Optimized Architecture to Maximize Solar Cell Efficiency via the Optimal Spatial Configuration of Existing or Future Transparent Thin-film PV Materials Targeting Different Regions of the Solar Spectrum

Abstract

A new type of PV cell is comprised of a purposefully unique spatial configuration of multiple pairs of transparent thin PV films stacked top down in order of decreasing bandgaps corresponding to increasing wavelengths. Each thin-film pair is made of a material of desirable bandgap, and consecutive films separated from each other in space by a layer of air to force confinement of light waves of wavelength matching bandgap, enabling an infinite number of reflections until the wave energy corresponding to each desired wavelength is absorbed. The PV thin-films are coated to ensure that light of each wavelength is confined as intended. They are passivated to minimize surface recombination. This spatial arrangement provides multiple opportunities for photovoltaic conversion of each intended wavelength hence increasing overall conversion efficiency.

Claims

1. A system for converting a larger fraction of the solar spectrum into electrical energy as compared with prior art solar cells, comprising: a. Transparent or translucent layers of PV film solar cells of pre-designated bandgaps and precisely separated in space by air, thus forming unique sandwiched spatial configurations, b. Said layers of the sandwiched spatial configurations being separated from each other by air in measured layers, c. Said spatial configuration more fully utilizing light within each wavelength range in the solar spectrum by confining the light to repeatedly reflect between the layers, resulting in a higher PV conversion efficiency.

2. In one embodiment, the system of claim 1 wherein the PV thin-films are arranged in matched pairs sandwiched together to coerce continual reflections between members of each said matched pair until all energy of a given wavelength is absorbed by said matched pair engineered for absorption of a specific wavelength range via correct choice of material with matching energy bandgap, while said subsequent consecutive matched pairs are engineered for different, progressively longer wavelengths (materials with smaller energy bandgaps) as sunlight traverses down through the said sandwiched layer of matched pairs.

3. In another embodiment, the system of claim 1 comprising single-layer matched PV thin-films are sandwiched together wherein each said single-layer PV thin-film is thick enough to confine light of a given desired wavelength within it by enabling multiple total internal reflections within its boundaries, causing light of that wavelength to bounce within the said single-layer sandwiched PV thin-film until it is absorbed by the material of matching bandgap, but transparent enough to transmit all other light of longer wavelengths to the next matched PV film in the sandwich, each consecutive film targeted at absorbing light with increasingly longer wavelengths.

4. The system of claim 2 further comprising coatings on the top side of the top member of each said matched pair and on the bottom side of the bottom member of each said matched pair to enable light of a specific wavelength to bounce continually between the said film pair of matching bandgap, a fraction of the light being absorbed by one of the films in each pair upon each entry into that film, each absorption resulting in an electron being excited across the bandgap.

5. The system of claim 3 further comprising coatings on the top and bottom side of each single-layer matched PV thin-film to enable light of a given wavelength to be confined within the single-layer PV thin-film of matching bandgap to the light's wavelength, and continually reflect at the edges of the material, a fraction of the light being absorbed between two consecutive reflections, each absorption resulting in an electron being excited across the bandgap.

6. The air between said members of a matched pair in the system of claim 3, serves to dissipate thermal energy generated from any non-radiative transfers or excess energy released from an excitation across a bandgap which is smaller than the energy corresponding to the wavelength, when the light of a given wavelength interacts with matter within each member of said matched pair.

7. The air between said matched pairs in the system of claim 3 serves to dissipate thermal energy generated from any non-radiative transfers or excess energy released from an excitation across a bandgap which is smaller than the energy corresponding to the wavelength, when the light of a given wavelength interacts with matter in the PV thin-films.

8. The air between said matched pairs between single-layer matched PV thin-films in the system of claim 4, serves to dissipate thermal energy generated from any non-radiative transfers or excess energy released from an excitation across a bandgap which is smaller than the energy corresponding to the wavelength, when the light of a given wavelength interacts with matter in the PV thin-films.

9. The system of claim 1 further comprising a battery to store the electrical energy thus produced.

10. The system of claim 1 further comprising loads in the circuit which use the electrical energy thus produced.

11. The system of claim 6 further comprising a mechanism by which the air between sandwiched layers can transport thermal energy to a heat sink that can convert it to useful energy, using prior art technology like a Stirling engine.

12. The system of claim 7 further comprising a mechanism by which the air between sandwiched layers can transport thermal energy to a heat sink that can convert it to useful energy, using prior art technology like a Stirling engine.

13. In the system of claim 2, the thickness of each member of said matched pair is determined by the optimal distance light of a given wavelength must travel within the material comprising each member so that it is comparable to the absorption depth for said material to ensure good conversion efficiency but not larger than the drift diffusion length to prevent recombination and ensure that charge generated is adequately separated until it is collected.

14. In the system of claim 2, the thickness of the gap between two members of a matched pair is determined by the index of refraction and thickness of the material comprising each said member and the coatings on each said member, hence the solid angle at which light enters and exits the material upon each reflection between matched pair members.

15. The thickness, texture and material of said coatings in the system of claim 4 are determined by the wavelength that needs to be confined by reflection between the matched pair, the material comprising members of said matched pair and its thickness, to ensure that light of the desired wavelength is continually reflected between the members of said matched pair until absorbed, and passivation layer at each edge of the PV material of each member of the matched pair prevents surface recombination while texturization on the top layer of the top member of each pair ensures transmission of desired wavelengths downward into the sandwiched pairs.

16. The thickness, texture and material of said coatings in the system of claim 5 are determined by the wavelength that needs to be confined by reflection within each single-layer PV thin-film in the sandwich, the material comprising each said PV thin-film and its thickness, to ensure that light of the desired wavelength is continually reflected within it until absorbed, and the passivation layers at each edge of the PV material prevents surface recombination while texturization on the top surface of each PV thin-film in said sandwich ensures transmission of desired wavelengths downward into the sandwich.

17. In the system of claim 2, losses at the edge of the PV thin-film sandwich can be minimized by ensuring that the dimensions of the films and the gaps between subsequent layers are such that the majority of reflections between members of a matched pair occur at solid angles that do not result in leakage of light through the gaps at the edges.

18. In the system of claim 2, a conducting grid along the layers of the sandwich can serve multiple purposes, said grid can serve to create and maintain an electric field that whisks electrons away as they are created, while also serving to create the skeletal structure that holds the layers at predetermined, optimized distance from each other to ensure maximal conversion efficiency.

19. In the system of claim 2, the latest, most advanced PV thin-film materials can be substituted in the said sandwich structure to leverage the benefits of materials with the best state of the art individual conversion efficiencies for a given wavelength, for a single traversal through the material, thus creating an overall solar cell sandwich with enhanced cumulative efficiencies due to multiple traversals for multiple wavelengths.

20. In the system of claim 3, the latest, most advanced PV thin-film materials can be substituted in the said sandwich structure to leverage the benefits of materials with the best state of the art individual conversion efficiencies for a given wavelength, for a single traversal through the material, thus creating an overall solar cell sandwich with enhanced cumulative efficiencies due to multiple traversals for multiple wavelengths.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The specifics of the present application will be explained in more detail with reference to the example embodiments and views shown in the drawings:

[0039] FIG. 1 is a schematic showing the high-level solar sandwich cell design composed of matched thin-film pairs, consecutive pairs with bandgaps matching the wavelengths they target to convert to electricity.

[0040] FIG. 2 is a schematic showing the high-level solar sandwich cell design composed of single layer matched PV thin-films with bandgaps matching the wavelengths they target to convert to electricity.

[0041] FIG. 3 is a schematic of a matched pair of PV thin-films showing the coatings needed to reflect, filter and transmit light selectively for each successive pair of thin-films.

[0042] FIG. 4 is a schematic that shows how light may scatter off of air molecules and as a result impinge on the thin-film from which it just exited or its matched pair, hence demonstrating the benefit of two parallel PV thin-films that confine light of their matching desired wavelength to reflect between them until absorbed and converted into electricity.

DETAILED DESCRIPTION

[0043] FIG. 1 is a schematic showing the high-level solar sandwich cell design 100 composed of matched thin-film pairs that target conversion of subsets of the solar spectrum to electricity with high efficiency by {i} matching the wavelength of light to the bandgap of the matched thin-film pair, and progressively targeting longer wavelengths down the sandwich, matched pairs separated from other matched pairs by layers of air to allow for reflection of light and dissipation of heat, {iii} members of a matched pair separated from each other by a layer of air to allow for reflection of light and dissipation of heat, {iv} the opportunity for multiple attempts at conversion of light into electricity by trapping light of a specific wavelength between the matched pair of thin-films. White light comprising the entire solar spectrum 104a is incident on the top surface of the upper layer of the uppermost matched pair 101 made with PV material with the highest bandgap tuned to the shortest target wavelength. Some of the light transmits unaffected through the upper layer 104b. Yet other light transmits into the lower layer of the matched pair. When it hits the bottom edge of this layer, light of the lowest wavelength (highest energy) 104c bounces back upward toward the uppermost matched pair, allowing it re-traverse material with the correct bandgap. Here it bounces back and forth between the matched pair appropriate for this wavelength, until it is absorbed e.g. 104d and converted into electricity. At the same time when light of the lowest wavelength 104c bounces back upward, the remaining light of longer wavelengths transmits 105a downward towards the lower matched pairs that have energy bandgaps suited for longer wavelengths (lower energy). Additionally, when light comprising the entire solar spectrum 104a impinges on the top layer of the uppermost matched pair, some of the light with wavelengths capable of exciting electrons across the largest energy bandgaps does its work right away creating electricity, while light with longer wavelengths 104e is transmitted on downward towards the subsequent matched pairs in the sandwich that are tuned to lower energy light. As the longer wavelength light 105g makes its way downward to the second matched pair 102, some of it may reflect 105h back upward. If this were to occur, the coatings on the underside of the upper matched pair would reflect the light back downward 105i where it, can be useful for conversion into electricity by exciting electrons across matched bandgaps, Once again the light of wavelengths pertinent to the second matched pair is confined 105c, 105d, to reflect between these layers 102, while transmitting longer wavelengths 106a downward towards PV thin-film layers with bandgaps matched to longer wavelengths. Eventually all the light of this wavelength is absorbed 105d in layers 102 by exciting electrons across the matched bandgap which is lower in energy than that for the upper layers 101 but matched perfectly to the wavelength of the light that excites electrons across the bandgap. This process repeats itself for the lower layers of the solar sandwich whose subsequent matched pairs are made from material of lower bandgaps to match light of longer wavelengths (lower energy).

[0044] FIG. 2 is a schematic showing the high-level solar sandwich cell design 200 composed of single layer matched PV thin-films each targeting conversion of a subset of the solar spectrum to electricity with high efficiency via {i} matching the wavelength of the targeted light to the bandgap of the thin-film material, and progressively targeting longer wavelengths down the sandwich, {ii} each thin-film separated from the next thin-film by a layer of air to allow for reflection of light and dissipation of heat, {iii} the opportunity for multiple attempts at conversion of light of each wavelength into electricity by trapping light via multiple reflections within each thin-film layer until absorbed. White light comprising the entire solar spectrum 204a is incident on the top surface of the uppermost single layer 201 made with PV material with the highest bandgap tuned to the shortest target wavelength. The light transmits into the upper layer 204b. When some of this light hits the bottom edge of this layer, light of the lowest wavelength (highest energy) 204c bounces back upward and remains within this PV thin-film, allowing it to re-traverse material with its matched bandgap. Here it bounces back and forth within this layer appropriate for its wavelength, e.g. 204c and 204d until it is absorbed and converted into electricity 204d. At the same time when light of the lowest wavelength 204c bounces back upward, the remaining light of longer wavelengths transmits 205a downward towards the lower single layers that have energy bandgaps suited for longer wavelengths (lower energy). Additionally, when the light comprising the entire solar spectrum 204a impinges on the top single layer matched PV thin-film, some of it with wavelengths capable of exciting electrons across the largest energy bandgaps does its work right away creating electricity, while light with longer wavelengths 204e is transmitted on downward towards the subsequent single layer PV thin-film that is tuned to lower energy light in the sandwich. As the longer wavelength light makes its way downward to the second layer 202, some of it may reflect 205g back upward. If this were to occur, the coatings on the underside of the upper matched pair would reflect the light back downward 205h where it can be useful for conversion into electricity by exciting electrons across matched bandgaps. Once again the light of wavelengths pertinent to the second layer is confined 205c, 205d, to reflect within the single layer 202, while transmitting longer wavelengths 206a downward. Eventually all the light of this wavelength is absorbed 205d in layer 202 by exciting electrons across the matched bandgap which is lower in energy than that for the upper layer 201. This process repeats itself for lower layers e.g., 203 within the sandwich whose matched pairs are made from material of lower bandgaps to match light of longer wavelengths (lower energy).

[0045] FIG. 3 is a schematic of a matched pair of PV thin-films showing the coatings needed to reflect and filter light selectively for each successive pair of thin-films in the solar sandwich 300. 301 is a coating that allows all wavelengths to pass through and none to be reflected. It can be textured as necessary to prevent reflection back upward. 302 allows all waves (with all wavelengths) hitting it from below to be reflected downward. 303 and 304 are a matched pair of thin-films that convert light of a specific wavelength into electricity. They are also passivated on both sides to minimize surface recombination. 305 when hit from above by waves of wavelengths targeted for the first two layers, reflects them back up to confine them to bounce between these layers. It allows all other wavelengths to pass through. 306 when hit from below by waves of longer wavelengths targeted for lower layers (with lower energy), reflects them back down towards those layers of the sandwich, while allowing shorter wavelengths to pass back upwards. When white light comprising the entire solar spectrum 307a is incident on the top surface it transmits through 307b into the top layer of the matched pair. If any of it tries to leave the confines of the matched pair, it is reflected back 307c and 307d to bounce between the two layers until it is absorbed and successfully excites electrons 308 across the matched energy bandgap for the shortest wavelengths, while light of longer wavelengths passes through to the next matched pair 307j. Light of longer wavelengths is allowed by coating 305 to leave 307g the confines so that it can excite electrons across smaller bandgaps, while the shorter wavelength light remains and bounces 307e and 307f, 307h and 307i between the 2 thin-films of the matched pair until it excites electrons 308. Longer wavelength light attempting to make its way back into the region of the first matched pair tuned to shorter wavelengths, is reflected back downward 309a and 309b by coating 306 where it can be useful. In subsequent matched pairs, the coatings equivalent to 301 and 302 will selectively allow longer wavelengths (as defined by the matched pair they belong to) to pass through into the confines of the next matched PV thin-film pair while reflecting shorter wavelengths back upwards.

[0046] FIG. 4 is a schematic 400 that shows how light 401, 403 may scatter off of air molecules 402 and as a result impinge on the thin-film from which it just exited or its matched pair, hence demonstrating the benefit of two parallel PV thin-films that confine light of their matching desired wavelength to reflect between them until absorbed and converted into electricity. For any scattering event, the probability that a light wave “leaks” out along the edges of the solar cell is a subset 404 of 4π steradians which is the total number of steradians in 3D around any given molecule off which the light wave scatters. The smaller the ratio of the gap 406 between the two thin-films to the dimensions of the thin-films 405, the smaller the probability that the light waves will leak out before being converted to electricity. Based on PV thin-film material selection and corresponding bandgaps for conversion efficiency, LCOE can be optimized by optimizing the dimensions of thin-films 405, coatings 407 and separations 406.