U.S. patent application number 15/780259 was filed with the patent office on 2018-12-06 for method for depositing a coating.
This patent application is currently assigned to PILKINGTON GROUP LIMITED. The applicant listed for this patent is PILKINGTON GROUP LIMITED. Invention is credited to PETER MICHAEL HARRIS, GARY ROBERT NICHOL, LIAM SONIE PALMER.
Application Number | 20180346374 15/780259 |
Document ID | / |
Family ID | 55177505 |
Filed Date | 2018-12-06 |
United States Patent
Application |
20180346374 |
Kind Code |
A1 |
PALMER; LIAM SONIE ; et
al. |
December 6, 2018 |
METHOD FOR DEPOSITING A COATING
Abstract
The present invention relates to a method of depositing a
coating comprising zinc oxide on a substrate; to a chemical vapour
deposition precursor mixture for use in same and to a coated glass
article and a photovoltaic cell prepared with a zinc oxide coating
prepared using the method which comprises: providing a substrate,
providing a precursor mixture comprising an alkyl zinc compound and
a phosphorus source, the phosphorus source comprising a compound of
formula O.sub.nP(OR).sub.3, wherein n is 0 or 1 and each R is
hydrocarbyl, and delivering the precursor mixture to a surface of
the substrate.
Inventors: |
PALMER; LIAM SONIE;
(SOUTHPORT, GB) ; HARRIS; PETER MICHAEL; (CHESTER,
GB) ; NICHOL; GARY ROBERT; (WARRINGTON, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PILKINGTON GROUP LIMITED |
LATHOM |
|
GB |
|
|
Assignee: |
PILKINGTON GROUP LIMITED
LATHOM
GB
|
Family ID: |
55177505 |
Appl. No.: |
15/780259 |
Filed: |
December 1, 2016 |
PCT Filed: |
December 1, 2016 |
PCT NO: |
PCT/GB2016/053781 |
371 Date: |
May 31, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 17/3411 20130101;
C03C 2217/216 20130101; C03C 2217/94 20130101; C03C 17/3417
20130101; C03C 2218/152 20130101; C03C 17/3464 20130101; C03C
17/002 20130101; C23C 16/407 20130101; C03C 17/245 20130101; C03C
2218/1525 20130101 |
International
Class: |
C03C 17/00 20060101
C03C017/00; C03C 17/34 20060101 C03C017/34; C03C 17/245 20060101
C03C017/245 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2015 |
GB |
1521165.9 |
Claims
1.-21. (canceled)
22. A method of depositing a coating comprising zinc oxide on a
substrate, the method comprising, providing a substrate, providing
a precursor mixture comprising an alkyl zinc compound and a
phosphorus source, the phosphorus source comprising a compound of
formula O.sub.nP(OR.sup.3).sub.3, wherein n is 0 or 1 and each
R.sup.3 is hydrocarbyl, and delivering the precursor mixture to a
surface of the substrate.
23. The method according to claim 22, wherein the precursor mixture
further comprises an oxygen source.
24. The method according to claim 22, wherein the alkyl zinc
compound is of formula R.sup.1R.sup.2Zn, wherein R.sup.1 and
R.sup.2 are each independently selected from a substituted or
unsubstituted C.sub.1-C.sub.4 alkyl or phenyl.
25. The method according to claim 24, wherein R.sup.1 and R.sup.2
are each independently selected from methyl or ethyl.
26. The method according to claim 25, wherein R.sup.1 and R.sup.2
are each methyl or each ethyl.
27. The method according to claim 22, wherein each R.sup.3 is
independently selected from a substituted or unsubstituted
C.sub.1-C.sub.4 alkyl.
28. The method according to claim 27, wherein each R.sup.3 is
propyl, ethyl or methyl.
29. The method according to claim 23, wherein the oxygen source
comprises an ester.
30. The method according to claim 29, wherein the ester is selected
from one or more of methyl acetate, ethyl acetate, propyl acetate,
butyl acetate, or a mixture of two or more of these esters.
31. The method according to claim 30, wherein the ester comprises
t-butyl acetate.
32. The method according to claim 22, wherein the precursor mixture
is a gaseous precursor mixture.
33. The method according to claim 22, wherein the method is
atmospheric pressure chemical vapour deposition.
34. The method according to claim 22, wherein the substrate
comprises glass.
35. The method according to claim 34, wherein the substrate
comprises float glass.
36. The method according to claim 22, wherein the surface of the
substrate is at a temperature in the range 300.degree. C. to
800.degree. C.
37. The method according to claim 36, wherein the surface of the
substrate is at a temperature in the range 580.degree. C. to
650.degree. C.
38. The method according to 22, wherein the coating comprising zinc
oxide is deposited on-line during the float glass production
process.
39. A chemical vapour deposition precursor mixture for use in the
method of claim 22, comprising an alkyl zinc compound, a phosphorus
source and, optionally, an ester, the phosphorus source comprising
a compound of formula O.sub.nP(OR.sup.3).sub.3, wherein n is 0 or 1
and each R.sup.3 is hydrocarbyl, the chemical vapour deposition
precursor mixture.
40. A coated glass article, comprising: a glass substrate; a silica
or tin oxide coating deposited on the glass substrate; a zinc oxide
coating; wherein the zinc oxide coating is deposited over the
silica or tin oxide coating by a method according to claim 22.
41. A photovoltaic cell comprising a coated glass article having a
zinc oxide coating deposited over a fluorine doped tin oxide
coating by a method according to any one of claim 22.
Description
[0001] The present invention relates to a method of depositing a
coating comprising zinc oxide on substrates, to chemical vapour
deposition precursor mixtures, to coated glass articles having
coatings comprising zinc oxide on at least one surface, and to
photovoltaic cells comprising such coated glass articles.
[0002] Metal oxide coatings on substrates have uses to modify the
properties (for example, electrical, optical, emissive or surface
properties) of the substrate. Metal oxide coatings on glass
substrates are particular useful. One metal oxide coating of
interest is zinc oxide.
[0003] Zinc oxide coated glass articles may be used as a
superstrate or as a substrate in the manufacture of solar cells.
Zinc oxide coatings may also have uses in low emissivity or solar
control coatings.
[0004] Metal oxide coatings are typically produced by deposition of
one or more thin film layers on, for example, a glass substrate.
One coating method is pyrolysis, wherein fluid precursors (often in
an inert carrier) are delivered to the substrate surface and react
thereby depositing a coating. Chemical vapour deposition (CVD) is a
type of pyrolysis whereby the precursors are delivered to the
substrate surface in vapour or gaseous form.
[0005] For example, JP-A-2007 234996 discloses a method of
manufacturing a thin film solar cell using a low-pressure CVD
method to deposit a transparent conductive layer comprising zinc
oxide using diethyl zinc or dimethyl zinc as a source of zinc, and
water or C.sub.1 to C.sub.5 alcohol as a source of oxygen.
[0006] WO2015177552 discloses a method of forming a zinc oxide
coating which comprises a certain level of sulphur, on a substrate
by atmospheric pressure chemical vapour deposition, which includes
the steps of forming a mixture of precursors comprising a zinc
source, a sulphur source and an oxygen source, and directing said
mixture to a surface of the substrate. The zinc source comprises at
least one of dimethyl zinc and diethyl zinc, the sulphur source
comprises at least one of an episulphide and a sulphoxide and the
oxygen source comprises at least one of nitrous oxide; a carboxylic
ester and dimethyl sulphoxide.
[0007] For glass substrates, an efficient coating method is on-line
deposition, involving a precursor mixture being delivered to the
surface of a glass ribbon during the float glass production
process. At the surface, the precursors react to form a coating
layer on the glass. This reaction is typically assisted by residual
heat remaining in the glass during the float process. For example,
WO-A-98/06675 describes the on-line coating of glass substrates by
CVD. In a successful on-line coating operation, the thin films or
layers produced are relatively mechanically and chemically durable
compared to most soft coat films or layers.
[0008] Alkyl zinc compounds, for example dialkyl zinc compounds
(for example, dimethyl zinc (DMZ) or diethyl zinc (DEZ)) are of
interest as precursors for the deposition of zinc oxide. However,
dialkyl zinc compounds are reactive and therefore may decompose in
the delivery apparatus before reaching the desired substrate
surface or, may pre-react with other components present in the
precursor mixture before delivery to the substrate surface, leading
undesirably to blockage of the CVD apparatus and exhaust systems
with reaction products. This is a particular problem when the
substrate temperature is above about 400.degree. C., and so may be
a particular problem, for example, when trying to operate such a
CVD process online during float glass production.
[0009] There have been attempts to incorporate additives in the CVD
precursor mixture to slow the pre-reaction of dialkyl zinc
compounds with the other components of the precursor mixture. Such
additives may become incorporated into the zinc oxide coating,
affecting the properties of the coating. In some cases, this may be
useful. However, there is a need for methods which do not lead to
incorporation of such additives.
[0010] There have been successful methods developed employing
separate precursor streams that mix at the substrate surface.
[0011] WO-A-2013/136052 discloses a CVD process for forming a
gaseous mixture of an alkyl zinc compound and an inert gas as a
first stream, providing a first gaseous inorganic oxygen-containing
compound in a second stream and providing a second gaseous
inorganic oxygen-containing compound in the second stream, a third
stream or in both the second and third streams, and mixing the
streams at or near a surface of the float glass ribbon during the
float glass production process thereby depositing a zinc oxide
coating.
[0012] In EP 0611733 A2, there is described a method of coating a
moving substrate to provide a silica coating having a continuously
varying chemical composition as the distance from the
substrate-coating interface increases, in order to improve the low
deposition rate of silica coatings by chemical vapour deposition.
The method comprises directing a vapour coating composition toward
a first predetermined position on the surface of the substrate,
moving a first portion of the vapour along a first region of the
substrate surface in a first direction and a second portion of the
vapour along a second region of the substrate surface in a second
direction opposite to the first direction. The first portion of the
coating composition is maintained on the first region of the
substrate surface for a longer period of time than the second
portion of the vapor on the second region of the substrate surface
to coat the substrate. The coating mixture includes tin containing
precursors and a silicon precursor. A phosphorus containing
precursor may also be used with the metal containing
precursors.
[0013] Likewise, in a paper by McCurdy in the journal of Thin Solid
Films, volume 351, 30 Aug. 1999, pages 66-72, entitled `Successful
implementation methods of atmospheric CVD on a glass manufacturing
line`, there is described the use of phosphates as a method of
accelerating silica deposition using chemical vapour deposition
techniques.
[0014] However, there remains a need for methods of depositing zinc
oxide coatings, on substrates, particularly coated glass
substrates, which do not require the provision of separate
precursor streams and which are able to ensure deposition of the
zinc oxide coating on the coated glass surface, rather than
producing a powder as a gas phase reaction.
[0015] The present invention according provides, in a first aspect,
a method of depositing a coating comprising zinc oxide on a
substrate, the method comprising, providing a substrate, providing
a precursor mixture comprising an alkyl zinc compound and a
phosphorus source, the phosphorus source comprising a compound of
formula O.sub.nP(OR.sup.3).sub.3, wherein n is 0 or 1 and each
R.sup.3 is hydrocarbyl, and delivering the precursor mixture to a
surface of the substrate. Optionally, the precursor mixture may
further comprise an oxygen source (that is, an oxidant).
[0016] This method is advantageous because it allows a pre-mixed
precursor to be used without unacceptable pre-reaction, and yet
does not lead to unacceptable incorporation of for example
phosphorus in the zinc oxide coating.
[0017] Preferably, the alkyl zinc compound is dialkyl zinc,
preferably a dialkyl zinc of formula R.sup.1R.sup.2Zn, wherein
R.sup.1 and R.sup.2 are each independently selected from a
substituted or preferably unsubstituted C.sub.1-C.sub.4 alkyl or
C.sub.6-C.sub.10 aryl (preferably phenyl). It is preferred that
R.sup.1 and R.sup.2 are each independently selected from methyl or
ethyl; and it is especially preferred that R.sup.1 and R.sup.2 are
each methyl or each ethyl. The most preferred alkyl zinc compounds
are diethyl zinc (DEZ) and/or dimethyl zinc (DMZ) because these
compounds react readily, allowing formation of good coatings of
zinc oxide at relatively high reaction rates.
[0018] Preferably, in the compound of formula
O.sub.nP(OR.sup.3).sub.3, each R.sup.3 is independently selected
from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.10 aryl, more
preferably C.sub.1-C.sub.4 alkyl; more preferably methyl, ethyl,
n-propyl, i-propyl, n-butyl or t-butyl. It is most preferred that
each R.sup.3 is methyl, ethyl, or propyl. Triethyl phosphite is
particularly advantageous because, surprisingly, it greatly reduces
or prevents pre-reaction when mixed with the alkyl zinc compounds
and yet, surprisingly, phosphorus is not significantly incorporated
in the zinc oxide coating layer.
[0019] The oxygen source may comprise an inorganic oxygen source,
for example water, carbon dioxide, nitric oxide, nitrogen dioxide,
nitrous oxide, oxygen (for example, from air) and/or mixtures
thereof. Preferably, however, the oxygen source comprises an
organic oxygen compound, more preferably the oxygen source
comprises an ester, most preferably an alkyl ester. The ester
advantageously comprises one or more alkyl acetates, for example,
methyl acetate, ethyl acetate, propyl acetate, butyl acetate, or a
mixture of two or more of these esters. The most preferred ester
comprises t-butyl acetate.
[0020] Organic oxygen sources, particularly esters, are preferred
because they may be mixed with the alkyl zinc compound in the
presence of the phosphorus source without significant pre-reaction
before delivery to the substrate surface. During delivery to the
surface, the precursor mixture may additionally comprise an
inorganic oxygen source as discussed above (for example,
oxygen).
[0021] The precursor mixture may, if desired, comprise at least one
dopant source, for example a boron containing compound, a magnesium
containing compound, a gallium containing compound and/or an
aluminium containing compound to dope the zinc oxide coating with
for example, boron (B), magnesium (Mg), gallium (Ga) and/or
aluminium (Al) respectively.
[0022] It is preferred that the precursor mixture is a gaseous
precursor mixture, so that the method is preferably atmospheric
pressure chemical vapour deposition.
[0023] The preferred substrate comprises glass, preferably coated
glass for example glass having a coating already present on the
surface and on which zinc oxide is deposited. The coated glass may
comprise for example, silica coated glass or tin oxide coated
glass. There may be further coatings deposited below the zinc oxide
coating and one or more additional coatings deposited above the
zinc oxide coating. The substrate preferably comprises float
glass.
[0024] The surface of the substrate is preferably at a temperature
at which the precursors react to form the zinc oxide coating. Thus,
the surface of the substrate is preferably at a temperature in the
range 300.degree. C. to 800.degree. C. More preferably, the surface
of the substrate is at a temperature in the range 400.degree. C. to
750.degree. C. Even more preferably, the surface of the substrate
is at a temperature in the range 410.degree. C. to 750.degree. C.
Still more preferably, the surface of the substrate is at a
temperature in the range 470.degree. C. to 750.degree. C. Most
preferably, the surface of the substrate is at a temperature in the
range 500.degree. C. to 650.degree. C. or 580.degree. C. to
650.degree. C.
[0025] The coating comprising zinc oxide is preferably deposited
on-line during the float glass production process. The relatively
high deposition rate that the precursor mixture provides enables
good quality zinc oxide coatings of the desired thickness to be
deposited, even on the moving (relative to the coating apparatus)
glass ribbon during the float glass process.
[0026] Usually, if deposited during the float glass process, the
coating comprising zinc oxide is deposited whilst a ribbon of the
float glass is in a float bath.
[0027] The precursor mixture preferably further comprises a carrier
gas. The carrier gas may comprise one or more gases selected from
the group consisting of: nitrogen, argon, hydrogen, helium and
mixtures thereof. The preferred carrier gas comprises nitrogen.
[0028] The present invention is particularly advantageous because
the precursor mixture may be mixed without unacceptable
pre-reaction, thereby preventing blockages of any apparatus used in
the method of the invention.
[0029] Thus, the present invention accordingly provides, in a
second aspect, a chemical vapour deposition precursor mixture
suitable for use according to the first aspect of the present
invention comprising: dialkyl zinc, a phosphorus source, and
optionally an ester, the phosphorus source comprising a compound of
formula O.sub.nP(OR.sup.3).sub.3, wherein n is 0 or 1 and each
R.sup.3 is hydrocarbyl.
[0030] All features discussed in relation to the first aspect of
the present invention also apply accordingly in respect of the
second aspect of the present invention.
[0031] The present invention also provides, in a third aspect, a
coated glass article, comprising: a glass substrate; a silica
coating deposited on the glass substrate; a zinc oxide coating
deposited over the silica coating by a method according to the
first aspect of the invention.
[0032] All features discussed in relation to the first aspect of
the present invention apply accordingly in respect of the third
aspect of the present invention.
[0033] One use of zinc oxide coated glass substrates (especially
when coated on at transparent conductive oxide coating) is in
photovoltaic (PV) cells.
[0034] Thus, the present invention accordingly provides, in a
fourth aspect, a photovoltaic cell comprising a coated glass
article having a zinc oxide coating deposited over a transparent
conductive oxide coating (for example, a fluorine doped tin oxide
coating) by a method according to the first aspect. All features of
the first aspect of the present invention therefore also apply
accordingly in respect of the fourth aspect of the present
invention.
[0035] The present invention will now be described further with
reference to the following examples and Figures in which:
[0036] FIG. 1 shows schematically a static coater used for
laboratory scale chemical vapour deposition experiments as used in
the Comparative Examples and Examples according to the method of
the present invention.
[0037] FIG. 2 shows a graph of the X-ray photoelectron spectroscopy
(XPS) depth profile for Comparative Example E.
[0038] FIG. 3 shows a graph of the XPS depth profile for Example
6.
[0039] FIG. 4 shows XPS depth profile for Example 33.
[0040] FIGS. 5 and 6 are scanning electron micrographs illustrating
the thickness `A1` of the zinc oxide layer for Comparative Example
E.
[0041] FIGS. 7 and 8 are scanning electron micrographs illustrating
the thickness `A2` of the zinc oxide layer for Example 6.
[0042] FIG. 9 is a scanning electron micrograph illustrating the
thickness `A3` of the zinc oxide layer in Example 33.
[0043] FIG. 10 is an x-ray photoelectron spectroscopy (XPS) depth
profile for Example 74.
[0044] FIG. 11 is a scanning electron micrograph (SEM) image of
Example 74, for which the thickness of the zinc oxide layer is
indicated by distance `A4`.
[0045] FIG. 12 is an x-ray photoelectron spectroscopy (XPS) depth
profile for Example 53.
[0046] FIG. 13 is a scanning electron micrograph (SEM) image of
Example 53, for which the thickness of the zinc oxide layer
indicated by distance `A5`.
[0047] FIG. 14 is an x-ray photoelectron spectroscopy (XPS) depth
profile for Example 77.
[0048] FIG. 15 is a scanning electron micrograph (SEM) image of
Example 77, for which the thickness of the zinc oxide layer
indicated by distance `A6`.
[0049] FIG. 16 is an x-ray photoelectron spectroscopy (XPS) depth
profile for Example 82.
[0050] FIG. 17 is an x-ray photoelectron spectroscopy (XPS) depth
profile for Example 83
[0051] FIG. 18 is a schematic representation of a photovoltaic cell
comprising a zinc oxide coating applied by the method of the
present invention to a coated glass substrate.
[0052] Referring to FIG. 1, processes for deposition of zinc oxide
coatings on glass substrates in relation to the present invention
were performed using a laboratory scale static coater. In the
laboratory scale static coater, premixed precursors move towards
the coater through a heated line 1 before reaching baffle section
2, which equalises the precursor flow before it enters the sealed
coating section. The glass substrate 4 sits on a heated carbon
block 3 which is heated to the desired temperature using either:
heating elements (not shown) inserted inside the carbon block; or,
by an induction coil (not shown) around the sealed coating section.
Any unreacted precursor or by-products are then directed towards
fish tail exhaust 5, and continue towards the incinerator 6. The
arrows in FIG. 1 show the direction in which the gaseous mixture
moves.
EXAMPLES
[0053] All experiments were carried out using a static coater as
described in relation to FIG. 1. Diethyl zinc (DEZ) was used as the
zinc precursor and either ethyl acetate
(CH.sub.3COOCH.sub.2CH.sub.3), or t-butyl acetate
(CH.sub.3COOC(CH.sub.3).sub.3) served as the oxygen source. Zinc
oxide (ZnO) films (also referred to herein as layers) were
obtained. Esters (including ethyl acetate (EtOAc) and t-butyl
acetate (tBuOAc)) were found to be efficient oxidants for the
process, speeding the reaction and producing thick films, and
allowing pre-mixing in the presence of the phosphorus with alkyl
zinc compounds without premature pre-reaction or excessive powder
formation.
[0054] The precursors were delivered in a nitrogen carrier gas via
vessels/bubblers with a total flow rate of about 12 standard litres
per minute (slm) to 13 standard litres per minute (slm) (litres
min.sup.-1, at standard temperature and pressure, (stp)). Delivery
lines were maintained at a temperature of about 150.degree. C. to
avoid condensation.
Comparative Examples A to F and Examples 1 to 35
[0055] In the Examples and Comparative Examples, t-butyl acetate
was added as oxidant.
[0056] In the Comparative Examples, no triethyl phosphite was
used.
[0057] The substrate for Comparative Example F and Examples 5, 7,
11 and 34 was float glass coated with a transparent conductive
oxide having the film sequence: glass/tin oxide, silicon
dioxide/fluorine doped tin oxide
(glass/SnO.sub.2/SiO.sub.2/SnO.sub.2:F) (available from NSG). The
substrate for all the other Comparative Examples and Examples was
float glass having a coating of silica approximately 25 nm
thick.
[0058] During deposition for each sample, the diethyl zinc (DEZ)
vessel temperature (.degree. C.) was between 67.degree. C. and
75.degree. C. and the DEZ carrier gas flow in litres per minute (L
min.sup.-1) at standard temperature and pressure, (stp) was between
0.44 L min.sup.-1 and 0.80 L min.sup.-1. The triethyl phosphite
(P(OCH.sub.2CH.sub.3).sub.3), vessel temperature (.degree. C.) was
64.degree. C. or 65.degree. C. and, for the Examples, the triethyl
phosphite carrier gas flow rate in litres per minute (L min.sup.-1)
at standard temperature and pressure (stp) was between 0.05 L
min.sup.-1 and 0.55 L min.sup.-1.
[0059] The oxidant was supplied through a syringe, and the oxidant
was injected into a carrier gas having a flow rate of 5.00 L
min.sup.-1 (at standard temperature and pressure (stp)).
[0060] Further details of the zinc oxide deposition for Comparative
Examples A to F and Examples 1 to 35 are provided in Table 1. The
molar ratios of diethyl zinc (DEZ) to triethyl phosphite, diethyl
zinc (DEZ) to oxidant and triethyl phosphite to oxidant are
provided in Table 2, together with approximate values for the
thickness of the coated layer of zinc oxide for some of the
samples.
[0061] The thickness of the deposited zinc oxide layer in the
examples was determined by examining the interference reflection
colour of the coating at the thickest position and estimating the
thickness, assuming a refractive index of 1.8.
[0062] The Examples show that a thicker zinc oxide layer is
deposited when a phosphorus source, in the form of triethyl
phosphite, is added to the precursor mixture compared to the
Comparative Examples without triethyl phosphite (when the DEZ
amount is the same).
[0063] When the zinc precursor flow rate is approximately constant,
the addition of triethyl phosphite improved the deposition
efficiency and in so doing also reduced the waste particulates
generated. The X-ray photoelectron spectroscopy (XPS) results
(described below and illustrated in FIGS. 2 to 4) show that there
was very little or no phosphorus incorporation in the layers and
that the layers had a stoichiometry close to ZnO. As discussed
herein, a further advantage of the use of triethyl phosphite in the
precursor mixture is in reducing the amount of powder generation,
and significantly increasing the stability of the precursor
mixture.
[0064] In addition, as the amount of triethyl phosphite in the
precursor mixture is increased, the thickness of the zinc oxide
coating layer obtained also generally increases. The quantity of
triethyl phosphite required to produce a thickness increase is
small with an increase seen at just 2% of the DEZ concentration.
When the amount of triethyl phosphite is increased to 15% of the
DEZ concentration, absorption was seen in the zinc oxide coating
layer, indicating that the deposition rate was high enough to
enable a fully oxidised zinc oxide layer to be produced at the
amount of oxidant used. The use of greater amounts of oxidant is
likely to lead to a fully oxidised layer.
[0065] Some of the Examples investigated whether the underlying
substrate had an influence on the zinc oxide layer (or film) growth
by using a glass substrate bearing a transparent conductive coating
as seen in Comparative Examples F and Examples 5, 7, 11 and 34. The
thickness of the zinc oxide layer was determined by looking at the
reflection colour. The data provided by the examples confirms that
a similar improvement in the thickness of the zinc oxide layer is
achieved by adding triethyl phosphite when a transparent conductive
coated substrate is used as when using a silica coated glass
substrate.
TABLE-US-00001 TABLE 1 Triethyl DEZ Phosphite Triethyl Example or
Reactor Carrier DEZ Carrier Gas Phosphite Oxidant Run Comparative
Temp Gas Flow vessel Flow vessel supply Time Example (CE) (.degree.
C.) (L/min) T (.degree. C.) (L/min) T (.degree. C.) (cm.sup.3/hr)
(s) CE A 600 0.75 69.0 0.00 -- 100 30 CE B 600 0.80 67.0 0.00 --
100 30 CE C 600 0.80 68.0 0.00 -- 100 30 CE D 600 0.71 70.0 0.00 --
100 30 CE E 600 0.61 73.0 0.00 -- 100 30 CE F* 600 0.64 72.0 0.00
-- 100 30 1 600 0.60 72.0 0.05 65.0 96 30 2 600 0.60 72.0 0.05 65.0
96 30 3 600 0.64 72.0 0.06 64.0 100 30 4 600 0.80 68.0 0.06 65.0
100 30 5* 600 0.64 72.0 0.06 65.0 100 30 6 600 0.70 70.0 0.14 65.0
100 30 7* 600 0.64 72.0 0.14 65.0 100 30 8 600 0.50 75.0 0.23 65.0
85 30 9 600 0.60 71.0 0.25 65.0 85 30 10 600 0.75 69.0 0.28 65.0
100 30 11* 600 0.64 72.0 0.28 65.0 100 30 12 625 0.61 73.0 0.28
65.0 100 8 13 625 0.68 71.0 0.28 65.0 100 9 14 600 0.61 73.0 0.28
65.0 100 10 15 625 0.71 70.0 0.28 65.0 100 5 16 625 0.61 73.0 0.28
65.0 100 10 17 600 0.64 72.0 0.28 65.0 100 15 18 600 0.71 70.0 0.28
65.0 100 9 19 475 0.64 72.0 0.28 65.0 100 60 20 475 0.71 70.0 0.28
65.0 100 60 21 475 0.64 72.0 0.28 65.0 100 90 22 450 0.64 72.0 0.28
65.0 100 120 23 425 0.58 74.0 0.28 65.0 100 120 24 575 0.64 72.0
0.28 65.0 100 10 25 550 0.61 73.0 0.28 65.0 100 12 26 525 0.71 70.0
0.28 65.0 100 14 27 525 0.71 70.0 0.28 65.0 100 16 28 500 0.68 71.0
0.28 65.0 100 19 29 500 0.68 71.0 0.28 65.0 100 24 30 500 0.71 70.0
0.28 65.0 100 30 31 500 0.75 69.0 0.28 65.0 100 50 32 600 0.55 69.0
0.41 65.0 73 30 33 600 0.75 69.0 0.55 65.0 100 30 34* 600 0.64 72.0
0.55 65.0 100 30 35 600 0.44 69.0 0.64 65.0 58 30 *Substrate is
float glass coated with a transparent conductive oxide
TABLE-US-00002 TABLE 2 Thickness Example or Estimate of Comparative
Molar Ratio Molar Ratio Zinc Oxide Example DEZ:Triethyl Molar Ratio
Triethyl layer (CE) Phosphite DEZ:Oxidant Phosphite:Oxidant (nm) CE
A 0.000 2.14 0.00 350-410 CE B 0.000 2.18 0.00 260-300 CE C 0.000
2.09 0.00 430-520 CE D 0.000 2.17 0.00 205-230 CE E 0.000 2.24 0.00
160-180 CE F* 0.000 2.22 0.00 260-300 1 0.018 2.28 129.64 260-300 2
0.018 2.27 128.94 300-320 3 0.019 2.22 117.04 160-180 4 0.019 2.09
111.93 300-320 5* 0.020 2.22 111.93 350-410 6 0.046 2.20 47.97
230-260 7* 0.046 2.22 47.97 410-430 8 0.086 2.14 24.82 205-230 9
0.092 2.10 22.83 300-320 10 0.089 2.14 23.98 430-520 11* 0.093 2.22
23.98 430-520 12 0.093 2.24 23.98 -- 13 0.091 2.18 23.98 70-100 14
0.093 2.24 23.98 -- 15 0.091 2.17 23.98 -- 16 0.093 2.24 23.98
70-100 17 0.093 2.22 23.98 160-180 18 0.091 2.17 23.98 70 19 0.093
2.22 23.98 70 20 0.091 2.17 23.98 -- 21 0.093 2.22 23.98 -- 22
0.093 2.22 23.98 -- 23 0.094 2.26 23.98 -- 24 0.093 2.22 23.98 --
25 0.093 2.24 23.98 -- 26 0.091 2.17 23.98 -- 27 0.091 2.17 23.98
-- 28 0.091 2.18 23.98 -- 29 0.091 2.18 23.98 -- 30 0.091 2.17
23.98 -- 31 0.089 2.14 23.98 100-130 32 0.178 2.13 11.96 180-205 33
0.175 2.14 12.21 350-410 34* 0.182 2.22 12.21 350-410 35 0.348 2.12
6.09 70-100 *Substrate is float glass coated with a transparent
conductive oxide
[0066] In Table 2, the thickness of the zinc oxide layer (in nm)
was estimated based on colour interference fringes seen on the
substrate after deposition. Below 70 nm, layers (or films) are
colourless and the thickness cannot be estimated in the same
way.
Comparative Examples G to K and Examples 36 to 48
[0067] Experiments were undertaken to investigate how the oxidant
affected the zinc oxide layer (or film) growth. The conditions used
for these Examples and Comparative Examples were generally similar
to those used for Examples 1 to 35 but using ethyl acetate as the
oxidant.
[0068] The substrate for Comparative Example K and Examples 38, 41,
44 and 47 was float glass coated with a transparent conductive
oxide having the sequence: glass/tin oxide, silicon
dioxide/fluorine doped tin oxide
(glass/SnO.sub.2/SiO.sub.2/SnO.sub.2:F) (available from NSG). The
substrate for the other Comparative Examples and Examples was float
glass having a coating of silica approximately 25 nm thick.
[0069] During the zinc oxide layer depositions, the diethyl zinc
(DEZ) vessel temperature (.degree. C.) was between 73.degree. C.
and 85.degree. C., and the DEZ carrier flow in litres per minute (L
min.sup.-1), at standard temperature and pressure (stp) was between
0.63 L min.sup.-1 and 1.20 L min.sup.-1. The triethyl phosphite
vessel temperature (.degree. C.) was 64.degree. C., 65.degree. C.
or 69.degree. C. and the triethyl phosphite carrier flow in litres
per minute (L min.sup.-1), for the Examples, was between 0.11 L
min.sup.-1 and 1.17 L min.sup.-1. The oxidant, ethyl acetate
(CH.sub.3COOCH.sub.2CH.sub.3) was supplied through a syringe,
injecting the oxidant into a carrier gas at a flow rate of 5.00 L
min.sup.-1 at standard temperature and pressure (stp).
[0070] Further details of the deposition of the zinc oxide layer
for Comparative Examples G to K and Examples 36 to 48 are given in
Table 3. The molar ratios of DEZ to triethyl phosphite and DEZ to
oxidant are given in Table 4 together with the approximate
thickness of the zinc oxide coating.
[0071] The thickness was determined by examining the interference
reflection colour of the zinc oxide coating at the thickest
position and estimating the thickness assuming a refractive index
of 1.8.
[0072] The results show an improved deposition efficiency as the
amount of triethyl phosphite is increased. Even with an increased
flow of ethyl acetate, the zinc oxide coatings were still slightly
thinner for Examples 36 to 48, compared with the Examples using
tertbutylacetate as oxidant. This indicates that ethyl acetate and
tertbutylacetate may both be used as effective oxidants.
TABLE-US-00003 TABLE 3 DEZ TEP Example or Reactor Carrier DEZ
Carrier TEP Oxidant Run Comparative Temp Gas Flow vessel T Gas Flow
vessel T Amount Time Example (CE) (.degree. C.) (L/min) (.degree.
C.) (L/min) T (.degree. C.) (cm.sup.3/hr) (s) CE G 600 0.65 85.0
0.00 -- 200 30 CE H 600 0.85 80.0 0.00 -- 200 30 CE I 600 1.00 77.0
0.00 -- 200 30 CE J 600 0.95 78.0 0.00 -- 200 30 CE K* 600 1.17
74.0 0.00 -- 200 30 36 600 1.20 73.0 0.11 65.0 194 30 37 600 1.11
75.0 0.11 65.0 200 30 38* 600 0.85 80.0 0.11 65.0 200 30 39 600
0.75 82.0 0.12 64.0 194 30 40 600 1.05 76.0 0.28 65.0 200 30 41*
600 0.90 79.0 0.28 65.0 200 30 42 600 0.83 78.0 0.48 65.0 175 30 43
600 1.05 76.0 0.55 65.0 200 30 44* 600 0.95 78.0 0.55 65.0 200 30
45 600 0.82 76.0 0.86 65.0 155 30 46 600 1.00 77.0 1.10 65.0 200 30
47* 600 1.11 75.0 1.11 65.0 200 30 48 600 0.63 77.0 1.17 69.0 126
30 *Substrate float glass coated with a transparent conductive
oxide
TABLE-US-00004 TABLE 4 Thickness Estimate Example or of Zinc
Comparative Ratio Oxide Example DEZ:Triethyl Ratio Molar Ratio
layer (CE) Phosphite DEZ:Oxidant TEP:Oxidant (nm) CE G 0.000 2.44
0.00 100-130 CE H 0.000 2.45 0.00 160-180 CE I 0.000 2.44 0.00
205-230 CE J 0.000 2.44 0.00 180-205 CE K* 0.000 2.43 0.00 230-260
36 0.102 2.42 23.79 300-320 37 0.099 2.43 24.52 205-230 38* 0.100
2.45 24.52 205-230 39 0.106 2.42 22.77 100-130 40 0.254 2.44 9.63
205-230 41* 0.253 2.44 9.63 230 42 0.496 2.44 4.92 160-180 43 0.498
2.44 4.90 430-520 44* 0.497 2.44 4.90 335-350 45 0.998 2.43 2.43
180-205 46 0.994 2.44 2.45 205-230 47* 1.002 2.43 2.43 205-230 48
2.000 2.44 1.22 100-130 *Substrate float glass coated with a
transparent conductive oxide
[0073] In Table 4, the thickness of the zinc oxide layer was
estimated based on the colour interference fringes seen on the
substrate after deposition. Below 70 nm layers (or films) are
colourless and thickness cannot be estimated in the same way.
[0074] X-Ray Photoelectron Spectroscopy (XPS) Analysis
[0075] X ray photoelectron spectroscopy (XPS) was performed on
Example 6, Example 33 and Comparative Example E.
[0076] XPS analysis was used to confirm the stoichiometry of the
zinc oxide coating layers as ZnO. Chlorine was detected throughout
the depth of all three samples. The value for Comparative Example E
was 0.4 atomic % and for Examples 6 and 33, the value was 1 atomic
%. Phosphorus was only detected within the silica layer of the
transparent conductive oxide coating for sample Example 33 at
around .about.0.5 atomic %. The XPS results for the zinc oxide
coating layers are shown in FIGS. 2, 3 and 4. In each of FIGS. 2, 3
and 4 the numbered curves refer to the species as indicated in
Table 5, below. The numbered curves for FIGS. 10, 12, 14, 16 and 17
are also indicated in Table 5 below.
TABLE-US-00005 TABLE 5 Reference Numeral assigned in FIGS. 2, 3, 4,
10, 12, 14, 16 and 17 Assignment 10 C 1s 12 Ca 2p3 14 Mg 1s 16 Na
1s 18 O 1s 20 O 1s Scan A 21 P 2p 22 Si 2p 23 Si 2p Scan A 24 Zn
2p3 26 Cl 2p 28 P 2p
[0077] Time of Flight Secondary Ion Mass Spectrometry
(ToF-SIMS)
[0078] An ION-TOF 5 Time of Flight Secondary Ion Mass Spectrometry
(ToF-SIMS) instrument was used to obtain a compositional positive
ion depth profile for each coating. The analysis beam was Bi.sup.3+
and the sputter beam was 1 keV Cs.sup.+ with a beam current of 70.2
nA. For each sample tested, the sputter beam was rastered over a
200.times.200 .mu.m area and the bismuth analysis beam was rastered
over a 50.times.50 .mu.m area at the centre of the sputtered
region.
[0079] Only Example 33 provided a phosphorus signal response at
just above the limit of detection.
[0080] Scanning Electron Microscopy (SEM)
[0081] Example 6, Example 33 and Comparative Example E were
analysed by SEM.
[0082] SEM was used to confirm the thickness of the zinc oxide
layer for Comparative Example E, which was measured to be 187-194
nm, as illustrated in FIG. 5 and FIG. 6.
[0083] SEM was also used to confirm the thickness of the zinc oxide
layer in Example 6, which was found to be 210-221 nm, as
illustrated in FIG. 7 and FIG. 8.
[0084] SEM was further used to confirm the thickness of the zinc
oxide layer in Example 33, which was found to 286 nm, as shown in
FIG. 9.
[0085] All 3 examples used the same amounts of diethyl zinc (DEZ)
and tertbutylacetate (tBuOAc) in the precursor mixture. The only
difference between the samples was the amount of triethyl phosphite
used.
[0086] The results and images show that by adding a small amount of
triethyl phosphite to the precursor mixture in accordance with the
method of the present invention, the thickness of the zinc oxide
layer deposited was increased by an amount of from 10 to 15%. In
addition, it was found that by adding a larger amount of triethyl
phosphite to the precursor mixture in accordance with the method of
the present invention the thickness of the zinc oxide layer
deposited could be increased by from 39 to 44%.
[0087] X-Ray Diffraction (XRD)
[0088] Example 6, Example 33 and Comparative Example E were
analysed by XRD.
[0089] X-ray diffraction (XRD) was performed using a Bruker D8
Discover X-ray diffractometer using monochromatic Cu K.alpha.1 and
Cu K.alpha.2 radiation of wavelengths 0.154056 and 0.154439 nm
respectively, emitted with a voltage of 40 kV and a current of 40
mA in an intensity ratio of 2:1. Diffraction patterns were obtained
by scanning the samples from 5 to 95.degree. 2.theta. using an
X'Celerator detector, allowing detection of crystalline phases in
the first 1 to 10 microns of the sample surface. A scanning time of
1 hour per sample was used.
[0090] The coating in each case exhibited crystalline phases
identified as zinc oxide (indexed to Zincite, ZnO, Hexagonal).
Information on the XRD results is provided in Tables 6 to 9,
below.
[0091] The crystallite size was approximately 9 to 18 nm (see Table
6 below). The crystallite size for Example 33 was smaller than that
of the other samples. All the samples showed some preferred
orientation in the (100) plane.
TABLE-US-00006 TABLE 6 Integral Integral Peak breadth breadth
position Crystallite Sample Reflection (sample) (std) (2.theta.)
size (nm) Comparative (100) 0.646 0.139 31.73 19 Example E (101)
0.608 0.138 36.21 21 (110) 0.992 0.133 56.56 13 Average -- -- -- 18
Example 6 (100) 0.668 0.139 31.75 19 (101) 0.701 0.138 36.23 18
(110) 1.091 0.133 56.56 11 Average -- -- -- 16 Example 33 (100)
1.066 0.139 31.66 11 (101) 1.391 0.138 36.08 8 (110) 1.445 0.133
56.43 8 Average -- -- -- 9
[0092] In Table 6 there is provided details of the crystallite size
of the zinc oxide layer for Comparative Example 5, Example 6 and
Example 33.
TABLE-US-00007 TABLE 7 Pos. d- Rel. Int. Rel. Int. Meas. spacing
FWHM Height Measured ICDD {hkl} (2.theta.) [.ANG.] (2.theta.) [cts]
[%] [%] I/Io (100) 31.73 2.8175 0.45 874 95.7 55.2 1.73 (101) 36.21
2.4788 0.48 913 100.0 100.0 1.00 (110) 56.56 1.6259 0.60 210 22.9
31.4 0.73
[0093] Table 7 details the peak parameters obtained by X-ray
diffraction for Comparative Example E.
TABLE-US-00008 TABLE 8 Pos. d- Rel. Int. Rel. Int. Meas. spacing
FWHM Height Measured ICDD {hkl} (2.theta.) [.ANG.] (2.theta.) [cts]
[%] [%] I/Io (100) 31.75 2.8164 0.49 2586 100.0 55.2 1.81 (101)
36.23 2.4776 0.64 424 16.4 100.0 0.16 (110) 56.56 1.6259 0.80 674
26.1 31.4 0.83
[0094] Table 8 details the peak parameters obtained by X-ray
diffraction for Example 6.
TABLE-US-00009 TABLE 9 Pos. d- Rel. Int. Rel. Int. Meas. spacing
FWHM Height Measured ICDD {hkl} (2.theta.) [.ANG.] (2.theta.) [cts]
[%] [%] I/Io (100) 31.66 2.8242 0.75 2078 100.0 55.2 1.81 (101)
36.08 2.4875 0.90 271 13.0 100.0 0.13 (110) 56.43 1.6294 1.15 629
30.3 31.4 0.96
[0095] Table 9 details the peak parameters obtained by X-ray
diffraction for Example 33.
[0096] Experiments to Evaluate Alternative Phosphorus Sources.
[0097] Different phosphorus sources were investigated in the method
of the present invention. The derivatives explored were: trimethyl
phosphite (TMP), triisopropyl phosphite (TIP) and triethyl
phosphate (TEPa). The different phosphorus containing precursors
are illustrated in Table 10.
TABLE-US-00010 TABLE 10 PHOSPHORUS PRECURSOR STRUCTURE Triethyl
Phosphite ##STR00001## Trimethyl Phosphite ##STR00002##
Triisopropyl Phosphite ##STR00003## Triethyl Phosphate
##STR00004##
[0098] Experiments were conducted again using a static coater as
described above in relation to FIG. 1. Diethyl zinc (DEZ) was used
as the zinc precursor and t-butyl acetate
(CH.sub.3COOC(CH.sub.3).sub.3) served as the oxygen source. The
phosphorus compounds identified in Table 10 were tested as part of
the precursor mixture in the deposition of a zinc oxide (ZnO)
layer.
[0099] The precursors were delivered in a nitrogen carrier gas via
vessels/bubblers with a total flow rate of about 12 standard litres
per minute (slm) to 13 standard litres per minute (slm), at
standard temperature and pressure, (stp)). Delivery lines were
maintained at a temperature in the region of about 150.degree. C.
to avoid condensation.
[0100] The experimental data obtained for each of the alternative
phosphorus sources investigated as part of the precursor mixture
according to the method of the present invention are illustrated in
Tables 11 and Table 12.
[0101] Example 53, Example 74, and Example 77 were analysed by SEM
and XPS. These Examples were chosen because a similar amount of
diethyl zinc (DEZ), tertbutylacetate (tBuOAc) and phosphorus
precursor were used for the deposition of the zinc oxide layer.
[0102] Example 74 provides a baseline example of the deposition of
zinc oxide (ZnO) using DEZ and tBuOAc. FIG. 10 is an x-ray
photoelectron spectroscopy (XPS) trace for Example 74. FIG. 10
illustrates that the film (or layer) deposited comprises zinc atoms
and oxygen atoms in the correct stoichiometry for ZnO, and in the
absence of any phosphorus atoms. This is to be expected since no
phosphorus containing chemicals were involved in the deposition of
the zinc oxide layer. FIG. 11 is a scanning electron micrograph
(SEM) image of Example 74, for which the thickness of the zinc
oxide layer indicated by distance A, was found to be in the range
of 267-287 nm.
[0103] Example 53 provides a zinc oxide (ZnO) layer deposited using
diethyl zinc (DEZ), tertbutylacetate (tBuOAc) and
trimethylphosphite (TMP). FIG. 12 is an x-ray photoelectron
spectroscopy (XPS) trace of Example 53. FIG. 12 illustrates again
that the coating layer deposited by the method of the present
invention comprises zinc (Zn) atoms and oxygen atoms in the correct
stoichiometry for ZnO. However, no phosphorus atoms were detected.
That is, the results are similar to the results seen when using
triethyl phosphite. FIG. 13 is a scanning electron micrograph (SEM)
image of Example 53 confirming the thickness of the zinc oxide
layer to be in the range of 292 to 300 nm. That is, in Example 53
there was observed an increase in the thickness of the zinc oxide
layer of between 4 and 9%, compared to the thickness of the zinc
oxide layer in Example 74. Therefore, it can be seen from Example
53 that trimethylphosphite (TMP) may also be used as a phosphorus
source in the method of the present invention.
[0104] In Example 77, a zinc oxide coating layer was deposited
using diethyl zinc (DEZ), tertbutylacetate (tBuOAc) and
triethylphosphate (TEPa). FIG. 14 is an x-ray photoelectron
spectroscopy (XPS) trace of the zinc oxide later of Example 77. The
x-ray photoelectron spectroscopy (XPS) trace, shows again that a
zinc oxide film is deposited which comprises zinc atoms and oxygen
atoms, in the correct stoichiometry for ZnO, in the absence of any
phosphorus atoms. That is, similar results are seen for Example 77
when using triethyl phosphite. FIG. 15 is an SEM image of Example
77 confirming the thickness of the zinc oxide layer to be in the
range of 396 to 406 nm. That is, there was an increase in the
thickness of the zinc oxide layer in Example 77 of from 41 and 49%
compared to the thickness of the zinc oxide layer obtained in
Example 74. These results indicate that triethylphosphate (TEPa)
may also be used as a phosphorus source for the deposition of a
zinc oxide layer according to the method of the present
invention.
[0105] Experiments were carried out using triisopropyl phosphite
(tripropan-2-yl phosphite) (TIP), as shown in Table 11. The
relevant vapour pressure data was not available, and hence, a
comparison between the efficiency of the samples could not be made.
However, the experiments still showed that it is possible to
deposit a zinc oxide coating using triisopropyl phosphite
(TIP).
TABLE-US-00011 TABLE 11 Table 11 provides details of the
experiments performed in accordance with the method of the present
invention using alternative phosphorus sources in the precursor
mixture. DEZ Phosphorus Example or Carrier Precursor Phosphorus
Comparative Phosphorus Reactor Gas DEZ Carrier Precursor Oxidant
Run Example Precursor Temperature Flow Vessel T Gas Flow Vessel T
Supply Time (CE) Used (.degree. C.) (L/min) (.degree. C.) (L/min)
(.degree. C.) (cm.sup.3/hr) (s) 49 TMP 600 0.58 74.0 0.00 0.0
100.00 30 50 TMP 600 0.61 73.0 0.00 0.0 100.00 30 51 TMP 600 0.64
72.0 0.05 29.0 100.00 30 52 TMP 600 0.64 72.0 0.15 29.0 100.00 30
53* TMP 600 0.64 72.0 0.30 29.0 100.00 30 54* TMP 600 0.64 72.0
0.59 29.0 100.00 30 55* TMP 600 0.64 72.0 0.15 29.0 100.00 30 56
TMP 600 0.68 71.0 0.00 0.0 100.00 30 57 TMP 600 0.64 72.0 0.30 29.0
100.00 30 58 TMP 600 0.70 72.0 0.00 20.0 100.00 30 59 TMP 600 0.70
72.0 0.00 20.0 100.00 30 60 TMP 600 0.70 72.0 1.00 30.0 0.00 30 61
TMP 600 0.70 72.0 1.00 81.0 0.00 30 62 TMP 600 0.70 72.0 2.00 81.0
0.00 30 63 TMP 600 0.70 72.0 2.00 81.0 10.00 30 64 TMP 600 0.70
72.0 0.06 81.0 100.00 30 65 TMP 600 0.70 72.0 2.00 81.0 0.00 30 66
TMP 600 0.70 72.0 2.00 81.0 10.00 30 67 TMP 600 0.70 72.0 0.06 81.0
100.00 30 68 TIP 600 0.58 74.0 0.50 26.0 100.00 30 69 TIP 600 0.58
74.0 0.50 34.0 100.00 30 70 TIP 600 0.61 73.0 0.50 46.0 100.00 30
71 TIP 600 0.58 74.0 0.50 55.0 100.00 30 72 TIP 600 0.58 74.0 0.25
57.0 100.00 30 73 TIP 600 0.58 74.0 1.00 55.0 100.00 30 74 TEPa 600
0.68 71.0 0.00 0.0 100.00 30 75 TEPa 600 0.68 71.0 0.05 113.0
100.00 30 76 TEPa 600 0.71 70.0 0.14 114.0 100.00 30 77 TEPa 600
0.71 70.0 0.28 114.0 100.00 30 78 TEPa 600 0.75 69.0 0.54 114.0
100.00 30 79 TEPa 600 0.64 72.0 0.28 114.0 100.00 30 80 TEPa 600
0.64 72.0 0.28 114.0 100.00 30 81 TEPa 600 0.71 70.0 0.28 114.0
100.00 30 *Substrate is float glass coated with a transparent
conductive oxide
TABLE-US-00012 TABLE 12 Table 12 provides the ratios of the
components in the precursor mixture for the deposition of a layer
of zinc oxide according to the present invention using alternative
phosphorus sources. Example or Comparative Molar Ratio Molar Ratio
Example DEZ:Phosphorus Molar Ratio Phosphorus (CE) Precursor
DEZ:Oxidant precursor:Oxidant 49 0.000 1.782 0.000 50 0.000 1.783
0.000 51 0.014 1.788 123.454 52 0.043 1.788 41.151 53* 0.087 1.788
20.576 54* 0.171 1.788 10.462 55* 0.043 1.788 41.151 56 0.000 1.770
0.000 57 0.087 1.788 20.576 58 0.000 2.029 0.000 59 0.000 2.029
0.000 60 0.330 0.000 0.000 61 2.992 0.000 0.000 62 5.983 0.000
0.000 63 5.983 0.203 0.034 64 0.179 2.029 11.304 65 5.983 0.000
0.000 66 5.983 0.203 0.034 67 0.179 2.029 11.304 74 0.000 1.770
0.000 75 0.013 1.770 134.559 76 0.039 1.782 46.071 77 0.077 1.782
23.035 78 0.149 1.774 11.944 79 0.078 1.788 23.035 80 0.078 1.788
23.035 81 0.077 1.782 23.035 *Substrate is float glass coated with
a transparent conductive oxide
[0106] Investigating the Presence of Phosphorus in Zinc Oxide
Layers
[0107] In the experiments discussed so far, all of the zinc oxide
layers deposited had little (.about.0.5 atomic %) to no phosphorus
inclusion in the layers. This was found to be in contrast to the
results analysed for analogous experiments performed by the
inventors and described in WO2015177552, which investigated the
deposition of zinc oxide layers using dimethylsulfoxide as part of
the precursor mixture. In the experiments which used
dimethylsulfoxide as part of the precursor mixture, all of the zinc
oxide layers appeared to contain sulphur.
[0108] Two samples 82 and 83, were prepared and analysed in which
no oxidant was used and for which diethyl zinc (DEZ) and triethyl
phosphite were mixed together in the precursor mixture. The
experimental conditions used for examples 82 and 83 are shown in
Table 13 and Table 14.
[0109] FIG. 16 is an x-ray photoelectron spectroscopy (XPS) trace
for Example 82. FIG. 16 illustrates that the layer (film) deposited
comprises zinc atoms and oxygen atoms and phosphorus atoms. Table
15 provides the stoichiometry of the zinc oxide layer for Example
82 as ZnO:P.sub.0.75.
[0110] FIG. 17 is x-ray photoelectron spectroscopy (XPS) trace for
Example 83. FIG. 17 illustrates that the film deposited comprises
zinc atoms, oxygen atoms and phosphorus atoms. Table 15 also
provides stoichiometry of the zinc oxide layer for Example 83 as
ZnO:P.sub.0.5.
[0111] Table 15 shows that it is possible to deposit both `pure`
zinc oxide films, that is, zinc oxide film which do not comprise
phosphorus, and also phosphorus doped zinc oxide films using
triethyl phosphite by the method of the present invention.
TABLE-US-00013 TABLE 13 DEZ TEP Oxidant Example or Reactor Carrier
DEZ Carrier TEP Amount Run Comparative Temperature Gas Flow vessel
T Gas Flow vessel T (cm.sup.3/ Time Example (CE) (.degree. C.)
(L/min) (.degree. C.) (L/min) (.degree. C.) hour) (s) 82 600 0.64
72.0 1.96 104.0 0.00 30 83 600 0.32 72.0 0.95 105.0 0.00 30
[0112] In Table 13 there is illustrated the experimental conditions
used for the preparation of examples 82 and 83.
TABLE-US-00014 TABLE 14 Example or Comparative Molar Ratio Molar
Ratio Molar Ratio Example (CE) DEZ:TEP DEZ:Oxidant TEP:Oxidant 82
3.003 0.000 0.000 83 3.014 0.000 0.000
[0113] In Table 13 there is illustrated the experimental conditions
used for the preparation of examples 82 and 83.
TABLE-US-00015 TABLE 15 Example or Average concentration in the
Comparative coating (atomic %) Example (CE) Zinc (Zn) Oxygen (O)
Phosphorus (P) 82 23.6 58.5 17.9 83 29.2 55.8 15.0
[0114] In Table 15 there is illustrated the average concentration
of each of the elements zinc, oxygen and phosphorus, present in the
zinc oxide layer prepared according to the present invention for
examples 82 and 83.
[0115] Therefore, by using the method of the present invention it
is possible to deposit a zinc oxide coating layer atop a substrate,
such as float glass. The zinc oxide coating may be applied to a
layer of silica oxide or tin oxide deposited on the glass substrate
such as float glass. The resultant coated glass may be used in a
range of applications, including but not limited to, a photovoltaic
cell. When used in a photovoltaic cell, the zinc oxide coating
prepared according to the present invention may be deposited over a
layer of fluorine doped tin oxide, the fluorine doped tin oxide
being part of a transparent conductive coating, applied above a
glass substrate such as float glass. In this regard, FIG. 18 is a
schematic representation of a photovoltaic cell comprising a zinc
oxide coating layer 120, applied above a transparent conductive
coating (TCO) 110, deposited on a glass substrate, such as float
glass 100. In a photovoltaic cell, photovoltaic material 130 such
as for example a cadmium telluride layer 130 may be applied above
the zinc oxide layer 120.
* * * * *