U.S. patent application number 10/296410 was filed with the patent office on 2003-09-18 for transparent substrate comprising an antireflection coating.
Invention is credited to Anderson, Charles, Blieske, Ulf.
Application Number | 20030175557 10/296410 |
Document ID | / |
Family ID | 8851037 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030175557 |
Kind Code |
A1 |
Anderson, Charles ; et
al. |
September 18, 2003 |
Transparent substrate comprising an antireflection coating
Abstract
The subject of the invention is a transparent substrate (6)
having at least one antireflection coating, made from a film (A)
comprising multiple thin layers of alternately high and low
refractive indexes. The multilayer film comprises, in succession: a
high-index first layer (1), having a refractive index n.sub.1, of
between 1.8 and 2.3 and a geometrical thickness e.sub.1 of between
5 and 50 nm; a low-index second layer (2), having a refractive
index n.sub.2 of between 1.30 and 1.70 and a geometrical thickness
e.sub.2 of between 5 and 50 nm; a high-index third layer (3),
having a refractive index n.sub.3 of between 1.8 and 2.3 and a
geometrical thickness e.sub.3 of at least 100 nm; a low-index
fourth layer (4), having a refractive index n.sub.4 of between 1.30
and 1.70 and a geometrical thickness e.sub.4 of at least 80 nm.
This antireflection coating can be used in solar modules.
Inventors: |
Anderson, Charles;
(Courbevoie, FR) ; Blieske, Ulf; (Monchengladbach,
DE) |
Correspondence
Address: |
PENNIE & EDMONDS LLP
1667 K STREET NW
SUITE 1000
WASHINGTON
DC
20006
|
Family ID: |
8851037 |
Appl. No.: |
10/296410 |
Filed: |
April 18, 2003 |
PCT Filed: |
June 6, 2001 |
PCT NO: |
PCT/FR01/01735 |
Current U.S.
Class: |
428/698 ;
428/432; 428/701; 428/702 |
Current CPC
Class: |
G02B 1/116 20130101;
G02B 1/16 20150115; B32B 2457/12 20130101; B32B 17/10174 20130101;
C03C 17/3417 20130101; Y10T 428/24975 20150115; C03C 17/3435
20130101; B32B 17/10091 20130101; Y02E 10/40 20130101; G02B 1/115
20130101; B32B 17/10036 20130101; B32B 17/10201 20130101; F24S
80/52 20180501; B32B 17/1077 20130101; C03C 2217/734 20130101 |
Class at
Publication: |
428/698 ;
428/701; 428/702; 428/432 |
International
Class: |
B32B 017/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2000 |
FR |
00/07271 |
Claims
1. Transparent substrate (6), especially made of glass, having on
at least one of its faces an antireflection coating, in particular
at least in the visible and in the near infrared, made from a film
(A) comprising multiple thin layers of a dielectric having
alternately high and low refractive indexes, characterized in that
the multilayer film comprises, in succession: a high-index first
layer (1), having a refractive index n.sub.1 of between 1.8 and 2.3
and a geometrical thickness e.sub.1 of between 5 and 50 nm; a
low-index second layer (2), having a refractive index n.sub.2 of
between 1.30 and 1.70 and a geometrical thickness e.sub.2 of
between 5 and 50 nm; a high-index third layer (3), having a
refractive index n.sub.3 of between 1.8 and 2.3 and a geometrical
thickness e.sub.3 of at least 100 nm or at least 120 nm; a
low-index fourth layer (4), having a refractive index n.sub.4 of
between 1.30 and 1.70 and a geometrical thickness e.sub.4 of at
least 80 nm or at least 90 nm.
2. Substrate (6) according to claim 1, characterized in that the
high-index first layer (1) and the low-index second layer (2) are
replaced with a single layer (5) of intermediate index e.sub.5 of
between 1.60 and 1.90, especially between 1.70 and 1.80.
3. Substrate (6) according to claim 2, characterized in that the
single layer (5) of intermediate index has a geometrical thickness
e.sub.5 of between 40 and 120 nm, especially between 60 and 100 nm
or between 65 and 85 nm.
4. Substrate (6) according to one of the preceding claims,
characterized in that n.sub.1, and/or n.sub.3 are between 1.85 and
1.15, especially between 1.90 and 2.10 or between 2.0 and 2.1.
5. Substrate (6) according to one of the preceding claims,
characterized in that n.sub.2 and/or n.sub.4 are between 1.35 and
1.55 or between 1.40 and 1.50.
6. Substrate (6) according to one of the preceding claims,
characterized in that e.sub.1 is between 10 and 30 nm, especially
between 15 and 25 nm.
7. Substrate (6) according to one of the preceding claims,
characterized in that e.sub.2 is between 15 and 45 nm, especially
between 20 and 40 nm, preferably less than or equal to 35 nm.
8. Substrate (6) according to one of the preceding claims,
characterized in that e.sub.3 is between 100 and 180 nm and is
especially between 140 and 160 nm.
9. Substrate (6) according to one of the preceding claims,
characterized in that e.sub.4 is greater than or equal to 90 nm and
is especially between 95 and 120 nm.
10. Substrate (6) according to claim 2 or claim 3, characterized in
that the layer (5) of intermediate index is based on a mixture
between, on the one hand, silicon oxide and, on the other hand, at
least one metal oxide, chosen from tin oxide, zinc oxide and
titanium oxide, or is based on a silicon oxynitride or oxycarbide
and/or on aluminium oxynitride.
11. Substrate (6) according to one of the preceding claims,
characterized in that the high-index first layer (1) and/or the
high-index third layer (3) are based on one or more metal oxides
chosen from zinc oxide, tin oxide, zirconium oxide or the zinc-tin
mixed oxide, or based on one or more nitrides chosen from silicon
nitride and/or aluminium nitride.
12. Substrate (6) according to one of the preceding claims,
characterized in that the high-index first layer (1) and/or the
high-index third layer (3) consist of a superposition of several
high-index layers, especially of a superposition of two layers such
as SnO.sub.2/Si.sub.3N.sub.4 or Si.sub.3N.sub.4/SnO.sub.2.
13. Substrate (6) according to one of the preceding claims,
characterized in that the low-index second layer (2) and/or the
low-index fourth layer (4) are based on silicon oxide, silicon
oxynitride and/or oxycarbide or on a mixed silicon-aluminium
oxide.
14. Substrate (6) according to one of the preceding claims,
characterized in that the said substrate is made of clear or
extra-clear glass, and is preferably toughened.
15. Substrate (6) according to one of the preceding claims,
characterized in that the multilayer antireflection film (A) uses,
at least for its high-index third layer, silicon nitride or
aluminium nitride so that it is capable of undergoing a heat
treatment of the toughening or annealing type.
16. Substrate (6) according to one of the preceding claims,
characterized in that the multilayer film (A) comprises the
following sequence of layers: SnO.sub.2 or
Si.sub.3N.sub.4/SiO.sub.2/SnO.sub.2 or Si.sub.3N.sub.4/SiO.sub.2 or
SiAlO.
17. Substrate (6) according to one of claims 1 to 15, characterized
in that the multilayer film (A) comprises the following sequence of
layers: SiON/Si.sub.3N.sub.4 or SnO.sub.2/SiO.sub.2 or SiAlO.
18. Substrate (6) according to one of the preceding claims,
characterized in that it has a transmission integrated over a
wavelength range between 400 and 1100 nm of at least 90%.
19. Use of the substrate (6) according to one of the preceding
claims as the external transparent substrate of solar modules (10)
comprising a plurality of solar cells (9) of the Si or CIS
type.
20. Solar module (10) comprising a plurality of solar cells (9) of
the Si, CIS, CdTe, a-Si, GaAs or GalnP type, characterized in that
it has the substrate (6) according to one of claims 1 to 18 as the
external substrate.
21. Solar module (10) according to claim 20, characterized in that
its efficiency, expressed in terms of integrated current density,
is increased by at least 1, 1.5 or 2% over a module using an
external substrate not having the multilayer antireflection film
(A).
22. Solar module (10) according to either of claims 20 and 21,
characterized in that it comprises two glass substrates (6, 8), the
solar cells (9) being placed in the inter-glass space into which a
curable polymer (7) is poured.
23. Process for obtaining the substrate (6) according to one of
claims 1 to 18, characterized in that the multilayer antireflection
film (A) is deposited by sputtering.
Description
[0001] The invention relates to a transparent, especially glass,
substrate provided on at least one of its faces with an
antireflection coating.
[0002] Antireflection coatings usually consist, in the simplest
cases, of a thin interferential layer whose refractive index is
between that of the substrate and that of air or, in the more
complex cases, of a film comprising multiple thin layers (in
general, an alternation of layers based on a dielectric having a
high refractive index and a dielectric having a low refractive
index).
[0003] In their more conventional applications, they are used to
reduce the light reflection from substrates in order to increase
their light transmission. Such substrates are, for example, the
glazing intended for protecting paintings and for producing island
displays, showcases or shop windows. They are therefore optimized
by taking only into account the wavelengths in the visible
range.
[0004] However, it turns out there may be a need to increase the
transmission of transparent substrates for special applications,
and not only in the visible range. These are, in particular, solar
cells (also called solar modules or collectors), for example
silicon cells. These cells need to absorb the maximum amount of
solar energy that they receive, not only in the visible but also
beyond it, most particularly in the near infrared. The "external"
substrate (that turned towards the sky) of the cells is generally
made of toughened glass.
[0005] It therefore seems to be advantageous, in order to increase
their efficiency, to optimize the transmission of solar energy
through this glass in the wavelengths important for solar
cells.
[0006] A first solution has consisted in using extra-clear glass,
having a very low content of iron oxide(s). Such is, for example,
the glass sold by Saint-Gobain Vitrage in the "DIAMANT" range.
[0007] Another solution has consisted in providing the glass, on
the outside, with an antireflection coating consisting of a
monolayer of porous silicon oxide, the porosity of the material
making it possible to lower the refractive index thereof. However,
the performance of this monolayer coating is not very high.
Furthermore, its durability, especially with regard to moisture, is
insufficient.
[0008] The object of the invention is therefore to develop a novel
antireflection coating which is capable of further increasing the
transmission through the transparent substrate carrying it (and of
further reducing the reflection therefrom), within a broad
wavelength band, especially both in the visible and in the
infrared.
[0009] Secondarily, the object of the invention is to develop a
novel antireflection coating suitable for solar cells.
[0010] Secondarily, the object of the invention is to develop such
coatings which are furthermore capable of undergoing heat
treatments, especially if the carrier substrate is made of glass
which, in its final application, must be annealed or toughened.
[0011] Secondarily, the object of the invention is to develop such
coatings which are sufficiently durable for outdoor use.
[0012] The subject of the invention is primarily a transparent
substrate, especially made of glass, having on at least one of its
faces an antireflection coating (A) comprising multiple thin layers
of a dielectric having alternately high and low refractive indexes.
It comprises, in succession:
[0013] a high-index first layer 1, having a refractive index
n.sub.1, of between 1.8 and 2.3 and a geometrical thickness e.sub.1
of between 5 and 50 nm;
[0014] a low-index second layer 2, having a refractive index
n.sub.2 of between 1.30 and 1.70 and a geometrical thickness
e.sub.2 of between 5 and 50 nm;
[0015] a high-index third layer 3, having a refractive index
n.sub.3 of between 1.80 and 2.30 and a geometrical thickness
e.sub.3 of at least 100 nm or at least 120 nm;
[0016] a low-index fourth layer 4, having a refractive index
n.sub.4 of between 1.30 and 1.70 and a geometrical thickness
e.sub.4 of at least 80 nm or at least 90 nm.
[0017] Within the context of the invention, the term "layer" is
understood to mean either a single layer, or a superposition of
layers in which each of the layers respects the refractive index
indicated and in which the sum of their geometrical thicknesses
also remains the value indicated for the layer in question.
[0018] Within the context of the invention, the layers are made of
a dielectric, especially of the oxide or nitride type, as will be
explained in detail below. However, it is not excluded for at least
one of them to be modified so as to be at least slightly
conductive, for example by doping a metal oxide, this being done,
for example, so as possibly to also give the multilayer
antireflection film an antistatic function.
[0019] The invention applies preferably to glass substrates, but it
may also apply to transparent substrates based on a polymer, for
example polycarbonate.
[0020] The invention therefore relates to an antireflection film of
the four-layer type. This is a good compromise since the number of
layers is large enough for their interferential interaction to
allow a significant antireflection effect to be achieved. However,
this number remains sufficiently reasonable for it to be possible
to manufacture the product on a large scale, on an industrial line,
on large substrates, for example using a vacuum deposition
technique of the sputtering type (magnetically enhanced).
[0021] The thickness and refractive index criteria used in the
invention make it possible to obtain a broadband antireflection
effect with a substantial increase in the transmission of the
carrier substrate, not only in the visible range but also beyond
it, especially in the infrared and more particularly in the near
infrared. This is high-performance antireflection over a wavelength
range extending at least between 400 and 1100 nm.
[0022] Perhaps the three most noteworthy features of the invention
are the following:
[0023] firstly, compared with a standard four-layer antireflection
film (intended to antireflect a glass in the visible), the
thickness of the low-index last layer has been increased: its
preferred thickness is greater than the .lambda./4 value normally
used (taking .lambda. as the centre of the visible spectrum);
[0024] secondly, the thickness of the high-index penultimate
(third) layer is relatively large; and
[0025] finally, it has been discovered that, unlike the choice of
high-index layers usually made, it is not essential to choose
materials having a very high index, such as TiO.sub.2 or
Nb.sub.2O.sub.5. It has turned that it was wiser on the contrary to
use materials with a more moderate refractive index, especially of
at most 2.3. This therefore goes counter to the known teaching with
regard to multilayer antireflection films in general.
[0026] The inventors have thus discovered that they could use
materials whose index is around 2, such as tin oxide SnO.sub.2 or
silicon nitride Si.sub.3N.sub.4 (which include within this formula,
silicon nitrides which may contain other elements in a minor amount
compared with silicon, such as a metal of the Al type, or boron,
the indicated stoichiometry of the nitrogen with respect to the
silicon therefore not being limiting, but merely for ease of
writing. The same applies to the oxygen stoichiometry of the metal
or silicon oxides mentioned in the present text). Especially
compared with TiO.sub.2, these materials have the advantage of
having very much higher deposition rates when the deposition
technique called sputtering is used. Within this moderate range of
indices, there is also a greater choice of materials that can be
deposited by sputtering. This provides more flexibility in
industrial manufacture and a greater possibility of adjusting the
properties of the multilayer film.
[0027] The inventors have thus selected thicknesses for the layers
of the multilayer film which are different from the thicknesses
usually chosen for conventional antireflection coatings intended to
reduce reflection only in the visible. In the present invention,
this selection has been made so as to antireflect the substrate not
only in the visible but also in part of the infrared.
[0028] Given below are the preferred ranges of the geometrical
thicknesses and of the indices of the four layers of the multilayer
film according to the invention:
[0029] in the case of the first and/or the third layer, those
having a high index:
[0030] n.sub.1, and/or n.sub.3 are advantageously between 1.85 and
2.15, especially between 1.90 and 2.10 or between 2.0 and 2.1,
[0031] e.sub.1 is advantageously between 10 and 30 nm, especially
between 15 and 25 nm,
[0032] e.sub.3 is advantageously between 100 and 180 nm, especially
between 130 and 170 nm or between 140 and 160 nm;
[0033] in the case of the second and/or fourth layer, those having
a low index:
[0034] n.sub.2 and/or n.sub.4 are advantageously between 1.35 and
1.55 or alternatively between 1.40 and 1.50,
[0035] e.sub.2 is advantageously between 15 and 45 nm, especially
between 20 and 40 nm, and is preferably less than or equal to 35
nm,
[0036] e.sub.4 is advantageously greater than or equal to 90 nm and
is especially less than or equal to 120 or 110 nm, e.sub.4
preferably being chosen between 95 and 115 nm.
[0037] According to a preferred variant of the invention, it is
possible to replace the high-index first layer 1 and the low-index
second layer 2 with a single layer 5 having a refractive index
e.sub.5 called "intermediate", especially one between 1.60 and
1.90, preferably between 1.70 and 1.80.
[0038] This layer preferably has a geometrical thickness e.sub.5 of
between 40 and 120 nm (preferably 60 to 100 nm or 65 to 85 nm).
[0039] In conventional three-layer antireflection films optimized
for the visible range in perpendicular viewing, this thickness is
instead generally chosen to be above 120 nm.
[0040] This intermediate-index layer has an optical effect similar
to that of a high-index layer/low-index layer sequence when this is
the first sequence, of the two layers closest to the carrier
substrate of the multilayer film. It has the advantage of reducing
the overall number of layers in the multilayer film. It is
preferably based on a mixture between, on the one hand, silicon
oxide and, on the other hand, at least one metal oxide chosen from
tin oxide, zinc oxide and titanium oxide. It may also be based on
silicon oxynitride or oxycarbide and/or based on aluminium
oxynitride.
[0041] The most appropriate materials for constituting the first
and/or the third layer, those having a high index, are based on one
or more metal oxides chosen from zinc oxide ZnO, tin oxide
SnO.sub.2 and zirconium oxide ZrO.sub.2. It may especially be a
mixed Zn/Sn oxide, of the zinc stannate type. It may also be based
on one or more nitrides chosen from silicon nitride Si.sub.3N.sub.4
and/or aluminium nitride AlN.
[0042] Using a nitride layer for one or other of the high-index
layers, especially at least the third layer, makes it possible to
add a functionality to the multilayer film, namely the ability to
better withstand heat treatments without its optical properties
being appreciably impaired. In point of fact, it is a functionality
which is important in the case of any glass which has to form part
of solar cells, since such glass must in general undergo a
high-temperature heat treatment, of the toughening type, in which
the glass must be heated between 500 and 700.degree. C. It then
becomes advantageous to be able to deposit the thin layers before
the heat treatment without this causing any problem, since it is
simpler from the industrial standpoint for the deposition to be
carried out before any heat treatment. It is thus possible to have
a single configuration of multilayer antireflection film, whether
or not the carrier glass is intended to undergo a heat
treatment.
[0043] Even if it is not intended to be heated, it is still
beneficial to use at least one nitride layer, as this improves the
mechanical and chemical durability of the multilayer film in its
entirety. This is all the more important in applications to solar
cells constantly exposed to the vagaries of the climate.
[0044] According to one particular embodiment, the first and/or the
third layer, those having a high index, may in fact consist of
several superposed high-index layers. This may most particularly be
a bilayer of the SnO.sub.2/Si.sub.3N.sub.4 or
Si.sub.3N.sub.4/SnO.sub.2 type. The advantage of this is the
following: Si.sub.3N.sub.4 tends to be deposited a little less
easily and slightly more slowly than a conventional metal oxide
such as SnO.sub.2, ZnO or ZrO.sub.2 by reactive sputtering.
Especially in the case of the third layer, which is the thickest
and the most important for protecting the multilayer film from any
deterioration resulting from a heat treatment, it may be beneficial
to divide the layer in two, so as to put down just the thickness of
Si.sub.3N.sub.4 sufficient to obtain the desired heat-treatment
protection effect and to "top up" the layer optically with
SnO.sub.2, ZnO or a zinc-tin mixed oxide of the zinc stannate
type.
[0045] The most appropriate materials for constituting the second
and/or the fourth layer, those having a low index, are based on
silicon oxide, silicon oxynitride and/or silicon oxycarbide or else
based on a silicon-aluminium mixed oxide. Such a mixed oxide tends
to have a better durability, especially chemical durability, than
pure SiO.sub.2 (an example of this is given in the Patent EP-791
562). The respective proportions of the two oxides may be adjusted
in order to obtain the expected improvement in durability without
excessively increasing the refractive index of the layer.
[0046] The glass chosen for the coated substrate of the multilayer
film according to the invention, or for the other substrates with
which it is associated in order to form glazing, may in particular
be, for example, extra clear of the "Diamant" type (a glass with a
low content of iron oxides in particular) or it may be a standard
silica-soda-lime clear glass of the "Planilux" type (both types of
glass are sold by Saint-Gobain Vitrage).
[0047] Two particularly beneficial examples of the coatings
according to the invention comprise the following sequences of
layers:
[0048] for a four-layer film:
[0049] SnO.sub.2 or Si.sub.3N.sub.4/SiO.sub.2/SnO.sub.2 or
Si.sub.3N.sub.4/SiO.sub.2 or SiAlO
[0050] (SiAlO corresponds here to an aluminium-silicon mixed oxide,
without prejudging their respective amounts in the material);
[0051] for a three-layer film:
[0052] SiON/Si.sub.3N.sub.4 or SnO.sub.2/SiO.sub.2 or SiAlO
[0053] (with the same convention for SiAlO, the formula SiON
denoting here an oxynitride, again without prejudging the
respective amounts of oxygen and nitrogen in the material).
[0054] Substrates of the glass type, especially extra-clear glass,
having this type of multilayer film may thus achieve transmission
values integrated between 400 and 1100 nm of at least 90%,
especially for thicknesses of between 2 mm and 8 mm.
[0055] The subject of the invention is also the substrates coated
according to the invention as the external substrates for solar
cells of the Si or CIS type.
[0056] In general, this type of product is commercially available
in the form of solar cells mounted in series and placed between two
transparent rigid substrates of the glass type. The cells are held
between the substrates by a polymer material (or several polymer
materials). According to a preferred embodiment of the invention
described in Patent EP 0739 042, the solar cells may be placed
between the two substrates and then the hollow space between the
substrates is filled with a cast polymer capable of curing, most
particularly a polyurethane-based polymer coming from the reaction
of an aliphatic isocyanate prepolymer and a polyether polyol. The
polymer may be cured hot (at 30 to 50.degree. C.) and possibly with
a slight overpressure, for example in an autoclave. Other polymers
may be used, such as ethylene-vinyl acetate EVA, and other
arrangements are possible (for example, one or more sheets of
thermoplastic polymer may be laminated between the two glass panels
of the cells).
[0057] It is the combination of the substrates, polymer and solar
cells that is called and sold as a "solar module".
[0058] The subject of the invention is therefore also the said
modules. Using the modified substrate according to the invention,
the efficiency of the solar modules can be increased by at least 1,
1.5 or 2% (expressed in terms of integrated current density) over
modules which use the same substrate but do not have the coating.
As it is known that solar modules are not sold to the square metre,
but by the delivered electric power (approximately, it may be
estimated that one square metre of solar cell can deliver about 130
watts), each additional per cent of efficiency increases the
electrical performance, and therefore the cost, of a solar module
of given dimensions.
[0059] The subject of the invention is also the process for
manufacturing glass substrates with an antireflection coating (A)
according to the invention. One process consists in depositing all
the layers, in succession, by a vacuum technique, especially by
magnetically enhanced sputtering or by plasma-enhanced sputtering.
Thus, it is possible to deposit the oxide layers by reactive
sputtering of the metal in question in the presence of oxygen and
the nitride layers in the presence of nitrogen. To do the SiO.sub.2
or Si.sub.3N.sub.4, it is possible to start with a silicon target
which is lightly doped with a metal, such as aluminium, in order to
make it sufficiently conductive.
[0060] It is also possible, as recommended in the Patent WO
97/43224, for some of the layers of the multilayer film to be
deposited by a hot deposition technique of the CVD type, the rest
of the multilayer film being deposited cold by sputtering.
[0061] The details and advantageous features of the invention will
now become apparent from the following non-limiting examples, with
the aid of the figures:
[0062] FIG. 1: a substrate provided with a three-layer or
four-layer antireflection film A according to the invention;
[0063] FIGS. 2, 3, 4, 6: graphs showing the transmission spectrum
for the coated substrates according to the invention and the
efficiency of the solar cells using them, compared with a reference
cell;
[0064] FIG. 5: a solar module incorporating the substrate according
to FIG. 1.
[0065] FIG. 1, which is highly schematic, shows, in cross section,
a glass substrate 6 surmounted by an antireflection film (A)
consisting of four layers 1, 2, 3, 4 or three layers 5, 3, 4.
EXAMPLE 1
[0066] This example uses a 4 mm thick substrate 6 made of
extra-clear glass, from the aforementioned DIAMANT range. It uses
the three-layer antireflection film.
[0067] The multilayer film was the following:
1 Refractive index Thickness (nm) SiON (5) 1.75 76 Si.sub.3N.sub.4
(3) 2.05 145 SiO.sub.2 (4) 1.47 105
[0068] (The thicknesses indicated above are the geometrical
thicknesses of the layers.)
[0069] The glass provided with the three layers was then
toughened.
EXAMPLE 2
[0070] Example 2 relates to a four-layer antireflection film, and
is the result of modelling.
[0071] In this example, the multilayer antireflection film used was
the following:
2 Refractive index Thickness (mn) SnO.sub.2 (1) 1.95-2.05 19
SiO.sub.2 (2) 1.47 29 SnO.sub.2 (3) 1.95-2.05 150 SiO.sub.2 (4)
1.47 100
[0072] (The SnO.sub.2 may be replaced, in the case of layer (1)
and/or layer (3), with Si.sub.3N.sub.4.)
EXAMPLE 2a
[0073] Example 2a was produced, this time experimentally, on a 4 mm
extra-clear glass from the aforementioned DIAMANT range.
[0074] The coated glass of Examples 1, 2 and 2a (by calculation in
the case of Example 2) were mounted as external glass panels of
solar modules. FIG. 5 shows highly schematically a solar module 10
according to the invention. The module 10 was formed in the
following manner: the glass panel 6 provided with the
antireflection coating (A) was combined with a glass panel 8 called
the "internal" glass panel. This glass panel 8 was made of
toughened glass 4 mm in thickness and of the extra-clear ("Planidur
DIAMANT") type. The solar cells 9 were placed between the two glass
panels and then a polyurethane-based curable polymer 7 in
accordance with the teaching of the aforementioned Patent EP 0 739
042 was poured into the inter-glass space.
[0075] Each solar cell 9 consisted, in a known manner, of silicon
wafers forming a p-n junction and printed front and rear electrical
contacts. The silicon solar cells could be replaced with solar
cells using other semiconductors (such as CIS, CdTe, a-Si, GaAs,
GalnP).
[0076] By way of comparison, a solar module identical to the
previous one was mounted, but this time with an external glass
panel 6 made of extra-clear glass without the antireflection
coating according to the invention.
[0077] FIG. 2 shows the results of the cell using Example 1:
[0078] plotted on the x-axis are the wavelengths (.lambda.) in
nanometres;
[0079] plotted on the y-axis (on the right) is the integrated
current density (d) generated by the cell in mA/cm.sup.2;
[0080] plotted on the y-axis (on the left) is the transmission (T)
as a percentage.
[0081] the curve with the triangles shows the degree of conversion
of the solar energy into electrical energy (EQE, standing for
External Quantum Efficiency) as a function of the wavelength;
[0082] the curve with circles represents the transmission T through
the external glass panel 6 of the solar module;
[0083] the curve with squares represents the "Air Mass 1.5"
integrated short-circuit current, taking into account the standard
solar spectrum according to the ASTM E892-87 standard.
[0084] FIG. 3, with the same conventions, shows the modelling
results obtained with the solar module using Example 2.
[0085] FIG. 6 shows the results obtained with the solar module
using the coating actually produced according to Example 2a:
[0086] the curve with triangles Cl corresponds to the EQE explained
above;
[0087] curve C2 corresponds to the transmission T through the
external glass panel when it is made only of a standard
silica-soda-lime glass 4 mm in thickness, from the Planilux range
sold by Saint-Gobain Glass (for comparison);
[0088] curve C3 corresponds to the transmission T when the external
glass panel is made of a glass 4 mm in thickness from the "DIAMANT"
range (for comparison);
[0089] curve C4 corresponds to an external glass panel according to
Example 2a, the glass once it had been provided with the
antireflection coating having been subjected, before being mounted,
to a toughening operation, followed by a moisture resistance test
known as a damp-heat test, which consists in leaving the coated
glass for 1000 hours at 85.degree. C. in a chamber whose atmosphere
has a controlled relative humidity of 85% (IEC 61215 standard);
[0090] curve CS corresponds to an external glass panel again
according to Example 2a, but this time the coated glass was
subjected, prior to mounting, to a chemical resistance test known
as a neutral salt-fog or NSF test, according to the EN ISO 6988
standard. This test consists in subjecting the glass to 20 cycles
consisting of 8 hours at 40.degree. C. and 100% relative humidity
in an atmosphere containing 0.67% by volume of SO.sub.2, followed
by 16 hours at 23.degree. C..+-.1.degree. C. in an atmosphere
having a relative humidity of 75%;
[0091] curve C6 (with squares) represents the integrated
short-circuit current, with the same conventions as in FIG. 2.
[0092] Plotted on the y-axis are the three integrated current
density values corresponding to curves C4, C3 and C2.
[0093] FIG. 4 shows, with the same conventions, the results
obtained with the cell using the extra-clear glass without the
antireflection coating, by way of comparison.
[0094] If the transmission curves of FIGS. 2 and 4 are compared, it
may be seen that with the extra-clear glass without the multilayers
(FIG. 4), the curve is flat in the 400 to 1100 nm range, at about
92%, unlike the transmission curve of Example 1 (FIG. 2).
[0095] These differences are manifested in the differences in the
performance of the solar cells. The integrated current density goes
from 31.34 mA/cm.sup.2 in the case of the comparative example (FIG.
4) to 32.04 mA/cm.sup.2 in the case of Example 1 and to 32.65
mA/cm.sup.2 in the case of Example 2.
[0096] Since these solar cells use crystalline silicon, the
efficiencies of conversion of solar energy into electrical energy,
as a function of the wavelength are, however, similar in the case
of the three cells.
[0097] These examples confirm that the antireflection coatings
according to the invention allow the performance of the solar cells
to be increased without excessively complicating their
manufacture.
[0098] The results of Example 1 show that the antireflection
coating (A) according to the invention is capable of undergoing
heat treatments of the toughening type. The experimental results of
Example 2a confirm the modelling results of Example 2, with
integrated current densities significantly higher than with glass
without an antireflection coating. It has also been verified that
these good results are obtained even when the coated glass has
undergone a toughening treatment and/or water-resistance and
chemical-resistance tests: the stability of the coating according
to the invention is thus proved.
[0099] The four-layer coatings have a slightly higher performance
than the three-layer coatings, but take a little longer to
manufacture.
[0100] The present invention is an improvement of the invention
described in Patent FR-2 800 998 which relates to antireflection
coatings suitable for optimizing the antireflection effect at
non-normal incidence in the visible (especially aimed at
applications for vehicle windscreens). However, the coatings
according to the present invention have thicknesses selected for a
particular application to solar modules, especially with a thicker
third layer (the thickness generally being at least 120 nm and not
at most 120 nm).
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