US 20070107773 A1
Provided is a bifacial photovoltaic arrangement comprising a bifacial cell which included a semiconductor layer having a first surface and a second surface, a first passivation layer formed on the first surface of the semiconductor layer and a second passivation layer formed on the second surface of the semiconductor layer, , and a plurality of metallizations formed on the first and second passivation layers and selectively connected to the semiconductor layer. At least some of the metallizations on the bifacial photovoltaic arrangement comprising an elongated metal structure having a relatively small width and a relatively large height extending upward from the first and second passivation layers.
1. A bifacial photovoltaic arrangement comprising:
a bifacial cell including, a semiconductor layer having a first surface and a second surface;
a first passivation layer formed on the first surface of the semiconductor layer and a second passivation layer formed on the second surface of the semiconductor layer; and
a plurality of metallizations formed on the first and second passivation layers and selectively connected to the first surface and the second surface of the semiconductor layer,
wherein at least some metallizations comprise an elongated metal structure having a relatively small width and a relatively large height extending upward from the first and second passivation layers.
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22. A method for producing a bifacial photovoltaic device, the photovoltaic device including a semiconductor layer, one or more doped regions, a first surface, a second surface, and a plurality of conductive lines disposed over the first surface and the second surface and contacting one or more doped regions at the first surface and the second surface, the method comprising:
forming a blanket passivation layer on each of the first surface and the second surface of the semiconductor; and
utilizing a direct-write metallization apparatus arrangement to deposit the conductive lines to contact the doped regions of the semiconductor layer.
23. The method of
utilizing a non-contact patterning apparatus arrangement to define a plurality of openings through the first passivation layer and the second passivation layer, each the openings exposing a corresponding one of the one or more doped regions of the semiconductor layer; and
utilizing the direct-write metallization apparatus to deposit contact portions into the openings.
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33. A bifacial photovoltaic arrangement comprising:
a bifacial cell including,
a semiconductor layer having a first surface and a second surface, and a thickness of about 150 microns or less;
a first passivation layer formed on the first surface of the semiconductor layer and a second passivation layer formed on the second surface of the semiconductor layer; and
a plurality of metallizations formed on the first and second passivation layers and selectively connected to the semiconductor layer, the metallizations on the first passivation layer and the metallizations on the second passivation layer having sufficiently similar mechanical moments to maintain the semiconductor layer substantially un-warped.
34. The photovoltaic arrangement according to
This application is a Continuation-in-Part Application of U.S. patent application Ser. No. 11/336,714, filed on Jan. 20, 2006, by David K. Fork et al., and entitled “Solar Cell Production Using Non-Contact Patterning and Direct-Write Metallization”; U.S. patent application Ser. No. 11/282,882, filed on Nov. 17, 2005, by David K. Fork et al., and entitled, “Extrusion/Dispensing Systems and Methods”; and U.S. patent application Ser. No. 11/282,829, filed on Nov. 17, 2005, by David K. Fork et al., and entitled, “Extrusion/Dispensing Systems and Methods,” each of which are hereby incorporated by reference in their entireties.
This application relates to the conversion of light irradiation to electrical energy, and more particularly, to methods and tools for producing bifacial photovoltaic devices (e.g., bifacial solar cells) and arrangements of bifacial devices (e.g., bifacial solar cell modules) that convert solar energy to electrical energy.
Solar cells are typically photovoltaic devices that convert sunlight directly into electricity. Solar cells commonly include a semiconductor (e.g., silicon) that absorbs light irradiation (e.g., sunlight) in a way that creates free electrons, which in turn are caused to flow in the presence of a built-in field to create direct current (DC) power. The DC power generated by several PV cells may be collected on a grid placed on the cell. Current from multiple PV cells is then combined by series and parallel combinations into higher currents and voltages. The DC power thus collected may then be sent over wires, often many dozens or even hundreds of wires.
Presently, the majority of solar cells are manufactured using a screen printed process which screen prints front and back contacts. The back contact is commonly provided as a layer of aluminum. The aluminum layer will cover most if not all the back layer of the silicon wafer, thereby blocking any light which would reflect onto the back surface of the silicon wafer. These types of solar cells therefore receive and convert sunlight only from the front exposed surface.
However, another type of known solar cell is a bifacial solar cell, which acquires light from both surfaces of the solar cell and converts the light into electrical energy. Solar cells which are capable of receiving light on both surfaces are available on the market. One example is the HIT solar cell from Sanyo Corporation of Japan, as well as bifacial solar cells sold by Hitachi Corporation, also of Japan.
Drawbacks with existing bifacial solar cells include those related to the manufacturing processes. Various ones of these drawbacks are similar to those drawbacks existing in the manufacture of single-sided solar cells, such as discussed, for example, in U.S. patent application Ser. No. 11/336,714, previously incorporated herein by reference. As discussed in that document, desired but largely unavailable features in a wafer-processing tool for making solar cells are as follows: (a) never breaks a wafer—e.g. non contact; (b) one second processing time (i.e., 3600 wafers/hour); (c) large process window; and (d) 24/7 operation other than scheduled maintenance less than one time per week. The desired but largely unavailable features in a low-cost metal semiconductor contact for solar cells are as follows: (a) Minimal contact area—to avoid surface recombination; (b) Shallow contact depth—to avoid shunting or otherwise damaging the cell's pn junction; (c) Low contact resistance to lightly doped silicon; and (d) High aspect metal features (to avoid grid shading while providing low resistance to current flow).
It is particularly desirable to provide feature placement with high accuracy for feature sizes below 100 microns. By minimizing the feature sizes, more surface area is available for the accumulation and conversion of solar light. Features on the order of 10 microns or smaller can suffice for extracting current. For a given density of features, such a size reduction may reduce the total metal-semiconductor interface area and its associated carrier recombination by a factor of 100.
Further, a major cost in solar cell production is that of the silicon layer itself. Therefore, the use of thinner layers is desirable as one way of reducing costs associated with the manufacture of solar cells. However, with existing technology, the manufacture of thin crystalline (silicon) layers (e.g., 150 microns or less) is not commercially feasible, if not impossible, due to the previously mentioned unavailable features, and because the contact layers such as silver, aluminum, etc., cause the semiconductor layers to warp or bow.
In addition, such thin devices in general have a problem that not all light is absorbed by the thin cell. To reach high efficiency using a thin silicon layer, cells require a design which permits a higher percentage of the light to be absorbed. Ideally, a high efficiency thin cell of any material in construction will accept light incident on it from either side with minimal loss, and then trap the useful portion of the solar spectrum so that it is absorbed to create photovoltaic energy.
Provided is a bifacial photovoltaic arrangement which includes a semiconductor layer having a first surface and a second surface. A first passivation layer is formed on the first surface of the semiconductor layer, and a second passivation layer is formed on the second surface of the semiconductor layer. A plurality of metallizations are formed on the first and second passivation layers and are selectively connected to the semiconductor layer. At least some of the metallizations include an elongated metal structure having a relatively small width and a relatively large height extending upward from the first and second passivation layers
In accordance with another aspect of the present application, a bifacial photovoltaic arrangement includes a bifacial cell having a semiconductor layer with a first surface and a second surface, and a thickness of about 150 microns or less. A first passivation layer is formed on the first surface of the semiconductor layer, and a second passivation layer is formed on a second surface of the semiconductor layer. A plurality of metallizations are formed on the first and second passivation layers, and selectively connect to the semiconductor layer. The metallizations on the first passivation layer and metallizations on the second passivation layer have sufficiently similar mechanical moments to maintain the semiconductor layer un-warped.
In accordance with a further aspect of the present application, a method is provided for producing a bifacial photovoltaic device. The method includes forming a blanket passivation layer on each of a first surface and a second surface of a semiconductor layer. A direct-write metallization apparatus arrangement is utilized to deposit the conductive lines to contact the doped regions of the semiconductor region.
These and other features, aspects and advantages of the present application will become better understood with regard to the following description, appended claims, and accompanying drawings, where:
FIGS. 12(A) and 12(B) are cross-sectional side views showing gridlines formed on a photovoltaic device by the extrusion nozzle during the metallization separation according to an embodiment of the present application;
The present application relates to improvements in bifacial photovoltaic devices (e.g., bifacial solar cells) and bifacial photovoltaic arrangements (e.g., bifacial solar cell modules) that can be used, for example, to convert solar power into electrical energy. The following description is presented to enable one of ordinary skill in the art to make and use the application as provided in the context of a particular application and its requirements. As used herein, directional terms such as “upper”, “lower”, “side”, “front”, “rear”, are intended to provide relative positions for purposes of description, and are not intended to designate an absolute frame of reference.
Further, the semiconductor material described herein is at times referred to as a semiconductor layer, it is to be understood this term and its variants are intended to be broadly understood as the material used in the solar device to absorb the solar radiation for conversion into electrical energy, while the term solar device is at times called a solar cell, photovoltaic cell, photoelectric cell, among other descriptions. Therefore, use of the term semiconductor layer (and its variants) will, among other descriptions, be understood to encompass wafers as well as thin film materials used to make solar devices, including bifacial solar devices. Various modifications to the preferred embodiment will be apparent to those with skill in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present application is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.
The flow diagram of
More particularly, once the semiconductor layer has been heated so as to set the deposited contact structures, the process moves to step 150 where the device is flipped or rotated to present the back side for processing. In step 160 another non-contact patterning apparatus is used to define openings in the second passivation layer. Thereafter, in step 170, another direct-write metallization apparatus is used to deposit contact structures through the defined openings of the second passivation layer and onto the second semiconductor layer surface over the doped diffusion regions. Of course, the above steps may be undertaken up to. step 130 or alternatively 140. In this case, a single side of the semi-conductor layer is processed, so the device can be employed as a single-sided photovoltaic (solar cell) device. At times when used as a single-sided device, the second passivation layer may not be needed.
Referring now to
After initial treatment, device 211T1 is transferred to an optional loading mechanism 220 of processing system (tool) 230, which loads device 211T1 onto a conveyor 235. In accordance with the present concepts, processing system 230 includes at least one non-contact patterning device 240, and at least one direct-write metallization device 250, sequentially arranged in the conveying direction of conveyor 235 (e.g., to the right in
A heater apparatus 260 may be provided when it is necessary to apply a sufficient temperature to the directly written metal material in order to set the directly written metal material such that when device 211T4 is flipped or turned, the metal material will not be smeared or otherwise negatively affected. In one embodiment, the heater apparatus may be an inductive heater, an electric heater, a microwave heater, or other appropriate heating mechanism located near conveyor 235 of processing system 230, whereby the device 211T4 is able to move past or through heater apparatus 260 without being removed from conveyor 235. To set the directly written metal material, the heater supplies a temperature based on the specific characteristics of the metal material. In many instances, the temperature necessary to set the metal material deposited by direct-write metallization apparatus 250 will be in the range of 120° C. to 140° C. However, the temperature and amount of heat applied may vary depending on the particular materials used.
In an alternative embodiment, heater apparatus 260 may be located distanced from conveyor 235, and therefore the processing system will include additional components to off-load device 211T4 to the distanced apparatus, and thereafter return device 211T4 back to the conveyor.
In another alternative embodiment, the metal bearing material may contain compounds that polymerize or otherwise stabilize mechanically (that is convert from liquid to solid) in the presence of heat or light (particularly ultraviolet light). A light source may be provided to cure a portion of the applied metal material causing it to substantially retain its shape throughout the remainder of the process flow.
With attention to still another embodiment, the direct-write metallization process may employ a hot-melt material. Such a material may come in the form of a phase charge paste, where for example, it is in a liquid state as it passes through a heated printhead, and then solidifies or freezes as it is placed into contact with a substrate. In this case, the substrate may be the passivation layers and/or surfaces of the semiconductor layer. One typical phase change paste will include wax as the hot melt material, along with the appropriate metal material.
Following setting of the metal material on device 211T5, the device is rotated or flipped by flipping apparatus 270 to place the front surface, which has been processed, face down on the conveyor 235 in order to expose the back surface for processing. Such a flipping apparatus would be well known in the art. To process the back surface of device 211T5, processing system 230 includes a second non-contact patterning apparatus 240′ and a second direct-write metallization apparatus 250′. By use of these components, the second surface of device 211T6 is processed by non-contact patterning apparatus 240′, and device 211T7 is processed by direct-write metallization apparatus 250′, in a manner similar to that as described in connection with non-contact patterning apparatus 240 and direct-write metallization apparatus 250.
Processing system 230 also includes an optional off-loading mechanism 280 for removing processed devices 211T8 from conveyor 235 after processing by direct-write metallization apparatus 250′ is completed. The removed devices are then transferred to a post-metallization processing system 290 for subsequent processing. Optional loading mechanism 220 and off-loading mechanism 280 operate in a manner well known to those skilled in the art, and therefore is not described in additional detail herein.
In an alternative embodiment, a heater apparatus similar to heater apparatus 260 may also be included in the system, following the direct-write metallization apparatus 250′. However, this heater is optional, since to fully process device 211T8, it will be heated to a temperature higher (e.g., approximately 600° C.-900° C.) than the setting temperature (e.g., 120° C. to 140° C.). Therefore, the setting of the metal material on the back surface and final heating of the entire device may be accomplished in a single step by a heater arrangement of the post-metallization processing system 290.
Of course, other process flows may be used depending on specific devices being manufactured, and the apparatuses and arrangement of apparatuses within the processing system. For example, a processing system employing the concepts of to-be-discussed
With continuing attention to processing system 230, conveyor 235 is depicted in
More particularly, and prior to continued discussion of
By positioning device 211T1 in a substantially vertical position, it is possible to undertake processing operations without the requirement of flipping device 211T1. Therefore, operations on the two sides may be done simultaneously, or sequentially. For example, non-contact patterning apparatuses 240 and 240′ may be aligned across from each other on opposite sides of device 211T1 (a similar arrangement may be made with direct-write metallization apparatuses 250, 250′). In an alternative arrangement, these apparatuses may be offset from each other, such that only a single operation is being performed on either side of the surface at one time. Still further, the overhead conveyor implementation of
It is to be appreciated that, while device 211T1 of
Returning now to
In an alternative embodiment, a particle-beam generating apparatus or other appropriate device which can form openings, such as openings 217, may be used in place of the laser-based patterning. It is to be appreciated that when non-contact patterning apparatus 240′ processes the back side of device 211T5, a similar layout of openings 217′ through passivation layer 215′ will be formed on the back side of the device. For convenience of explanation, a separate figure is not provided, and as such a two-sided processing is depicted in
In a further alternative embodiment, the non-contact patterning device is not a laser- or particle-beam generating device used to form the contact openings through the passivation layers. Rather, a solar paste may be used which can include a glass frit in an organic vehicle. Upon heating, the organic vehicle decomposes and the glass frit softens and then dissolves the surfaces of the passivation layers, creating a pathway to the semiconductor layer.
It is to be appreciated the embodiments used to make connections from the semiconductor layer to the metallizations, such as the contact portions, gridlines, etc. may result in situations where less than all of the intended connections are made, due, for example, to imperfect manufacturing, such as misalignment over a doped region, incomplete formation of openings, etc. Therefore, the connections may be considered to be selective connections, where this may mean all the intended connections, or some amount less than all of the intended connections, are actually made.
In accordance with a specific embodiment to form the above-mentioned openings 217,
In an alternative embodiment, laser-based non-contact patterning apparatus 240-1 includes a femtosecond laser. The advantage of using a femtosecond laser is that the laser energy can be focused to sufficient power that the electric field is strong enough to ionize the atoms in the passivation layer. This enables energy absorption in spite of the fact that the laser's photon energy may be less than the band gap energy of the dielectric passivation. Thus, passivation material can be ablated with less debris or finer debris. Debris that are generated can be removed by a stream of gas flow to prevent their redeposition onto the device.
Returning again to
Next, device 211T8 is provided to optional wafer-off loading mechanism 280, which transports device 211T8 to post-metallization processing system 290. Thus, in this embodiment, openings 217′, contact (metallization) portions 218′, and current-carrying conductive gridlines 219′, are formed in a manner similar to that as described in connection with the processing of the first or upper side of device 211T1-211T3. It is to be understood, however, even though the present embodiment employs similar processes on the front surface and back surface of device 211, this is not required. Also, the placement of openings 217, 217′, contact portions 218, 218′ and conductive gridlines 219, 219′, do not need to have corresponding patterns and locations on each side of the device. Still further, the materials used for metallization on each side do not need to be the same. Rather, it is common to use different materials for the different sides.
Turning attention to
The immediate execution of metallization following the formation of contact openings 217 provides the additional advantage of limiting the air-exposure of exposed portions 213A. This short-duration exposure prevents the formation of an oxidized silicon layer that can otherwise interfere with the formation of the subsequently formed silicide (discussed below). Subsequent heating of the device after the set heating by heating apparatus 260, for example, during the post-metallization processing 290 of
In an alternative embodiment of the present application, the direct-write metallization devices of the application may be utilized to print a seedlayer metallization material (e.g., Ni, Cu or Ag) inside each opening and in a predetermined pattern on the passivation layers to form one or more seedlayers. After removal from the conveyor, device is subjected to plating processes, whereby conductive lines are formed on seedlayers using known techniques. This embodiment provides an inherently self-aligned process particularly well suited to fabrication of bifacial solar cells. In a preferred embodiment, seedlayer metallization material would be jet printed, fired, and then plated with additional metal. It is to be appreciated that in order to form a bifacial cell, such processing is performed of both sides of the device.
In accordance with another aspect of the present application, the direct-write metallization apparatuses may be an inkjet-type printhead or an extrusion-type dispensing nozzle, as described in the following exemplary embodiments. By arranging such non-contact, direct-write metallization apparatuses immediately downstream of the non-contact patterning apparatus (described above), the present application enables the precise placement of metallization over the just-formed contact openings without an expensive and time-consuming alignment step.
Print assembly 450 includes a print head 430 and an optional camera 470 (having high magnification capabilities) mounted in a rigid mount 460. Print head 430 includes one or more ejectors 440 mounted in an ejector base 431. Ejectors 440 are configured to dispense droplets of the appropriate metallization material in a fluid or paste form onto device 211T2 in the manner described above.
Control circuit 490 is configured in accordance with the approaches described below to provide appropriate control signals to printing support structure 480. Data source 491 can comprise any source of data, including input from an in-line sensor (as described below), a networked computer, a pattern database connected via a local area network (LAN) or wide area network (WAN), or even a CD-ROM or other removable storage media. The control signals provided by computer/workstation 490 control the motion and printing action of print head 430 as it is translated relative to device 211T2.
Note that the printing action can be provided by printing support structure 480, by conveyor 235, or by both in combination. Computer/workstation 490 is optionally coupled to receive and process imaging data from camera 470. In one embodiment, camera 470 provides both manual and automated calibration capabilities for printing apparatus 250-1.
By properly calibrating and registering printing apparatus 250-1 with respect to device 211T2 the metallization pattern (e.g., contact portions 218 and metal portions 219L and 219U, described above with reference to
Creating nozzle 510 for laminar flow mitigates and/or minimizes mixing of materials as the materials traverse through nozzle 510 and out of opening 515. The N channels may also be shaped to counteract the effects of surface tension on the materials as they progress from nozzle 510 to device 211T2.
Each channel may be uniquely and/or similarly shaped, including uniform and/or non-uniform shapes. Similar to the inkjet-type printing apparatus (discussed above), nozzle 510 may be moved over device 211T2 during dispensing of the materials in order to produce the desired metallization structures. Curing component 520 and/or quenching component 530 may be utilized to limit the tendency for the dispensed materials to intermix after extrusion. For example, curing component may be used to cure the dispensed materials by thermal, optical and/or other means upon exit from nozzle 510. Alternatively, quenching component 530 can be used to cool wafer 212, thereby cooling and solidifying the dispensed materials immediately after extrusion.
Of course, an extrusion type dispensing apparatus, such as extrusion-type dispensing apparatus 250-2, may also be used in processing of device 211T5, i.e., the back surface.
To further describe the exemplary embodiment of the extrusion concepts, attention is directed to
As set forth in the following exemplary embodiments, the processing methods described above may be modified to optimize the production of bifacial cell-type photovoltaic devices. Particularly, using direct-write metallization apparatuses as described herein, the metallized area (e.g., gridlines, bus bars, contact portions) of a surface can, as previously mentioned, be less than 10% to 4%of the total surface area of a device.
In one embodiment, the metallization applied over the contact openings by the direct write metallization devices described above (i.e., inkjet-type printing apparatus 250-1 and/or extrusion-type dispensing apparatus 250-2) may, after subsequent thermal processing, serve as the complete cell metallization in preparation for tabbing and stringing the cells for module assembly. Alternatives to tabbing may also be applicable, for example the adhesive bonding of the cells to a flexible backplane.
In another alternative embodiment, instead of linearly arranged contact openings 217, 217′, continuous line openings (not shown) are formed by laser pulses LP that are used to provide contact between the gridlines and the N-type diffusion region.
Turning to another aspect of the present application, and as previously mentioned, a large cost in the manufacture of a solar cell, is the cost of the semiconductor silicon layer. Therefore, it is desirable to employ as thin a semiconductor silicon layer as possible. In existing solar cells, the semiconductor layer is between 250 and 300 microns in thickness. However, due to the non-contact concepts of the present application, semiconductor layers of 150 microns to 100 microns, or even less, may now be considered for use.
However, when such thin semiconductor layers are attempted to be used, problems may occur. For example, for nearly all processing methods, including screen printing, as well as the above non-contact processing concepts, when a thin semiconductor silicon layer is employed in construction of a solar cell (such as a single-sided, square solar cell), an undesirable effect results. As shown in
This effect will also occur for bifacial cells which have gridlines on each surface, since there will also be a mismatch of thermal expansion between the materials. For example, in existing bifacial cells, silver is commonly used on one surface (e.g., the top metallization), and aluminum is used on the other surface (e.g., the bottom metallization). In this instance, since aluminum and silver, as well as the silicon of the semiconductor layer, have significantly different coefficients of thermal expansion, the bifacial cell warps (e.g., bows) when a thin semiconductor layer is used (e.g., silicon of about 150 microns or less). Although, depending on the semiconductor layer type and metal material, bowing may occur for semiconductor layers thicker than 150 microns.
An aspect of the present application which addresses this issue, is to manufacture a bifacial cell to insure that the mechanical moments of the gridlines on the upper surface and the lower surface are equal. By matching the mechanical moments, the semiconductor layer itself can be made thinner than presently possible, while avoiding the warping effect. As shown by the bifacial cell 1008 of
Use of the materials in the present application results in the difference in the coefficient of thermal expansion between the two sides to be sufficiently minimized so as to maintain the wafer non-warped. Alternatively, if metals of significantly different coefficients of thermal expansion are used on the different sides of the bifacial cell, for example, where silver might be used as the metal material on one surface and aluminum used as the other metal material, the present application provides a manner to even out the stresses. As depicted by dotted line layer 1018 in
Silicon has a coefficient of thermal expansion of 2.8×10−6/° C. The expansivity of most metals is substantially higher. Silver, which is the commonly used material for front emitter contact gridlines, has a coefficient of thermal expansion of 18.9×10−6/° C. Aluminum, which is the commonly used material for the blanket collector metallization, has a coefficient of thermal expansion of 23.1×10−6/° C. When the metal is fired at a temperature on the order of 850° C., it is either liquid in the case of aluminum, or it is softened. Stress accumulates during cooling from the firing temperature. The metal structures attempt to contract more than the silicon, and thereby develop a tensile stress. This occurs in existing cells which use a blanket layer of aluminum, because the aluminum layer covers nearly the entire back surface and is typically over 20 microns thick, and it has a much larger mechanical moment than the front surface metallization. This causes the silicon layer to bow toward the aluminum side. Given that the gridlines on the front surface of a typical screen printed semiconductor layer cover about 10% of the area, the mechanical moment of the silver metallization on the front is more than 10× smaller than mechanical moment of the aluminum metallization on the back. The bowing problem becomes more severe as the semiconductor layer becomes thinner.
On the other hand, since the present embodiments provide an improved contact structure on the back surface of the semiconductor layer, less contact area is needed, and therefore blanket metallization is unnecessary. By breaking the back surface metallization into gridlines and bus bars rather than a blanket layer, it will be appreciated that the quantity of metal can be reduced by over 90%. This has the desired improvement that the mechanical moments of the front and back layers are comparable. The present disclosure permits for the mechanical moments can be matched even closer by one or more of the following procedures: (1) The respective widths of the metallizations on each side of the semiconductor layer can be tailored to equalize the mechanical moments; (2) The respective thicknesses on each side of the semiconductor layer of the metallizations can be tailored to equalize the mechanical moments; (3) The respective volumes of the metallizations on each side of the semiconductor layer can be tailored to equalize the mechanical moments; (4) For multilayer metallizations, for example on the backside of the semiconductor layer, one might use an aluminum—nickel—silver layered metallization to produce the desired matching mechanical moment to silver metallization on the front side of the semiconductor layer. Other ones of these embodiments take advantage of the fact that (a) if the lines on the front and back of the semiconductor layer are of primarily the same metal, e.g. silver, if the volumes are approximately equal, the mechanical moments will also be approximately equal and (b) silver is a better electrical conductor than aluminum. One method for producing the multilayer line is to employ vertical coextrusion described in U.S. patent application Ser. No. 11/282,882, filed on Nov. 17, 2005, and entitled, “Extrusion/Dispensing Systems and Methods.”
The individual solar cells constructed in accordance with the previously described processes are commonly incorporated in a bifacial photovoltaic arrangement such as a bifacial solar module shown in
During the module forming process, the layers are compressed and heated to permit the plastic laminate 1104 to melt and solidify the layers into a single module.
With attention to reflector 1112, insertion of reflector 1112 permits light entering through front surface 1102, which passes through the module without being originally absorbed by bifacial solar cells 1106, or which do not actually pass through solar cells 1106, to be reflected to the back side surface of solar cells 1106, whereby efficiency in the collection and conversion of the light to electricity is improved. It is to be understood reflector 1112 is sized and positioned to reflect light to the bifacial solar cells throughout the module, where the module may include multiple solar cells extending in horizontal and vertical directions in the same plane. Thus, in one embodiment, the reflector will be capable of reflecting light to all or at least a majority of the backsides of the bifacial solar cells of the module.
Turning to yet another embodiment, module 1130 of
Additionally, the previously described bifacial cells may be configured to have the passivation layer configured as an amorphous silicon surface passivation against the crystalline silicon wafer to reduce recombination of the electrons and holes. Further, the metallization scheme will include a transparent conducting oxide (such as but not limited to ITO) on each side. Such a cell could be designed to be operationally similar to that of an HIT cell from Sanyo Corporation. In this design, the metal paste used for the structures on the solar cell will be a curable material with a cure temperature below 400° C. This enables forming the metal gridlines without removing the hydrogenation in the amorphous silicon. Such metal pastes are available from vendors such as Cermet, Inc. of Atlanta, Ga.
With further attention to the embodiments of
Although the present application has been described with respect to certain specific embodiments, it will be clear to those skilled in the art that the inventive features of the present application are applicable to other embodiments as well, all of which are intended to fall within the scope of the present application. For example, although the description above is primarily limited to silicon-based photovoltaic devices, the various aspects of the present application may also be utilized in the production of photovoltaic devices on wafers formed by amorphous silicon, CdTe (Cadmium Telluride), or CIGS (copper-indium-gallium-diselenide), among others. In another example, although co-extrusion has been described as a procedure for obtaining high aspect ratio metal lines, other procedures such as mono-extrusion could be used where applicable. Also, the preceding may of course be used to manufacture a single-sided photovoltaic device.