PROTECTIVE REGION FOR METALLIZATION OF SOLAR CELLS
Methods of fabricating a solar cell including metallization techniques and resulting solar cells, are described. In an example, a first and second semiconductor regions can be formed in or above a substrate, where a separation region is disposed between the first and second semiconductor regions. A protective region can be formed over the separation region. A first metal layer can be formed over the substrate, where the protective region prevents and/or inhibits damage to the separation region during the formation of the first metal layer. Conductive contacts can be formed over the first and second semiconductor regions.
Photovoltaic (PV) cells, commonly known as solar cells, are devices for conversion of solar radiation into electrical energy. Generally, solar radiation impinging on the surface of, and entering into, the substrate of a solar cell creates electron and hole pairs in the bulk of the substrate. The electron and hole pairs migrate to p-doped and n-doped regions in the substrate, thereby creating a voltage differential between the doped regions. The doped regions are connected to the conductive regions on the solar cell to direct an electrical current from the cell to an external circuit. When PV cells are combined in an array such as a PV module, the electrical energy collected from all of the PV cells can be combined in series and parallel arrangements to provide power with a certain voltage and current.
Efficiency is an important characteristic of a solar cell as it is directly related to the capability of the solar cell to generate power. Likewise, efficiency in producing solar cells is directly related to the cost effectiveness of such solar cells. Accordingly, techniques for increasing the efficiency in the manufacture of solar cells, are generally desirable.
The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter of the application or uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
This specification includes references to “one embodiment” or “an embodiment.” The appearances of the phrases “in one embodiment” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure.
Terminology. The following paragraphs provide definitions and/or context for terms found in this disclosure (including the appended claims):
“Comprising.” This term is open-ended. As used in the appended claims, this term does not foreclose additional structure or steps.
“Configured To.” Various units or components may be described or claimed as “configured to” perform a task or tasks. In such contexts, “configured to” is used to connote structure by indicating that the units/components include structure that performs those task or tasks during operation. As such, the unit/component can be said to be configured to perform the task even when the specified unit/component is not currently operational (e.g., is not on/active). Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. §112, sixth paragraph, for that unit/component.
“First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.). For example, reference to a “first” semiconductor region does not necessarily imply that this semiconductor region is the first semiconductor region in a sequence; instead the term “first” is used to differentiate this semiconductor region from another semiconductor region (e.g., a “second” semiconductor region).
“Based On.” As used herein, this term is used to describe one or more factors that affect a determination. This term does not foreclose additional factors that may affect a determination. That is, a determination may be solely based on those factors or based, at least in part, on those factors. Consider the phrase “determine A based on B.” While B may be a factor that affects the determination of A, such a phrase does not foreclose the determination of A from also being based on C. In other instances, A may be determined based solely on B.
“Coupled”—The following description refers to elements or nodes or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically.
“Inhibit”—As used herein, inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, and/or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.
In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and “inboard” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.
In the following description, numerous specific details are set forth, such as specific operations, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known techniques are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure.
Approaches to prevent and/or inhibit solar cell performance degradation induced during metallization processes are described herein. Embodiments of the present disclosure include the formation of a protective region over portions of a solar cell to prevent and/or inhibit impingement of energetic ions and/or ionizing radiation into the solar cell during a metallization process. In an example, protective regions can be used to inhibit charge carrier lifetime degradation over a trench and/or passivation region of a solar cell during a metal sputter deposition process.
Methods for metallization of solar cells and the resulting solar cells are also described herein. In the following description, numerous specific details are set forth, such as specific solar cell structures and process flow operations, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known fabrication techniques, such as lithography and patterning techniques, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.
Disclosed herein are methods of fabricating solar cells. In an exemplary process flow,
As disclosed herein, a conductive contact can include a metal contact structure formed over a semiconductor region of a solar cell. In an embodiment, the conductive contact can also be referred to as a metal contact. In an example, a conductive contact and/or metal contact can include one or more metal layers. In one example, the conductive contact includes aluminum, titanium tungsten, tungsten, and/or copper, among other metals.
Disclosed herein are methods for forming conductive contacts for solar cells. In a one exemplary process flow,
Also, disclosed herein is another method for forming conductive contacts for a solar cell. In a an exemplary process flow,
Embodiments described herein include fabrication of a solar cell 400 according to one or more of the above described approaches. Referring to
In an embodiment, the substrate 406 is a monocrystalline silicon substrate, such as a bulk single crystalline N-type doped silicon substrate. It is to be appreciated, however, that substrate 406 may be a layer, such as a multi-crystalline silicon layer, disposed on a global solar cell substrate. In an embodiment, the thin dielectric layer 408 is a tunneling silicon oxide layer having a thickness of approximately 2 nanometers or less. In one such embodiment, the term “tunneling dielectric layer” refers to a very thin dielectric layer, through which electrical conduction can be achieved. The conduction may be due to quantum tunneling and/or the presence of small regions of direct physical connection through thin spots in the dielectric layer. In one embodiment, the tunneling dielectric layer is or includes a thin silicon oxide layer. In an embodiment, the first and second semiconductor regions 410, 412 are N-type and P-type emitter regions, respectively. In an example, the N-type and P-type emitter regions are formed in the substrate itself, in which case distinct semiconductor regions (such as regions 410 and 412) and the dielectric layer 406 would not be included.
In an embodiment, the first and second semiconductor regions 410 and 412, respectively, are formed polycrystalline silicon formed by, e.g., using a plasma-enhanced chemical vapor deposition (PECVD) process. In one such embodiment, the first semiconductor region 410 is doped with an N-type impurity, such as phosphorus (e.g., N-type semiconductor region). The second semiconductor region 412 is doped with a P-type impurity, such as boron (e.g., P-type semiconductor region).
Referring to
In an embodiment, the light receiving surface 418, is a texturized light-receiving surface, as is depicted in
Solar cell substrates can be susceptible to performance degradation during a solar cell metallization process. In an example, the deposition of a metal seed layer via metal sputtering can involve collision of highly energetic metal species and damaging plasma-induced radiation at the separation region 414 resulting in solar cell performance degradation. Thus, in an embodiment, approaches to prevent and/or inhibit metallization-induced damage at the separation region 414 of the substrate 406 are presented.
Referring to
In an embodiment, the formation of the protective region 428 over the separation region 414 of the solar cell 400 can prevent and/or inhibit impingement of energetic ions and/or ionizing radiation into the solar cell 400 during a subsequent metallization process. In an example, ionizing radiation can include electromagnetic radiation such as in the ultraviolet (UV) and/or x-ray wavelengths. In one example, protective regions 428 can be used to inhibit the impingement of energetic ions and/or ionizing radiation over a trench and/or passivation region 414 of a solar cell 400 during a metal sputter deposition process. In the same example, the protective regions 428 can prevent and/or inhibit charge carrier lifetime loss at the trench and/or passivation region due to the impingement of energetic ions and/or ionizing radiation at those regions.
In an embodiment, prior to forming the blanket protective layer 424, an intervening layer 420 can be formed over the substrate 406. In an embodiment, the intervening layer 420 can also be referred to as an insulating layer. In one embodiment, the intervening layer 420 includes a back anti-reflective coating (BARC). In an example, the intervening layer 420 includes silicon nitride and/or amorphous silicon. Referring to
In an embodiment, openings 430 are formed in the intervening layer 420 to accommodate direct contact of a first metal layer to the first and/or second semiconductor regions 410 and 412 (e.g., as shown in
Referring to
In an example, the first metal layer 432 is formed from a blanket deposition process. In one example, a sputtering process can be used to form the first metal layer 432. In an embodiment, the protective region 428 protects the separation region 414 during the sputtering process. In one embodiment, the protective region 428 can prevent and/or inhibit damage to the separation region 414 during the sputtering process. In an embodiment, the first metal layer 432 can include one or more metals and/or metal alloys. In an example, the first metal layer 432 can include aluminum, titanium tungsten, tungsten, and/or copper, among other metals.
In an embodiment, forming the first metal layer 432 can include performing a mask and etching process. In an example, a mask can be formed over portions 436 of the first metal layer. Subsequent to forming the mask, other portions 434 of the first metal layer 432 can be etched to remove the other portions 434 of the first metal layer. Subsequent to etching the first metal layer 432, the mask can be removed.
In one embodiment, the first metal layer 432 can instead be formed in a pattern, where the first metal layer 432 is formed directly over the first and second semiconductor regions 410, 412 (e.g., not as an uninterrupted layer or in contrast to performing a mask and etching process as described above). In an example, forming the first metal layer 432 can include forming a patterned metal seed layer. In an embodiment, the patterned metal seed layer can be formed in alignment with the first and second semiconductor regions 410, 412.
Alternative embodiments used in the manufacture of solar cells can include forming the first metal layer 434 without a protective region 428. In this particular embodiment, energetic ions and ionizing radiation can impinge upon separation region 414 of the substrate 406 during metallization processes. In an example, ionizing radiation can include electromagnetic radiation such as in the ultraviolet (UV) and/or x-ray wavelengths. This metallization-induced damage at the separation region 414 can reduce charge carrier lifetime and cause overall solar cell performance degradation. One way to recover the charge carrier lifetime would be to perform an anneal at high temperatures, in an example, greater than 300 degrees Celsius. In this manner, materials used in the fabrication of the solar cell would be required to be thermally stable at high temperatures, e.g., exposure to greater than 300 degrees Celsius for a duration of 5-30 minutes. In an embodiment, forming the protective region 428, as described above, can eliminate the need for using a subsequent heating and/or annealing process to recover charger carrier lifetime lost subsequent to the formation of the first metal layer 432. In one embodiment, forming the protective region 428 allows for the use of fabrication materials on the solar cell that are thermally stable at temperatures less or equal to 300 degrees Celsius. In an embodiment, using the protective region 428 can allow for performing a reduced heating and/or annealing process subsequent to forming the first metal layer 434. In an example, the reduced heating and/or annealing process can be performed at temperatures less than or equal to 300 degrees Celsius.
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In an exemplary process flow,
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In an embodiment, metal foil 640 is an aluminum (Al) foil having a thickness approximately in the range of 5-100 microns and, preferably, a thickness of less than approximately in the range of 50 microns. In one embodiment, the Al foil is an aluminum alloy foil including aluminum and second element such as, but not limited to, copper, manganese, silicon, magnesium, zinc, tin, lithium, or combinations thereof. In one embodiment, the Al foil is a temper grade foil such as, but not limited to, F-grade (as fabricated), O-grade (full soft), H-grade (strain hardened) or T-grade (heat treated).
Referring to
Embodiments described herein include fabrication of a solar cell according to one or more of the above described approaches. Referring to
Referring to
In some embodiments, for example where the protective region 628 includes polysilicon, the protective region 628 can be removed. In one embodiment, the polysilicon region can be removed by a subsequent mask and etch process.
In an embodiment, although the solar cells 4-14 shown are back-side contact solar cells, the methods and structures described above can be used for front-side contact solar cells.
Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure.
The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.
Claims
1. A method of fabricating a solar cell, the method comprising:
- forming a first and second semiconductor regions in or above a substrate, wherein a separation region is disposed between the first and second semiconductor regions;
- forming a polysilicon region over the separation region;
- forming an insulating layer between the polysilicon region and substrate, wherein the insulating layer includes openings;
- forming a first metal layer over the polysilicon region, insulating layer and within the openings of the insulating layer, wherein the polysilicon region inhibits damage to the separation region during the formation of the first metal layer; and
- forming conductive contacts over the first and second semiconductor regions; and
- removing the polysilicon region.
2. The method of claim 1, wherein forming the first metal layer comprises performing a sputtering process to form the first metal layer over the polysilicon region, insulating layer and within the openings of the insulating layer, wherein the polysilicon region inhibits damage to the separation region during the sputtering process.
3. The method of claim 1, wherein the separation region is a trench region.
4. The method of claim 1, wherein forming the first metal layer comprises forming a metal seed layer over the polysilicon region, insulating layer and within the openings of the insulating layer.
5. The method of claim 1, wherein forming the first metal layer comprises forming a patterned metal seed layer over the polysilicon region, insulating layer and within the openings of the insulating layer.
6. The method of claim 1, wherein forming the polysilicon region over the separation region comprises depositing the polysilicon region over the separation region.
7. The method of claim 1, wherein forming the polysilicon region over the separation region comprises:
- forming a blanket polysilicon layer over the substrate;
- forming a mask over portions of the blanket polysilicon layer;
- etching exposed portions of the blanket polysilicon layer to form a polysilicon region over the separation region; and
- removing the mask.
8. The method of claim 1, wherein forming conductive contacts over the first and second semiconductor regions comprises:
- forming a mask over portions of the first metal layer;
- plating a second metal layer to exposed portions of the first metal layer;
- removing the mask; and
- performing an etching process to form conductive contacts over the first and second semiconductor regions.
9. The method of claim 1, wherein forming conductive contacts over the first and second semiconductor regions comprises:
- placing a metal foil over the first metal layer;
- bonding the metal foil to the first metal layer; and
- patterning the metal foil and first metal layer to form conductive contacts over the first and second semiconductor regions.
10. A method of fabricating a solar cell, the method comprising:
- forming a first and second semiconductor regions in or above a substrate, wherein a separation region is disposed between the first and second semiconductor regions;
- forming a protective region over the separation region;
- forming an insulating layer between the protective region and substrate, wherein the insulating layer includes openings;
- forming a first metal layer over the protective region, insulating layer and within the openings of the insulating layer, wherein the protective region inhibits damage to the separation region during the formation of the first metal layer;
- forming a mask over portions of the first metal layer;
- plating a second metal layer to exposed portions of the first metal layer;
- removing the mask; and
- performing an etching process to form conductive contacts over the first and second semiconductor regions.
11. The method of claim 10, wherein forming a protective region over the separation region comprises forming a protective region thermally stable at temperatures of at less than or equal to 300 degrees Celsius.
12. The method of claim 10, wherein forming the first metal layer comprises performing a sputtering process to form the first metal layer over the protective region, insulating layer and within the openings of the insulating layer, wherein the protective region inhibits damage to the separation region during the sputtering process.
13. The method of claim 10, further comprising:
- heating the substrate to a temperature of less than or equal to 300 degrees Celsius, wherein the protective region inhibits damage to the separation region during the heating.
14. The method of claim 10, wherein the separation region is a trench region.
15. The method of claim 10, wherein forming the first metal layer over the protective region, insulating layer and within the openings of the insulating layer comprises forming a metal seed layer over the protective region, insulating layer and within the openings of the insulating layer.
16. The method of claim 10, wherein forming the protective region over the separation region comprises forming a polymer over the separation region.
17. The method of claim 16, wherein forming the polymer over the separation regions comprises forming a polyimide, silicone, polymeric silsesquioxane, epoxy or acrylic over the separation region.
18. A method of fabricating a solar cell, the method comprising:
- forming a first and second semiconductor regions in or above a substrate, wherein a separation region is disposed between the first and second semiconductor regions;
- forming a protective region over the separation region;
- forming an insulating layer between the protective region and substrate, wherein the insulating layer includes openings;
- forming a first metal layer over the protective region, insulating layer and within the openings of the insulating layer, wherein the protective region inhibits damage to the separation region during the formation of the first metal layer;
- placing a metal foil over the first metal layer;
- bonding the metal foil to the first metal layer; and
- patterning the metal foil and first metal layer to form conductive contacts over the first and second semiconductor regions.
19. The method of claim 18, wherein forming a protective region over the separation region comprises forming a protective region thermally stable at temperatures of less than or equal to 300 degrees Celsius.
20. The method of claim 18, wherein forming the first metal layer comprises performing a sputtering process to form the first metal layer over the protective region, insulating layer and within the openings of the insulating layer, wherein the protective region inhibits damage to the separation region during the sputtering process.
21.-26. (canceled)
Type: Application
Filed: Jul 1, 2016
Publication Date: Jan 4, 2018
Inventors: Benjamin Ian Hsia (Fremont, CA), David Aaron Randolph Barkhouse (Menlo Park, CA), Todd Richards Johnson (San Jose, CA), Michael Cudzinovic (Sunnyvale, CA)
Application Number: 15/201,324