Methods of Building Crystalline Silicon Solar Cells for Use in Combinatorial Screening
Embodiments of the current invention describe methods of forming different types of crystalline silicon based solar cells that can be combinatorially varied and evaluated. Examples of these different types of solar cells include front and back contact silicon based solar cells, all-back contact solar cells and selective emitter solar cells. These methodologies all incorporate the formation of site-isolated regions using a combinatorial processing tool and the use of these site-isolated regions to form the solar cell area. Therefore, multiple solar cells may be rapidly formed on a single crystalline silicon substrate for use in combinatorial methodologies. Any of the individual processes of the methods described may be varied combinatorially to test varied process conditions or materials.
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This application is a Continuation Application and claims priority to U.S. application Ser. No. 12/886,533 filed on Sep. 20, 2010, which claims priority to U.S. Provisional Application Ser. No. 61/244,052 filed on Sep. 20, 2009, each of which are herein incorporated by reference for all purposes.
FIELD OF THE INVENTIONThe present invention relates generally to crystalline silicon solar cell processing. More specifically, methods of forming crystalline silicon solar cell test substrates for use in combinatorial methodologies are described.
BACKGROUND OF THE INVENTIONCombinatorial processing has been used to evaluate materials, processes, and devices formed in semiconductor processing as well as other industries such as batteries, catalysts, pharmaceuticals, and biotechnology. Significant efforts to apply combinatorial processing to solar applications have not been made. In particular, the development of solar cell test substrates for the combinatorial evaluation of silicon-based solar cells has not been done.
Some exemplary solar processing operations for the formation of silicon-based solar cells include operations for adding (depositions) and removing layers (etching or texturing), defining features, preparing layers (e.g., cleans or surface treatments), doping, etc. Improvements, whether in materials, unit processes, or process sequences, are continually being sought for the solar processes. However, solar companies conduct research and development (R&D) on full substrate processing. This approach has resulted in escalating R&D costs and the inability to conduct extensive experimentation in a timely and cost effective manner.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings:
A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
The process of forming solar cell test substrates to combinatorially test materials, processes, and devices is described herein. Combinatorial processing enables multiple experiments to be performed on a single substrate and the rapid evaluation of solar cell processing operations and solar cell materials. The solar cell test substrates are designed to run the different combinatorial processes either in parallel, serial or some combination of the two. Embodiments of the current invention describe methods of forming different types of crystalline silicon based solar cells that can be combinatorially varied and evaluated. Examples of these different types of solar cells include front and back contact silicon based solar cells, all-back contact solar cells, and selective emitter solar cells. These methodologies all incorporate the formation of site-isolated regions using at least one combinatorial processing tool and the use of these site-isolated regions to form the solar cell area. Therefore, multiple solar cells may be rapidly formed on a single crystalline silicon substrate for use in combinatorial methodologies. Any of the individual processes, process conditions, or materials of the methods described may be varied combinatorially to test the effect of the variation on a solar cell.
In
At block 101 of
At block 102 of the flowchart in
At block 103 of the flowchart in
At block 104 of the flowchart of
At block 105 of the flow chart of
At block 106 the site-isolated regions of the crystalline silicon substrate are n-doped. As illustrated in
In an alternate embodiment, the crystalline silicon substrate may be doped within the combinatorial wet processing tool 300 where the dopant is diffused from a liquid solution. In this embodiment, multiple processes of the crystalline silicon substrate 200 could be processed in the combinatorial wet processing tool: the etching of the diffusion barrier 202 at block 103, the texturing of the crystalline silicon substrate 200 at block 104, the optional cleaning process at block 105, and the n-doping of the crystalline silicon substrate 200 at block 106. The liquid dopant solution could be combinatorially varied if applied in the combinatorial wet processing tool 300. The liquid dopant solution contains phosphor for the doping and in one embodiment may be a solution of a solvent and POCl3. Alternately the phosphor n-dopant may be applied as a POCl3 paste that can be screen printed or spun onto the frontside of the crystalline silicon substrate 200 and then dried. After drying of the liquid or the paste the substrate 200 is placed in a furnace to diffuse the dopant into the crystalline silicon substrate. The patterned frontside diffusion barrier 202 and the backside diffusion barrier 204 ensure that the dopant only diffuses into the exposed surface of the crystalline silicon substrate 200 in the site-isolated textured regions 210 to form the doped region 214. The substrate 200 is then placed in a furnace to diffuse the phosphor into the textured exposed regions 210 to form the doped regions 214 as illustrated in
At block 107 a passivation layer 216 is formed over the doped site-isolated regions 214 and over the patterned frontside diffusion barrier layer 202, as illustrated in
At
At block 108 of the flowchart in
Similar methods to those described above may be used to build alternative solar cells such as selective emitter solar cells or all-back contact solar cells. An all-back contact solar cell is metalized only on the backside of the substrate to maximize the amount of sunlight that penetrates the crystalline silicon solar cells because there are no longer any shadows on the frontside created by frontside metallization. Referring to the Flowchart in
In
In
Selective emitter crystalline silicon solar cells may also be formed and evaluated combinatorially using the methodology outlined in the flowchart of
In one embodiment, the processes of the flowchart in
In one particular embodiment
In an alternate embodiment,
After a crystalline silicon solar cell test substrate is formed according to any of the methods described, the combinatorially varied solar cells are characterized. The characterization may be performed by measuring the electrical performance of each of the varied solar cells on the test substrate. For example, the current vs. the voltage of each of the cells can be measured or the quantum efficiency of the cell may be determined. The varied solar cells having the best performance may then be identified and tested on another test substrate or scaled up to manufacturing.
Combinatorial processing may include any processing that varies the processing in two or more regions of a substrate. The combinatorial methodology, in embodiments of the current invention, may include multiple levels of screening to identify, for example, materials, process conditions, process ordering, or process integration for further variation and optimization.
Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive.
Claims
1. A crystalline silicon solar cell test substrate, comprising:
- a diffusion barrier material deposited onto a frontside and a backside of a crystalline silicon substrate;
- a plurality of site-isolated regions defined on the frontside of the crystalline silicon substrate, wherein the site-isolated regions are defined by etching regions of the diffusion barrier material to expose regions of crystalline silicon, and wherein the exposed regions of crystalline silicon are textured after the etching of the diffusion barrier material, and wherein the exposed regions of crystalline silicon are doped with an n-type dopant after the texturing of the exposed regions of crystalline silicon;
- a passivation layer formed over the site-isolated regions;
- an electrical contact formed to the doped exposed regions of crystalline silicon within each of the site-isolated regions; and
- a plurality of electrical contacts formed to the backside of the crystalline silicon substrate, wherein at least one electrical contact formed to the backside of the crystalline silicon substrate is aligned with one of the site-isolated regions defined on the frontside of the crystalline silicon substrate.
2. The silicon solar cell test substrate of claim 1, wherein the diffusion barrier material comprises one of silicon nitride or silicon dioxide.
3. The silicon solar cell test substrate of claim 1, wherein the n-type dopant comprises phosphorous.
4. The silicon solar cell test substrate of claim 1, wherein the passivation layer comprises one of silicon nitride or silicon dioxide.
5. The silicon solar cell test substrate of claim 1, further comprising electrical lines and contact points to allow testing of solar cells formed within each site-isolated region.
6. A crystalline silicon solar cell test substrate, comprising:
- a diffusion barrier material deposited onto a frontside of a crystalline silicon substrate;
- a plurality of site-isolated regions defined on the frontside of the crystalline silicon substrate, wherein the site-isolated regions are defined by etching regions of the diffusion barrier material to expose regions of crystalline silicon, and wherein the exposed regions of crystalline silicon are textured after the etching of the diffusion barrier material, and wherein the exposed regions of crystalline silicon are doped with an n-type dopant after the texturing of the exposed regions of crystalline silicon;
- a passivation layer formed over the site-isolated regions defined on the frontside of the crystalline silicon substrate;
- a plurality of alternating n-doped and p-doped regions defined on the backside of the crystalline silicon substrate, wherein the alternating n-doped and p-doped regions are defined by photolithography, and wherein at least one n-doped region and at least one p-doped region are aligned with each of the site-isolated regions defined on the frontside of the crystalline silicon substrate;
- a passivation layer formed over the plurality of alternating n-doped and p-doped regions defined on the backside of the crystalline silicon substrate; and
- an electrical contact formed to each of the plurality of alternating n-doped and p-doped regions defined on the backside of the crystalline silicon substrate.
7. The silicon solar cell test substrate of claim 6, wherein the diffusion barrier material comprises one of silicon nitride or silicon dioxide.
8. The silicon solar cell test substrate of claim 6, wherein the n-type dopant comprises phosphorous.
9. The silicon solar cell test substrate of claim 6, wherein the passivation layer formed over the site-isolated regions defined on the frontside of the crystalline silicon substrate comprises one of silicon nitride or silicon dioxide.
10. The silicon solar cell test substrate of claim 6, wherein the passivation layer formed over the plurality of alternating n-doped and p-doped regions defined on the backside of the crystalline silicon substrate comprises one of silicon nitride or silicon dioxide.
11. The silicon solar cell test substrate of claim 6, further comprising electrical lines and contact points to allow testing of solar cells formed within each site-isolated region.
12. A crystalline silicon solar cell test substrate, comprising:
- a diffusion barrier material deposited onto a frontside and a backside of a crystalline silicon substrate;
- a plurality of site-isolated regions defined on the frontside of the crystalline silicon substrate, wherein the site-isolated regions are defined by etching regions of the diffusion barrier material to expose regions of crystalline silicon, and wherein the exposed regions of crystalline silicon are textured after the etching of the diffusion barrier material, and wherein the exposed regions of crystalline silicon are lightly doped with an n-type dopant after the texturing of the exposed regions of crystalline silicon, and wherein a portion of each site-isolated region is heavily doped with an n-type dopant after the lightly doping of the exposed regions of crystalline silicon;
- a passivation layer formed over the site-isolated regions;
- an electrical contact formed to the heavily doped exposed regions of crystalline silicon within each of the site-isolated regions; and
- a plurality of electrical contacts formed to the backside of the crystalline silicon substrate, wherein at least one electrical contact formed to the backside of the crystalline silicon substrate is aligned with one of the site-isolated regions defined on the frontside of the crystalline silicon substrate.
13. The silicon solar cell test substrate of claim 12, wherein the diffusion barrier material comprises one of silicon nitride or silicon dioxide.
14. The silicon solar cell test substrate of claim 12, wherein the n-type dopant comprises phosphorous.
15. The silicon solar cell test substrate of claim 12, wherein the passivation layer comprises one of silicon nitride or silicon dioxide.
16. The silicon solar cell test substrate of claim 12, further comprising electrical lines and contact points to allow testing of solar cells formed within each site-isolated region.
17. The silicon solar cell test substrate of claim 12, wherein the lightly doped exposed regions of crystalline silicon have a sheet resistance of approximately 70-100 ohms/square.
18. The silicon solar cell test substrate of claim 12, wherein the heavily doped exposed regions of crystalline silicon have a sheet resistance of approximately 20-30 ohms/square.
Type: Application
Filed: Aug 23, 2013
Publication Date: Dec 26, 2013
Applicant: INTERMOLECULAR, INC. (San Jose, CA)
Inventors: Jian Li (Fremont, CA), James Craig Hunter (Los Gatos, CA), Nikhil Kalyankar (Mountain View, CA), Nitin Kumar (Fremont, CA), Minh Anh Nguyen (San Jose, CA)
Application Number: 13/974,433