TOSHIBA MITSUBISHI-ELECTRIC INDUSTRIAL SYSTEMS CORPORATION

Patent Trials and Appeals Board

Mar 25, 2021

2020002861 (P.T.A.B. Mar. 25, 2021)

UNITED STATES PATENT AND TRADEMARK OFFICE
UNITED STATES DEPARTMENT OF COMMERCE
United States Patent and Trademark Office
Address: COMMISSIONER FOR PATENTS
P.O. Box 1450
Alexandria, Virginia 22313-1450
www.uspto.gov
APPLICATION NO. FILING DATE FIRST NAMED INVENTOR ATTORNEY DOCKET NO. CONFIRMATION NO.
15/305,397 10/20/2016 Takahiro SHIRAHATA 13761US01 7800
154930 7590 03/25/2021
XSENSUS LLP
200 Daingerfield Road
Suite 201
Alexandria, VA 22314
EXAMINER
VETERE, ROBERT A
ART UNIT PAPER NUMBER
1712
NOTIFICATION DATE DELIVERY MODE
03/25/2021 ELECTRONIC
Please find below and/or attached an Office communication concerning this application or proceeding.
The time period for reply, if any, is set in the attached communication.
Notice of the Office communication was sent electronically on above-indicated "Notification Date" to the
following e-mail address(es):
Faith.Baggett@xsensus.com
Sandy.Miles@Xsensus.com
anaquadocketing@Xsensus.com
PTOL-90A (Rev. 04/07)
UNITED STATES PATENT AND TRADEMARK OFFICE
BEFORE THE PATENT TRIAL AND APPEAL BOARD
Ex parte TAKAHIRO SHIRAHATA, HIROYUKI ORITA,
TAKAHIRO HIRAMATSU, and HIROSHI KOBAYASHI
Appeal 2020-002861
Application 15/305,397
Technology Center 1700
Before LINDA M. GAUDETTE, JAMES C. HOUSEL, and
DONNA M. PRAISS, Administrative Patent Judges.
GAUDETTE, Administrative Patent Judge.

Appeal 2020-002861
Application 15/305,397

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DECISION ON APPEAL1
The Appellant2 appeals under 35 U.S.C. § 134(a), from the
Examiner’s decision finally rejecting claims 1–6.3
We REVERSE.
CLAIMED SUBJECT MATTER
The invention relates to a buffer layer film-forming method and buffer
layer. The Specification explains that “[i]n a CIS-based solar cell, in order to
improve conversion efficiency, a buffer layer is disposed between a light
absorbing layer and a transparent conductive film, and a conduction band
offset (band offset) is formed between the light absorbing layer and a
buffer layer.” Spec. ¶ 2. “The buffer layer is a layer of a thin film, and has a
large effect on the performance of a solar cell resulting from formation of
the . . . band offset.” Id. ¶ 3. The Specification further describes the buffer
layer as “neither a conductive body nor an insulating body.” Id. ¶ 66.
Claims 1 and 5, reproduced below, are illustrative of the claimed
subject matter:

1 The following documents are of record in this appeal: Specification filed
Oct. 20, 2016, as amended (“Spec.”); Final Office Action dated April 10,
2019 (“Final Act.”); Corrected Appeal Brief filed Oct. 30, 2019 (“Appeal
Br.”); Examiner’s Answer dated Jan. 7, 2020 (“Ans.”); and Reply Brief filed
Mar. 3, 2020 (“Reply Br.”).
2 “Appellant” refers to “applicant” as defined in 37 C.F.R. § 1.42. The
Appellant identifies the real party in interest as Toshiba Mitsubishi-Electric
Industrial Systems Corporation. Appeal Br. 1.
3 We have jurisdiction under 35 U.S.C. § 6(b).

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Application 15/305,397

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1. A method for film-forming a buffer layer to be used for
a solar cell, the buffer layer being disposed between a light
absorbing layer and a transparent conductive film comprising:
(A) forming a solution containing zinc and aluminum as
metal raw materials of the buffer layer into a mist by applying
an ultrasonic wave to said solution,
(B) heating a substrate disposed in an atmosphere within
a chamber, and
(C) spraying a mist of said solution atomized in said step
(A) to said substrate in said step (B),
wherein the buffer layer has a resistivity that is 10 Ω•cm
or greater.
5. A buffer layer to be used for a solar cell, the buffer layer
being disposed between a light absorbing layer and a
transparent conductive film,
wherein said buffer layer is a Zn1-xAlxO film containing
zinc and aluminum, provided that 0 < x < l.
Appeal Br. 10–11 (Claims App.).
REFERENCES
The Examiner relies on the following prior art:
Name Reference Date
Barnhart US 2001/0003139 A1 June 7, 2001
Döbler US 2003/0094600 A1 May 22, 2003
Wang US 2004/0230271 A1 Nov. 18, 2004
O’Malley US 2013/0309613 A1 Nov. 21, 2013
Kawai4 JP 2014-063873 Apr. 10, 2014

4 Citations to Kawai are to the machine translation of record.
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Kim et al., “Effect of aluminum doping on zinc oxide thin film grown by
pulsed laser deposition for organic light-emitting devices,” 377–378 Thin
Solid Films 798–802 (2000) (“Kim”).
Kawaharamura et al., “Effect of O3 and Aqueous Ammonia on
Crystallization of MgO Thin Film Grown by Mist Chemical Vapor
Deposition,” 52 Japanese J. of Applied Physics 035501 (2013)
(“Kawaharamura”).
REJECTIONS
1. Claims 1 and 6 are rejected under 35 U.S.C. § 103 over Kawai,
Kim, and Wang. Final Act. 3.
2. Claim 4 is rejected under 35 U.S.C. § 103 over Kawai, Kim,
and Wang, as evidenced by Barnhart. Final Act. 3.
3. Claim 5 is rejected under 35 U.S.C. § 103 over Kawai, Kim,
and Wang, as evidenced by Döbler. Final Act. 3.
4. Claims 2 and 3 are rejected under 35 U.S.C. § 103 over Kawai,
Kim, Wang, and Kawaharamura. Final Act. 5.
5. Claims 1 and 6 are rejected under 35 U.S.C. § 103 over Kawai,
Kim, and O’Malley. Final Act. 5.
6. Claim 4 is rejected under 35 U.S.C. § 103 over Kawai, Kim,
and O’Malley, as evidenced by Barnhart. Final Act. 5.
7. Claim 5 is rejected under 35 U.S.C. § 103 over Kawai, Kim,
and O’Malley, as evidenced by Döbler. Final Act. 5.
8. Claims 2 and 3 are rejected under 35 U.S.C. § 103 over Kawai,
Kim, O’Malley, and Kawaharamura. Final Act. 7.

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OPINION
Claim 1
As found by the Examiner, Final Act. 4, Kawai discloses a method of
forming a buffer layer (14) between a light absorbing layer (13) and a
transparent electrode (15) in a thin film solar cell, Kawai, code (57). As
further found by the Examiner, Final Act. 4, Kawai discloses that the buffer
layer (14) is preferably formed by spray coating a heated substrate with a
solution comprising a solvent and the buffer layer material, for example
ZnO, Kawai ¶¶ 27, 51–52. Citing Kim’s disclosure, the Examiner found that
the ordinary artisan would have included aluminum in Kawai’s ZnO solution
to form a buffer layer having improved electrical properties. Final Act. 4
(citing Kim 800). The Examiner relied on Wang or O’Malley for a
suggestion of using ultrasonic waves to generate a mist for spray coating
Kawai’s solution. Final Act. 4, 6.
The Appellant argues that the Examiner relied on improper hindsight
reasoning in determining that the applied prior art discloses or suggests a
method that includes a step of “forming a solution containing zinc and
aluminum as metal raw materials” to produce a buffer layer having “a
resistivity that is 10 Ω•cm or greater,” as recited in claim 1. See generally
Appeal Br. 4–7. The Appellant’s arguments are persuasive for the reasons
discussed below.
Kim describes the effect of aluminum doping on zinc oxide thin films.
Kim, Title. Kim discloses that aluminum-doped zinc oxide (AZO) films
have been used as transparent conducting electrodes in solar cells. Id. at 799,
col. 1. The Examiner did not identify, nor do we find, any disclosure in Kim
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regarding zinc oxide films used as buffer layers in solar cells. Kim discloses
that “[p]ure zinc oxide films are highly transparent in the visible range (400–
700 nm) and have low electrical conductivity,” whereas AZO films have
high conductivity—low resistivity of 2–4 x 10-4 Ω•cm. Id. at 798. Kim
conducted testing of AZO films containing up to 4 wt.% aluminum, finding
that “the resistivity of the AZO films after reaching a minimum (at 0.8 wt.%
of Al) gradually increases with a further increase in the Al content up to 4
wt.%.” Id. at 800, col. 1. Kim further found that for an undoped ZnO film
“the transmittance is greater than 80% in the whole visible and near infrared
(IR) region up to 3000 nm. For the Al-doped film (0.8 wt.%), the
transmittance is greater than 85% in the visible range but decreases from 85
to 5% in the near IR region between 1200 and 3000 nm.” Id. at 801, col. 1.
Kim concluded that “0.8-wt. % of Al is the optimum doping amount in the
target to achieve the minimum film resistivity and the maximum film
transmission.” Id. at 801–02, Conclusion.
Kawai discloses that ZnO is a suitable buffer layer material in a thin-
film solar cell, but indicates that In2S3 is preferred. Kawai ¶ 27. Kawai
discloses that a volume phase (19) may be included between the solar cell’s
buffer layer (14) and transparent electrode (15). Id. ¶ 32. Kawai discloses
that when a volume phase (19) is included, it preferably consists of ZnO to
provide a high resistance buffer layer, and the transparent electrode (15) is
ZnO that contains aluminum as a dopant material, preferably in an amount
of more than 0.01 mass % and less than 10 mass %. Kawai ¶ 33. Thus,
although Kawai and Kim suggest including aluminum in the transparent
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electrode layer of a solar cell, we find no teaching or suggestion in Kawai or
Kim of including a dopant material in a ZnO buffer layer.
The Appellant directs us to Specification paragraphs 20 and 22,
Appeal Br. 5,5 which describe the difference between an Al-doped film used
as a transparent electrode layer (conductive film), and a buffer layer
produced by the inventive method:
An object of the present invention is a “buffer layer”, and is not
a “conductive film” which is low in resistance. . . . []Al-doped
ZnO[ film] is a conductive body (resistivity is about 10-3 Ω•cm
or less), and the amount of aluminum introduced thereinto is at
most about 1 % with respect to the amount of zinc. . . . [W]hen
aluminum is introduced into the zinc oxide film as a dopant,
transmittance tends to be reduced in the film to be film-formed
(particularly, the transmittance of light of a wavelength of 1500
nm or longer tends to be significantly reduced).
Spec. ¶ 20.
[I]n the present invention, aluminum to be mixed is employed
as metal raw materials of the buffer layer to be produced (that
is, aluminum is contained as a mixed crystal in the film . . . ).
Accordingly, the Zn1-xAlxO film according to the present
invention includes aluminum in an amount larger than the
amount in the case where aluminum is introduced as a dopant.
In the present invention, an amount of aluminum relative to an
amount of zinc in a raw material solution is, for example, 10%
or more. Further, the resistivity of the Zn1-xAlxO film is 10
Ω•cm or more, and the film is not said to be a conductor.
Id. ¶ 22. The Specification further discloses that in a buffer layer produced
by the inventive method “high transparency is maintained (for example, a

5 Specification paragraphs 20 and 22 correspond to published application
paragraphs 28 and 30, cited by the Appellant.
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high value is maintained even in the transmittance of light of a wavelength
of 1500 nm or longer . . .).” Id. ¶ 21.
The Examiner contends that “regardless of the reasons Kim has for
including aluminum in the ZnO film, a person of ordinary skill in the art
would have understood that introducing aluminum in excess of 0.8 wt% in
the ZnO film of Kawai would increase the resistivity of the film based on the
plane [sic] language of the Kim disclosure.” Ans. 5. As is apparent from the
above cited Kim and Kawai disclosures, the problem with the Examiner’s
position is that the references disclose adding aluminum only to a conductive
film or transparent electrode layer, not to a buffer layer. Further, Kawai
indicates that including aluminum in the transparent electrode (15) is
beneficial only when an undoped ZnO layer (volume phase (19)) acts as a
buffer between the buffer layer (14) and the transparent electrode (15).
Further, both Kawai and Kim suggest adding aluminum to ZnO in amounts
that the Specification suggests are insufficient to achieve a layer having a
resistivity that is 10 Ω•cm or greater, as required by claim 1. Compare
Kawai ¶ 33 (electrode layer containing less than 10 mass % Al) and Kim
800–82 (conductive film containing 0.8 wt% Al), with Spec. ¶ 20 (buffer
layer containing 10% Al or more).
In sum, we are persuaded that the Examiner’s obviousness
determination as to claim 1 is based on impermissible hindsight reasoning.
The Examiner’s rejections of claim 1 and its dependent claims 2–4 and 6 are
reversed.
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Claim 5
Unlike claims 1–4 and 6, claim 5 is a product claim, and recites a
buffer layer comprising a Zn1-xAlxO film containing zinc and aluminum,
where 0 < x < l. The Examiner found that “Kim teaches that the buffer layer
is aluminum-doped zinc oxide (also known as AZO) p. 800). Döbler
explains that AZO is doped zinc oxide wherein aluminum dopant replaces
zinc atoms in the ZnO compound (¶ 0054). Therefore, the AZO compound
in Takahashi has the formula Zn1-xAlxO.” Final Act. 6.
The Examiner’s findings are insufficient to support a conclusion of
obviousness as to claim 5 for two reasons. First, the Examiner refers to “the
AZO compound in Takahashi.” Final Act. 6. However, Takahashi is not
cited in the statement of any rejections. Second, assuming the Examiner
intended to cite Kawai, for the reasons discussed above regarding the claim
1 rejections, the Examiner has identified only a teaching of a conductive film
or transparent electrode layer comprising AZO. The term “buffer layer,” as
used in the present Specification, defines a layer disposed between a light
absorbing layer and a transparent conductive film in a solar cell that
improves conversion efficiency. See, e.g., Spec. ¶¶ 1–2. The Examiner has
not identified evidence, or otherwise explained why Kawai’s transparent
electrode or Kim’s conductive film are a “buffer layer,” as claimed.
Accordingly, we do not sustain the rejections of claim 5.
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Application 15/305,397

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DECISION SUMMARY
Claim(s)
Rejected
35 U.S.C. § Reference(s)/Basis Affirmed Reversed
1, 6 103 Kawai, Kim, Wang 1, 6
4 103 Kawai, Kim,
Wang, Barnhart
4
5 103 Kawai, Kim,
Wang, Döbler
5
2, 3 103 Kawai, Kim,
Wang,
Kawaharamura
2, 3
1, 6 103 Kawai, Kim,
O’Malley
1, 6
4 103 Kawai, Kim,
O’Malley, Barnhart
4
5 103 Kawai, Kim,
O’Malley, Döbler
5
2, 3 103 Kawai, Kim,
O’Malley,
Kawaharamura
2, 3
Overall
Outcome

1–6
REVERSED