US20100154998A1

US20100154998A1 - Alternate use for low viscosity liquids and method to gel liquid

Info

Publication number: US20100154998A1
Application number: US12/626,363
Authority: US
Inventors: Qing Yuan Ong
Original assignee: Solexel Inc
Current assignee: Ob Realty LLC; Beamreach Solar Inc
Priority date: 2007-08-17
Filing date: 2009-11-25
Publication date: 2010-06-24
Also published as: US8512581B2; US9093323B2; WO2009026240A1; US20140127834A1; US20090042320A1; WO2009026240A8

Abstract

The present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, and apply it towards beneficially coating dopant liquid in the manufacture of a three-dimensional thin-film solar cell substrate. As an alternate to using high viscosity dopants, a dopant coating liquid, which is typically distributed in low viscosity alcohol based liquid forms, may instead be utilized as a dopant material in a gelatinous state towards the manufacture of a three-dimensional thin-film solar cell substrate. The methods and devices disclosed herein provide for enhancing the high viscosity characteristics of a dopant material. The present disclosure teaches the use of the dopant material in its gelatinous state towards an exemplary cavity filling method. The more cotable dopant material is applied in an exemplary coating layout and an exemplary integrated coating system to achieve improvements in coating coverage with regards to uniformity, which may be, but is not limited to, homogeneity, color uniformity, opacity, and density of the dopant material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. Patent Application is a continuation-in-part of pending U.S. patent application Ser. No. 12/193,415 filed Aug. 18, 2008 entitled “METHODS OF LIQUID TRANSFER COATING OF THREE-DIMENSIONAL SUBSTRATES” by inventor David Xuan-Qi Wang, et al., which claims the benefit to priority of U.S. Provisional Patent Application No. 60/956,388, filed Aug. 17, 2007, entitled, “LIQUID TRANSFER COATING APPARATUS AND METHODS” by inventor David Xuan-Qi Wang, et al., which is incorporated herein by reference in its entirety.
This U.S. Patent Application is also a continuation-in-part of pending U.S. patent application Ser. No. 12/477,095 filed Jun. 2, 2009 entitled, “ALTERNATE USE FOR LOW VISCOSITY LIQUIDS AND METHOD TO GET LIQUID” by inventor Rob (Qing Yuan) Ong, which claims the benefit of priority to U.S. Provisional Patent Application No. 61/007,549, filed Jun. 2, 2008, entitled, “ALTERNATE USE FOR LOW VISCOSITY LIQUIDS AND METHOD TO GET LIQUID” by inventor Rob (Qing Yuan) Ong, which is incorporated herein by reference in its entirety.

FIELD

This disclosure relates in general to the field of photovoltaics and solar cells, and more particularly the methods and apparatus for coating solar cell substrates. And more particularly, the presently disclosed subject matter relates to methods and apparatus to gel liquids. Even more particularly, the presently disclosed subject matter relates to the use of a liquid coating material for specially manufactured three-dimensional thin-film solar cell substrates.

DESCRIPTION OF THE RELATED ART

It is often desirable to form a thin layer of film from a liquid coating material on the surfaces or ridges of three-dimensional thin-film solar cell substrates. An example of such a substrate is a honeycomb-prism silicon substrate with hexagonal-prism sidewalls, among others. Applications of such substrates may include photovoltaic cells, micro-electro-mechanical systems (MEMS), and other semiconductor microelectronic devices.
Substantial literature exists describing the manufacture of thin-film photovoltaic devices, in which one or more coatings may be applied in layers directly on the surface of the cells of such devices. Coating is the process by which liquid layers may be applied to the surface of a solid, and is a process of dynamic wetting of a web. Several layers of coating material may be applied simultaneously to a moving web, but there may be a risk of imperfections.
Coating liquid such as, but not limited to, spin-on dopant is typically distributed in low viscosity alcohol based liquid forms and its stability is determined by how long it remains a liquid. When it starts to gel or solidify, manufacturers such typically consider this as a detrimental change because the material is no longer usable for spin-coating applications. Typically, the material is only used to the point when it starts to gel or solidify and do not attempt to understand the subsequent dopant characteristics. Manufacturers often attempt to slow down this process by storing the material at low temperatures. In addition, spin-on dopant may not be designed to transition through the gel state.
Using the teachings of the commonly referenced application, which is expressly incorporated in the pending U.S. patent application Ser. No. 12/193,415 filed Aug. 18, 2008 entitled “METHODS OF LIQUID TRANSFER COATING OF THREE-DIMENSIONAL SUBSTRATES” by inventor David Xuan-Qi Wang, et al., certain needs arise for the processing of dopants for use in association with said solar cell substrate, which may include a need to provide methods and devices for evaporating the solvent from the dopant material, for monitoring the consistency of said dopant material, for injecting additional dopant material into said reservoir to maintain a pre-determined consistency of dopant, for maintaining the homogeneity of the dopant material, for maintaining the color uniformity of the dopant material, for maintaining the opacity of the dopant material, for maintaining the density of the dopant material, for increasing the evaporation rate of a dopant material, for increasing the evaporation rate of a dopant material through agitation, and for maintaining the desired consistency of dopant material.

SUMMARY

The following description is not to be taken in a limiting sense, but is made for the purpose of describing the general principles of the present disclosure. The scope of the present disclosure should be determined with reference to the claims. And although described with reference to the manufacture and coating of three-dimensional thin-film solar cell substrates, a person skilled in the art could apply the principles discussed herein to the manufacture and coating of any multi-dimensional solar cell substrate.
The subject matter of the present disclosure may be applied in the preparation of a gelatinous dopant material, which could be used, for example, with a solar cell substrate. Such a solar cell substrate is disclosed in the commonly referenced pending U.S. patent application Ser. No. 12/193,415 filed Aug. 18, 2008 entitled “METHODS OF LIQUID TRANSFER COATING OF THREE-DIMENSIONAL SUBSTRATES” by inventor David Xuan-Qi Wang, et al. (which is incorporated by reference as if fully set forth herein), of which the present disclosure is a continuation-in-part. More specifically, the '415 application discloses selective coating of the top surface or top ridges of substrates having 3-D topography features with a liquid coating material.
The present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, and apply the dopant material towards beneficially coating dopant liquid in the manufacture of a solar cell substrate. As an alternate to using high viscosity dopants, a dopant coating liquid, which is typically distributed in low viscosity alcohol based liquid forms, may instead be utilized as a dopant material in a gelatinous state towards the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate. The methods and devices disclosed herein provide for enhancing the high viscosity characteristics of a dopant material. According to one aspect of the disclosed subject matter, there are provided methods and devices for aging a dopant material in a reservoir. The present disclosure teaches the use of the dopant material in its gelatinous state towards an exemplary cavity filling method. The more cotable dopant material is applied in an exemplary coating layout and an exemplary integrated coating system to achieve improvements in coating coverage with regards to uniformity, which may be, but is not limited to, homogeneity, color uniformity, opacity, and density of the dopant material.
These and other advantages of the disclosed subject matter, as well as additional novel features, will be apparent from the description provided herein. The intent of this summary is not to be a comprehensive description of the claimed subject matter, but rather to provide a short overview of some of the subject matter's functionality. Other systems, methods, features and advantages here provided will become apparent to one with skill in the art upon examination of the following FIGURES and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the accompanying claims.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present subject matter will now be described in detail with reference to the drawings, which are provided as illustrative examples of the subject matter so as to better enable those skilled in the art to practice the subject matter. Notably, the figures and examples are not meant to limit the scope of the present subject matter to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements and, further, wherein:

FIG. 1 depicts a gelation process for coating a dopant material that may be implemented in the manufacture of a solar cell substrate.

FIG. 2 outlines an embodiment of an exemplary process flow for selectively coating a three-dimensional thin-film solar cell substrate by using a cavity filling method and a dopant material as described in the present disclosure.

FIG. 3 shows an exemplary coating layout for coating a solar cell substrate by using the dopant material as described in the present disclosure.

FIG. 4 shows a photograph of an exemplary dopant material in an integrated coating system for the manufacture of a solar cell substrate.

FIG. 5 shows an exemplary three-dimensional thin-film solar cell substrate wafer coated with liquid coating material retaining coating properties as described in the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

In the present specification, an embodiment showing a singular component should not be considered limiting. Rather, the subject matter encompasses other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present subject matter encompasses present and future known equivalents to the known components referred to herein by way of illustration.
The subject matter of the present disclosure may be applied in the preparation of a gelatinous dopant material, which could be used, for example, with a solar cell substrate. Such a solar cell substrate is disclosed in the commonly referenced pending U.S. patent application Ser. No. 12/193,415 filed Aug. 18, 2008 entitled “METHODS OF LIQUID TRANSFER COATING OF THREE-DIMENSIONAL SUBSTRATES” by inventor David Xuan-Qi Wang, et al. (which is incorporated by reference as if fully set forth herein), of which the present disclosure is a continuation-in-part. More specifically, the '415 application discloses selective coating of the top surface or top ridges of substrates having 3-D topography features with a liquid coating material.
The common approach to create high viscosity dopants is to change the dopant composition using additives and/or different solvents so as to obtain a stable liquid that has high viscosity from the very beginning. This process may be complicated by the lack of high purity semi-grade additives to increase the viscosity.
The gelatinous nature of the dopant may be ideal for a coating application as it has high viscosity and very little tendency to flow, even when it is heated or dried. As such, an unexpected use for the dopant material, herein called dopant material, may be to coat the surface of a wafer in the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate.
The gelatinous nature of the dopant material may generally be a solution in which the chains are cross-linked by a more permanent means than mere physical entanglements. The cross-links may be chemical bonds; alternatively, they may be crystalline regions linked by chains which pass through more than one of these regions.
As an alternate to using high viscosity dopants, coating liquid such as, but not limited to, spin-on dopant, which is typically distributed in low viscosity alcohol based liquid forms, may instead be utilized as a coating liquid in the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate.
While manufactures of a solar cell substrate might consider the transition of a low viscosity liquid into becoming a gel or starting to solidify as a detrimental change, the present disclosure considers such a transition as being beneficial towards coating dopant liquid in the manufacture of a solar cell substrate.
Manufacturers typically consider a low viscosity liquid that becomes a gel or solidifies as a detrimental change because the material is no longer usable for spin-coating applications. Typically, the material is only used to the point when it starts to gel or solidify and do not attempt to understand the subsequent dopant characteristics. Manufacturers often attempt to slow down this process by storing the material at low temperatures. In addition, spin-on dopant may not be designed to transition through the gel state.
However, the present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, and apply it towards beneficially coating dopant liquid in the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate.
FIG. 1 depicts a gelation process layout 20 of a coating liquid that may be implemented in the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate. The gelation process layout 20 may create a more cotable liquid and may result in a longer shelf life for the dopant material 10 on a solar cell substrate. The gelation process layout 20 may include, but is not limited to, roller 12, pressing tool 14, agitator 18, dopant material 10, and reservoir, which may be, but is not limited to being, doctor bar reservoir 16.
In alternative embodiments of the present disclosure, the dopant material 10 may be, but is not limited to being an emulsion, a solvent (that may contain dispersed particles), solid content, glass beads, surfactants, a gel, a sol-gel, a wax, a paste (that may be or already pre-coated on a another transfer surface, such as tape), an adhesive, a powder (that may have particle sizes ranging from nanometers to several micron dimensions), an ink, a glue, a photosensitive material, a dopant (such as phosphorous and boron), a metal-organic liquid metal (such as aluminum and silver), a resist, an etch paste (such as an acidic one), and polymers (such as silicone). Further, the dopant material 10 may be comprised of subcomponents that each have a different viscosity, volatility, flammability, stability, acidity, color, wetability, etc.
The present disclosure teaches a method and apparatus to age the dopant material 10 in doctor bar reservoir 16, evaporate solvent from the dopant material 10, monitor the consistency of the dopant material 10, and injecting additional dopant material 10 into doctor bar reservoir 16 to maintain a pre-determined consistency of the dopant material 10.
The dopant material 10 does not gel or solidify at appreciable rates when left undisturbed at ambient conditions, and may require timings in excess of at least one hour to form a gelatinous state. To quickly create a gel from the dopant material 10, a continuous feed of the liquid onto roller 12 from doctor bar reservoir 16 that may be stirred, which may significantly increase the evaporation rate at room temperature. Further agitation may ensure that the dopant material 10 forms a gel instead of a solid. Once a desired consistency is obtained, the dopant material 10 may be used to coat the surface of a wafer in the manufacture of a solar cell substrate to achieve significantly improved coverage. Further, the gelation process layout 10 may include improve the coating characteristics of the dopant material 10 via a series of steps, which may occur singly or jointly, such as aging the dopant material 10, evaporating the solvent from the dopant material 10, monitoring the consistency of the dopant material 10, and injecting additional dopant material 10 into a doctor bar reservoir 16 to maintain a pre-determined consistency of the dopant material 10.
More particularly, the present disclosure teaches a method and apparatus to increase the evaporation rate while agitating the liquid dopant material 10. The dopant material 10 may reside in the doctor bar reservoir 16 or in a separate dispenser that may be dispensed to match the volume being consumed and to maintain equilibrium so that the liquid does not evaporate, thicken over time, and affect the amount of material coated. The agitator 18 may agitate the dopant material 10 with the use of pressing tool 14.
The agitation of the dopant material 10 may permit an aging process in the dopant material 10, which may allow for viscosities much greater than 50,000 centiposes, which is the theoretical limit that may be permissible by chemical modification alone. The step of aging the dopant material 10 may occur together with the step of heating the dopant material 10, which may be, but not limited to, through ultraviolet heating. Further, the step of aging the dopant material 10 may be associated with a predetermined shelf-life of the dopant material 10. The agitator 18 may increase the viscosity of the dopant material 10 up to, but not limited to, 200,000 centiposes.
The pressing tool 14 may press the dopant material 10 onto the surface of the roller 12 in the gelation process layout 20. The gelation process may pull away the dopant material 10, thereby increasing the surface area for solvent evaporation to aid in gelation. Further, the gelation process layout 20 may evaporate the solvent from the dopant material 10, which may be associated with, but not limited to, the evaporation of organic binders.
This gelatinous state of the dopant material 10 can be stabilized by the continued injection of fresh dopant material 10 to compensate for the evaporated solvent so as to maintain the desired consistency. Further, the gelatinous state of the dopant material 10 may be monitored for uniformity, which may be, but is not limited to, consistency, homogeneity, color uniformity, opacity, and density of the dopant material, among other properties, during the process of continued injection of fresh dopant material 10. Further, the monitoring of dopant material 10 may require a controlled environment, which may be associated with an environment saturated with certain solvents, temperature, humidity, and wind control. More particularly, with respect to consistency, the dopant material 10 may be maintained at a pre-determined consistency while residing in the doctor bar reservoir 16 or in a separate dispenser.
The gelatinous state of the dopant material 10 significantly improves the type of coating achieved using the same dopant material 10 in terms of the coverage, and process simplicity. The presently disclosed gelation process layout 20 of the dopant material 10 may be associated with the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate. The gelatinous dopant material improves the coating characteristics for use in association with said solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate.
More particularly, with regards coating characteristics, the present disclosure teaches a method and apparatus to maintain the uniformity, which may be, but is not limited to, the homogeneity, the color uniformity, the opacity, and the density of the dopant material in the manufacture of a solar cell substrate. Further, the present disclosure teaches a method and apparatus to gel the liquid dopant material while remaining in a well-mixed state, while being no more than ten percentage heterogeneous with respect to particulate count, and while preserving its color uniformity.
FIG. 2 derives from the commonly referenced pending U.S. patent application Ser. No. 12/193,415 filed Aug. 18, 2008 entitled “METHODS OF LIQUID TRANSFER COATING OF THREE-DIMENSIONAL SUBSTRATES” by inventor David Xuan-Qi Wang, et al., of which the present disclosure is a continuation-in-part. The subject matter of the present disclosure may be applied in the preparation of a gelatinous dopant material, which could be used, for example, with a solar cell substrate. Such a solar cell substrate is disclosed in the commonly referenced '415 application (which is incorporated by reference as if fully set forth herein), of which the present disclosure is a continuation-in-part. More specifically, the '415 application discloses selective coating of the top surface or top ridges of substrates having 3-D topography features with a liquid coating material.
FIG. 2 outlines an embodiment of an exemplary process flow 30 for selectively coating a three-dimensional thin-film solar cell substrate once a desired consistency is obtained of the dopant material 10 that is associated with the gelatinous dopant material resulting from the gelation process layout 20. The exemplary process flow 30 may be used to coat the surface of a wafer in the manufacture of a three-dimensional thin-film solar cell substrate to achieve significantly improved coverage by using a cavity filling method and a liquid dopant material 10 as described in the present disclosure.
The gelatinous nature of the dopant material 10 may be ideal since it has high viscosity and very little tendency to flow, even when it is heated or dried. This method begins with a 3-D substrate 32. Then the micro cavities 34 are either fully or partially filled or covered prior to applying a liquid coating filling material. After the micro cavities have been filled, then the step of removing excess filling material exposes the top surfaces or ridges to be coated 36. The exposed surface of the substrate is then coated with a dopant material 10 followed by the step of partial curing of the coating material 37. The said partial curing of the dopant material 10 results full or partial solidification of the dopant material 10 by baking, driving out the solvents, or curing by exposure of UV, IR or regular light sources. The curing condition should not affect the removability of the filling material. The filling material is then removed from the micro cavities leaving the selected substrate surfaces coated with a liquid coating material in the step of remove filling material from substrate micro cavities 38. Baking then fully cures the coating material, and the process is then complete with the step of completing curing the coating material coated on the 3-D substrate 39 and ready to begin again.
When filling the 3-D surface micro cavities 34, the filling material may either be a liquid dopant material 10 or dopant material 10 hardened by a baking or curing process or dopant material 10 resulting from a gelation process layout 20 as described in FIG. 1. If the filling material is to remain a liquid during coating, it must be immiscible with the dopant material 10. If the filling material is baked or cured and solidifies before coating, proper selection of the filling material assures that the dopant material 10 preferably does not wet the cured filling material surface and that the dopant material 10 does not react with the filling material.
Alternatively, a positive tone photoresist material may be used as the filling material in which case the top surfaces to be coated could be exposed after partial UV exposure followed by a resist developing process. The process controls the UV exposure dose so that only the photoresist on top surfaces and ridges is fully exposed and removed in the photoresist developing process. The photoresist in the micro cavities are under exposed so that they could not be fully removed in the resist developing process. As a result, the sidewall and bottom surfaces of the micro cavities are fully covered by the photoresist layer.
In yet another embodiment, the photoresist on the top surfaces and ridges may be removed in a photolithography step using an aligned photo mask. In this case, since the photoresist in the micro cavities are not exposed to the UV exposure, it does not need to actually fill the micro cavities—only to cover the sidewall and bottom surfaces.
Filling the micro cavities 34 with filling material may be performed by a variety of methods including immersion, dipping, spraying, volume-controlled dispensing, and spinning. In step of filling the micro cavities 34, the surface cavities of the 3-D substrate may be filled by planarizing the 3-D substrate with a sacrificial layer. The sacrificial filling material is then etched back to expose the top surfaces or ridges to be coated. The step of removing excess filling material exposes the top surfaces or ridges to be coated 36 may be performed by squeegeeing, spinning, or etching away excess filling material.
Optionally, the exposed surface of the substrate may be cleaned according to a plasma descum/ashing step after the step of removing excess filling material exposes the top surfaces or ridges to be coated 36.
FIG. 3 shows a coating layout 50, which may be, but is not limited to, a reverse roll system, for the coating of a solar cell substrate once a desired consistency is obtained of the dopant material 10 that is associated with the gelatinous dopant material resulting from the gelation process layout 20. The present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, and apply the more cotable liquid towards beneficially coating dopant liquid in the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate.
The coating layout 50 may be comprised of subcomponents, which may include, but is not limited to, applicator roll 52, transport roll 54, conveyance plane 56, wafer 58, dopant material 10, cleaning blade 62, dosing roll 64, and pneumatic 66. Various modifications to these coating layout embodiments and coating configurations may exist. Furthermore, alternate commercial coating systems may be implemented to achieve the presently disclosed subject matter.
More particularly, the conveyance plane 56 may be, but is not limited to, a belt, a roll-to-roll plane, a walking beam transport, or carriers that move from start to end and then get recirculated after going through cleaning steps among others. Further, the coating layout 50 may occur in a controlled environment saturated with certain solvents, temperature, humidity, and wind control.
Further, the dopant material 10 may be associated with liquid or paste materials that may be capable of being coated on the tips of any apertures that may be less than or equal to four millimeters width in terms of longest dimension. Further, the wafer 58 may have a substrate that may include, but is not limited to, the following characteristics: The shape of the wafer 58 may be, but is not limited to being, circular or rectangular, hexagon as panels. The size of the wafer 58 may be, but is not limited to being, a few inches to a few feet. The thickness of the wafer 58 may be, but is not limited to being tens of microns to several millimeters to varying throughout the substrate. The material of the wafer 58 may be, but is not limited to being, semiconductor materials such as silicon, ceramic, metal, polymers, glass, plastics, or a thin film material, which may be but is not limited to, oxide, nitride, a chemical surface treatment for improving wetting, adhesion, color, etc.
In the coating layout 50, the wafer 58 may move from the right to the left on the conveyance plane 56. Further, in the coating layout 50, the wafer 58 may be stationary and the coating head may be moved on the piece that needs to be coated. The coating layout 50 may depend on the transport system used. The transport roll 54 may rotate, thereby causing the movement of the conveyance plane 56 and resulting in the movement of the wafer 58 on the conveyance plane 56. During the process of coating a three-dimensional thin-film solar cell substrate, the pneumatic 66 may provide electrical energy input to the dosing roll 64, thereby mechanically-rotating the dosing roll 64 and compressing the dosing roll 64 against other rollers/surfaces. The rotation of the dosing roll 64 may permit mechanical rotation of the applicator roll 52, which may apply the dopant material 10 to the applicator roll 52. Further, the speeds of the various rollers and belts may not be the same, but instead they may be all different. The cleaning blade 62 may prevent inadequate build-up of dopant material 10 on the applicator roll 52, thereby creating a thin and uniform layer of coating material 10 on the applicator roll 52. While the wafer 58 may be moving on the conveyance plane 56, the applicator roll 52 may transfer the coating material onto wafer.
Further, the coating layout 50 may coat wafers on both sides simultaneously. In such a case, the transport system may feed the wafer 58 in and retrieve the wafer 58 from the other side since the moving rollers will move the wafer through.
Heating may occur on the conveyance plane 56, applicator roll 52, transport roll 54, and/or dosing roll 64. The process of heating may be applied to the dopant material 10, which may make the dopant material 10 thinner or may dry out the solvents and make transform the dopant material 10 into a higher viscosity or higher solid content. Further, the process of heating may be accomplished by using infrared lamps, UV (not shown), conduction coils (not shown), a heating element (not shown), hot air oven (not shown), or other heating means (not shown).
Further, compression may occur between the surface of the conveying plane 56 and the dopant material 10. More particularly, a roller surface may be used for evaporation, instead of heating, vacuum, air, etc.; in such a case, the dopant material 10, which may be a dopant gel, may need to be “pressed” against the roller surface. Such a compression process may further thin the dopant material 10. The material of choice for the applicator roll 52 may be a compressible material, so that the applicator roll 52 may conform to the different regions and uneven surfaces of the wafer 58. Further, the applicator roll 52 or the dosing roll 64 may not have a flat surface or may have microgrooves designed to hold fixed volumes. The microgrooves and microholes may be in the shape of, but not limited to, a diamond, square, or rectangular. Further the microgrooves and microholes may contain liquid for transferring from the dosing roll 64 to applicator roll 52 to control the film thickness independent of other factors. The dosing roll 64 and the applicator roll 52 might also have texturing, which may enable pattern printing; if they have texturing, it may be on the hard roller, which may then transfer to the soft roller for printing onto the wafer 58. The dosing roll 64 and the applicator roll 52 may have positive or negative patterns depending on the material properties and how it is to be coated.
FIG. 4 presents an exemplary integrated coating system 80 for the coating a solar cell substrate once a desired consistency is obtained of the dopant material 10 that is associated with the gelatinous dopant material resulting from the gelation process layout 20. The present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, and apply the more cotable liquid towards beneficially coating dopant liquid in the manufacture of a three-dimensional thin-film solar cell substrate. The gelatinous nature of the dopant material 10 may be ideal for use in the integrated coating system 80 since dopant material 10 has high viscosity and very little tendency to flow, even when it is heated or dried.
The integrated coating system 80 may be modified to control the amount of dopant material 10 that may transferred during the coating process and to control the amount and thinness of coating material that may be applied to the uneven surfaces of the wafer 58.
The integrated coating system 80 may include, but is not limited to, microcoater 82, microdryer 84, leveling conveyor 86, and recirculation-pump-filtration unit 88. The leveling conveyor 86 may move the conveyance plane 56, thereby transporting the wafer 58 during the coating process. The microdryer 84 may further heat the dopant material 10 and/or may remove of the volatile components of dopant material 10. However, a drying device other than a microdryer 84 may perform post coat drying via vacuum bake, air gun, etc. The microdryer 84, which may be, but is not limited to being, a vacuum oven may be used to pre-heat wafers which are manually transferred to the integrated coating system 80, and back for bakes with or without vacuum. The recirculation-pump-filtration unit 88 may recirculate, pump, and/or filter the dopant material 10 during the process of coating a three-dimensional thin-film solar cell substrate.
The present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, and apply it towards the manufacture of a three-dimensional thin-film solar cell substrate, which may include the use of integrated coating system 80. The pressure may be the most important factors for controlling the coating a three-dimensional thin-film solar cell substrate. Other factors that may be important include, but are not limited to: the direction that the wafer 58 was loaded; the amount of compression; the presence of vacuum bake; the choice of wafer orientation, with respect to facing upward or downward during bake; the number of roller coats; the bake temperature; the relative speeds of rollers with respect to each other; the pressure between various rollers and surfaces; the speed of the conveyance plane 56; the wafer 58 loading direction, whether it is loaded edge first or point first; the position of the wafer 58 on the conveyance plane 56 relative to the vacuum holes; the rotating direction of the rollers; the placement of the wafer 58, whether the wafer 58 is placed on a carrier or directly onto the conveyance plane 56. Further, key factors impacting gelation include, but are not limited to, the evaporation rate, temperature, agitation etc., which are described in detail in FIG. 1 in the description of a gelation process layout 20.
FIG. 5 shows a depiction of a three-dimensional thin-film solar cell substrate wafer after application of the dopant material 10 that is associated with the gelatinous dopant material resulting from the gelation process layout 20 of the present disclosure. The present disclosure teaches a method and apparatus to gel a dopant material, which may be a low viscosity liquid, enhance the high viscosity characteristics of the dopant material 10, and apply the dopant material 10 towards beneficially coating dopant liquid in the manufacture of a three-dimensional thin-film solar cell substrate.
The methods and devices of the present disclosure may provide an exemplary coated profile 90 of a honeycomb structure of a three-dimensional thin-film solar cell substrate. The top view of the coated material 94 shows the applied dopant material 10 on the top ridge of the honeycomb structure 92. One will note the good coverage obtained on top. This coverage was obtained by pre-heating the wafer and then applying six coats of gel dopant using a soft roller. Between each coat, the wafer has a one minute vacuum bake at 135 degrees Celsius and then a final bake after all coats. The obtained coverage is more variable than the below example method and had a depth reaching as much as 50-80 um. The obtained coverage achieves improvements in coating coverage with regards to uniformity, which may be, but is not limited to, homogeneity, color uniformity, opacity, and density of the dopant material 10.
As discussed above in the description of FIG. 5 and also in the in the description of a gelation process layout 20 in FIG. 1, the solvent evaporation and agitation enhance the high viscosity characteristics of the dopant material 10. The evaporation could be achieved by heating, vacuum, application in a thin layer on a roller, etc. Furthermore, the agitation could be accomplished by a stir-bar, roller, or other item.
Additionally, embodiments depend on equipment. For example, if rollers are to be utilized, a soft roller setup as opposed to a hard anodized aluminum roller setup achieves more favorable results. If using stamp, vacuum contact as opposed to proximity contact or soft contact. For tape/film lamination, adhesive as opposed to hot stamp foil. Although the foregoing lists specific equipment, other embodiments could utilize split die, angled spray coating, thickeners (e.g. fumed/colloidal silica, glycerol, higher molecular weight alcohol), and or other dopant “drying” techniques (e.g. sublimation). In the preferred embodiment, a soft roller setup is utilized.
In summary, the present disclosure teaches methods and devices for aging a dopant material in a reservoir, to gel a dopant material, which may be a low viscosity liquid, and apply the dopant material towards beneficially coating dopant liquid in the manufacture of a solar cell substrate. As an alternate to using high viscosity dopants, a dopant coating liquid, which is typically distributed in low viscosity alcohol based liquid forms, may instead be utilized as a dopant material in a gelatinous state towards the manufacture of a solar cell substrate, which may be, but is not limited to, a three-dimensional thin-film solar cell substrate. The methods and devices disclosed herein provide for enhancing the high viscosity characteristics of a dopant material. The present disclosure teaches the use of the dopant material resulting from the gelation process towards achieve improvements in coating coverage. The present disclosure teaches the use of gelatinous dopant material in an exemplary cavity filling method, an exemplary coating layout, and an exemplary integrated coating system.
The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments in which the presently disclosed process can be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other embodiments.
The detailed description includes specific details for providing a thorough understanding of the presently disclosed method and apparatus. However, it will be apparent to those skilled in the art that the presently disclosed process may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the presently disclosed method and system.
The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the claimed subject matter. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the innovative faculty. Thus, the claimed subject matter is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. It is contemplated that additional embodiments are within the spirit and true scope of this disclosed method and system as claimed below.

Claims

1. A method for increasing the viscosity of a dopant material to achieve a gelatinous state for use in association with a solar cell substrate by performing at least one of the following steps:

placing a dopant material in a reservoir;

aging said dopant material for at least one hour;

compressing said dopant material until achieving a viscosity of no more two-hundred thousand centiposes;

agitating said dopant material until achieving a viscosity of at least fifty-thousand centiposes;

heating said dopant material to at least greater than room temperature;

evaporating solvent from said dopant material; and

injecting additional said dopant material into said reservoir to maintain a pre-determined consistency of said dopant material.

2. The method of increasing the viscosity of a dopant material to achieve a gelatinous state for use in association with a solar cell substrate in claim 1, said method further comprising the step of monitoring the consistency of said dopant material, said step of monitoring associated with a controlled environment.

3. The method of claim 1, wherein said solar cell substrate further comprises a three-dimensional thin-film solar cell substrate.

4. The method of claim 1, wherein said step of evaporating further comprises evaporating of organic binders.

5. The method of claim 1, wherein said step of heating further comprises ultraviolet heating.

6. The method of claim 1, wherein said dopant material is associated with at least one of the following: solvent, solid content, binders, glass beads, and surfactants.

7. An apparatus for increasing the viscosity of a dopant material to achieve a gelatinous state for use in association with a solar cell substrate, said apparatus comprising:

a doctor bar reservoir, said doctor bar reservoir for aging dopant material and for evaporating solvent from said dopant material;

a roller, said roller for compressing said dopant material;

a pressing tool, said pressing tool for monitoring the consistency of said dopant material; and

an agitator, said agitator for increasing the viscosity of the dopant material.

8. The apparatus of claim 7, further comprising a controlled environment.

9. The apparatus of claim 7, wherein said controlled environment is associated with monitoring the consistency of said dopant material.

10. The apparatus of claim 7, further comprising a system of rollers for agitating said dopant material.

11. The apparatus of claim 7, wherein said agitator ages said dopant material, said dopant material in said reservoir.

12. The apparatus of claim 7, wherein a solvent is evaporated from said dopant material, said evaporation associated with organic binders.

13. The apparatus of claim 7, wherein said reservoir is associated with injecting additional dopant material.

14. The apparatus of claim 7, further comprising a pre-determined consistency of dopant material.

15. The apparatus of claim 7, wherein said dopant material is associated with a predetermined shelf-life.