FIELD OF INVENTION
The present invention relates to thin film solar cell module. More particularly, it
relates to a method of edge isolation of thin film solar cell module by sand
blasting.
BACKGROUND OF THE INVENTION
For edge isolation of Thin Film Solar Cell Module fabricated on glass and metal
substrate, different technique are used like thermal drum processor system and
laser scribing method having vision recognition system. Plasmaetching technique
is used in c-Si Solar Cells before development of module. The equipments used
for the above described techniques are very costly, and the processing time is
also very high. Also there is a constraint for performing the edge isolation
processon very large area thin film modules.
The use of sand blasting techniqu~ for removal of thin film in thin film solar cell
module on glass to have the edge isolation is not yet prevalent. But the sand
blasting technique is used to remove the deposits attached and corroded
products attached to a submerged structure of submarine. Accordingly there exists a need to find a method which can eliminate the
disadvantagesof prior art.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of edge isolation
of thin film solar cell module by sand blasting which is capable of protecting
active device from degradation due to moisture ingression through edges and
stopping electro migration.
Another object of the invention is to propose a method of edge isolation of thin
film solar cell module by sand blasting which is a low cost simple process.
A still another object of the invention is to propose a method of edge isolation of
thin film solar cell module by sand blasting which improves the active life of the
device as well as reliability.
A further object of the invention is to propose a method of edge isolation of thin
film solar cell module by sand blasting which prOVides electrical insulation
between the edges and the active device. SUMMARY OF THE INVENTION
A low cost process which is rugged and less time consuming for edge isolation
has been developed under this invention. With the help of sand blasting the
electrically conducting and semi electrically conducting thin films (layers required
for a solar cell) deposited at the boundaries of thin film solar cell module are
removed. The lamination was carried out on thin film solar cell Module after
sandblasting process. It has been found out that this process provides a longer
life to thin film solar cell module as it avoids the ingression of water/moisture
into the active layers of the module. In sand blasting technique, there is no
constraint for module size in both the directions i.e. length and width. Also
isolation thus created, provides dielectric protection from leakage of high
voltage. The sand blasting technique is also very easy to perfon .1.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - a photograph of solar cell module roughed edge after sand blasting
Fig.2 - a photograph of sand blasted solar cell module
Fig.3 - a cross section view of thin film solar cell module with sand blasted edges
Fig.4 - a line diagram of sand blasted solar cell moduleDETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The sand blasting technique provides the dielectric protection to the solar cell
module by removing the electrically conducting layer i.e. Sn02 from the glass
substrate. After removing thin layer of about 10 mm width, the charge generated
in the solar cell module does not get any electrical path to travel towards the
edges of glass substrate even under high humidity condition. After using the
sand blasting technique on solar cell module the surface of glass substrate
becomes textured and in turn the lamination process on solar cell module
provides a complete protection to- the active area of solar cell module from
atmospheric moisture to ingress in the solar cell module. Therefore the electrical
corrosion does not take place at the edges of solar cell module as the
encapsulation of Tedlar does not peel off at the edges.
Presently, the edge isolation in thin film modules is done by the Laser Scribing
method having vision recognition system. Using the technique of Laser, the thin
film deposited on glass substrate is removed but the surface of glass remains
smooth and the scribed area is also very small i.e. 2-3 mm from the edge of
glass substrate. Therefore after lamination of thin film solar cell module, there
are chances of ingression of water/moisture into the module. Due to ingression
of water/moisture, the lamination also gets peeled off after two to three yearsFor making the thin film module very stable and long lasting, the top surface of
Solar Cell Module along all the four sides needs to be cleared off any deposition,
before lamination of module with Tedlar.
After performing of the sand blasting on the edges (E) of the solar cell module,
the roughness of surface was checked on surface Profilometer. The optical
microscopic picture of surface after sand blasting is shown in Fig.1. Many
experiments were performed with lamination with different roughness on edges
of solar cell module, and it is found that the average roughness of surface should
be approximately 2.9 micron whereas peak to peak roughness may be upto 20.5
micr.onto get the best lamination results. Fig.2 shows a picture of a thin film
solar cell module (M) whose edges (E) have been sand blasted. FigA shows a
line diagram of the sand blasted module (M) with four edges (E). The particles
diameter of the sand used for the sand blasting of module is in the range of 300
micron to 500 micron. The active area of the module has been protected by
covering with a glass/plastic sheet of suitable size, such that the edges were left
free for edge isolation by sand blasting. The sand is blown on the surface of the
edges of the solar cell module with the help of sand blasting gun at a pressure of
5-6 kg.per cm2•
The development of the sand blasting technique for edge isolation of thin film
solar cell module have met the requirement of removing the thin layers of solar
cell module and also textured the surface of glass substrate to achieve goodresults adhesion of EVA(Ethyl Venyl Acetate) and Tedlar with the glass substrate
during lamination process of solar cell module with Tedlar. Therefore, by using
the sand blasting technique for edge isolation a very stable and long lasting
module has been developed. Sand blasting technique removes all the active
layers which are shown in Fig.3 in the cross section view of thin film solar cell
module. Fig.3 shows a layer of glass of 3 mm thick (1) and deposition of
different layers (2) such as TCO, a-Si, silver sputtering, etch resist printing,
lamination of solar cell for a thickness of about 100-300 IJm. The surface (3) of
four edges after sand blasting is also shown in fig (3). Items (4) and (5) are
positive and negative terminal of module. Sand blasting also removes the TCO
(Transparent Conductive Oxide) layer which is very hard and deposited on glass
substrate to provide the (+) ve contact to the thin film Solar Cell Module. After
removal of TCO from glass substrate, we are able to provide the dielectric
protection from leakages of high voltage from the module, when modules are
connected in series for use in electrical applications.
This low cost process is simple and rugged. It makes the product sUitablefor use
for high voltage applications (up to 500 V DC). It also makes the product suitable
to be used as a frameless laminates.
WE CLAIM
1. A method of edge isolation of thin film solar cell module (M) by sand
blasting characterizing the steps of:
covering the active area of the solar cell module (M) with a glass or plastic
sheet leaving the four edges (E) free;
blowing sand on the surface of the four edges (E) of the solar cell;
sand blasting the said edges till thin active layers of solar cell module are
removed and surface of glass substrate is textured;
checking roughness of surfaces of said four edges on surface
profilometer; and
the said module (M) having four rough edges is laminated with ethyl venyl
acetate and Tedlar for developing a very stable and long lasting module
(M).
2. A method of edge isolation of thin film solar cell module (M) as claimed in
claim 1, wherein the average roughness of surface is about 2.9 micron
and peak to peak roughness is about 20.5 micron.
3. A method of edge isolation of thin film solar cell module (M) as claimed in
claim 1, wherein the sand blasting is carried out with a sandblasting gun
at a pressure of 5-6 kg. per cm2•
4. A method of edge isolation of thin film solar cell module (M) as claimed in
claim 1, wherein about 10 mm width of thin layer of the solar cell is
removed from the surface of four edges (E).
5. A method of edge isolation of thin film solar cell module (M) as claimed in
claim 1, wherein the diameter of the sand particles used for the sand
blasting is between 300 micron to 500 micron.