoltaic and thermovoltaic conversion into electrical current . WO88/02556 describes a combined photovoltaic-thermo electric solar cell. A thermal gradient is maintained across a semiconductor p/n junction so that contributions from both the photovoltaic and thermovoltaic effects are achieved. However, the device may only be operated at a single temperature which must be low enough to support the
PV element, i.e. cool enough to maintain a useable efficiency, see for example Wysocki and Rappaport, J". Appl . Phys. 31 (1960) , pp. 571-578, who show the profound drop of efficiency of PV elements based on Si with increasing temperature (the efficiency drops to essentially zero above 250 0C) ; but high enough to achieve a sufficient thermo electric effect, which conversely requires a high temperature gradient. These opposing requirements result in a compromise temperature providing a low efficiency for both PV and TV electric conversion.
Therefore, there is required a solar cell that more efficiently utilises the available solar radiation. Summary of the Invention
In accordance with a first aspect of the present invention there is provided an apparatus for converting electromagnetic radiation into an electrical current , the apparatus comprises a photovoltaic element and a thermovoltaic element arranged to absorb a portion of the incident radiation before the incident radiation reaches the photovoltaic element. The PV element utilises predominantly the visible and near-UV band of the incident radiation and the TV element utilises predominantly the IR and NIR region with the added benefit that because the IR and NIR wavelengths may be effectively filtered from the incident radiation before reaching the PV element, the PV element may be kept cooler (and therefore run more efficiently) than if it were exposed directly to the full wavelength range. Moreover, the TV element hot junction side can be kept at a much higher temperature without affecting the efficiency of the PV element. This also improves thermal management of the apparatus.
Optionally, the thermovoltaic element may be separated from the photovoltaic element. This further keeps the PV element cooler. Preferably, the thermovoltaic element may comprise a hot junction.
Preferably, the thermovoltaic element may further comprise a cold junction.
Optionally, the thermovoltaic element may further comprise a heat sink for cooling the cold junction. The heat sink or heat radiator enables a higher temperature gradient by keeping the cold junction closer to ambient temperature . Advantageously, the thermovoltaic element may further comprise an infrared absorber. This further increases the temperature of the TV element and further filters out IR and
NIR before reaching the PV element. Optionally, the infrared absorber may be selected from the group consisting of CuY1-XCaxO2,
Figure imgf000005_0001
AlxO, LiNbO3,
Ga2O3, CuInTe2 and CuInGaSe2 although other suitable materials may be used.
Preferably, the thermovoltaic element may be substantially transparent in the visual and/or UV wavelength regions. This allows more of the shorter wavelengths (or higher energies) to reach the PV element.
Advantageously, the thermovoltaic element may further comprise one or more substantially transparent electrodes. The electrodes may be transparent at least in the visible and/or UV wavelength range so that they do not block useful radiation from reaching the PV element.
Optionally, the one or more substantially transparent electrodes may be indium tin oxide (ITO) . ITO is a suitable transparent conductor but other transparent conductors may be used within the TV or PV elements to provide electrical contacts. Transparent electrodes may be applied across the face of layers in the solar cell rather than around the periphery leading to a simpler construction. Advantageously, the solar cell may further comprise a thermal insulating layer between the thermovoltaic element and the photovoltaic element.
Optionally, the thermal insulating layer may be a vacuum or an airgap. Optionally, the photovoltaic element may further comprise a heat sink. This heat sink or heat radiator may be used to further cool the PV element. Advantageously, the solar cell may further comprise a protective layer. This protective layer may be used to protect the solar cell from environmental damage or other physical damage. The protective layer may be a transparent or semi-transparent material such as glass or a plastics material and may also be coloured or otherwise filter out particular wavelengths.
Optionally, the solar cell may further comprise an insulating layer between the protective layer and the thermovoltaic layer.
Optionally, the first current may be arranged in parallel or in series with the second current. In parallel a higher output current may be achieved and in series a higher voltage may be achieved. Preferably, the thermovoltaic element comprises a p-n junction. The PV element may also comprise one or more p-n junctions .
Optionally, the thermovoltaic element may comprise an array of quantum dots, nanowires and/or quantum wells. These structures may combine the required semiconductor properties and IR absorption.
The apparatus may be a solar cell.
Optionally, the photovoltaic element may comprise one or more materials selected from the group consisting of: single-crystalline silicon, poly-crystalline silicon, thin film silicon, amorphous silicon, gallium arsenide, ceramic- based semiconductors, polymeric materials, polymeric hybrid materials, organic material, carbon nanotubes, graphite, Highly ordered pyrolytic graphite, HOPG, graphene and carbon nanofibers and inorganic material. Using appropriate organic and inorganic materials the complete apparatus may be made flexible as well making it suitable for many "building integrated photovoltaic" (BIPV) applications. Preferably, the portion of the incident radiation absorbed by the thermovoltaic element has a longer wavelength than a substantial part of the incident radiation not absorbed. At least some of the higher wavelengths may be filtered out by the TV element.
According to a second aspect of the present invention there is provided a method of converting electromagnetic radiation into an electric current comprising the steps of: applying a flux of electromagnetic radiation on to a thermovoltaic element generating a first current such that a portion of the electromagnetic radiation is absorbed by the thermovoltaic element; and directing the remainder of the flux of electromagnetic radiation on to a photovoltaic element generating a second current. Preferably, the portion of the electromagnetic radiation absorbed by the thermovoltaic element has a longer wavelength than a substantial part of the electromagnetic radiation not absorbed. The portion that is not absorbed may then be absorbed by the photovoltaic element to generated the second current.
Preferably, the photovoltaic element may be maintained at a lower temperature than the thermovoltaic element . Various techniques to maintain this temperature difference may be used including for instance, insulation and direct cooling.
Advantageously, the electromagnetic radiation may be solar radiation. However, other sources of electromagnetic radiation may be utilised.
According to a third aspect of the present invention there is provided an electrical distribution system comprising the apparatus described above together with any one or more of: temperature sensor or sensors, a thermal control system and an electrical storage system. Brief description of the Figures
The present invention may be put into practice in a number of ways and embodiments will now be described by way of example only and with reference to the accompanying drawings, in which:
FIG. 1 shows a graph of an approximated solar spectrum; and FIG. 2 shows a schematic diagram of a cross section through a solar cell according an embodiment of the present invention, given by way of example only.
It should be noted that the figures are illustrated for simplicity and are not necessarily drawn to scale.
Detailed description of a preferred embodiment
Figure 2 shows a solar cell 10 according to one embodiment. The solar cell 10 is formed as a stacked arrangement and shall now be described layerwise starting with the first layer that is encountered by incident solar radiation falling on the solar cell 10 from above (as shown in figure 2), in use. A transparent protective cover 30 is formed over the surface of the solar cell 10. The next layer is a vacuum layer 40, which provides thermal insulation between the transparent protective cover 30 and the electrically active components beneath. Vacuum seals (not shown in figure 2) are used to maintain the vacuum. Under the vacuum layer 40 is a thermovoltaic (TV) element comprising a p-type semiconductor layer 50, an n- type semiconductor layer 60 and a single crystalline substrate 70. The TV element is preferably transparent to the visible, near-UV and/or UV portion of the solar spectrum. The interface between the p-type and n-type semiconductor layers acts as a hot junction 55 of the TV element. The interface between the n-type semiconductor layer 60 and the single crystalline substrate 70 acts as a cold junction 65 of the TV element.
In order to improve efficiency of the TV element the p- type semiconductor layer 50 (or the 'hot' side of the TV element) may be dyed with an IR absorber such as for instance: organic dyes, this may include but not limited to Solvent Soluble Near Infrared Dyes, Water Soluble Near
Infrared Dyes and/or Metal Complex Near Infrared Dyes. This IR absorber may coat the p-type (or n-type) semiconductor layer 50 or be incorporated throughout it.
Each element of the TV layer may preferably be manufactured from a semiconductor material that is substantially transparent at least to visible or near-UV radiation. Suitable transparent materials include n-ZnO, p- CuAlO, CuYi-XCaxO2, YZn1-XAlxO, LiNbO3, Ga2O3, CuInTe2 or CuInGaSe2 but others may be used. The single crystalline substrate 70 is kept cold by a heat sink 80 (or heat radiator) . The heat sink 80 extends sideways beyond the solar cell 10 stack and may be bonded to the single crystalline substrate 70 by In solder 90, or any other method that provides high thermal conductivity of the joint.
In use, after solar radiation 20 has passed through the layers of the TV element a substantial portion of the longer wavelengths of the incident radiation may be absorbed leaving the shorter wavelengths 20' typically in the near-UV and visible region.
A second vacuum layer 100 provides additional optional thermal insulation between the TV element and a photovoltaic (PV) element below. Again, vacuum seals (not shown in figure 2) may be used to maintain the vacuum. The PV element may be of any suitable type and may preferably be efficient when exposed to the visible, near-UV and/or UV wavelengths of incident solar radiation. Semiconductor p-type layer 110 and n-type layer 120 form the PV element and operate in a way known in the art of PV cells.
The lower layer 120 of the PV element may optionally be kept cool by a further heat sink 130 or heat radiator. The heat sink 103 may extend across the entire back surface of the solar cell 10 as this layer does not need to be transparent. The PV element may be bonded to heat sink 130 in any suitable way such as, for instance, by In soldering or bonded with high thermal conductivity resin. From the point of view of electrical efficiency the two elements (TV and PV) represent two different voltage/current sources. They can thus have different source parameters, namely open-loop voltages, short-circuit currents and internal resistances among others. Several solar cells 10 may be connected together in a battery arrangement in order to increase the source voltage and/or current .
The solar cell 10 may be used to generate electricity where an efficient source of power is required. Space vehicle and satellite applications particularly benefit from the combined high efficiency nature of the device and its high power to weight or size ratio. In space applications a requirement of maintaining sealed vacuum chambers may also be removed leading to further weight reductions. Other vehicle or portable device applications may also benefit from this device.
As will be appreciated by the skilled person, details of the above embodiment may be varied without departing from the scope of the present invention, as defined by the appended claims.
For example, the TV and PV elements may be of any suitable type. For instance, the TV element layers do not necessarily have to be semiconductors. Metals, oxides, conductive polymers, organic materials and/or other conductors may be used.
Where a semiconductor is described as being p-type it may be replaced with an n-type material and visa versa. Independently of the substrate/film combination (p-type on n-type or vice versa) the hot junction should preferably be at the top (as shown in figure 2) , i.e. towards the incident solar radiation, and the cold junction at the bottom. Placing the cold junction between the hot junction and PV element has a benefit of reducing the effect of radiation heating the PV element, which may unnecessarily occur if the hot junction is facing or adjacent the PV element .
The TV and PV elements may abut without any insulation or separation.
The TV element may instead be formed from a single oxide layer. Areas of different type (p for n-type substrate and n for p-type substrate) may be formed by, but not exclusively, with the help of diffusion, ion beam implantation.
For PV elements that are sensitive at longer wavelengths but which may have lower quantum efficiency there may still be a benefit of filtering these wavelengths out before radiation reaches the PV element as they may still operate cooler and therefore more efficiently.
Although the above embodiment shows a single TV element with a single hot and cold junction multiple elements may be used in which case additional stacked layers may be formed. For example, a TV element may be located on the backside of the solar cell .
In particular, the TV element may comprise one or more thermoelectric devices, such as thermoelectric modules for example. Any suitable type of thermoelectric device may be used, and suitable thermoelectric devices may comprise thermoelectric materials such as filled skutterdites, chlathrate structured compounds, fine grain sized thermoelectric materials, and film shaped thermoelectric materials, ZnO, Carbon nanotube composites, for example. The thermoelectric devices may comprise single stage devices, or multistage cascade structures, for example. The thermoelectric devices may also comprise thin-film thermoelectric materials, or may be thermoelectric devices comprising organic or polymer thermoelectric materials.
The PV element may comprise one or more photovoltaic devices. Any suitable type of photovoltaic device may be used, and suitable photovoltaic devices may comprise materials such as conventional crystalline silicon, thin film silicon, amorphous silicon, gallium arsenide and other semiconductor materials. Suitable photovoltaic devices also include single junction or multi-junction solar cells, and dye-doped solar cells based on titanium dioxide using any carbon based materials such as, but not restricted, to carbon nanotubes, graphite, Highly ordered pyrolytic graphite (HOPG), graphene and carbon nanofibers. Suitable photovoltaic devices also include photovoltaic materials such as ceramic-based semiconductors, polymeric or polymeric hybrid materials. The photovoltaic devices may also include optics such as concentrator lenses and mirrors, antireflective coatings, textured cell surfaces, metamaterials and back reflectors. The PV and TV elements may be manufactured by a variety of methods including vacuum deposition, screen printing and spaying onto a substrate, for example.
The PV and/or TV elements may be formed from inorganic (e.g. Si, Ge or AlGas) or organic (e.g. polyaniline, tetrathiotetracene (TTT) iodides) materials.
The PV and TV elements may be formed as separate or a single layer.
Whilst the examples provided above describe embodiments as a solar cell the origin of electromagnetic radiation is not restricted to the sun but other emitters of electromagnetic radiation such as thermal emitters and atomic batteries, for example. Furthermore, the wavelength of the electromagnetic radiation is not limited to the visible spectrum but may for instance extend into the ultraviolet or infrared spectrum.
Many combinations, modifications, or alterations to the features of the above embodiments will be readily apparent to the skilled person and are intended to form part of the invention.

Claims

CLAIMS ;
1. Apparatus for converting electromagnetic radiation into an electrical current comprising: a photovoltaic element for generating a first current from incident radiation; and a thermovoltaic element for generating a second current arranged to absorb a portion of the incident radiation before the incident radiation reaches the photovoltaic element.
2. The apparatus according to claim 1, wherein the thermovoltaic element is separated from the photovoltaic element .
3. The apparatus of claim 1 or claim 2, wherein the thermovoltaic element comprises a hot junction.
4. The apparatus of any previous claim, wherein the thermovoltaic element further comprises a cold junction.
5. The apparatus of any previous claim, wherein the thermovoltaic element further comprises a heat sink.
6. The apparatus according to any previous claim wherein the thermovoltaic element further comprises an infrared absorber.
7. The apparatus according to claim 6, wherein the infrared absorber is selected from the group consisting of
CuYi-XCaXO2, YZni_x AlxO, LiNbO3, Ga2O3, SrTiO3, CuInTe2 and CuInGaSe2.
8. The apparatus according to any previous claim wherein the thermovoltaic element is substantially transparent in the visual and/or UV wavelength regions.
9. The apparatus according to any previous claim wherein the thermovoltaic element further comprises one or more substantially transparent electrodes.
10. The apparatus according to claim 9, wherein the one or more substantially transparent electrodes is/are indium tin oxide .
11. The apparatus according to any previous claim further comprising a thermal insulating layer between the thermovoltaic element and the photovoltaic element.
12. The apparatus according to claim 11, wherein the thermal insulating layer is a vacuum or an airgap.
13. The apparatus according to any previous claim, wherein the photovoltaic element further comprises a heat sink.
14. The apparatus according to any previous claim further comprising a protective layer.
15. The apparatus according to claim 14 further comprising an insulating layer between the protective layer and the thermovoltaic layer.
16. The apparatus according to any previous claim, wherein the first current is arranged in parallel or in series with the second current .
17. The apparatus according to any previous claim wherein the thermovoltaic element comprises a p-n junction.
18. The apparatus according to any previous claim wherein the thermovoltaic element comprises an array of quantum dots .
19. The apparatus according to any previous claim, wherein the thermovoltaic element comprises nanowires.
20. The apparatus according to any previous claim, wherein the thermovoltaic element comprises quantum wells.
21. The apparatus according to any previous claim, wherein the wavelength of the portion of the incident radiation absorbed by the thermovoltaic element is longer than a portion not absorbed.
22. The apparatus according to any previous claim, wherein the thermovoltaic element comprises one or more materials selected from the group consisting of: filled skutterdites, chlathrate structured compounds, fine grain sized thermoelectric materials, and film shaped thermoelectric materials, ZnO, carbon nanotube composites, organic material and inorganic material.
23. The apparatus according to any previous claim, wherein the photovoltaic element comprises one or more p-n junctions, Schottky junctions, metal-insulator semiconducting junctions, and heterojunctions .
24. The apparatus according to any previous claim, wherein the photovoltaic element comprises one or more materials selected from the group consisting of: single-crystalline silicon, poly-crystalline silicon, thin film silicon, amorphous silicon, gallium arsenide, ceramic-based semiconductors, polymeric materials, polymeric hybrid materials, organic material, carbon nanotubes, graphite,
Highly ordered pyrolytic graphite, HOPG, graphene and carbon nanofibers and inorganic material .
25. The apparatus according to any previous claim, wherein the photovoltaic element further comprises one or more of: a concentrator lens, a mirror, an antireflective coating, a textured cell surface and a back reflector.
26. The apparatus according to any previous claim, wherein the photovoltaic element and the thermovoltaic element are integral .
27. An electrical distribution system comprising: apparatus according to any of claims 1-25; and an electrical storage system.
28. The electrical distribution system according to claim 27 further comprising a thermal control system.
29. A method of converting electromagnetic radiation into- an electric current comprising the steps of : applying a flux of electromagnetic radiation on to a thermovoltaic element generating a first current such that a portion of the electromagnetic radiation is absorbed by the thermovoltaic element; and directing the remainder of the flux of electromagnetic radiation on to a photovoltaic element generating a second current .
30. The method of claim 29, wherein the portion of the electromagnetic radiation absorbed by the thermovoltaic element has a longer wavelength than a substantial part of the electromagnetic radiation not absorbed.
31. The method of claim 29 or claim 30 wherein the photovoltaic element is maintained at a lower temperature than the thermovoltaic element.
32. The method according to any of claims 29-31, wherein the electromagnetic radiation is solar radiation.
PCT/GB2008/001436 2007-04-25 2008-04-23 Solar cell WO2008132445A2 (en)

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US7858876B2 (en) 2007-03-13 2010-12-28 Wisconsin Alumni Research Foundation Graphite-based photovoltaic cells
RU2515214C2 (en) * 2009-08-11 2014-05-10 Айвьютек Ко., Лтд Electronic device
FR2958453A1 (en) * 2010-04-02 2011-10-07 Commissariat Energie Atomique Current generating device for use on roof of building, has shield arranged in front of active surface of element and designed to stop infrared wavelengths at level of active surface of element
US20110290295A1 (en) * 2010-05-28 2011-12-01 Guardian Industries Corp. Thermoelectric/solar cell hybrid coupled via vacuum insulated glazing unit, and method of making the same
WO2011149509A3 (en) * 2010-05-28 2012-11-22 Guardian Industries Corp. Thermoelectric/solar cell hybrid coupled via vacuum insulated glazing unit, and method of making the same
CN103026503A (en) * 2010-05-28 2013-04-03 葛迪恩实业公司 Thermoelectric/solar cell hybrid coupled via vacuum insulated glazing unit, and method of making the same
CN103026503B (en) * 2010-05-28 2016-11-30 葛迪恩实业公司 Thermoelectricity/solaode the hybrid power coupled by vacuum thermal insulation glass unit and method thereof
EP2634817A4 (en) * 2010-10-29 2017-06-07 Stanley Electric Co., Ltd. Power generation device, thermal power generation method and solar power generation method
CN102180437A (en) * 2010-12-07 2011-09-14 中国科学技术大学 Graphene-based infrared smart transparent film device and preparation method thereof
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WO2012134807A2 (en) 2011-03-29 2012-10-04 California Institute Of Technology Graphene-based multi-junctions flexible solar cell
DE102012107100A1 (en) * 2012-08-02 2014-02-06 Dynamic Solar Systems Inc. Enhanced layered solar cell for use in control circuit of power source of e.g. portable, manually transportable apparatus, has upper side photovoltaic layer sequence connected to functional layer sequence of cell for improving current yield
DE102017127267A1 (en) * 2017-11-20 2019-05-23 Bpe E.K. Photo-thermal generator
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