Patent Application
20250126928
Conventional approaches to space photovoltaics largely focus on optimal efficiency due to large launch and deployment expenses. These are most often multi-junction solar cells whose laboratory efficiencies have been improved substantially in recent years and are offered commercially with approximately 32% efficiency. Although less expensive thin film and bulk silicon technologies exist, efficiency is perhaps a factor of two lower. Still, terrestrial photovoltaics based on these semiconducting materials are behind the drive to very low-cost terrestrial photovoltaics. Indeed, terrestrial photovoltaic costs can be an astounding three orders of magnitude lower than space photovoltaic qualified multi-junction devices.
Moreover, the most widely used space photovoltaics cost approximately $200/Watt in high volumes. For a 1 megawatt system, this is hundreds of millions of dollars. The cost is largely due to complicated materials and epitaxy stacks used to form the multi-junction cells. With thin film photovoltaics those problems are avoided, and the cost is orders of magnitude lower. Unfortunately, the highest efficiency yet demonstrated is around 22% as compared to multi-junction cells at over 44%. These are not viable for creating a large amount of power in a limited area. Improving the efficiency of thin film photovoltaics such as Perovskites will substantially reduce the cost of space solar power.
In order to overcome the issues described above, a combination of metrics is necessary for generating space photovoltaic power. Described here is an effective and well-controlled technique to create devices which are substantially more cost effective and scalable than existing multi-junction photovoltaics while also achieving higher efficiency with possibly better light angle sensitivity than any silicon or thin film photovoltaic approaches. Such technology is necessary, for example, for large space solar power systems. The apparatus and method of the disclosed invention are based on V-shaped and parabola-approximating structures for solar power generation not previously reported in the literature and not applied to Perovskites.
These advantages and others are achieved, for example, by a light trapping photovoltaic device that includes a substrate that has a top surface having openings that define a plurality of recesses on the top surface, and a plurality of light trapping photovoltaic cells disposed in the recesses. Each light trapping photovoltaic cell includes a plurality of photovoltaic layers configured to produce electricity in response to an external light. Each of the photovoltaic layers is inclined at a predetermined angle with respect to a normal direction of the top surface of the substrate so that a front face of each of the photovoltaic layers is exposed to the external light through the opening. The predetermined angle is greater than zero degrees and smaller than ninety degrees. Top edges of the photovoltaic layers are disposed along a perimeter of the opening defining the recess in which the light trapping photovoltaic cell is disposed. Each of the photovoltaic layers comprises perovskite.
The predetermined angle with respect to a normal direction of the top surface may be in a range of 15 to 25 degrees. Each light trapping photovoltaic cell may have an inverted pyramid shape with a base of the inverted pyramid shape corresponding to the opening defining the recess. Each light trapping photovoltaic cell may have a paraboloid shape with an aperture of the paraboloid corresponding to the opening defining the recess. Bottom edges of the photovoltaic layers may be electrically coupled to each other. The photovoltaic layers of each of the light trapping photovoltaic cells may include a first and second photovoltaic layers that directly face each other, forming a V-shape cross-section of the first and second photovoltaic layers. An angle between the first and second photovoltaic layers may be in a range of 30 to 50 degrees.
Each of the photovoltaic layers may include a photovoltaic medium layer configured to produce electricity in response to the external light, a front electrode layer disposed on a front side of the thin film photovoltaic layer, a rear electrode layer disposed on a rear side of the thin film photovoltaic layer, an anti-reflection layer disposed on a front side of the front electrode layer, and a reflective layer disposed on a rear side of the rear electrode layer. The photovoltaic medium layer may include a photovoltaic absorber, an electron transfer layer disposed on a side of the photovoltaic absorber, and a hole transfer layer disposed on an opposite side of the photovoltaic absorber. The photovoltaic absorber may include the perovskite. The reflective layer may be a Lambertian reflector that has a diffusely reflecting surface.
These advantages and others are further achieved, for example, by a method for fabricating a light trapping photovoltaic device. The method includes steps of providing a substrate, performing an anisotropic etching on a top surface of the substrate to form a plurality of recesses on the top surface, and forming a plurality of light trapping photovoltaic cells in the recesses. The step of forming a plurality of light trapping photovoltaic cells includes steps of forming a reflective layer in the recesses, forming a first electrode layer on the reflective layer, depositing a photovoltaic medium layer on the first electrode layer, forming a second electrode layer on the photovoltaic medium layer, and forming an anti-reflection layer on the second electrode layer. The photovoltaic layer is configured to produce electricity in response to an external light and includes perovskite. Each recess includes a plurality of faces. Top edges of the faces form a loop defining a perimeter of an opening of the recess. Each of the faces is inclined at a predetermined angle with respect to a normal direction of the top surface of the substrate. The predetermined angle is greater than zero degrees and smaller than ninety degrees.
The predetermined angle with respect to a normal direction of the top surface may be in a range of 15 to 25 degrees. Each recess may have an inverted pyramid shape with a base of the inverted pyramid shape corresponding to the opening of the recess. Each recess may have a paraboloid shape with an aperture of the paraboloid corresponding to the opening of the recess. The faces of each recess may include a first and second faces that directly face each other, forming a V-shape cross-section of the first and second faces. An angle between the first and second faces may be in a range of 30 to 50 degrees. The step of depositing the photovoltaic medium layer may include steps of depositing one of an electron transfer layer and a hole transfer layer on the first electrode layer, depositing a photovoltaic absorber comprising perovskite on said one of an electron transfer layer and a hole transfer layer, and depositing the other of the electron transfer layer and the hole transfer layer on the photovoltaic absorber.
The preferred embodiments described herein and illustrated by the drawings hereinafter are to illustrate and not to limit the invention, where like designations denote like elements.
The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to make or use the embodiments of the disclosure and are not intended to limit the scope of the disclosure, which is defined by the claims. It is also to be understood that the drawings included herewith only provide diagrammatic representations of the presently preferred structures of the present invention and that structures falling within the scope of the present invention may include structures different than those shown in the drawings.
With reference to
The light trapping photovoltaic cell 120 includes a plurality of lateral photovoltaic layers 121-124 that are photovoltaic members configured to produce electricity in response to an external light 133. Each of the light trapping photovoltaic cells 120 may have an inverted pyramid shape in which a base of the inverted pyramid corresponds to the opening 111a defining the recess 111 and the lateral faces of the inverted pyramid correspond to the lateral photovoltaic layers 121-124. The inverted pyramid shape includes an inverted square pyramid shape, an inverted pentagonal pyramid shape, an inverted hexagonal pyramid shape, etc. Additionally, each of the light trapping photovoltaic cells 120 may have a paraboloid shape with a parabola cross-section.
In an embodiment, the light trapping photovoltaic cells 120 may have the inverted square pyramid shape having lateral photovoltaic layers 121-124 as shown in
The photovoltaic layers 121-124 completely cover lateral surface of the recess 111. Therefore, top edges of the photovoltaic layers 121-124 are disposed along a perimeter of the opening 111a defining the recess 111 in which the light trapping photovoltaic cell 120 is disposed. In other words, the top edges of the photovoltaic layers 121-124, when combined, completely form the perimeter of the opening 111a. The bottom sides of the photovoltaic layers 121-124, opposite to the top edges, may form an apex portion of the inverted pyramid. In this structure, a cross-sectional view of the first and second photovoltaic layers 121, 122 may form a V-shape as shown in
Each of the photovoltaic layers 121-124 is inclined at a predetermined angle 130 with respect to a normal direction 113 of the top surface of the substrate 110 so that a front face of each of the photovoltaic layers 121-124 is exposed to the external light 133 through the opening 111a. The predetermined angle 130 is greater than zero (0) degrees and smaller than ninety (90) degrees. The predetermined angle 130 may be in a range of 15 to 25 degrees. In an embodiment, the photovoltaic layers 121-124 may include a first and second photovoltaic layers 121-122 or 123-124 that directly face each other, forming a V-shape cross-section of the first and second photovoltaic layers 121-122 or 123-124. An angle between the first and second photovoltaic layers 121-122 or 123-124 may be in a range of 30 to 50 degrees. In another embodiment, the photovoltaic layer 121c of the light trapping photovoltaic cell 120c forms a parabola-approximating cross-section, as shown in
The light trapping photovoltaic cell 120 may have dimensional features larger than the wavelength of visible light, which is around 0.5 m, to efficiently utilize the reflection and refraction effects of the visible light. The width 131 and height 132 of the inverted pyramid structure may be in the order of microns scale. The width 131 may be no less than 0.5 m, and the height 132 may be no less than 0.5 m. The thickness of the photovoltaic layers 121-124 may be smaller than 0.2 am. Each of the first and second photovoltaic layers 121, 122 may include multiple thin film layers such as a backside contact metal, a backside reflector that may be roughened to form a Lambertian reflector, the thin film perovskite photovoltaic layer that may include an absorber and any electron and hold transfer layers, and a patterned front contact and a front side anti-reflection coating.
With reference to
Each of the photovoltaic layers 121-124 includes thin film photovoltaic medium layer 140 configured to produce electricity in response to the external light 133, front electrode layer 141 disposed on the front side of the thin film photovoltaic medium layer 140, rear electrode layer 142 disposed on the rear side of the thin film photovoltaic medium layer 140, anti-reflection layer 143 disposed on the front side of the front electrode layer 141, and reflector or reflective layer 144 disposed on the rear side of the rear electrode layer 142. Herein, for description purpose, the front side is referred to as the top side of each layer, and the rear side is referred to as the bottom side of each layer.
The front and rear electrode layer 141, 142 provide electrical contact with the thin film photovoltaic medium layer 140. The front electrode layer 141 may be a patterned electrode layer. The front electrode 141 may be made of a transparent conductive material such as indium-tin-oxide (ITO). The photovoltaic layers 121-124 may be electrically coupled to each other via the front electrode layers 141 or the rear electrode layers 142. For example, the rear electrode layers 142 of the photovoltaic layers 121-124 may be electrically connected to each other, and the front electrode layers 141 of the photovoltaic layers 121-124 may be electrically connected to each other.
The backside reflector 144 may be a Lambertian reflector that has a diffusely reflecting surface. The light trapping photovoltaic cells 120 of the disclosed invention may utilize the backside Lambertian reflectors 144 in order to return uncaptured photons back into the absorbing portion of the perovskite film which may be included in the thin film photovoltaic medium layer 140. The thickness of the Lambertian reflector 144 may be on the scale less than 300 nm. This technique is especially useful for thin film photovoltaic layers and aides in the trades between thicker, more absorbing films and recombination losses.
The anti-reflection layer 143 may include various combinations of materials to maximize the anti-reflection effect based on the wavelength of the incident light 133. Refractive indexes of the materials for the anti-reflection layer 143 may be optimized based on the refractive indexes of the materials of the thin film photovoltaic medium layer 140. For instance, a dual layer antireflective coatings of silicon nitride can be used, or coatings of zinc sulfide (ZnS)/magnesium fluoride (MgF2) may be used. The anti-reflective approach can be used on a larger geometric scale. The anti-reflective approach increases the efficiency by which photons enter the absorbing medium layer 140, and therefore, provides improved light trapping effect. In additions to the optimized anti-reflective coatings 143 and backside reflectors 144, light trapping can be accomplished within the absorbing layer 145 of the thin film photovoltaic medium layer 140.
The thin film photovoltaic medium layer 140 includes photovoltaic absorber 145, electron transfer layer (ETL) 147 disposed on a side of the photovoltaic absorber 145, and hole transfer layer (HTL) 146 disposed on the opposite side of the photovoltaic absorber 145. The photovoltaic absorber 145 may include perovskite.
Among the competing photovoltaic technologies, perovskites have become widely embraced due to several promising characteristics: (1) As a thin film technology, perovskites hold the promise of rapidly scaling to large area, light, low cost and potentially flexible arrays, (2) perovskites demonstrated efficiency of over 20% has been shown, and (3) perovskites have been shown to substantially outperform in tolerance to space radiation effects. Perovskite cells may be made in multi-junction perovskite cells to improve stability and to optimize design and improve manufacturing characteristics.
The light trapping photovoltaic device 100 of the disclosed invention provides multiple advantages beyond that possible with a planar thin film Perovskite photovoltaic. First, the amount of photovoltaic material per unit area of incident light is substantially increased. This may create not only higher efficiency of photon conversion to electricity but also may improve sensitivity with light incident at large angles. Another advantage is an increase in the number of passes of light through the thin film photovoltaic medium layer 140. Photons that are not absorbed in the first pass through the perovskite absorbing layer 145 are reflected into another direction for another opportunity to be absorbed in the thin film photovoltaic layer 145 on their way returning track though the thin film. Upon reaching the front side of the thin film photovoltaic medium layer 140, unabsorbed photons might escape the film. However, photons escaping the film have yet another opportunity to pass across the V-shape lateral layers 121-122 and become re-absorbed with another sequence of passing and reflecting from the backside reflecting surface.
For example, as shown in
By these processes, the light trapping photovoltaic device 100 described here can be expected to substantially improve the external efficiency of the photovoltaic due to the increase in available photo-sensitive material and the trapping of photons. Importantly, the structure does not preclude the use of other optimizing techniques including backside reflectors, anti-reflective coatings, multi-junction absorbers, quantum dot absorbers and so on. When Perovskite is used for the thin film photovoltaic layer 123, distributed absorption may be achieved throughout the Perovskite layers.
With reference to
With reference to
Etching is performed on the substrate 110 to form recesses or trap structures 111 by using anisotropic etching technique, block S202. In general, a silicon substrate can be etched with any of a number of KOH-based wet etching materials anisotropically in directions creating well-defined, for example, steep 54.7 degrees slopes, by preferring to attack the <100> plane relative to others. Various surfactants may be used to create more complicated shapes. The orientation of the silicon and the KOH-based chemistry and conditions such as temperature may be used in conjunction with a sacrificial mask layer in order to create arrays of, for example, inverted pyramidal shapes with angles suitable to form the basis of the photovoltaic light trap structure described above.
Through etching process S202, recesses 111, including a plurality of faces, are created. Top edges of the faces of each recess 111 form a loop defining a perimeter of an opening 111a of the recess 111. Each of the faces is inclined at a predetermined angle 130 with respect to a normal direction 113 of the top surface of the substrate 110, where the predetermined angle 130 is greater than zero (0) degrees and smaller than ninety (90) degrees. The predetermined angle 130 with respect to a normal direction of the top surface may be in a range of 15 to 25 degrees.
Each recess 111 may have an inverted pyramid shape in which a base of the inverted pyramid corresponds to the opening 111a defining the recess 111 and the lateral faces of the inverted pyramid correspond to the lateral faces of the recess 111. The inverted pyramid shape includes an inverted square pyramid shape, an inverted pentagonal pyramid shape, an inverted hexagonal pyramid shape, etc. as shown in
After the recesses 111 are formed, a reflector or reflective layer 144 is formed inside the recesses 111, block S203, by using any known method. A rear electrode layer 142 is formed on the reflector 144, block S204, by using, for example, metal deposit method. A thin film photovoltaic medium layer 140 is deposited on the rear electrode layer 142, block S205, by using any known deposit method. A front electrode layer 141 is formed on the thin film photovoltaic medium layer 140, block S206. A front anti-reflection layer 143 is formed on the front electrode layer 141, block S207.
Coatings of these layers may be made by using typical thin film coating techniques or coating techniques that provide conformal cover for the sharp structural features of the light trapping photovoltaic cell. For example, additive manufacturing methods, such as a method for printing Perovskite solar cells on thin substrate, may be used.
Since many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Consequently, the scope of the invention should be determined by the appended claims and their legal equivalents.
This application claims the benefit under 35 U.S.C. § 119(e) of provisional patent application No. 63/544,070, filed Oct. 13, 2023, the contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63544070 | Oct 2023 | US |
