A portable laser scanner prototype has been developed to remotely identify defects in solar cells for educational purposes. The scanner uses an Arduino board to raster a laser across solar cell samples, while a DAQ system records the current generated. Data is analyzed in MATLAB to generate 3D plots locating defects and grain boundaries that correlate with cell efficiency. The low-cost system allows students to remotely study real solar cell samples and better understand manufacturing defects.

1. Summary:
A
portable,
low-­‐cost
laser
system
is
being
explored
for
educa9onal
and
research
purposes.
Here,
we
employ
this
system
for
iden9fying
defects
in
solar
cells.
In
polycrystalline
solar
cells,
for
example,
one
can
determine
the
loca9on
of
these
grain
boundaries
and
the
degree
of
granularity,
and
correlate
it
with
the
cell’s
efficiency.
This
module
can
be
used
as
a
learning
tool
that
can
supplement
classroom
learning
for
the
Manufacturing
Materials
course
that
presents
samples
of
solar
cells
at
various
stages
of
manufacturing
to
the
students.
The
module
has
been
developed
with
an
inten9on
of
being
remotely
operated
to
enhance
and
empower
the
online-­‐classroom
learning
experience
and
help
the
students
beCer
understand
solar
cell
defects.
Remotely
accessible
laser
scanner
prototype
to
study
solar
cells
defects
Introduc9on
• Despite
ever-­‐improving
fabrica3on
methods
for
semi-­‐conductors,
crystallographic
defects
can
be
common
and
the
fabricated
structures
usually
require
to
be
tested.
• Light
Beam
Induced
Current
(LBIC)
is
a
common
tes3ng
method,
where
a
light
beam
rasters
the
surface
of
the
semiconductor
material
and
the
current
so
generated
is
measured
and
mapped
against
respec3ve
coordinates.
[1]
• Photovoltaics
(PVs)
consist
of
large
planar
semiconductor
surfaces
whose
efficiency
is
directly
related
to
the
density
of
defects.
[2]
Low-­‐cost
PVs
are
polycrystalline
and
contain
substan3ally
larger
density
of
defects
compared
to
single-­‐crystal
PVs,
which
makes
tes3ng
them
impera3ve.
• An
LBIC
setup
consists
of
a
monochroma3c
light
source,
a
raster
tool
to
move
the
wafer,
a
data
acquisi3on
and
a
data
processing
system.
Project
Requirement
Hardware
SoIware
Data
Collec3on
NI
DAQ
(USB-­‐6211)
LabVIEW
Data
Processing/
Analysis
Computer
MATLAB
Laser
Scanner
Module
Arduino
UNO,
Stepper
Motors
and
Driver,
Laser
Arduino
IDE
Pranav
Ram
Kamarajugadda,
Chetana
Bayas,
Faculty
Advisors:
Dr.
Richard
Chiou,
Dr.
Michael
G
Mauk
Department
of
Engineering
Technology,
Division
of
Engineering
Management
and
Technology,
College
of
Engineering,
Drexel
University
Methodology
• The
laser
scanner
is
programmed,
on
Arduino
pla>orm,
to
perform
the
ac?on
of
rastering
on
an
area
of
36
sq.
mm.
• Solar
cells
are
placed
on
the
movable
plate
of
the
laser
scanner
module.
The
laser
scanner
plate
moves
in
steps
such
that
the
en?re
scan
takes
place
in
seven
steps.
• As
each
step
of
the
rastering
is
performed,
the
current
generated
by
the
cell
is
recorded
via
the
NI
DAQ
on
LabVIEW
and
stored
in
a
text
file
for
post
processing.
• ANer
the
comple?on
of
the
rastering,
the
data
stored
on
the
text
file
is
imported
into
MATLAB
to
make
a
3
dimensional
plot
of
the
defects/
disturbance
posi?ons
on
the
solar
cell.
Results
• A
polycrystalline
solar
cell
with
a
lot
of
granular
irregulari?es
is
scanned
with
externally
induced
disturbance,
an
insula?ng
ball
of
tape,
at
known
posi?ons.
The
current
outputs
when
ploRed
in
3
dimensional
space
approximately
locate
the
disturbances.
Conclusion
• A
working
module
of
laser
scanner
was
developed
that
may
be
used
as
a
learning
tool
to
study
the
granular
defects
of
solar
cells.
The
results
prove
that
iden?fica?on
of
defects
is
successful.
This
module
can
be
used
by
students
in
classroom
to
operate
on
and
familiarize
themselves
with
three
popular
pla>orms,
LabVIEW,
MATLAB
and
Arduino.
Future
Work
• Development
of
a
tool
to
support
data
collec?on
and
post
processing
• Develop
a
Virtual
Network
for
two
loca?ons,
for
remotely
accessing
this
device
to
enhance
the
online
classroom
community
Acknowledgement
This
work
was
supported
by
the
US
Department
of
Educa3on
under
joint
DHSIP
Program
with
University
of
Texas
at
El
Paso,
PR/Award
No.:
P031S120131
and
by
US
Na3onal
Science
Founda3on
TUES
Grant
1044708
and
NSF
DUE
Award
1245872.
The
authors
wish
to
express
sincere
gra3tude
for
their
financial
support.
References
[1]
Santo
Mar3nuzzi
and
Michael
Stemmer
“Mapping
of
defects
and
their
recombina3on
strength
by
a
light-­‐beam
induced
current
in
silicon
wafers”,
Material
Science
and
Engineering,Volume
24,Issues
1-­‐3,May
1994,
Pages
152–158
[2]
Inves3gación
y
Desarrollo.
"Defects
in
solar
cells
made
of
silicon
iden3fied."
ScienceDaily.
ScienceDaily,
2
January
2015
Figure
1:
Proposed
LBIC
Lab
setup
Arduino-­‐
controlled
laser
raster
system
Data
Acquisi3on
using
NI
DAQ/
LabVIEW
Data
Processing/
Analysis
using
MATLAB
Figure
3:
Students
performing
a
test
raster
Figure
2:
Experimental
setup
Figure
4:
(leN)
Solar
cell
with
external
disturbance.
(right)
A
waterfall
plot
of
the
current
values
detect
the
external
disturbance
in
approximately
the
correct
loca?ons
Student
Benefits
and
skills
improvement
• The
tes?ng
phase
helps
students
to
develop
crea?ve
solu?ons/
modifica?ons
to
troubleshoo?ng
issues
• Equips
students
with
developing
skills
with
LabVIEW,
MATLAB
and
Arduino