Patent Application
20190157486
The present invention pertains to the field of photovoltaic power generation and in particular to three dimensional photovoltaic power generation apparatus, such as solar cells.
Most photovoltaic solar cells are flat designs where sunshine harvest takes place on a 2-D semiconductor layout. This is due to the fact that most of photons carried in solar radiation can only penetrate into the solid state semiconductor by a few microns (the probability for a photon to reach deeper areas inside a solar cell decreases exponentially with the depth), and so photovoltaic interaction between photons from the solar radiation and electrons in semiconductors mainly takes place on the surface of the solar cells. Due to advances in nanotechnology, semiconductor materials can be manipulated at molecular and atomic levels, and it has been possible stack a few (two or three) PN junction layers on a solar cell to produce so-called tandem solar cells with higher photovoltaic conversion rate by harvesting more solar radiation energies in broader spectrums. Nevertheless, further stacking of such layers is limited by the fact that photons simply cannot reach even deeper layers of solid-state materials.
As a consequence, the photovoltaic conversion rate is limited by the Event Cross Section (ECS), defined by the surface area of a given photovoltaic solar cell where the photovoltaic interaction (the ‘event’) takes place. As typical state of art a conversion rate of about 10-20% have been achieved, which means only 10-20% of energy carried out by the solar radiation that reaches this area is converted into the electric power.
Efforts have been made to provide photovoltaic structures/devices/cells with improved conversion rate. US 20120279561 discloses a hollow photovoltaic fiber, which includes semiconductor formed on the inner surface of a hollow tube or on a flexible substrate subsequently formed into a hollow tube. The hollow photovoltaic fiber can be suitable for a variety of semiconductor devices, including solar cells. This references discloses that light entering the hollow photovoltaic fiber deposits energy in the semiconductor as it travel through the tube. The hollow tubes allow the incident light coming from all directions and a big portion of photons that cannot participate in a photovoltaic event and not to be absorbed by the tube would escape from tube and have no chance to contribute again.
US 2013/0104979 discloses a solar device, which includes a light condenser, a light guide member, a number of optical fibers and a converter end. The light condenser is configured for condensing incident light. The light guide member converts the condensed light into a plurality of focused light beams. The optical fibers receive the condensed light beams. The converter end includes a photoelectric converter configured for receiving and converting light from the optical fibers into electricity.
US 2013/0186452 discloses a photovoltaic structure, which includes an array of photovoltaic nanostructures, and a photovoltaic device, the photovoltaic device being at least semi-transparent. The array is positioned relative to the photovoltaic device such that light passing through the photovoltaic device strikes the array. The nanostructure disclosed in this reference includes an array of nanocables extending from a substrate. The nanocables have a spacing and surface texture defined by inner surfaces of voids of a template; an electrically insulating layer extending along the substrate; and at least one layer overlaying the nanocables.
US 2015/0263302 discloses photovoltaic device comprising patterned nanofibers. The nanofiber comprises a core, which extends along the axis of the nanofiber, and its main component includes Ag(NH3)2+ or AgNO3; a shell, which extends along the nanofiber and coats the core of the nanofiber, and its main component of the shell structure includes: PVP, TBAP, SDS, grapheme, PMAA or PFBT nanoparticle.
US 2016/0043250 discloses three-dimensional photovoltaic devices comprising non-conductive cores. The photovoltaic structure disclosed in this reference comprises a dielectric material layer comprising a planar portion having a uniform thickness and an array of protruding portions extending from a planar surface of the planar portion; and a layer stack located on the dielectric material layer and comprising a core conductive material layer, a photovoltaic material layer, and a transparent conductive material layer. The core conductive material layer is in contact with the planar surface and the protruding portions of the dielectric material layer, the transparent conductive material layer is spaced from the core conductive material layer by the photovoltaic material layer and each combination of a protruding portion of the dielectric material layer and portions of the layer stack surrounding the protruding portion constitutes a photovoltaic bristle. The basic building blocks in the device of this reference are the photovoltaic bristles, which also allow incident lights coming from all directions and also allow escape of a large portion of light without being able to participate in photovoltaic event.
There is still a need for photovoltaic power generator structures/solar cells which can exhibit an improved conversion rate from solar radiations to electric power.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
An object of the present invention is to provide three dimensional photovoltaic structures and a power generation apparatus comprising same.
In accordance with an aspect of the present invention, there is provided a photovoltaic structure, comprising: a light transmitting solid optical core having a longitudinal axis, having a top end, a bottom end and one or more side walls. The top end having an exposed outer surface to receive light. A photovoltaic layer surrounding at least a portion of one or more of the side walls of the optical core, and an optical cladding layer surrounding the photovoltaic layer.
In accordance with another aspect of the present invention, there is provided a three-dimensional photovoltaic power generation apparatus, comprising: a base structure having an upper surface and a lower surface; a plurality of photovoltaic structures, each having a longitudinal axis, a top end and a bottom end, and comprising: a light transmitting solid optical core having a top end, a bottom end and one or more side walls, the top end of the core having an exposed outer surface to receive light; a photovoltaic layer surrounding at least a portion of one or more of the side walls of the optical core; and an optical cladding layer surrounding the photovoltaic layer, wherein the bottom end of each of the plurality of photovoltaic structures is in direct or indirect association with the upper surface of the base structure.
Embodiments of the present invention provide improved photovoltaic structures to systematically increase the ECS for a given solar cell with given surface area, without altering the physical and chemical properties of the semiconductor. The photovoltaic structures of the present invention provide increased area of ECS so that the photons carried in solar radiation have more opportunities to meet and interact with the electrons in the material. The optical core of the present invention provides an ideal chamber to seal the incident light inside the photovoltaic structure and increases the likelihood of photons interacting with the electrons of the photovoltaic layer. The presence of optical cladding layer further assists in increasing the ECS.
As used herein, the term “about” refers to a +/−10% variation from the nominal value. It is to be understood that such a variation is always included in a given value provided herein, whether or not it is specifically referred to.
As used herein, the term “geometric prism” refers to a three-dimensional shaped structure, for example a microstructure, having top and bottom faces connected by flat or curved sidewalls. This type of shape is also referred to herein as a microprism, and includes cylinders, cubes, cuboids, rectangular prisms, hexagonal prisms, and the like. In various embodiments, the top and bottom faces are parallel and are similarly sized and shaped. However, it is also envisioned that the structure may have differently sized and/or shaped top and bottom faces, for example in accordance with a frustro-conical shape.
As used herein, the term “conical shape” refers to a three dimensional shaped structure having a top face and non-parallel sidewalls tapering to a point, or tapering to a bottom face having a small but possibly nonzero area. The absence or reduction in size of the bottom face mitigates the need for a photovoltaic structure at this location. The conical shaped structures can have a cross section shape of circle, triangular, square, pentagon, hexagon, etc. Conical shaped structures may be cones, pyramids, or the like.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The present invention provides three dimensional photovoltaic structures and a power generation apparatus comprising same.
In one aspect of the present invention, there is provided a three dimensional photovoltaic structure, one or more of which can be used in a power generation apparatus.
The photovoltaic structure of the present invention has a longitudinal axis, a top end and a bottom end, and comprises a light transmitting solid optical core having a top end, a bottom end and side wall(s). The photovoltaic structure further comprises a photovoltaic layer which surrounds the walls of the core, an optical cladding layer which surrounds the photovoltaic layer, and optionally an outermost stuffing layer. The top end of the optical core has an exposed outer surface to receive light.
Layered
The photovoltaic layer surrounds at least a portion of at least one (i.e. one or more) of the sidewalls. In some embodiments the photovoltaic layer surrounds substantially all of at least one sidewall. In some embodiments the photovoltaic layer surrounds substantially at least part of all of the sidewalls. In some embodiments, the photovoltaic layers surrounds substantially all parts of all of the sidewalls. It should be understood that a photovoltaic layer of larger surface area can in various embodiments result in greater photovoltaic activity. However, at least some photovoltaic activity can still be provided even when the photovoltaic layer does not surround all parts of all sidewalls (i.e. when there are gaps in the photovoltaic layer). Gaps can similarly be provided in the optical cladding layer.
In some embodiments, the sidewalls are substantially flat between their upper end and there lower end. In other embodiments, the sidewalls may be curved between their upper and lower ends. The sidewall upper end refers to the sidewall terminal portion which is proximate to the region of the apparatus which is exposed to light, while the lower and refers to the opposite side will terminal portion.
The optical core can be made of non-conductive and/or non-opaque materials, known for making the cores of optical fibers. In one embodiment, the optical core is made of a highly optically permeable material. In various embodiments, substantially the entire interior of the solid optical core is composed of such material.
The refractive index of the optical core and/or photovoltaic layer is higher than the refractive index of the optical cladding layer. In some embodiments, the optical core has a refractive index greater than a refractive index of the photovoltaic layer. In one embodiment, the optical core has a refractive index which is approximately equal to a refractive index of the photovoltaic layer.
The solid optical core in the photovoltaic structures of the present invention conducts incident light with acceptably low or minimal loss of radiation energy, thus making the power generation apparatus/solar cell comprising photovoltaic structures well adaptive to ambient lights and scattered lights, which increases its harvest rate of solar radiation energy in all weather conditions of all seasons.
As depicted in
The photovoltaic structures of the present invention allow a significant portion of the incident lights to be reflected when it penetrates through the photovoltaic layer and hits the optical cladding layer. This reflected light would continue to travel through the photovoltaic structures until they eventually reach the bottom, during which they would meet the walls of the photovoltaic structures a number of times, thereby increasing the opportunities for the photons in the light to meet and interact with the photovoltaic layers.
In some embodiments, the photovoltaic structure of the present invention further comprises an additional layer at or near the top end, having an anti-reflective light transmitting outer surface and a highly reflective inner surface. The additional layer has limited or minimal impact to the incident light but can significantly reduce the amount of light tending to escape from the photovoltaic structure to the air. In such embodiments, a portion of the photons in the light are reflected back to continue to travel within the photovoltaic structure.
The photovoltaic structures of the present invention can have one of a variety of shapes such as a cylinder, a geometric prism, a cone, a pyramid, a cube, a cuboid, a rectangle and any combination thereof.
The cone shaped photovoltaic structures can have a variety of cross sectional shapes such as hexagonal, square, rectangular, circular, etc.
In Non-conical photovoltaic structures (such as geometric prisms, cylinders, cubes, etc.), the bottom end of optical core is also surrounded by a photovoltaic layer and an optical cladding layer, so that when the light photons reach the bottom, they get reflected back at the optical cladding layer of the bottom, after a portion of them interact with the photovoltaic layer at the bottom. In such embodiments, reflected light photons would continue to travel from bottom to the top, and may hit the walls a number of times in the journey and continue to interact with the photovoltaic layers on the walls. In such embodiments, the optical cladding layer on the walls and at the bottom of the photovoltaic structures, together with the additional layer, form a substantially closed optical chamber to increase or maximize the likelihood for the incident light to participate in the photovoltaic interactions inside the photovoltaic structures. As a result, the ECS is significantly increased. Furthermore, embodiments wherein the optic core is made of materials with high optical permeability would ensure that the light loss when travelling in this chamber is mitigated or even minimized.
An example of such an embodiment is depicted in
In case of conical photovoltaic structures the bottom end is defined by the apex or vertex of the cones. In such embodiments, the light-sealing chamber is formed by the walls of the cones and the additional layer at the top. However, in this case the bottom portion of the structure is reduced to a point, or nearly a point, and the sidewalls of the structure are non-parallel, thereby changing the paths of incident and reflected light.
The photovoltaic layer is where the photovoltaic conversion takes place. In some embodiments, the photovoltaic layer comprises a multi-layer structure.
In some embodiments, the photovoltaic layer comprises an interior metallic layer in contact with the optical core, one or more conductive layers surrounding the interior metallic layer, and an outer metallic layer surrounding the one or more conductive layers.
In some embodiments, the one or more conductive layers are semiconductor layers, (also referred to as PN junction layers), comprising one or more PN junctions. The PN junctions are configured to generate an electrical voltage in response to photonic bombardment and penetration, in accordance with a photovoltaic effect.
In some embodiments, the photovoltaic layer comprises one semiconductor layer/PN junction layer with its associated interior metallic layer and exterior metallic layer. In some embodiments, the photovoltaic layer comprises a plurality of semiconductor layers/PN junction layers, each with their own respective interior metallic layers and exterior metallic layers.
In this disclosure, a semiconductor layer/PN junction layer is referred to as a semiconductor structure formed by two types of semiconductor material, p-type and n-type. Candidate materials and processes for the implementation of the PN junction layers are well known in the art. Suitable material ranges from silicon to non-silicon elements or compounds. In a typical embodiment one may choose thin-film solar cell materials such as amorphous silicon (a-Si), micro-crystalline silicon (μc-Si), or nano-crystalline silicon (nc-Si). In some embodiments, a PN junction layer may be understood as a P-I-N layer where “I” is meant to be an intrinsic semiconductor layer.
Depending on the polarity of the PN junctions (i.e. the relative locations of the positively and negatively doped semiconductor regions) in the photovoltaic layer in any specific embodiment, the activated electrons may move towards the direction of optical core, or towards the direction of optical cladding layer, when a photovoltaic interaction takes place. In one embodiment, the electrons move toward the direction of the optical core when a photovoltaic event takes place.
In some embodiments, solar radiation spectrum-selectivity is considered when choosing different materials for implementing the photovoltaic layer for the photovoltaic structures of the present invention. While some materials are best tuned to absorb solar energy carried by shorter wavelength photons, some other materials are best tuned to react to longer wavelength photons. The three-dimensional structural nature of the photovoltaic structures provides a possibility of optimizing spatial distribution of semiconductor materials along the circular, axial, and/or radial dimensions.
By applying photovoltaic materials that are best tuned to different wavebands of light to different segments of the photovoltaic structure, one can obtain the spectrum selectivity along the axial direction. An approach in one embodiment is to apply an amorphous silicon coating to the upper part of the photovoltaic structure (microprism or micro-cone) with best spectrum response to green and blue lights wavelengths, and to apply certain μc-Si or nc-Si coating to the lower part of the microprism or micro-cone with best spectrum response to red and infrared wavelengths. Depending on particular considerations a designer can play with this axial spectrum selectivity in a variety of ways in different embodiments.
By overlaying photovoltaic materials that are best tuned to different wavebands of light on successive coating layers surrounding the optical core, one can obtain a photovoltaic structure with spectrum selectivity along the radial direction. An approach in one embodiment is to mimic the tandem PN junctions configuration that has been in industry practice for years, where an amorphous silicon coating is first applied with best spectrum response to green and blue light wavelengths, and then a μc-Si or nc-Si coating is overlaid on top of amorphous silicon coating with best spectrum response to red and infrared wavelengths.
By applying photovoltaic materials that are best tuned to different wavebands of light to different segments of the same photovoltaic coating layer, one can obtain a photovoltaic structure with spectrum selectivity along the circular direction. An approach in one embodiment is to apply an amorphous silicon coating to one half side of the microprism or micro-cone, with best spectrum response to green and blue lights wavelengths, and a μc-Si or nc-Si coating to the other half side of the microprism or micro-cone, with best spectrum response to red and infrared wavelengths.
The functions of the interior metallic layer and an exterior metallic layer associated with each conductive layer are to capture and collect the electrons (or holes) in the conductive layer that are displaced into the metallic layers as a result of the photovoltaic interaction, and to provide a cathode (anode) electrical connection for the photovoltaic structure, for example to electrically connect with other photovoltaic structures of the same cell. The terms “interior” and “exterior” are meant in respect to the optical core: when the light travels from the optical core to the optical cladding layer, it first meets the interior metallic layer of each conductive layer, then the conductive layer itself, and then the exterior metallic layer. On the other hand, when the light travels from the optical cladding layer to the optical core, it first meets the exterior metallic layer of each conductive layer, then the conductive layer itself, and then the interior metallic layer. The photovoltaic layer typically includes electrical connections such as probes, conductive traces or wires which are electrically coupled to the metallic layers. The electrical connections of multiple photovoltaic structures can be connected in series and/or parallel to provide direct current electrical power, as would be readily understood by a worker skilled in the art.
The interior metallic layer and exterior metallic layers are made of materials with high optical permeability and/or with good electric conductivity. In some embodiments, ITO (Indium Tin Oxide) and TCO (transparent conductive oxide) can be good candidate materials to implement these metallic layers.
The metallic layers may cover the entire height of the photovoltaic structures, or from the bottom up to the level “h” where the additional layer having anti-reflective outer surface is placed.
The function of the optical cladding layer is to make the photovoltaic structures a good chamber for containing the incident light inside the photovoltaic structures so as to increase or even maximize the area of photovoltaic ECS. Its index of refraction is smaller than the refraction indices of all the other layers and of the optical core.
The similar principle applies to cone shaped photovoltaic structures. In case of conical photovoltaic structures the bottom end is defined by the apex or vertex of the cones. In such embodiments, the light-sealing chamber is formed by the walls of the cones and the additional layer at the top. However, in this case the bottom portion of the structure is reduced to a point, or nearly a point, and the sidewalls of the structure are non-parallel, thereby changing the paths of incident and reflected light.
The cross sectional shapes of the optical core, the photovoltaic layer, the optical cladding layer and the stuffing layer can be same or different. In one embodiment, the cross sectional shape of the optical core, the photovoltaic layer, and the optical cladding layer is same (i.e.
In another aspect of the present invention, there is provided a three dimensional photovoltaic power generation apparatus comprising a plurality of photovoltaic structures of the present invention as described above. The power generation apparatus comprises a base structure having an upper surface and a lower surface, wherein the lower surface is in direct or indirect association with the bottom end of each of the photovoltaic structures. In one embodiment, the photovoltaic power generation apparatus is a solar cell.
In some embodiments, the base structure comprises side wall(s) 114 to encase the plurality of the photovoltaic structures (
In some embodiments the side walls wrap all photovoltaic structures together like a solid ‘brick’.
In some embodiments, the photovoltaic structures can be packed together with gluing materials, and there may or may not be a case that contains all of the photovoltaic structures in a cell.
The three dimensional photovoltaic power generation apparatus/solar cell viewed from top can have a variety of geometrical shapes such a rectangular, square, triangle, hexagonal, etc. (for example as shown in
The heights of all photovoltaic structures in a photovoltaic power generation apparatus/solar cell can be the same as shown in
Although in various illustrated embodiments the bottom face of the non-conical photovoltaic structures is flat, it is possible that the bottom face may be curved. For example, the structure may be hemispherical in shape.
In some embodiments, the upper surface of the base structure has a plurality of receiving structures shaped to accommodate the shape of the bottom of a corresponding photovoltaic structure. For example, in the case of non-conical photovoltaic structures (such as microprisms), the base structure seals the bottoms of all photovoltaic structures of the same cell with all functions that are provided by the walls of the photovoltaic structures (
In some embodiments, the photovoltaic layer and the cladding layer surround the bottom end of the optical core. In some embodiments of non-conical photovoltaic structures (such as microprisms, cube, etc.), the portion of the photovoltaic layer and the cladding layer surrounding the bottom end of the optical core is integral to the base structure. For example, referring to a microprism shaped photovoltaic structure, the base structure contains a plurality of units each of which connects to one and exactly one microprism that stands on it. The base structure is prepared with all the units having exactly the same layered structure as the walls of the microprisms, that is, a photovoltaic layer which may contain a plurality of PN junction layers and their associated metallic layers, and an optical cladding layer as the outermost layer. The one-to-one correspondence of these layers of the base structure with the layers of the walls makes a seamless encapsulation around the optic core of the microprisms, leaving only the top open with an antireflection layer slightly underneath the top (for example as shown in
In the embodiments comprising cone shaped photovoltaic structures there is no such step of bottom processing.
As discussed above, the photovoltaic structures of the present invention optionally comprise a stuffing layer surrounding the optical cladding layer. The plurality of photovoltaic structures can be assembled with or without an additional stuffing layer between the assembled photovoltaic structures.
In one embodiment, non-conical photovoltaic structures are assembled with or without an additional stuffing layer. In one embodiment, conical photovoltaic structures are assembled with an additional stuffing layer.
The function of the stuffing layer is to provide the power generation apparatus/solar cell with mechanical features (such as load bearing) or operational features (such as sensor) as desired or required.
In some embodiments, for the case of cone shaped photovoltaic structures, a stuffing layer is provided in order to make a rectangular 3-D solar cell.
The power generation apparatus of the present invention also comprises electrical wiring and connections to convert the energy of light into electricity by the photovoltaic effect. The electrical wiring and connections are as known in the art.
The top ends of all photovoltaic structures are directly exposed to the sunlight, and therefore the power generation apparatus/solar cells have one side that receives the solar radiation, for example as shown in
Finished power generation apparatus of the present invention can be used in a wide range of applications, for example to construct pavements on virtually any surfaces.
In another aspect of the present invention there is provided a systematic method to significantly increase the ECS for a given solar cell with given surface area.
It is obvious that the foregoing embodiments of the invention are examples and can be varied in many ways. Such present or future variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2017/050523 | 4/28/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62329461 | Apr 2016 | US |
