Patent Application
20100154877
The present invention relates to methods and apparatus for providing an opto-electronic or a photovoltaic device, such as a device in which a semiconductor photo-sensitive core is integrated within a cladding layer or layers to produce an opto-electronic or a photovoltaic structure.
Photovoltaic solar cells are attractive mechanisms for generating electrical energy as they do not produce greenhouse gasses as a byproduct. Conventional superstrate or substrate photovoltaic devices include a flat substrate to which a flat semiconductor material is coupled. The semiconductor material (which may be crystalline silicon) includes a p-n junction, which has the characteristic of creating unbound charges (electrons and holes) and generating a voltage V across a pair of conductors when light passes through the junction.
The primary issues with conventional solar cell approaches are cost, efficiency, and form factor associated with fabrication of the solar cell. Various single crystal or thin film processes have been developed in an attempt to address these issues in the superstrate or substrate devices. Single crystal solar cells can have high efficiency, but the process is quite expensive. Thin film semiconductor fabrication techniques can be less expensive, but the energy conversion efficiency is normally quite low.
For the above reasons, and others, the cost of solar energy is about 2-3 times more expensive than conventional grid power. In some solar energy sectors, such as roof top applications in homes, apartment complexes, industrial parks or applications where grid power is not easily available, low weight and form factor may be a significant advantage. Accordingly, there is a need in the art for a new approach to providing photovoltaic solar cells, which enjoy characteristics of low cost, high efficiency, low weight and low form factor.
It is noted that the body of prior art associated with optical fiber fabrication and design has relevance to the context and discussion of one or more embodiments of the present invention. In this regard, there are differences in meaning between the structures and applications associated with an optical “fiber” and a “cane” structure. For example, an optical fiber is generally considered to be flexible, to have an outside diameter of about 125-500 um, and to be used primarily in optical communications applications. A cane structure, on the other hand, is somewhat stiffer than a fiber, has an outside diameter of about 1-5 mm, and may be used in solar energy conversion applications.
In accordance with one or more embodiments of the present invention, a cane having optical and/or opto-electronic properties includes: a core formed of a semiconductor material; and a transparent cladding formed of glass, glass-ceramic, or polymer coaxially oriented about the core.
The cane may be fabricated by: preparing a hollow blank suitable for use in a blank redraw process; introducing a semiconductor material into the hollow portion of the blank; heating the blank and semiconductor material in a redraw furnace such that the blank and the semiconductor material flow; and simultaneously drawing the blank and the semiconductor material such that a core of the semiconductor material is coaxially oriented within a cladding produced from the hollow blank, thereby forming a cane.
The above structures and techniques may be employed to produce a photovoltaic device, including: a semiconductor core including at least one p-n junction, defined by respective n-type and p-type regions; a substantially transparent cladding in coaxial relationship with the semiconductor core(s), forming a longitudinally oriented cane; and first and second electrodes, each being electrically coupled to a respective one of the n-type and p-type regions.
Other aspects, features, advantages, etc. will become apparent to one skilled in the art when the description of the invention herein is taken in conjunction with the accompanying drawings.
For the purposes of illustrating the various aspects of the invention, there are shown in the drawings forms that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
With reference to the drawings, wherein like numerals indicate like elements, there is shown in
In one or more embodiments herein, the semiconductor core 102 may be formed from an amorphous, a micro- or nano-crystalline, a polycrystalline, or a substantially single-crystal semiconductor material. The term “substantially” is used in describing the semiconductor core 102 to take account of the fact that semiconductor materials normally contain at least some internal or surface defects either inherently or purposely added, such as lattice defects or a few grain boundaries. The term substantially also reflects the fact that certain dopants may distort or otherwise affect the crystal structure of the semiconductor material. For the purposes of discussion, it may be assumed that the semiconductor core 102 is formed from silicon. The above features (and those described later herein) may be applied using other inorganic semiconductor materials such as the type III-V GaAs, copper indium gallium diselenide, InP, etc. Still other semiconductor materials may be employed, such as the IV-IV (i.e. SiGe, SiC), the elemental (i.e. Ge), or the II-VI (i.e. ZnO, ZnTe, etc.). Organic semiconductors can also be employed with proper consideration.
When the semiconductor core 102 and cladding 104 are used in a photovoltaic device, the semiconductor core 102 may be formed from materials selected to cover a broad range of wavelengths for efficient absorption of the solar energy spectrum. For example, single crystal semiconductor materials, poly-silicon, amorphous silicon, and/or other materials may be employed, with Si, Si—Ge, Ge, GaAs, etc. being some of the suitable materials. Additionally, crystal semiconductor materials may also be combined with polymer semiconductor materials. The solar energy absorption coefficient varies from a very large value to a small value as a function of solar wavelength, particularly near the band edge. For example, for single crystal silicon, the wavelength range of interest is from around 350 nm to about 1100 nm. The absorption coefficient for single crystal silicon at 400 nm is about 8.89E+04 cm−1. In contrast, the absorption coefficient for single crystal silicon at 900 nm is only 2.15E+02 cm−1.
The substantially transparent cladding 104 may be formed of glass, glass-ceramic, or polymer. In the case of the cladding 104 being formed from an oxide glass or an oxide glass-ceramic, suitable compositions include CORNING INCORPORATED GLASS COMPOSITION fused silica, Vycor™, other outside vapor deposition compositions, or other compositions that are melted from raw materials and formed by traditional techniques.
For reliability of operation over cycling thermal conditions, the cladding 104 may have a similar thermal coefficient of expansion as the semiconductor core 102. For example, the thermal expansion coefficients of the core 102 and the cladding 104 may be between about 2.0-3.0 ppm, such as 2.6 ppm (assuming that the semiconductor material of the core 102 is silicon).
For purposes of fabricating the cane 100A (which will be discussed later herein), it is desired that the material used to form the cladding 104, such as glass, have a softening point that is close to, but higher than, the melting point of the semiconductor core 102 material. For example, the material used to form the cladding 104 may have a softening point between about 100-300° C. above a melting point of the semiconductor material of the core 102. Assuming that the semiconductor material of the core 102 is single crystal silicon, the melting point of such material would be approximately 1410° C. Thus, a suitable composition for the cladding 104 may have a softening point of between about 1500-1700° C., such as about 1550-1600° C.
Taking into consideration both the thermal expansion issue and the fabrication issue, a suitably matched composition for the cladding 104 may have a softening point of around 1550-1600° C. and a thermal expansion coefficient around 2.6 ppm (again, assuming that the semiconductor material of the core 102 is single crystal silicon).
For a core 102 formed from silicon, a glass composition cladding 104 may be silica-based with one or more added dopants, such as boron, phosphorous, germanium, aluminum, titanium, fluorine, etc. The dopants may be used to modify the thermal expansion coefficients and the softening temperatures of the glass cladding 104. Alternatively or additionally, and as will be discussed later herein, the dopants may be used to provide a source of ions for diffusing into the semiconductor material of the core 102, in order to attain desirable electrical characteristics for certain applications, such as solar applications. An example of a composition suitable for forming a glass-based cladding 104 is a B2O3-GeO2-SiO2 glass with 5-25% B2O3 and 10-13% GeO2. Such glasses may be fabricated in the form of tubes or blanks using vapor deposition processes, or other well known techniques, and shaped or drawn to the required sizes.
Dimensionally, the cane 100A may be many meters long depending on the fabrication process used. The diameter of the core 102 may be between about 1-500 um, such as between about 50-500 um, such as about 100 um. In some embodiments discussed herein, the diameter of a single semiconductor core may be much smaller, such as between about 0.1-10 um, such as about 5 um. For opto-electronic fiber applications, especially with photonic bandgap fiber designs with multiple solid core and air regions, the feature sizes in the core may also be submicron. The diameter of the cladding 104 may be between about 1-10 mm; or between about 1-5 mm, such as between about 2-4 mm. Those skilled in the art will appreciate from the description herein that particular applications for the cane 100A may dictate the specific dimensions of the core 102 and cladding 104, some of which may be important. In the context of photovoltaic applications, the above dimensions of especially the core 102 may permit practically complete absorption of even long wavelength solar radiation, possibly without any need for multiple passages of the light rays through the core 102. This optical characteristic is advantageous for high photo-cell efficiency. The dimensions of the core 102 may also minimize the amount of semiconductor material used, thereby controlling manufacturing costs.
In some applications, such as the aforementioned photovoltaic applications, it may be advantageous to form the core 102 from a substantially single crystal semiconductor material, and maintain as near to a single crystal material as possible through and after the cane fabrication process. Preferably, there are substantially no grain boundaries within the core 102 in a radial direction of the cane 100A. Additionally or alternatively, there are preferably substantially no grain boundaries in the core 102 within a range of about 1 mm to about 10 cm in an axial direction (into and out of the illustrated page) of the cane 100A. Additionally or alternatively, there are preferably substantially no grain boundaries in the core 102 within a range of about 10 mm to about 1 cm in the axial direction of the cane, such as within a range of about 5 mm to about 15 mm in the axial direction.
The ability to achieve a long, relatively smaller diameter cane 100A with high axial and radial stresses may help in the formation of a long single crystal or polycrystalline core 102. The few grain boundaries (or absence thereof) along the radial direction of the core 102 over few mm to one or more cm of length along the axial direction may be very advantageous in terms of achieving a high solar conversion efficiency, especially if charge collecting electrodes are placed along the radial direction where there are very few or no grain boundaries to trap the charged particles (as will be discussed later herein).
It is noted that, although the core 102 and the cladding 104 are illustrated as being of circular cross-section, which is preferred, other cross-sections are permitted.
As will be explored further herein, a cladding 104 of the transparent variety may serve multiple advantageous functions. The cladding 104 may provide the support for the semiconductor core 102 and protects the core 102 from environmental effects. In photo-voltaic applications, the cladding 104 may act as a dopant source for the formation of the p-n junction during the manufacturing process. In photovoltaic applications with the canes illuminated transverse to the long axis of the canes, the transparent cladding with cylindrical shape can act as an integrated concentrator lens. This concentration allows a larger area of the solar radiation to be focused on a much smaller area of the semiconductor junction. This concentration can be optimized by locating the semiconductor core closer to the focal point of the cylindrical cladding lens.
For purposes of discussion, it may be assumed that the blank 202 is formed from glass or glass-ceramic. The blank 202 is advantageously hollow and suitable for use in a blank redraw process. The process by which the glass blank 202 is produced may be derived from known methods of manufacturing a soot optical fiber preform. The glass blank 202 may be formed by depositing silica-containing soot onto the outside of a rotating and translating mandrel or bait rod of glass. This process is known as the outside vapor deposition (OVD) process. (It is understood, however, that other techniques that employ melting raw materials and forming using traditional techniques may also be employed. The soot is formed by providing a glass precursor in gaseous form to the flame of a burner, thereby oxidizing the glass precursor. A fuel, such as methane (CH4), and a combustion supporting gas, such as oxygen, are provided to the burner and ignited to form the flame. Mass flow controllers meter the appropriate amounts of a suitable dopant compound, a silica glass precursor, fuel and combustion supporting gas to the burner. The soot perform may be consolidated in a consolidation furnace to form the hollow, consolidated blank 202. The blank 202 may also be shaped as needed by processes such as grinding to obtain the cross-sectional shapes needed. An alternative tube (202 blank) fabrication processes may involve the extrusion of a glass tube, core-drilling a glass/glass ceramic rod or forming a glass/glass ceramic by casting into a mold.
A semiconductor material 206 is introduced into the hollow portion of the blank 202. The semiconductor material 206 may be in the form of one or more of semiconductor rods, bars, plates, powders, pieces, and powders. The semiconductor material may also be deposited as thick layers using CVD, PECVD processes, or slurry casting. In order to control reasonable variations in the rates of draw and desirable dimension tolerances (as well as electrical and optical characteristics) semiconductor rods or bars may be preferred. The rods or bars of semiconductor material 206 are of suitable dimensions (length and diameter) and the dimension of the central hollow of the blank 202 are determined and controlled such that after redraw, the core 102 diameter is within the preferred range and tolerance.
The semiconductor material 206 may be formed from at least one of an amorphous, a micro- or nano-crystalline, a polycrystalline, a substantially single-crystal, and an organic semiconductor material, such as Si, GaAs, InP, SiGe, SiC, Ge, ZnO, and ZnTe.
The manufacturing process further includes heating the blank 202 and the semiconductor material 206 via heating elements 204 in the redraw furnace 200A such that the blank 202 and the semiconductor material 206 flow. The blank 202 should be purged of any oxygen or air to prevent any oxidation or reaction with the semiconductor material 206, which might degrade the desired properties of the core 102. Simultaneously, the blank 202 and the semiconductor material 206 are drawn out of the furnace 200A such that the core 102 of semiconductor material is coaxially oriented within the cladding 104.
The heating step may be such that a temperature of the blank 202 and the semiconductor material 206 is above a melting point of the semiconductor material 206 but below a melting point of the blank 202. By way of example, the temperature of the blank 202 and the semiconductor material 206 may be less than about 300° C. (such as between about 100-300° C.) above the melting point of the semiconductor material 206. For example, the when the semiconductor material 206 is silicon, the temperature of the blank 202 and the semiconductor material 206 may be between about 100-300° C. above about 1400° C. This puts the redraw temperature at between about 1500-1700° C.
The material used to form the blank 202 may also be controlled such that its thermal coefficient of expansion substantially matches that of the semiconductor material 206. For example, the coefficient of thermal expansion of the blank 202 may be established at between about 2.0-3.0 ppm (such as 2.6 ppm) in order to match the thermal expansion coefficient of silicon.
When the blank 202 is formed from a silica-based glass composition, one or more dopants may be added to the silica-based glass composition to modify at least one of the thermal expansion coefficient and softening temperatures thereof. The dopants include at least one of boron, phosphorous, germanium, aluminum, fluorine and titanium, etc.
For example, the silica-based glass composition may be a B2O3-GeO2-SiO2 composition, such as about 5-25% B2O3 and about 10-13% GeO2. As will be discussed later herein, the dopants may be added for other reasons related to the electrical properties of the semiconductor material of the core 102.
The above-discussed B2O3-GeO2-SiO2 composition may be well suited to form the glass blank 202, since the resultant softening point would be close to, but higher, than the melting point of a silicon semiconductor material used to form the core 102 (e.g., a redraw temperature of about 1650-1700° C.), and the resultant thermal expansion coefficient would be in the range of about 2.0-2.6 ppm.
At the above temperatures, the glass blank 202 softens and a tapered root section is formed at a base thereof. The semiconductor material 206 also melts and flows to the root section of the glass blank 202. The blank 202 and the semiconductor material 206 preferably form a “gob section,” from which the cane 100A is drawn, where the blank 202 is soft (but not molten) and the semiconductor material 206 is at least partially molten 206A.
It is preferred that care be taken so that the semiconductor material 206 (such as the rods or bars) are placed slightly above the initial gob section of the glass blank 202. This may assist in the formation of a smooth root section and also satisfactory core 102 formation. In other words, the introduction of the semiconductor material 206 into the hollow portion of the blank 202 includes positioning the non-molten section of the semiconductor material 206 away from the gob section in a direction opposite to the direction that the cane 100A is drawn. During the draw, the semiconductor material 206A close to the root section in the hot zone is molten and the un-melted semiconductor material 206 (particularly the rod formation) continuously feeds down and remains in contact with the molten semiconductor material 206A. While the invention is not bound by any theory of operation, it is believed that the above molten semiconductor material 206A, the continuous feeding of the non-molten material 206, and the draw of the glass blank 202 and semiconductor material 206 into a long, smaller diameter cane 100A lead to high axial and radial stresses, which may result in the formation of long single crystal or polycrystalline semiconductor structures within the core 102.
Using the fabrication process discussed herein, the original outer diameter of the blank 202, the inner diameter of the hollow thereof, the semiconductor material 206 (e.g., rod) diameter, and the final redraw diameter (among other variables of redraw) dictate the core 102 dimension and semiconductor usage rate. In this regard, in combination with heating, the blank 202 and the semiconductor material 206 are simultaneously drawn such that the core 102 of semiconductor material 206 is coaxially oriented within the cladding 104. A control system (not shown) varies the tension applied to the cane 100A by suitable control signals to a tension mechanism 208, shown as two tractor wheels, to draw down the cane 100A at the proper speed and tension. In this way, it is possible to derive a length of core cane 100A having a desired inner diameter for the core 102 and a desired outer diameter for the cladding 104. For example, as discussed above, in photovoltaic applications, there may be significant advantages to controlling the diameter of the core 102 of the cane 100A to between about 1-500 um, such as between about 50-500 um, such as about 100 um. In some other applications (such as multi-cane structures within a single cladding, which will be discussed later herein), smaller diameter cores 102 are desirable, such as between about 0.1-10 um, 3-8 um, such as about 5 um. In applications involving opto-electronic fiber devices with photonic band-gap designs, the feature sizes within the multiple segments in the core 102 may be smaller than a micron.
The cane 100A is cooled as it is drawn down below the furnace and measured for final diameter by a non-contact sensor. One or more coatings may be applied and cured using suitable coating apparatus and processes known in the art. The specific types of coatings that may be suitable depend on the application to which the cane 100A is directed. The cane 100A may be wound via by a feedhead onto a storage spool if the cane diameter is small enough, i.e., as a fiber may be wound on a spool. If the cane diameter is too large for such winding, the canes can be cut to the required lengths and stored. Usually cane diameters less than 150 microns may be spooled. While spooling cane diameters of up to 350 microns are possible, the spool diameter has to be increased.
The parameters of the above fabrication process are preferably adjusted and controlled to achieve further structural characteristics of the core 102 of the cane 100A. In particular, the semiconductor material 206 may be formed from substantially single crystal material and may be maintained as near to a single crystal material as possible through and after the cane 100A fabrication process as discussed above.
With reference to
In some embodiments, the individual cores 102 may include a sub-cladding 104A, 104B, 104C, respectively. The process may include forming a plurality of separate canes 100A-1, 100A-2, 100A-3, etc., using the steps of preparing, introducing, heating and drawing discussed above with respect to
While it is possible to spool the canes 100A-1, 100A-2, 100A-3, etc., if the diameters thereof are small enough, the material is not always in the form of a fiber that can be spooled. Most often, the size of the multiple canes 100A-1, 100A-2, 100A-3 inserted in the tube are a few mm in diameter and cannot be spooled. When the diameters of the canes 100A-1, 100A-2, 100A-3 prevent spooling, the canes are inserted in the blank 222 after being prefabricated using the same draw process. These canes 100A-1, 100A-2, 100A-3 may be stacked inside the blank 222 and redrawn into the final structure 100B. An additional/alternative step may be to machine an outer diameter of the canes 100A-1, 100A-2, 100A-3 such that they fit into the outer blank 222.
Although the semiconductor-core cane 100A of
The photovoltaic device 110 includes a substantially transparent cladding 104, such as a glass cladding in coaxial relationship with the semiconductor core 102, such as silicon. The core 102 is constructed such that at least one photo-sensitive p-n junction 106 exists therein. One side of the p-n junction 106 may be formed via an n-doped region 102A of the core 102, while the other side of the p-n junction 106 may be formed via a p-doped region 102B of the core 102. At least one electrode 105A, 105B provides an electrical connection to each of the respective sides of the p-n junction 106.
It is understood that the structural and electrical details of the photo-sensitive p-n junction 106 are relatively complex, but are very well known and understood in the art. In solar-cell technologies, p-n junctions are formed in semiconductor materials to convert solar radiation into electrical current. These p-n junctions separate the electron-hole pairs created by the absorption of radiation to generate useful electrical current for an external load. Depending on the semiconductor material and process used, various types of solar-cell designs have been developed in the art. Some are simple p-n junctions, while others are more complex and are optimized for higher efficiency. More complicated junctions include p-i-n junctions. In some cases, p+ and n+ layers are added to the p-n and/or p-i-n junctions for improved charge collection and electrode/solar cell fabrication. In this application, when a p-n junction is referred to, it may include any of the various junctions indicated above, others known from existing literature, and/or those developed hereafter.
It is noted that the cladding 104 of the photovoltaic device 110 exhibits a desirable light directing characteristic. Indeed, the curvate characteristic of the outside contour of the cladding 104 tends to improve the collection of light into the cladding 104 and toward the p-n junction 106 for conversion into electricity.
Among the methods that may be employed to produce the photovoltaic device 110, it is preferred to employ one or more modified versions of the redraw processes discussed above with respect to
For example, for a p-n junction 106 formed within a silicon core 102, boron would be a suitable dopant for diffusing into the silicon core 102 and forming a p-type semiconductor region. On the other hand, phosphorous would be a suitable dopant for diffusing into the silicon core 102 and forming an n-type region. Placing the dopants within the precursor material, such as glass, of the blank 202 will produce the diffusion of the dopants into the core 102 during the cane drawing process. The high temperatures of the draw may lead to diffusion of the dopant into the semiconductor material (e.g., silicon) to form the p-n junction 106.
With reference to
An example of a composition suitable for forming a blank 202 with the desired dopants is: B2O3-GeO2-SiO2 glass with 5-25% B2O3 and 10-13% GeO2.
Such in-situ formation of the p-n junction 106 may be a very cost effective process. If fast, low cost redraw of the cane 100A could not be optimized to lead to such in-situ formation of the p-n junction 106, the canes 100A may be further heat treated in a furnace to lead to further dopant diffusion from the cladding 104 into the core 102 to optimize the p-n junction 106 characteristics. Such a batch process can be scaled to efficient manufacture by stacking a very large number of canes 100A in a suitable oven or furnace. The equipment for performing such a process would not need to be very expensive as the relatively thick (mm scale) glass cladding 104 around the semiconductor of the core 102 provides a natural protection against contamination, oxidation, etc. This allows the high purity of the p-n junction 106 to be maintained without the need for expensive controlled atmosphere, high purity equipment or controls.
In an alternative embodiment, the cane 100B of
In yet another embodiment, the core 100B of
Using the techniques and structures discussed above, in addition to further disclosure and discussion herein, those skilled in the art will appreciate that there are many different solar applications which may be served by various aspects of the invention. With reference to
The photovoltaic device 110A includes a substantially transparent cladding 104, such as a glass cladding in coaxial relationship with the semiconductor core 102, such as silicon. The core 102 includes at least one photo-sensitive p-n junction 106. In this example, the device 110A includes a p-type silicon core 102P formed from a p-type material. The p-n junction 106 is defined by a generally cylindrical region of n-type material 102N around the p-type material of the core 102. The n-type material 102N may be formed using the in-situ process discussed above with respect to
The photovoltaic device 110A may include a first channel 120A extending longitudinally along the cladding 104 such that at least a portion thereof is adjacent to and in communication with the n-type region 102N of the core 102. The photovoltaic device 110A may include a second channel 102B extending longitudinally along the cladding 104 such that at least a portion thereof is adjacent to and in communication with the p-type region 102P of the core 102. In one or more configurations, such as in the illustrated embodiment of
Respective n+ and p+ portions, 102N+ and 102P+, are disposed at respective terminal ends of the first and second channels 120A, 120B in order to facilitate electrical connections to the respective n-type region 102N and p-type region 102P of the core 102. A first conductive material, such as conductive paste or epoxy, metallization, a wire, etc., may be disposed within the first channel 120A to form a first electrode 105A; and a second conductive material may be disposed within the second channel 120B to form a second electrode 105B. In one or more configurations, a wire may be maintained within the given channel 120 via a conductive epoxy. The channels 120A, 120B, n+ and p+ portions, 102N+ and 102P+, and the first and second electrodes 105A, 105B are located, sized and shaped such that voltage and current generated by the p-n junction 106 is accessible outside the cladding 104.
There are any number of fabrication processes that may be employed to produce the device 110A. In accordance with one of more aspects of the present invention, the device 110A may be fabricated by preparing a blank 202 from a material including at least one slot on an exterior surface thereof. The slot extends lengthwise in a longitudinal direction of the blank 202 and extends radially toward but not through to the hollow of the blank 202. The blank 202 and the semiconductor material 206 are drawn such that the slot 122 extends longitudinally along the cladding 104 and radially toward the core 102.
The first and second channels 120A, 120B may be formed via etching or laser ablation within the slot 122, such that the channels 102 extend longitudinally along the slot 122 of the cladding 104, and such that at least a portion of each is adjacent to and in communication with a respective one of the n-type and p-type regions 102N, 102P of the core 102. The etching may be achieved using ammonium bi-fluoride, HF acids, or any other suitable etchant. Using such acids, the etching process can be precisely controlled to make the channels 120. Laser ablation is also an attractive process for formation of the channels 120. In particular CO2 laser may be advantageous as it heats and ablates glass material, but is not absorbed by a silicon semiconductor material of the core 102. The characteristics may provide a self limiting channel formation and the ablation may stop once all the glass is ablated and the semiconductor is exposed for electrical contact formation.
The conductive material may then be introduced into the channels 120 in order to form the electrodes 105A, 105B. In one or more embodiments, a spin-on dopant or other similar liquid may be introduced into the channels 120A, 120B in order to form the n+ and p+ portions, 102N+ and 102P+. For example, the p+ portion 102P+ may be produced by introducing a spin-on dopant gel containing boron may be introduced into the channel 120B, which may come into contact with the p-type region 102P of the core 102. A heat treatment may then be applied to cause an excess of p-type ions to diffuse into the p-type region 102P, thus creating the p+ portion 102P+. The n+ portion 102N+ may be produced by introducing a spin-on dopant gel containing phosphorus may be introduced into the channel 120A, which may come into contact with the n-type region 102N of the core 102. A heat treatment may then be applied to cause an excess of n-type ions to diffuse into the n-type region 102N, thus creating the n+ portion 102N+.
Reference is now made to
In this example, the device 110B includes a substantially longitudinally oriented surface 124 (shown in cross-section) on which respective portions of the n-type region 102N and the p-type regions 102P of the core are exposed. The substantially longitudinally oriented surface 124 defines a substantially flat region characterizing the core 102 and cladding 104 in semi-circular cross-section. By way of example, the surface area of the semi-circular cross-section is greater than about 50% of a full circular cross section thereof. A first conductive layer 126A of material is disposed on the surface 124, is electrically coupled with the n-type region 102N, and forms a first electrode. A second conductive layer 126B of material is disposed on the surface 124 (adjacent to the layer 126A), is electrically coupled with the p-type region 102P and forms a second electrode. The layers 126A, 126B may be formed from conductive paste, epoxy, deposited metallization, etc., and may be deposited on the surface 124 using any of the known or hereinafter developed processes.
With reference to
In this example, the device 110C also includes a substantially longitudinally oriented surface 124 (shown in cross-section) on which respective portions of the n-type region 102N and the p-type regions 102P of the core 102 are exposed. A first conductive layer 126A of material is disposed on the surface 124, is electrically coupled with the n-type region 102N, and forms a first electrode. A layer of oxide 128, such as SiO2, prevents an electrical connection between the conductive material 126A and the p-type region 102P. A second conductive layer 126B of material is disposed on the surface 124 (adjacent to the layer 126A), is electrically coupled with the p-type region 102P and forms a second electrode.
Although there may be any number of ways to produce the longitudinally oriented surface 124, one considered desirable for purposes of one or more embodiments of the present invention is to polish the surface 124 into the cladding 104 to expose the respective portions of the n-type region 120N and the p-type region 120P of the core 102. Thereafter, the first and second conductive layers 126A, 126B may be disposed on the surface 124 such that they are electrically coupled with the respective n-type region 102N, and the p-type region 102N. The formation of the conductive layers 126A, 126B may be achieved, for example, via a vacuum deposition process.
Reference is now made to
The photovoltaic device 110D (
The photovoltaic device 110E (
There may be any number of ways to manufacture the photovoltaic devices 110D, 110E of
The n-type and p-type semiconductor plates 132N, 132P may be disposed within the channel such that they are in electrical communication with one another, such as in one of the orientations illustrated in
The blank, the semiconductor plates 132N, 132P, and the plug 101 may then be heated in a redraw furnace, and simultaneously drawn such that the semiconductor plates 132N, 132P are disposed within the cane 100C and/or 100D in a generally circular cross-section. Thereafter, some of the material of the cane 100C and/or 100D may be removed (if necessary, e.g., via etching, laser ablation or polishing) to expose at least some portion of the semiconductor plates 132N, 132P. Respective electrode material, such as conductive paste, epoxy, wire, metallization, etc., may then be disposed within or on the cane 100C and/or 100D and in electrical communication with each of the semiconductor plates 132N, 132P such that voltage and current generated by the p-n junction 106 is accessible outside the cane 100C and/or 100D.
Reference is now made to
The cane 100E may be used in any number of applications, although one example is the use in a photovoltaic application. In such an application, two electrodes are required to collect the charge generated at the p-n junction of the cell. From one or more embodiments above (such as is illustrated in
With reference to
The advantages of using conductive wire 140, such as a W (tungsten) or Al (aluminum) wire, is that such wires are highly conductive and provide little or no internal resistance, even in a meter-long cane-type solar cell. This may improve the charge collection and the solar cell efficiency. Also, such metal wires are relatively inexpensive as compared to using a vacuum deposition process to deposit metallization for the electrodes. Also, an advantage of such a co-drawn wire configuration is that the electrode formation step is combined with the semiconductor core formation, which approach is quite cost effective.
As will be appreciated by a skilled artisan from the disclosures herein, the cane 100E may be used to form a photovoltaic device (specific embodiments of which will be discussed later herein). In this regard, it may be desirable to produce an in-situ p-n junction 106 within the cane 100E during the heating and drawing process. This approach may be achieved by coating the conductive wire 140 with a dopant operating to provide a source of dopant atoms for diffusing into the semiconductor material of the core 102 during the heating and drawing process to form a p-n junction. For example, the dopant may include at least one of boron, phosphorous, germanium, aluminum, and titanium. For example, for a p-n junction formed within a silicon core 102, boron would be a suitable dopant for diffusing into the silicon core 102 and forming a p-type semiconductor region. On the other hand, phosphorous would be a suitable dopant for diffusing into the silicon core 102 and forming an n-type region. Placing the dopants on the wire 140 may produce diffusion of the dopants into the core 102 during the cane drawing process to form the p-n junction 106.
Reference is now made to
There may be any number of ways to manufacture the photovoltaic device 110F. An exemplary process for such fabrication includes using some or all of the techniques discussed above with respect to forming the cane 100E (FIGS. 12-13) in order to obtain the first electrode 105A coaxially within the core 102. In addition, the dopant diffusing techniques discussed above with respect to forming the device 110A (
In some situations, depending on the heating and drawing temperatures of the fabrication process, the conductive wire 140 might not be able to withstand the high processing temperatures. In some cases, the heating of the wire 140 and/or diffusion of ions from the wire 140 may contaminate the semiconductor material of the core 102. As discussed above, a coating may be applied to the wire 140 to ameliorate these problems. Another approach, however, is to form the core 102 such that the conductive wire 140 may be “inserted” therein after the cane is drawn. This can be done at a room temperature, or a relatively low temperature process, and would not lead to some of the problems mentioned above. In this regard, reference is now made to
With reference to
Using similar techniques as those discussed above with respect to forming p-n junctions 106 for photovoltaic applications, the one or more tubes 144A, 144B may be coating with, or formed from, a dopant operating to provide a source of dopant atoms for diffusing into the semiconductor material of the core 102 during the heating and drawing process. Again, the dopant may include one or more of boron, phosphorous, germanium, aluminum, titanium, etc.
An etching process may be used to remove the glass material of the tubes 144A, 144B and leave only the apertures 142A, 142B (which would be slightly larger in diameter) as shown in
Reference is now made to
A first conductor is disposed coaxially within the core 102 and serves as a first electrode 105A coupled to one of the n-type and p-type regions, in this example the p-type region 102P. A second conductor is disposed coaxially within the core 102 and serves as a second electrode 105B coupled to the other of the n-type and p-type regions, in this case the n-type region 102N. First and second tubes 144A, 144B, each surround a respective one of the first and second conductors 105A, 105B. The p-type region 102P of the cylindrically-shaped portion surrounds the first and second tubes 144A, 144B. Each of the tubes 144A, 144B includes respective longitudinally extending slots 146A, 146B, which extend through respective walls of the tubes 144A, 144B such that the first and second conductors are in electrical communication with the respective n-type and p-type regions 102N, 102P of the core 102.
As indicated previously, the cane drawing process can be repeated multiple times to obtain secondary canes. In this process the first set of canes can be obtained with cores of different semiconductor materials such as Si, Ge or a combination of Si and Ge in separate draw runs. The shape of the first set of canes can also be varied by shaping the cladding blank. The canes from these draw runs can be inserted in a second cladding blank to draw the second set of canes. This multiple draw process provides a number of advantages in the core segment materials and their composition and shape. For example, the core segments may include various p-n junctions of the same semiconductor type, or different semiconductor types. Further, the core segments may include a combination of semiconductor and optically transparent core and air/vacuum segments. Such processes may be suitable to make optoelectronic fibers and canes incorporating well known photonic band-gap fiber designs also. With such flexibility in the formation of the blank, various sized and shaped tubes and rods of different materials can be assembled for redraw. For example, with such structures and materials, it is possible to have p-n junctions in silicon material and also si-Ge material in the same blank. In addition to layering them, it is possible to have spatially separated p-n junctions, with Silicon p-n junction in one part of the core and si-Ge or Ge p-n junction in another part. Thus, various cross-sectional shapes and redraw process features permit not only multi-junction cells, but also spatially separated multi-junction cells for optimum solar collection.
An exemplary process for fabricating the photovoltaic device 110G includes using some or all of the techniques discussed above with respect to forming the cane 100F (
Reference is now made to
In this example of the photovoltaic device 110H, the plurality of photovoltaic cells 110j are disposed one next to the other such that the cladding 104 of a given one of the cells 110j is in close proximity, or touching, the cladding 104 of an adjacent one of the cells 110j. It is noted that all of the photovoltaic devices discussed above that include the cladding 104 exhibit a desirable light directing characteristic. Indeed, the curvate characteristic of the outside contour of the cladding 104 tends to improve the collection of light into the cladding 104 and toward the p-n junction 106 for conversion into electricity. In
The long axes of the cylindrical shaped devices 110j may be oriented the East-West direction so that the long length of the devices 110j allows the capture of the solar radiation as the sun moves over the horizon during the day. For low concentration designs, the high NA of the cladding 104 may capture the radiation without significant efficiency reduction even if the illumination is not on axis during the seasonal changes of sun's position on the horizon.
In addition to the embodiments discussed herein, additional optical mechanisms may be employed to enhance the absorption of solar energy and electrical power generation. For example, one or more lenses, prisms, reflectors, scattering surfaces, etc. that redirect the solar radiation for improved collection of light energy within the cladding 104 and toward the core 102.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
