`
`International application number. PCT/US2009/03 1886
`
`International filing date:
`
`23 January 2009 (23.01.2003
`
`Document type:
`
`Certitied copy of priority document
`
`Document details:
`
`Country/Office: US
`Number:
`61/023 342
`Filme date:
`24 January 2008 (24.01.2008)
`
`Date of receipt at the International Bureau:
`
`03 February 2009 (03.02.2009)
`
`Remark:
`
`Priority document submitted or transmitted to the International Bureau in
`compliance with Rule 17. 1(a) or (b}
`
`
`
`World Intellectual Property Organization (WIPO) - Geneva, Switzerland
`Organisation Mondiale de la Propriété Intellectuelle COMPI} - Geneve, Suisse
`
`
`
`
`
`THIS IS TO CERTIFY THAT ASNEXED HERETO IS A TRUE COPY FROM
`THE RECORDS OF THE UNITED STATES PATENT AND TRADEMARRE
`OFFICE OF THOSE PAPERS OF THE BELOW IDENTIFEED PATENT
`APPLICATION THAT MET THE REQUIREMENTS TO BE GRANTED A
`FILING DATE.
`
`
`
`a,foMeerady
`
`bouder Seeretary of Carnmierce
`for Dytellectual Property
`and rector af Che Liadtad States
`Potent aud Tracienark CNfisw
`
`LSVTPED SPAPES
`
`PARTMENT OF COMMERCE
`
`Unlted States Patent and Pradomarch OWee
`
`February 02, 2008
`
`APPLICATION NUMBER: 6//023,3242
`PILING DATE: fanuary 24, 2008
`RELATED PCT APPLICATION NUMBER: PCT/US08/3 1886
`
`THE COUNTRY CODE AND NUMBER OF YOUR PRIORITY
`APPLICATION, TO BE USED FOR FILING ABROAD UNDER THE PARIS
`CONVENTION, ES US6IM23,342
`
`
`
`EFS IB:
`
`Application Number:
`
`international Application Number:
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`Confirmation Number:
`
`Tis of Invention:
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`electronic Acknowledgement Receipt
`
`27eaiti
`
`improved Hit Solar Cell Structure
`
`First Named inventor/Applinant Name:
`
`Peter G. Borden
`
`Filer:
`
`Filer Authorized By:
`
`Attorney Docket Number:
`
`Receipt Date:
`
`Filing Date:
`
`Time Stamp:
`
`Application Type:
`
`Mark J. Danieison/Bobbie Jutras
`
`Mark... Danielson
`
`012981 /NBNP/CKIM
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`24-JAN-2008
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`Provisional
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`Payment information:
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` i Payrnant was succeastuily reacived in RAM
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`i The Diractor of the USPTO is nereby authorized to charge indicated faes and credit any overoayment as follows:
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`Charge any Additional Fees requirec under 37 C.F.R. Section 1.16 (National applicailon filing, search, and examination fees}
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`Gharge any Additional Fees required under 37 C.F.R. Section 1.17 (Patent application and reexamination processing feés}
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`Authorized User
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`| Flie Listing:ee
`Document |
`ees
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`File Siza(Bytes}
` Mulfi
`| Pages
`Number
`|
`Document Description
`File Name
`{Message Digest: Part /.zip!
`(if appl.)
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`1532513
`1
`AMAT12981 pdf ee ves
`|
`15
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`lechoY1Se4iat a
`78STOEADT
`{
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`Multioart Description/PDF files in zip description
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`Document Description
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`Drawings-only black and white line drawings
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`Provisional Cover Sheet (S316)
`Lnbn
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`Specification
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`Claims
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`Abstract
`benier
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`Appendix to the Specification
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`12
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`15
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`i Warnings:
`information:
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`mM
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`Fee Worksheet (PTO-08}
`fee-info.pef oer no
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`ho
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`Warnings:
`information:
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`i
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`| This Acknowledgement Recaist evidences receipt on the noted date by the USPTO of the indicated documents,
`| characterized by the applicant, and including page counts, where applicable.
`it serves as evidence of receipt
`i Similar to a Post Card, as described in MPEP 503.
`
`i New Applications Under 35 US.0. 114
`if a new application is being Hied and the application includes the necessary components for a fing date (see
`| 37 CFR 1.53(b}-(e) and MPEP 506}, a Filing Receipt (37 CFR 1.54) will be issued in due course and the date
`shown on this Acknowledgement Receipt will establish the Ting date oi the application.
`
`| National Stage of an International Application under 35 ULS.C. 371
`if a timely submission to enter the national stage of an international application is compliant with the conditions
`| of 35 U.S.C. 377 and other aoplicable requirements a Form PCT/DO/E0/903 indicating acceptance of the
`i application as a national stage submission under 35 U.S.C. 371 will be issued in addition to the Filing Receipt,
`i
`in due course.
`
`New international Application Filed with the USPTO as a Receiving Office
`ii a new International application is being filed and the International application includes the necessary
`| components for an international filing date (see PCT Article 11 and MPEP 1810), a Notification of the
`international Application Number and of the international Filing Date (Farm PCT/AG/104) wil be issued in due
`| course, subject to prescriptions concerning national security, and the date shown on this Acknowledgement
`Receipt will establish the imernational filing date of the application.
`
`
`
`
`
`IMPROVED HIT SOLAR CELL STRUCTURE
`
`(O00)
`
`The preseni invention relates io phatoveltaic devices, and more particularly to
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`FIELD OF THE INVENTION
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`methods and apparatuses for providing an improved structure of a HIT type or polysilicon emitter
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`type solar cells.
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`BACKGROUND
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`[0002]
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`HIT type solar cells are high efficiency devices with relatively simple structures.
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`Sanyo Corporation of Japan has reported lab efficiencies of 21.5% and manufacturing efficiency
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`in the mid-19% range. Many other groups have worked on this device, although nens has shown
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`as high efficiencies.
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`{G803}
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`A typical HITtype solar cell structure is shown in FIG. 1. The device is
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`symmetric, with the front and back of the n-type substrate both coated with thin arnorphous
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`silicon (a-5:), thicker transparent conducting oxide (TCO) and metal grid line layers. As shown
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`in the blowup portion of FIG. 1, the amorphous silicon layer consists of two layers, an intrinsic
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`layer under a p-type layer on the front, and an intrinsic (1} layer under an n-type layer on the back.
`
`{GG04)
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`The purpose ofthe thin a-Si layers are to both passivate the surface and to provide
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`a heterojunction with a widebandgap windowlayer to improve the opencircuit voltage, as _
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`shown in the graph in the right portion of FIG. 1. However, these layers alse introduce
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`considerable complexityinto the fabrication of the HIT cell. For example, the layers rnust be
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`formed on a carefully prepared surface, whose preparation details have not been published.
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`Further, they must net crystallize, as can happen when the amorphous silicon is seeded by the
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`erystal silicon subsirate, as this will eliminate the passivation and heterojunction effects.
`
`Peter G. Borden
`TOQGSTE L4y]
`
`i
`
`AMAT 12981
`
`
`
`10805]
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`Therefore, there is a need for an improved interface that is well conirclled and
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`understood and easy to manufacture, and does not seed crystal growth.
`
`SUMMARY
`
`[9006]
`
`The present invention relates to improved HITtype or polysilicon emitter solar
`
`cells. According to certain aspects, the Invention includes forming a masking oxide layer on the
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`front and back of the cell and then patterning holes in the masking oxide, A HIT cell structure or
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`polysilicon emitter solar cell structure is then formed overthe patterned oxide, creating the cell
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`junction only in the areas where holes have been cut. Benefits of the invention include that ut
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`provides a controlled interface for the HIT cell through insertion of a thin tunnel oxide.
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`Moreover, the tunnel oxide prevents epitaxial growth of amorphous silicon, allowing it to remain
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`amorphous for the optimum band structure. Still further, it provides a layer to protect the surface
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`from plasrna damage during deposition of the a-Si layer. Further, it may be used in conjunction
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`with a point contact structure to further increase efficiency.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`fOG07]
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`These and other aspects and features of the present invention will become
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`apparent to those ordinarily skilled in the art upon review of the following description of specific
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`ernbodiments of the invention in conjunction with the accompanying figures, wherein:
`
`(0008)
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`{G009]
`
`§9010]
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`Figure | shows a HIT cell and its band structure.
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`Figure 2 shows the structure of the invention and its band structure.
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`Figure 3 shows a process flow to formthe structure of this invention.
`
`Peter G. Borden
`FOOS4 TS 1av)
`
`2
`
`AMAT 1298)
`
`
`
`DETAILED DESCRIPTION
`
`(0814)
`
`The present invention will now be deseribed in detail with reference to the
`
`drawings, which are provided as illustrative examples of the invention so as to enable those
`
`skilled in the art to practice the invention. Notably, the figures and examples beloware not meant
`
`to limit the scope ofthe present invention to a single embodiment, but other embodiments are
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`possible by way ofinterchange of someorall of the described or illustrated elements. Moreover,
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`where certain elements of the present invention can be partially or fully implemented using
`
`known components, only those portions of such known components that are necessary for an
`
`understanding ofthe present invention will be described, and detailed descriptions ofother
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`portions of such known components will be orniited so as not to obscure the invention.
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`In the
`
`present specification, an embodiment showing a singular component should not be considered
`
`limiting; rather, the invention is intended to encornpass other embodiments including a plurahty
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`of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover,
`
`applicants do not intend for any termin the specification or clams to be ascribed an uncommon
`
`or special meaning unless explicitly set forth as such. Further, the present invention
`
`encompasses present and future known equivalents to the known components referred to herem
`
`by way of illustration.
`
`{0012}
`
`In general, the present invention forms a masking oxide layer on the front and
`
`back ofthe cell and then patterning holes in the masking oxide. A HIT cefl structure or
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`polysilicon emitter solar cell structure is then formed over the patterned oxide, creating the cell
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`function Only in the areas where holes have been cut.
`
`[o0T3)}
`
`The present inventors recognize that thin fine! oxide layers can be used in solar
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`cells. For example, MIS cells are made using aluminum over tunnel oxides. The present
`
`Peter G. Borden
`TO09471B14v4
`
`3
`
`AMAT 12981
`
`
`
`inventors further recognize that tunnel oxides can be used between a heavily doped or insulating
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`layer of polysilicon and a crystal silicon substrate, forming a polysilicon emitter solar cell. Such
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`a solar cell has a similar band structure to a HIT cell, essentially replacing the TCO and a-Si
`
`layers with polysilicon. However, such cells do not provide the heterojunction and its benefit of
`
`a higher cell voltage due to the higher bandgap of a-Si.
`
`10614]
`
`In this invention, a thin dielectric layer is inserted between the a-Si layer and the
`
`substrate in a HIT cell. The dielectric layer should be thin, on the order of 8-15A,in order to
`
`support a tunneling current. This structure and the associated band structure is shownin FIG. 2.
`
`The thin layer can be formed using conventional methods such as rapid thermal oxidation,
`
`furnace oxidation, or the Chemox process (formation in an ozonated H,O, bath}.
`
`In some cases,
`
`the layer maybe nitnided or formed using other matenals such as silicon nitride or silicon
`
`oxynitride,
`
`{8035}
`
`. The benefits of this layer are several-fold. For example, it may be formed using
`
`conventional surface cleaning and preparation methods, as are used to rake MOS gates for ICs.
`
`Therefore, the surface preparation is well known and understood, and routinely implemented in
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`high volume-manufacturing. Moreover, as it 1s an amorphous layer, if separates the subsequent
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`a-Si layer from the substrate, preventingepitaxial seedingof crystal.growth inthe a-Silayer.
`
`Further, it provides an intervening layer to protect the crystal silicon surface from plasma damage
`
`during deposition of the a-&i layer.
`
`{O016]
`
`FIG. 3 shows an example of the process flaw used to make this structure. First,
`
`the front surface of the n-type substrate is textured. This may be accomplished using
`
`conventional etching, such as isopropyl alechol and ROH. Next, the surface is provided with a
`
`standard MOS clean to remove native oxides, ionic contamination, and organics.
`
`in one
`
`Peter G. Borden
`POG Fad yd
`
`4
`
`AMAT 12981
`
`
`
`embodiment, a rapid thermal oxide process is used to form a thin tunnel oxide, typically i2A
`
`thick, on the front surface. In another embodiment,the oxide is formed on both front and back at
`
`the same firne. Next, the a-Si layers are deposited on the front surface.
`
`In one embodiment, the
`
`a-Si is formed as a two layer stack, with an intrinsic a-Si, 20-50 A thick, under a p-type a-Si, 20-
`
`50 A thick.
`
`in another embodiment, only a p-type layer is formed, without the i-type layer. The
`
`TCO is deposited, which may be a quarter wave thick layer of indium tin oxide. The wafer is
`
`then flipped over, and the structure is deposited in the same manner on the back side, now using
`
`n-type a-Si instead of p-type. Finally, contacts are formed by screen printing or sputtering.
`
`{een
`
`Additionally or alternatively, a method te form point contacts for HIT or
`
`polysilicon emitter solar cells, as described in co-pending application No. (AMAT-12964),
`
`the contents of which are incorporated herein by reference in their entirety, may be used.
`
`{U018]
`
`‘The attached Appendix forms part of the present disclosure and is incorporated
`
`herein by reference.
`
`(0019)
`
`Although the present invention has been particularly described with reference to
`
`the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the
`
`ari that changes and modifications in the form and details may be made without departing from
`
`thespirit and scopeof theinvention.
`
`[t is intended that theappendedclaims encompass such.
`
`changes and modifications.
`
`Peter G. Borden
`WOOT ae)
`
`5
`
`AMAT12981
`
`
`
`APPENDIX
`
`
`
`
`
`P beg bates,
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`
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`
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`
`back
`
`FIG. 2
`
`we aBiLG) 0A
`
`oxide
`
`ont
`
`
`
`Yexture front
`
`surface
`
`aSig
`
`pi
`
`a-Si(doped)
`
`
`
`
`
`ABSTRACT
`
`The present invention relates to improved HIT type or polysilicon emitter solar cells,
`
`According (o certain aspects, the invention includes forming a masking oxide layer on the front
`
`and back of the cell and then patterning holes in the masking oxide. A HIT cell structure or
`
`polysilicon emiter solar cell structure is then formed over the patterned oxide, creating the cell
`
`junction only in the areas where holes have been cut. Benefits of the invention include that it
`
`provides a controlled interface for the HIT cell through insertion of a thin tumnel oxide.
`
`Moreover, the tunnel oxide prevents epitaxial growth of amorphous silicon, allowing if to remain
`
`araorphous for the optirnurn band structure. Stull further, it provides a layer to protect the surface
`
`from plasma damage during deposition ofthe a-Si layer. Further, it may be used in conjunction
`
`with a point contact structure io further increase efficiency.
`
`Peter G. Borden
`7009478 avd
`
`7
`
`AMAT 12981
`
`
`
`WHAT IS CLAIMED 18:
`
`A solar cell including a passivation structure consisting of a tunnel dielectric interposed
`L.
`between a substrate and a layer of an amorphous semiconductor.
`
`Z.
`
`A solar cell ag in claim | in which the substrate is silicon and the tunnel dielectric is a
`
`layer of silicon dioxide.
`
`3.
`
`A solar cell as in claim }] in which the substrate is silicon and the tunnel dielectric
`
`includes nitrogen.
`
`4,
`
`A solar cell as in claim 1 in which the amorphous semiconductoris silicon.
`
`Peter G. Borden
`TORT Avi
`
`§
`
`AMAT 12581
`
`
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