TITLE: METHOD FOR FABRICATION OF PHOTOVOLTAIC MODULES OF RATING
12-VOLT, 80-WATT INCORPORATING 72 ONE-THIRD CUT 156-MM SIZE MULTI
CRYSTALLINE SILICON SOLAR CELLS
FIELD OF INVENTION
The invention relates to the field of solar photovoltaic (PV) modules in general
and to manufacture of solar photovoltaic modules with one third cut 156 mm size
multi crystalline silicon solar cells in particular.
BACKGROUND OF THE INVENTION
The world top PV manufacturers have changed over to 156-mm multi / mono
crystalline silicon solar cells from 125-mm size solar cells. This is due to the
increase in power output to 3.6 - 3.7-watts (15% efficiency) per cell for 156-mm
size cells from 2.3-watts per cell for 125-mm size cells. All the solar cell
production machines have now been made for processing cells of 156-mm size.
Hence, the production throughout increases by 60%, if 156-mm cells are
processes as against 125-mm solar cells. The wafer manufacturers, in turn, have
now changed over to 156-mm wafers. Hence, the availability of 125-mm wafers
is becoming increasingly difficult, especially for multi-crystalline wafers. The PV
module manufacturers, world-wide are now manufacturing PV modules using
156-mm size solar cells. Hence, it is important to develop modules using 156-mm
solar cells for catering to the growing market.

Modules with full 36-nos. of 156-mm solar cells (each cell giving a power output
of 3.6 to 3.7 watts) shall give a output in he range of 120 to 130-watts. For
catering to the requirement of 75 to 80-watts PV modules (for stand-alone
domestic / street lighting application), presently the modules are manufactured
using 36-nos. of 125-mm mono / multi crystalline silicon solar cells (each cell
giving a power output of 2.1 to 2.2 watts). As the availability of cells in 125-mm
size is becoming difficult, a need is felt to develop 80-watts PV modules using
36-nos. of 156-mm cut solar cells. 156-mm full cells is required to be laser cut
into 2/3rd and 1/3rd portions giving a power output of 2.4 watts and 1.2 watts
respectively. 80-watts PV modules can be made straight away with 36 nos. of
156-mm 2/3rd cut cells in series configuration for 12-V application. In order to
effectively utilize balance one-third cut cells, an alternative method of fabrication
is invented by using 72-nos. of 156-mm one-third cut cells (with a power output
of 1.2 watts) in series-parallel configuration for manufacture of 80-watts PV
modules for 12-Volt application.
A search was carried out to identify development PV modules of similar
application. The following related patents were located.
1. WO/2004/038814 - Process for assembly of Photovoltaic Modules
This patent describe the interconnection of one cell to another by means of
conducting glue or soldering paste, positioning of cells on a panel of suitable
material, hot application of Ethylene Vinyl Acetate (EVA) and a sheet of glass to

cover the panel. Whereas the present claim is for series-parallel interconnection
of solar cell strings by means of copper interconnects and solar cells are
laminated in a vacuum laminator.
2. WO/2007/053306 - Photovoltaic Modules and Interconnect methodology for
fabricating the same.
In this patent, the front contacts and back contacts are accessible from the back
side of same cell. Further, the photovoltaic cells are interconnected by
interconnect leads that are coupled from a tab on the front contact point on the
backside of a second photovoltaic cell. Whereas in this patent, the photovoltaic
cells used are of conventional type having front and back contacts on the front
side and backside of the photovoltaic cell respectively. The cells are
interconnected from front contact of one cell to back contact of next cell by
means of soldering copper interconnects.
3. WO/2003/065392 - Photovoltaic Cell Interconnection
This patent describe photovoltaic modules which include photosensitized nano-
matrix layer and a charge carrier media, the cells are interconnected in series
and electrical connection layers each include conductive and insulative regions.
Whereas the present invention uses 72-nos. of one-third cut 156-mm multi-
crystalline silicon solar cells connected in series-parallel to obtain the required
current and voltage.

4. WO/1994/027327 - Series Interconnected Photovoltaic Cells and method for
making same.
This patent describe cells having a bottom electrode, a photoactive layer and a
top electrode layer. Adjacent cells are connected in electrical series by way of
conductive-buffer line. Whereas the present invention uses 72-nos. of one-third
cut 156-mm multi-crystalline silicon solar cells connected in series-parallel to
obtain the required current and voltage.
Websites search :
1. www.wipo.int/portal/index.html.en
2. www.ipo.gov.uk
3. www.uspto.gov/patft/
4. strategis.ic.gc.ca/sc_mrksv/cipo/
OBJECTS OF THE INVENTION
To overcome the above drawbacks of the prior art, the following innovative
remedial actions were under taken to improve it;

(a) to propose a method for replacing 36 nos. of 125-mm size solar cells with
72 nos. of one-third cut 156-mm size solar cells connected in series
parallel configuration to get 12-volt and 80-watts power output.
(b) to propose a method for development of a Phenyl Resin Bonded Cotton
Fibre (PRBCF) lay-up jig for interconnection of 72 - nos. of one-third cut
156-mm size solar cells.
(c) to propose a method for laser cutting of 156-mm full solar cells into two-
third and one-third cut solar cells, so that 80 watts PV modules can be
made straightaway with 36 nos. of 156-mm 2/3rd cut cells in series
configuration for 12V application and to utilize effectively the balance
1/3rd cut cells for series connection of 2 sets of parallel strings (2*18 nos.
of 156-mm 1/3rd cut cells).
BRIEF DESCRIPTION OF ACCOMPANYING DRAWING
The invention will now be described with the help of accompanying drawings
which depict an exemplary embodiment of invention. However, there can be
other embodiments all of which are deemed covered by the description.
Fig. 1: shows the Solar cell manufacturing process.

Fig. 2: shows the PV Module manufacturing process.
Fig. 3: shows PV modules made with 36-nos. of 125-mm size solar cells.
Fig. 4: shows full and cut 156-mm solar cells
Fig. 5: shows the lay-up jig with 72-nos. of 156-mm one-third cut solar cells.
Fig. 6: shows PV module made with 72-nos. of 156-mm one-third cut solar cells.
Fig. 7: shows the Current-Voltage characteristic curve of 80-watts PV modules
made with 72-nos. of 156-mm size one-third cut solar cells.
As shown in Fig. 1, the sequential steps of solar cell production process starting
from wafer comprises various steps like, precleaning of saw damage
removal/degreasing, texturisation, diffusion for p-n junction formation, plasma
etching for edge junction removal, anti reflection coating with Silicon Nitride,
printing and drying, firing and testing under illuminated light and then classified
into various bins as per the power output.
Fig. 2 shows the sequential steps of manufacturing Photovoltaic (PV) modules
starting from solar cells, comprising of tabbing, stringing with interconnection of
cells, transfer and inspection, lamination with Ethylene vinyl acetate and poly

vinyl based film in vacuum laminator, curing, edge trimming, framing of
laminates in anodized aluminium edge frames, fixing of junction box for PV
modules to be interconnected in an array and to the load and testing of such
solar cells with a sun simulator for measurement of output power.
Fig. 3 shows the PV module of prior art having 36 Nos. 125 mm size mono/multi
crystalline solar cells, which are not now available easily. To overcome the above
draw back as in Fig. 3, full and cut 156 mm solar cells are introduced as shown
Fig. 4. 36 Nos. 156 size solar cells PV module has been developed for 75-80
watts PV modules, 156 mm size full cells is required to be laser cut into 2/3rd and 1/3rd portions. 80 watts PV modules can be made with 36 Nos. of 156 mm size
2/3rd cut cells in series configuration of 12-V application. To save the wastage,
the balance as shown in Fig. 6, one third cut cells are utilized, by using 72 Nos.
of 156 mm size solar cells in series-parallel configuration for manufacture of 80
watts PV modules for 12v-application, where cells are arranged for series
connection of two parallel sets of 2x18 nos. of such solar cells. The said 72 Nos. 1/3rd cut 156 mm size cells are interconnected in string in lay up jig. (Fig. 5) on
phenyl Resin Bonded Cotton Fibre (PRBCF).
A current-voltage characteristic curve for 80 watt PV modules (Fig. 6) is shown in
Fig. 7, obtained from testing of the modules in a sun simulator under simulated
light for measuring the electrical power output.

DETAILED DESCRIPTION OF THE INVENTION
According to this invention there is provided a method for manufacture 12-volt,
80-watt Photovoltaic (PV) modules incorporating 72 one-third-cut, 156-mm multi
crystalline silicon solar cells (series connection of 2 sets of parallel strings of
2*18 nos. of 156-mm one-third cut cells).
Design and incorporate two parallel strings each containing 18 serially connected
156-mm one-third cut cells and two such sub-sets in series to get open-circuit
voltage of 22-volts and power output of 80-watts.
A Phenyl Resin Bonded Cotton Fibre (PRBCF) lay-up jig having 72 slots for
interconnecting the one-third cut cells and the sub-strings.
In the present invention, an engineering solution is applied to replace the
conventionally used 125-mm size solar cells with 156-mm one-third cut solar
cells.
The process flow chart of solar cell is as given in Fig. 1. The process steps
include the following:
1. Saw damage removal and texturisation
2. p-n junction formation by thermal diffusion
3. Edge junction removal by plasma etching

4. Phosphorous Silicate Glass (PSG) removal
5. Silicon Nitride Anti-Reflection Coating (ARC) by Plasma Enhanced Chemical
Vapour Depostion(PECVD),
6. Metalisation and firing of contacts
7. Testing and classification of Solar Cells.
The as-cut p-type boron-doped CZ silicon wafers are chemically etched in
concentrated alkali solution to remove saw damages followed by a dilute alkali
texturising step to form pyramid-like structures on the wafer. Process parameters
such as alkali concentration, solution temperature and process time are
optimized to get well-defined normal random pyramids which enhance the
surface area of the wafer for greater light absorption and at the same time,
facilitate total internal reflection of light.
A p-n junction is then formed on the textured silicon wafer through a high-
temperature, solid-state diffusion process in a quartz furnace. In this process,
phosphorous oxy-chloride (POCI3) liquid dopant is deposited on the wafers and is
driven in when a thin n-type layer is formed. The wafers are coin-staked and
etched using Freon-oxygen gas mixture in a dry plasma etch machine so as to
remove the junction regions created on the edges. The wafers are then
chemically etched to remove the oxides and phosphorous glass from the surface.
A thin film of silicon nitride (anti-reflection coating) is deposited on the wafer to
lower the reflection of light further and to passivate the solar cell against harmful

environment such as humidity, ionizing radiation and reactive module lamination
materials. The silicon nitride anti-reflection coating enhances the solar cell
' conversion efficiency by almost 1%
Front and back contacts on the wafer surface are established by screen printing
a suitable metallic pastes on them. A fine-line grid pattern (Silver) is formed on
the front side which is designed to reduce the contact resistance and at the same
time increase the aperture for light absorption. Busbars (Silver-aluminium) are
printed on the back side for facilitating solder contacts, and rest of the area is
covered with aluminium paste to create the back surface field (BSF). The printed
pastes are dried and sintered in an infra-red belt furnace where temperature and
belt speed are optimized to achieve a sharp temperature profile. The cells are
then tested under illuminated light and classified into various bins as per the
power output.
The flow chart of PV module fabrication process is shown in Fig. 2. The process
steps include the following:
1. Interconnection of solar cells and formation of a string.
2. Lamination of the interconnected solar cells are curing.
3. Framing and junction box fixing
4. Testing with a Sun Simulator

Tinned copper interconnects are soldered on the front busbars of matched solar
cells in terms of output current. These are strung together (front contact of one
cell connected to the back contact of the next cell through the interconnects) in
a specially designed lay-up jig, terminating in positive and negative output leads.
The strung solar cell array is sandwiched between a layer of Ethylene Vinyl
Acetate (EVA, a thermo plastic resin formulated with cross-linking additives) and
a tempered glass superstate with high transmission (91%) and low iron content
on one side and a similar EVA layer and a Tedlar-Polyester-Tedlar PVF (Poly Vinyl
Fluoride) film as a substrate on the other. The entire assembly is bonded within
a specially designed and developed vacuum laminator at high temperature and in
vacuum. During this process, the EVA film melts and forms a bond between solar
cells and glass on one side and solar cells and Tedlar on the other and thus
laminate is formed. This makes the assembly resistant to moisture and
environmental effects.
The laminate is framed with anodized aluminium edge frames so as to provide
support and flexibility in mounting the PV modules at site as well as providing
strength against high wind velocity. A junction box is provided for enabling the
PV modules to be interconnected in an array and to the load. The module is then
tested with a sun simulator, under simulated light for measuring the electrical
power output.
Conventional 12-V, 80-W PV modules (Fig. 3) manufactured with 125-mm solar
cells (36 cells of 2.2-watt in 9*4 configuration) have the overall dimension of
1203*528*38.5 mm3 with following electrical characteristics:

Open-circuit voltage (Voc): 22 V, Short-circuit current (Isc): 5.0 A
Voltage at maximum power point (Vmp) : 17.5 V, Current at maximum power
point (Imp) : 4.57 A.
The power output of 125-mm mono-crystalline or multi-crystalline solar cells
range from 2.2 to as high as 2.4-watt. A typical module made with 36-nos. of
125-mm size solar cells (each of 2.2-watt) produces 80-watt power output.
Similarly, a module fabricated with 36-nos. of 156-mm size solar cells (each of
3.6 watts) produces a power output of 120 to 130 watts. Hence, 156-mm solar
cells is required to be cut to smaller size so as to suitable for delivering 80-watts
power output. Two-third cut 156-mm cells shall give a power output of 2.4 watts
and one-third cut cells, a power output of 1.2 watts approximately. It is derived
that a module fabricated with 36-nos. of 156-mm two-third cut solar cells (each
of 2.4 watts) produces a power output of 80-watts and a module fabricated with
36-nos. of 156-mm one-third cut solar cells (each of 1.2 watts) produces a
power output of 40-watts. Hence, for utilizing 156-mm one-third cut cells for
delivering 80-watts power output, two nos. of such 40-watt modules are required
to be paralleled to realize 80 watts for 12-volt application. This concept is used
here for manufacture of 12-V, 80- modules using 72 one-third cut solar cells. A
picture of full and two-third cut and one-third cut 156-mm square multi
crystalline silicon solar cell is shown in Fig. 4. 2 strings each of 18 one-third cut
cells are paralleled and then connected in series with another set of 18*2 strings
to realize the open-circuit voltage of 21-Volt, short-circuit current of 5.0-Amp and

power output in the range of 80 to 85 watts. The array design is of 18*4
configuration with an overall module size of 1023*663*38.5 mm3. The specially
developed lay-up jig and the laminated 80-watt module are shown in Fig. 5 and
Fig. 6 respectively.
These newly developed PV modules have met the design specification of voltage
and power adequately. The current-voltage characteristics as measured using
Sun Simulator is given in Fig. 7. The total area of the module remain almost
same as that made with 36-cell (125-mm size) configuration. Out door
performance tests have been carried out and the initial results indicate that the
performance stability of these modules are well within acceptable limits, as
already observed in the case of generic modules using similar cells.
EXAMPLE
Few proto type PV modules of the new invention have been manufactured using
72-nos. of 156-mm one-third cut multi crystalline silicon solar cells.
Characteristics of a typical module measured using a Sun Simulator (Spire, 460i)
are as given below.

WE CLAIM
1. The method of fabrication of Photovoltaic modules of rating 12-volt 80
watt incorporating 72 one third cut 156 mm size multi crystalline silicon
solar cells comprising the following steps;
- laser cutting of 156 mm full size solar cells into 2/3rd and 1/3rd
portion;
- interconnection of solar cells and formation of a string;
- lamination of the interconnect solar cells and curing;
- framing, fixing of junction box and testing with a sun simulator;
characterized in that the said Photovoltaic module comprises of 72 Nos.
1/3rd cut, 156 mm size solar cells, which are arranged for series
connection of two sets of parallel stirngs of 2x18 nos. of such cells.
2. The method as claimed in claim 1, wherein the formation of a string with
the solar cells is made terminating in positive and negative output leads
and their interconnection is done in lay up jig where phenyl Resin bonded
cotton fibre (PRVCF) is provided.

3. The method as claimed in claim 1, wherein the said interconnection is
made with tinned copper interconnects which are soldered on the front
busbars of matched solar cells.
4. The method as claimed in claim 1, wherein the said lamination comprises
of two layers, one layer comprising of Ethylene Vinyl Acetate (EVA) and
high transmission tampered glass applied on one side and a second layer
of combined Polyester and Poly Vinyl Fluride based film applied on the
other side of strung solar cells.
5. The method as claimed in claim 1, wherein the laminates, formed in the
process of said lamination is framed with anodized aluminium edged
frames.
6. The method as claimed in claim 1, wherein the said junction box is fixed
for photovoltaic modules to be interconnected in the array and to the
load.
7. The method as claimed in claim 1, wherein the said testing of Photovoltaic
module, so framed, is done with a sun simulator, under simulated light for
measuring the electrical power output.

ABSTRACT

TITLE : METHOD FOR FABRICATION OF PHOTOVOLTAIC MODULES OF RATING
12-VOLT, 80-WATT INCORPORATING 72 ONE-THIRD CUT 156-MM SIZE MULTI
CRYSTALLINE SILICON SOLAR CELLS
The method of fabrication of Photovoltaic modules of rating 12-volt 80 watt
incorporating 72 one third cut 156 mm size multi crystalline silicon solar cells
comprising the following steps; laser cutting of 156 mm full size solar cells into
2/3rd and 1/3rd portion; interconnection of solar cells and formation of a string;
lamination of the interconnect solar cells and curing; framing, fixing of junction
box and testing with a sun simulator; characterized in that the said Photovoltaic
module comprises of 72 Nos. 1/3rd cut, 156 mm size solar cells, which are
arranged for series connection of two sets of parallel strings of 2x18 nos. of such
cells.