JP2015530746A - Photovoltaic system including optical module with light capture filter - Google Patents

Abstract

A light capture optical module comprising an optical randomized dielectric slab having a first surface and a second surface; and a first surface of the slab having a lower energy bandgap than the energy of onset of absorption of the dielectric slab A first battery adjacent to the second surface of the dielectric slab, at least one filter element in optical contact with the second surface of the dielectric slab, and a sub battery array including a plurality of photovoltaic sub batteries. A photovoltaic system for converting incident light into electrical energy, wherein at least one of them has a first surface in optical contact with at least one filter element. [Selection] Figure 2

Description

PRIORITY This patent application is filed on August 30, 2012, and is dated January 25, 2013, US Provisional Patent Application No. 61 / 695,216, entitled OPTICS FOR FULL SPECTRUM, ULTRAHIGH EFFICENCY SOLAR ENERGY CONVERSION. The application claims priority from US provisional patent application 61 / 756,804 entitled PHOTOVOLTAIC SYSTEM INCLUDING LIGHT TRAPPING FILTERED OPTICAL MODULE, all of which are hereby incorporated by reference in this patent application. Incorporated.

  The present invention relates to a photovoltaic device that converts incident light into electrical energy. In particular, the present invention relates to a photovoltaic device including a light capturing optical module comprising a dielectric slab connected to a sub-cell array.

  Photovoltaic cells, also called solar cells or PV cells, are useful for converting incident light, such as sunlight, into electrical energy. These batteries can be used, for example, as single-junction batteries having a specially defined band gap, which usually results in essentially low conversion efficiency. This is because only photons with energies that exceed the single band gap of the battery can be used to provide an effective effect, and all of the energy of the photons with a band gap larger than the band gap of the battery is essential. This is because it is heated. Thus, the single-junction type reacts only to a portion of the spectrum in a photovoltaic manner and is not very efficient for most of the wavelengths that are reacted. For this reason, many methods have been used and proposed to improve the efficiency of solar cells.

  A method often used to achieve higher photovoltaic efficiency is to supply sunlight to a multi-junction solar cell instead of a single junction solar cell. Multi-junction batteries allow the highest energy photons to be converted using batteries with a high band gap, which minimizes thermalization, while intermediate wavelengths are supplied to batteries with an intermediate band gap Will be. Multi-junction cells extend the overall spectral response by using a base junction with less energy than that provided by an optimal single-junction cell. Such multi-junction solar cells are made of a specific semiconductor material, and the selected band gap energy extends to the solar spectrum. Photons with energies greater than the highest band gap are first collected by the highest energy gap subcell. Photons having low energy are transmitted through the highest energy bandgap subcell to the next subcell having the highest energy bandgap. This repetition is repeated until a sub-cell having the lowest energy band gap is reached. In this way, the energy of absorbed photons that is larger than the band gap of the absorbing cell that is heated and disappears as heat is minimized. In addition, more bandgap usually means that in an optimized case, a larger portion of the total solar spectrum can be absorbed by the multijunction cell as compared to a single junction cell.

  Multi-junction solar cells provide an advantage over single-junction solar cells, but using light splitting optics to split incident solar radiation and direct the light to different solar cells achieves further efficiency gains it can. The narrower band of light is directed to subcells having different band gaps and / or to multi-junction cells having different sets of band gaps. Each targeted subcell is designed to have a band gap that is tuned to fit the spectral band directed to that subcell in order to optimize energy conversion. That is, the split optical element splits the incident light into segments or slices and directs the slices individually to the photovoltaic sub-cells with the appropriate band gap.

  Photovoltaic systems that use spectrum splitting optical elements to improve solar conversion efficiency have been published in the patent and technical literature. Examples include US 2011/028054 (Wanlass), Gu et al. , Renewable Energy and the Environment Technical Digest, “Common-Plane Spectrum-Splitting Concentrating Modulation Design and Development.” 1-3 (2011), Imenes et al. , Solar Energy Materials and Solar Cells, “Specular Beam Splitting Technology for Increased Convergence Efficiency in Solar Concentration, 4”. , Optics Express “Organic Photovoltaic Cell in Lateral-Tandem Configuration Employing Continuously-Tuned Microcavity Sub-Cells,” 16 (24) 19987 1994 et al. , Solar Energy Materials and Solar Cells, “Light Trapping, a New Approach to Spectrum Splitting,” 92 (12) 1570-1578 (2008), and Peters, Ian Marip, 200 Fraunhofer Institute for Solar Energy Systems.

  Photovoltaic systems using spectrum splitting technology with solar cells have improved the efficiency for converting incident light into electrical energy, but the demand for systems that enable higher conversion efficiencies continues. .

  It is an object of the present invention to provide a photovoltaic system that converts incident light into electrical energy, also called a collector with a light capture filter. Such a system can be used to improve the performance of the solar cell, thereby achieving as high a conversion efficiency as possible. One embodiment of the present invention includes a light capturing optical module having a plurality of photovoltaic sub-cells arranged in a normal array, and a dielectric that captures incident light and transfers the captured light to the photovoltaic sub-cells Provide a slab. The dielectric slab is made of a material having a relatively high refractive index, for example, greater than 2.0 at a wavelength of 550 nm. In addition, filter elements or arrays are included, which can be patterned or deposited on the base of the dielectric slab so that the subcell can be attached to the filter elements or array. In other words, the slab base can be configured in a special way to function as a filter. Alternatively, the filter elements or arrays can be formed or increased on the secondary battery. In either case, the filter element can be placed between the plurality of sub-cells and the dielectric slab to perform the desired light filtering before the light reaches the sub-cells. As the filter element, for example, a photonic crystal that can be patterned at least in one dimension on the base surface of the slab may be used. In one example, the photonic crystal is patterned in three dimensions to affect all directions. The light capture optics module can also have an anti-reflective coating on the top surface of the dielectric slab and / or the cell location on the dielectric slab.

  Light can also be randomized within the dielectric slab so that it is dispersed in all directions. Randomization can be performed on the top surface of the slab and / or in the slab material itself. The secondary battery of this system may be composed of a multi-junction battery such as a single-junction battery or a three-junction battery. In one embodiment of the invention, the plurality of sub-cells for the system includes a first group of sub-cells having a first band gap set, and a second group of sub-cells having a second band gap set. In this case, the filter array is composed of first and second filter regions corresponding respectively to the first and second groups of subcells. In one embodiment, the first and second filter regions are arranged in a grid so that the first sub-cell set is aligned with the first filter set and the second sub-cell set is aligned with the second filter set. Be placed.

  The photovoltaic system can be equipped with an optical condensing module including a single optical condensing element or a plurality of optical condensing elements depending on the situation. It can also be arranged in series to provide a relatively compact optical condensing module with a large concentrating level. In one example, the optical condensing module may include a combination of a first optical element composed of a Fresnel lens and a second optical element composed of a compound parabolic concentrator. The output of the optical condensing module may be a relatively small aperture, and for example, it can be aligned with the region of the light capturing optical module that receives this output.

  In one particular embodiment, a photovoltaic system is provided for the purpose of converting incident light into electrical energy. The system includes a light capture optics module comprising a light randomized dielectric slab having a first surface, a second surface, and a first battery adjacent to the first surface of the dielectric slab. As a result, the first battery has a band gap of energy smaller than the absorption start energy generated in the dielectric slab. The system further comprises at least one filter element in optical contact with the second surface of the dielectric slab, and a sub-cell arrangement comprising a plurality of photovoltaic sub-cells, whereby the sub-cells At least one has a first surface in optical contact with the at least one filter element.

  The present invention will be further described with reference to the accompanying drawings. Throughout the drawings, like structures are given like reference numerals and are briefly described below.

FIG. 1 is a perspective view of a part of the photovoltaic system of the present invention including an optical condensing element. FIG. 2 is an enlarged perspective view of a condenser with a light trapping filter of the type shown in combination with the optical condenser of FIG. FIG. 3 is an enlarged perspective view of the photovoltaic cell of the type shown in FIG. FIG. 4 is an enlarged perspective view of a collector with a light trapping filter that does not include the top absorption battery. FIG. 5 is a perspective view of a collector with a light capturing filter of the present invention that can be incorporated into a printed circuit board. FIG. 6 is a three-dimensional graph representing the design space for maximizing optical efficiency with respect to the number of cells and the refractive index of the inductive light trapping slab. FIG. 7 is a graph showing exemplary device efficiency as a light collection function using the device and concept of the present invention.

  The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, each embodiment is chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the present invention. All patents, pending patent applications, published patent applications, and technical literature referenced throughout this specification are incorporated by reference in their entirety for all purposes.

  Referring now to the figures, and initially with reference to FIGS. 1-3, an exemplary embodiment of a photovoltaic system 10 is shown, which typically includes an optional optical concentrator or optical concentrator module 12. And a light capturing optical module 14. The system 10 can be used for photovoltaic conversion of incident light into electrical energy, as described in detail below. If a concentrator is used, the system 10 may be referred to as a concentrator with a light capture filter.

  The optical module 14 is a dielectric that can capture light that is normally supplied (eg, light supplied from an optical condensing module or directly from the sun) and transfer it to a plurality of photovoltaic cells or sub-cells 22, 22 '. A slab or dielectric layer 24 is included. The secondary battery used here may vary in its structure, but usually receives a specific range of wavelengths from an optical spectral splitting or filtering element and matches a range of wavelengths that affect itself or Includes single-junction or multi-junction solar cells having a series of band gaps. As an example, the red wavelength is supplied to a sub-cell having a band gap optimized for red light, while the green wavelength is supplied to a sub-cell having a band gap optimized for green light. Etc. The filter can be used for a band gap battery depending on the situation, thereby improving the conversion efficiency based on parasitic absorption of the battery.

  In an embodiment of the present invention, an uppermost battery 26 that contacts one surface of the dielectric slab 24 is provided, while the secondary battery optically contacts the other surface of the dielectric slab 24. Typically, when the elements of module 14 are in optical contact with each other, they are in close physical contact, and more preferably any gap is much smaller than the wavelength of light, which is This is also referred to as “operational contact”. In any case, it is desirable to use a multilayer coating to minimize gaps or refractive index differences between the various surfaces and / or reduce reflected light.

  One embodiment of the dielectric slab 24 is non-conductive and has a high refractive index (eg, greater than 2.0 at 550 nm, or preferably greater than 3.0 at 550 nm), for example, GaP or titania. Although it is a solid substance, of course, other materials can be used. Typically, the material for the dielectric slab 24 has a relatively high refractive index that passes wavelengths of interest beyond the most solar spectrum (ie, wavelengths of energy lower than those absorbed by the top cell and converted to electrical energy). Any material can be used. This high refractive index can maintain the capture of light entering the slab 24 until it is absorbed by one of the subcells. The dielectric slab 24 is textured on any of its top surfaces and / or randomizes incident light to disperse light in all directions within the slab. Such texturing can be used as a physical texture on one side of the slab so that the texture itself is uneven or more aligned, as achieved by a fine surface (eg, an etched fine surface). Can be In addition to what is specifically described here, many types of structures and configurations can be used to achieve light randomization.

  The thickness of the dielectric slab can be selected to have characteristics that allow it to achieve predetermined performance characteristics. For example, it is desirable to use a slab having at least the same thickness as the width of the sub battery. In one example, the system includes a sub-cell that is approximately 1 mm on each side and a dielectric slab that is approximately 1 mm thick. For relatively thin slabs, the rate of light incident on the same battery type is twice per row, which is relatively high compared to thick slabs.

As explained here, the optical efficiency is usually divided by the total number of photons that pass through the spectral divider and deposit on a given subcell by the total number of photons that affect the top layer of the light capture optics module. Refer to the results. System efficiency can be characterized by the amount of electrical energy produced by the device divided by the total amount of solar energy entering the device. For example, a device that produces 500 W of electrical energy under 1000 W / m ² of solar illumination has an overall efficiency of 50%.

  The top surface 20 of the dielectric slab 24 may be adjacent to a layer 25, which is an adhesive layer and / or an anti-reflective coating that is used so that incident light that reaches the slab is not reflected from the slab 24. It may be a layer. The slab 24 further includes a top or first battery 26 on the top surface 20, which may be, for example, a light absorbing 2.2 eV GaP battery, also referred to as a “pre-blue” absorber. In one embodiment of the present invention, the refractive index of the slab 24 and the first cell 26 can also be used for total internal reflection to capture incident light in the slab 24 and the first cell 26, thereby Incident light will affect the subcell with filter more than once before entering the subcell. Although the terms “first” and “top” are used for battery 26, these terms are limited because it can be seen that one or more additional layers can be placed on top of or outside the battery. It should be noted that it is not used in the sense that By using the battery 26 in combination with a dielectric slab, the refractive index of the slab 24 can be increased because a portion of incident light (eg, at least a portion of blue light and ultraviolet light) is absorbed. is there. That is, at least a portion of the high energy light that would otherwise be absorbed by the slab is instead absorbed by the first or top battery 26 so that it does not disappear within the slab. Thus, in one embodiment of the present invention, the first or top battery 26 is adjacent to the first surface of the dielectric slab, thereby causing the first or top battery 26 to be less than the onset of absorption energy produced in the dielectric slab. It has a low band gap so that the onset energy of absorption occurs at the lowest energy (ie, the longest wavelength) at which absorption within the material is significant. Usually, it is considered that the absorption becomes significant when the light absorption length in the material is less than 10 times the thickness of the slab. The first or top battery 26 may further include an antireflection film.

  In a special embodiment of the present invention, the first or top cell 26 is optimized to match the blue portion of the spectrum, which increases the efficiency of capturing light in the dielectric slab, increasing the refractive index. This is because materials that rise with and have a high refractive index typically tend to absorb instead of transmitting higher energy wavelength regions, such as ultraviolet and blue light. Thus, if the blue / ultraviolet light is not absorbed by the first battery, it is parasitically absorbed by the slab and disappears. By using a high energy light absorbing cell on top of the dielectric slab, the blue light can be converted into electricity depending on the situation before the remaining light enters the dielectric slab. In this way, higher overall efficiency can be achieved by avoiding parasitic absorption of blue / ultraviolet light in the high index slab.

  The first or top battery 26 may be either a single junction battery or a multi-junction battery. The present battery 26 and sub batteries 22, 22 ′ can be laminated or adhered to the dielectric slab 24 in order to minimize the number of interfaces between the battery and the slab. For example, by having an air interface between the slab 24 and the sub-cell and / or light-absorbing cell, it is possible to introduce unwanted reflections into light loss. An exemplary adhesive that can be used to bond these elements together is a TiO2 sol-gel, which provides a relatively high refractive index to avoid unwanted reflections at the interface.

  In the structure of the optical module of the present invention, it may be possible to omit the first or top battery 26, because the refractive index of the slab 24 minimizes the high energy wavelength in the slab 24, or In order to avoid the parasitic absorption, it is preferable that it is at least slightly lower. In this system, the efficiency in solar energy conversion is usually slightly reduced as compared with the structure including the first or uppermost battery 26. One such embodiment is shown in FIG. 4 because, even though it has a similar structure to FIG. 3, some of the light is not absorbed before reaching the slab 24. The refractive index of the slab 24 may be limited or decrease.

  Referring to FIG. 3 again, when the optical module 14 is provided with the uppermost battery 26, the battery is mounted on the slab 24, but various methods are possible, for example, the adhesive layer 25 (eg, titania sol-gel adhesive). Or can be mounted directly on top of the slab 24 as a monolithic structure. When such an adhesive layer 25 is used, it is desirable to have a high refractive index so that light can reach the slab 24 through the adhesive layer 25 relatively easily. In some embodiments, the first or top battery 26 may be a single junction solar cell, a photovoltaic cell, or a multi-junction cell.

  Additional reflectors can be provided on one or more of the sides to maximize light capture in the slab. Alternatively, a battery or battery stack can be provided on one or more sides of the slab. However, it is desirable to provide such a structural filter on both side surfaces, and such a filter can be provided as a patterned surface on both side surfaces of the sub-cell and / or slab 24.

  The light capturing optical module 14 further includes a plurality of photovoltaic sub-cells 22 and 22 '. Each subcell is tuned to photovoltaically absorb a predetermined subset of the light spectrum. As described above, each of the sub-cells 22 and 22 ′ may be a multi-junction solar cell, more specifically, a three-junction solar cell. As best shown in FIG. 3, the first battery stack 22 is positioned adjacent to the second battery stack 22 ′, with each battery stack having three junctions within a single battery structure. Which has six stacked photovoltaic cells, so that the system as a whole can be equipped with six differently tuned photovoltaic cells (however, when the top battery is used, the seventh Used for photovoltaic cells, again all 6 other batteries are adjusted differently). For electrical isolation, a space is provided between each battery 22 and adjacent battery 22 ', for example, an insulating material (eg, UV curable dielectric polymer or functional equivalent) that holds the batteries in a spaced configuration. Can be provided. In one embodiment, the cells are considered adjacent to each other in that they are placed in close proximity to each other without actually being in electrical contact. That is, the batteries are spaced apart from each other by a distance of 1 micron to 1 mm, or are placed closer together, for example in the range of 1-100 microns. Normally, each battery stack is designed to respond most efficiently to a predetermined light wavelength of incident light directed at the stack.

  In the illustrated exemplary embodiment, the second battery stack 22 ′ includes a number of layers, such as a front abutment grid 50, a first battery 52, a second battery 56, and a third battery 60, a second battery. The first tunnel junction 54 is included between the first battery 52 and the second battery 56, the second tunnel junction 58 and the back-side contact portion 62 are included between the second battery 56 and the third battery 60. . The adjacent first battery stack 22 also includes many layers, such as the front contact grid 70, the first battery 72, the second battery 76, the third battery 80, the first battery 72, and the second battery. A first tunnel junction 74 is included between the batteries 76, a second tunnel junction 78 is provided between the second battery 76 and the third battery 80, and a back side contact portion 82.

  With continued reference to the exemplary embodiment of the battery stack of FIG. 3, the first battery 52, which is the top battery of the second battery stack 22 ′, has a wavelength in the range of 670 nm to 564 nm. A 1.85 eV band gap can be obtained by adjusting to absorb the spectral bandwidth portion of the incident light it has (eg, having band gap characteristics). The spectral bandwidth portion of the incident light that is out of this wavelength range reaches the adjacent battery 56. The second battery 56, which is an intermediate battery of the second battery stack 22 ', is tuned to absorb a spectral bandwidth portion of incident light having a wavelength in the range of 785 nm to 670 nm (eg, a band A 1.58 eV band gap can be obtained (with gap characteristics). The spectral bandwidth portion of the incident light deviating from this wavelength range reaches the adjacent battery 60. The third battery 60, which is the lowest battery in the second battery stack 22 ′, is tuned to absorb the spectral bandwidth portion of incident light having a wavelength in the range of 898 nm to 785 nm (eg, 1.38 eV band gap can be obtained (with band gap characteristics).

  As described above, the first battery stack 22 is adjacent to the second battery stack 22 ′, and the first battery 72, which is the uppermost battery of the first battery stack 22, is from 1088 nm to 898 nm. Adjusted to absorb the spectral bandwidth portion of incident light having a wavelength in the range of (for example, to have bandgap characteristics), a 1.14 eV bandgap can be obtained. The spectral bandwidth portion of the incident light that is out of this wavelength range reaches the adjacent battery 76. The second battery 76, which is an intermediate battery of the first battery stack 22, is tuned to absorb a spectral bandwidth portion of incident light having a wavelength in the range of 1333 nm to 1088 nm (eg, a band gap). 0.93 eV band gap can be obtained (with characteristics). The spectral bandwidth portion of the incident light that is out of this wavelength range reaches the adjacent battery 80. The third battery 80, which is the lowest battery of the first battery stack 22, is tuned to absorb the spectral bandwidth portion of incident light having a wavelength in the range of 1771 nm to 1333 nm (eg, the band A 0.70 eV band gap can be obtained (with gap characteristics). The wavelength ranges described above and their associated band gaps are used only to provide exemplary device structures, and embodiments of the present invention are at least slightly different from those of the present embodiment in batteries and battery stacks. It can be seen that the body can also be used.

  The first battery or battery stack 22 can include a bus bar 40 that is used for batteries having a relatively lower bandgap, and the second battery or battery stack 22 'can be further banded higher. A bus bar 42 used for batteries with gaps can be provided. The isolated intersection 44 is disposed at a location where the bus bars 40 and 42 intersect. Alternatively, other contact methods and structures can be used, such as non-crossing isolated contact to the backside conduction path.

  In this manner, the sub-cells 22 and 22 ′ are arranged in an alternating or “lattice” pattern throughout the entire area determined by the length and width of the optical module 14. As also shown in FIG. 2, the optical module 14 can include one or more filters 30 that are typically disposed between the dielectric slab 24 and the sub-cells 22, 22 ′. Such a filter 30 is used to verify that incident light has entered the appropriate sub-cell because light that does not enter the appropriate sub-cell should be reflected. In order to provide the desired filtering, a textured slab is provided with a corresponding filter grid pattern, the first set of subcells aligned with the first set of filters, and the subcell firsts. It is also possible to arrange according to a battery arrangement in which the two sets are aligned with the second set of filters. As an alternative structure, the grid pattern can also comprise a battery on a relatively low bandgap or a filter on a battery stack (eg, battery or battery stack 22). This causes some photons with low energy to be absorbed parasitically by a battery or battery stack (eg, battery stack 22 ') having a relatively high band gap. In embodiments of the photovoltaic system, adjacent cells in the grid pattern can accept different wavelengths from the spectrum splitter. This increases the likelihood that photons having the desired wavelength will reach a particular subcell having the minimum number of internal reflections in the dielectric slab 24. The filters used here can have many different embodiments, whether fully periodic or not, such as multilayer dielectric stacks, photonic crystals, and the like.

  The filter used in module 14 may be, for example, a two-dimensional or three-dimensional photonic crystal type filter that can be selected to achieve better omnidirectional compared to a single layer filter, or a one-dimensional filter. The photonic crystal type filter may be used. One-dimensional photonic crystal filters can achieve omnidirectional performance, but such filters are efficient when light is incident from a high refractive index material, such as the high refractive index slab described herein. May be reduced. For this reason, careful consideration is required as to whether to use in the present invention. Photonic crystals can have a variety of different structures and properties, but as described herein, are usually composed of periodic dielectric nanostructures. This periodic dielectric nanostructure defines the permitted and prohibited electrical energy bands and affects the propagation of electromagnetic waves. In essence, a photonic crystal includes internal regions having high and low dielectric constants that repeat periodically. Photons (behaving as waves) propagate through this structure depending on their wavelength. The wavelength of light that is allowed to propagate is known as a mode, and a group of allowed modes can form a band. Bands with forbidden wavelengths are called photonic band gaps, which make it possible to distinguish, for example, self-emission prohibition, highly reflective omnidirectional mirrors, and low loss dynamic optical phenomena. Since the basic physical phenomenon is based on diffraction, the periodicity and dielectric characteristics of the photonic crystal structure are approximately the same length scale as the electromagnetic waves in the photonic crystal material (ie for a one-dimensional photonic crystal mirror). It can be set to 1/4 of the wavelength in the material.

  Each of the module 14 dielectric cells has a number of features such as a central cell active area, back contact and reflector, one or more contact grid areas, anti-reflective coating / filter, and / or adhesive. There are layers that can be included. Each of the photovoltaic cells is normally tuned to have a band gap characteristic that allows the cell to absorb a predetermined spectral bandwidth portion of the incident light to which the cell is exposed, reflecting the unabsorbed portion A reflector can be provided on either the top or the base of the battery that makes it possible. In operation, each of the photovoltaic cells is such that incident and reflected light is absorbed and reflected in each of the cell stacks from highest energy to lowest energy (eg, blue is absorbed before green and red Before the orange is absorbed, etc.).

  As described above, the optical module 14 is illustrated and described to include two different battery stacks. Each battery stack has three band gaps that utilize six different solar cells in the module when the first battery is out of scope. However, nearly two such battery stacks are instead provided for a specific optical module, so that a specific subset of the light spectrum that each battery absorbs and reflects is for the six-junction structure described above. It is different from the thing. In addition, the wavelength range associated with each of the solar cells described above may be narrower or wider depending on the particular material used, the adjustment of the system, and the arrangement of the system.

  One or more photovoltaic systems of the present invention can be incorporated into a module that includes multiple systems. The system itself and / or modules containing the system can be implemented in a common framework in turn, so that the entire framework and / or individual modules are tracked according to the situation depending on the system and its desired performance Or a non-tracking function can be provided.

  The relatively high conversion efficiency achievable for the photovoltaic system of the present invention can be achieved for a variety of reasons. One of the reasons is that the solids of the dielectric slab improve the conversion efficiency, so that the incident light and the solar cell are brought into optical contact and the light is randomized to This is because the light is trapped in the slab due to the high refractive index made possible by the battery (for example, a blue battery). Another reason is that an efficient split of the light spectrum is performed, which is done to receive a unique subset of the light spectrum that each solar cell absorbs most efficiently. The filter used may be an omni-directional filter that can block the appropriate wavelength of light relatively efficiently over a wide range of angles. When such an omnidirectional filter is used, angle average reflection and propagation are relatively high in the corresponding band.

  The optical module 14 described above can optionally include an optical concentrator module 12 that can include at least one concentrator. In an exemplary system using two concentrators, a first optical element or collector 16 and a second optical element or collector 18 are provided. The illustrated first concentrator 16 is a Fresnel lens, while the second concentrator 18 is a compound parabolic concentrator. For the first concentrator 16, any type of lens or concentrator can be used in place of the Fresnel lens, and the advantage of the Fresnel lens is that it has a relatively large surface area lens (eg, 30 cm wide × 30 cm). The incident light can be efficiently collected over a considerably small area using a lens that is much thinner than a typical lens. This allows both standard and Fresnel lenses to efficiently collect light from large to small areas to achieve the desired light collection level, while lightweight Fresnel lenses provide additional structural advantages. Can bring. The second concentrator or optical element can further collect using the collected light output from the first concentrator, if desired. In the present exemplary embodiment, the second concentrator 16 has a top surface that is separated from the bottom surface of the Fresnel lens by a distance of about 30 cm, depending on the characteristics of the first concentrator 12 and the system. May vary greatly depending on the desired conversion efficiency. When a concentrator such as a Fresnel lens is used, a large surface area of the lens is exposed to incident light and collected in an area corresponding to the input area of the second concentrator 18.

  In this embodiment, the second concentrator 18 is illustrated as a composite parabolic concentrator, but alternative or additional second / third concentrators may be used instead or in addition. Is also possible. As an example, the second concentrator may be a parabolic concentrator characterized as a flat surface light funnel, which is typically less optically efficient than a compound parabolic concentrator. Nevertheless, the conversion efficiency is acceptable. The relative shape and dimensions of the illustrated second concentrator 18 are exemplary in that the concentrator can take a variety of different curvilinear shapes in addition to the shape illustrated for the concentrator region. It is used as. The characteristic shape and dimensions of the second light collector 18 were designed and selected to optimize the light collecting power of the light incident on the system and mounted on the optical module 14. In an alternative form of the invention, the system 10 does not include a plurality of optical concentrators operating in series, but instead, for example, for a system with concentrating power using only a compound parabolic concentrator. As such, only a single or first optical concentrator is provided. Additional concentrators (eg, a third concentrator) can be used in series with the first and second concentrators shown and described in connection with the exemplary embodiment. You can also see that.

  The amount and type of concentrator used for a special optical concentrator module 12 is selected to obtain a predetermined desired concentrating power over a predetermined range. For example, the light collecting power of the light collector 12 includes a light collecting power between 100 times and 1000 times. However, light gathering power levels below 100 times or above 1000 times are considered to be within the scope of the present invention. The selected light collecting power level provides a relatively compact light collecting module 12 while minimizing component thermal loads and costs. The light collection module shown is only one exemplary light collection device or system. That is, many types of light collection systems can be used alternatively or in addition to the light collectors shown and described. The light capturing optical module 14 is disposed below the output end of the light collecting module 12 and is disposed so that the output end of the module 12 is in optical communication with the light capturing optical module 14. This is best illustrated in the enlarged view of FIG.

  FIG. 5 is a perspective view of a collector with a light capturing filter of the present invention that can be incorporated into the multilayer printed board 90. In particular, the light capture optical module 14 is illustrated using a wire 92 to the top battery bus bar, a wire 93 to the back contact of the top battery, and a wire 94 to the back or back contact. The back mounted heat sink 96 is also illustrated in an exemplary relationship related to the battery stack 22, 22 ′ of the module 14.

FIG. 6 is a three-dimensional graph representing the design space for maximizing optical efficiency with respect to the number of cells and the refractive index of the inductive light trapping slab. In particular, the graph shows the need for a high refractive index material for slabs and a relatively small number of subcells to achieve a relatively high optical efficiency. As an example, a system with two subcells under a slab (eg, glass (SiO ₂ )) having a refractive index of 1.5 is calculated to have an optical efficiency of about 69%. In a system with five subcells under the slab having a refractive index of 5, it was calculated to have an optical efficiency of about 36%. In yet another example, a system with two subcells under a slab (eg, GaP) having a refractive index of 3.5 was calculated to have an optical efficiency of about 92%.

  FIG. 7 is a graph showing exemplary device efficiency as a light collection function using the device and concept of the present invention.

  The present invention has been described above with reference to several embodiments thereof. The entire disclosure of any patent or patent application recognized herein is incorporated by reference. The foregoing detailed description and examples have been given for clarity of understanding only. Unnecessary limitations should not be understood therefrom. It will be apparent to those skilled in the art that many changes can be made to the embodiments described above without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the configurations described herein, but only by the structures described by the claims and the equivalents of those structures.

Claims (15)

A photovoltaic system that converts incident light into electrical energy,
A light capturing optical module, the light capturing optical module comprising:
An optical randomized dielectric slab having a first surface and a second surface;
A first battery adjacent to the first surface of the dielectric slab, the first battery including a band gap of energy lower than the energy of the dielectric slab to start absorption;
At least one filter element in optical contact with the second surface of the dielectric slab;
A sub-cell arrangement comprising a plurality of photovoltaic sub-cells, wherein at least one of said sub-cells comprises a first surface in optical contact with said at least one filter element; A photovoltaic system comprising:   2. The photovoltaic system according to claim 1, wherein the band gap of the first battery is higher than at least one band gap of the plurality of sub-cells.   The light of claim 1, wherein the second surface of the dielectric slab comprises a plurality of filter elements, each of the plurality of filter elements being in optical contact with one of the plurality of sub-cells. Electromotive force system.   The photovoltaic system of claim 1, wherein the second surface of the dielectric slab comprises the at least one filter element.   The photovoltaic system according to claim 1, wherein at least one of the plurality of sub-cells includes the at least one filter element.   The photovoltaic system of claim 1, wherein the at least one filter element comprises one of a multilayer dielectric stack, a lattice, and a photonic crystal.   The photovoltaic system of claim 1, wherein the at least one filter element comprises an omnidirectional filter element.   The photovoltaic system according to claim 1, wherein each of the plurality of sub batteries includes a multi-junction battery.   The photovoltaic system according to claim 1, wherein the plurality of sub-cells includes an array of stacked photovoltaic cells.   The plurality of sub-cells include a first plurality of sub-cells having a first band gap and a second plurality of sub-cells having a second band gap, wherein the at least one filter element is a first sub-cell. The photovoltaic system of claim 1, comprising one and a second filter element, each of which corresponds to one of the first and second sub-cells.   The photovoltaic system of claim 1, wherein the first surface of the first battery includes an antireflective material.   The photovoltaic system of claim 1 in combination with a printed circuit board.   The refractive index of the dielectric slab is greater than 2.0 at a wavelength of 550 nm, and the refractive index of the dielectric slab and the first battery is such that incident light is incident on the dielectric slab and the first battery. The photovoltaic system of claim 1, providing total internal reflection to capture.   The optical condensing module further comprises an input region where incident light enters the condensing module and an output region where the collected light exits the condensing module, the output region comprising: The photovoltaic system of claim 1 in optical communication with the optical module. The photovoltaic system of claim 1, wherein each of the subcells of the subcell array is spaced from each adjacent subcell and is electrically insulated by an insulating material.

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