DSSC and TF Poly-Si
Solar Cells
Dye-sensitized TiO2 and thin film polysilicon solar cells: fabrication and
measurements of photon-to-electron
conversion efficiencies using LabView
National Nano Device Laboratory
Tainan Science Park
Taiwan Tech Trek (TTT) 2006 Interns:
 Eric Chang
Department of Electrical Engineering and Computer Sciences
University of California at Berkeley
 Kevin Chen Ying Chang
Department of Electrical and Computer Engineering
University of California at San Diego
 Yu-Kai (Kevin) Su
Department of Biomedical Engineering
Washington University in St. Louis
The Clean Room
 Different levels - NDL
Tainan is level 10,000 per
cubic feet
 Requires standard
uniforms
 For our clean room, we
have to have specialized
hats, gloves, jackets,
shoes, and mouth covers
 Temperature, pressure,
and humidity are
constantly monitored so
room condition can be
kept at an optimal level
Standard Lab Clothing
The Equipments and Technology
 Wet bench
 Consists of four different
chemical solutions to eliminate
extra foreign particles
 PECVD (Plasma Enhanced)
- produces organic thin film
by growing silicon
dioxide/poly-silicon
 Furnace is LPCVD (Low
Pressure) – same function
as PECVD requiring longer
time for processing but better
quality
Wet Bench
The Equipments and Technology
(Continued)
 Photolithography
 Includes following
processes in order: priming,
putting on photo resist (PR),
pre-baking, UV exposure
with mask, and then hard
bake
 Exposure - uses a mask to
allow entrance of UV light to
hit target wafer, which causes
chemical reaction with the PR
 Area uses yellow light so PR
is not damaged
Photolithography
The Equipments and Technology
(Continued)
 PR spin coated onto wafer
(manually or automatically)
 Track (automatic) –
 Can perform all steps
necessary for coating the
wafer using an automated
computer system
 Spin Coater (manual)
 Choose desired size of target
 Manually test optimal
parameters
(RPM/time/position)
Spin Coater
Spin Coating
Main purpose: to achieve an even surface
Side View of an Uneven Surface
slide
Side View of an Even Surface
slide
Spin Coating Demonstration
The Equipments and Technology
(Continued)
 Thermal Evaporator and
Sputter - both coat thin film
of metal on the target wafer
 Thermal evaporator –
evaporated metal on
bottom hits wafer on top,
then molten metal
gradually spreads evenly
from center of wafer to coat
surface
 Sputter – molten metal on
top rains down droplets at
numerous positions to coat
the wafer on the bottom
Sputter
The Equipments and Technology
(Continued)
 The ICP and RIE are
both machines that
are used for etching
 ICP is better since it
can etch out the whole
target wafer while the
RIE cannot
 Etchant is very
corrosive and
dangerous, so
protective gear is
required
Protective Mask
The Equipments and Technology
(Continued)
 AFM – scans out 3D image of target’s surface
 Nano-scale probe vibrates with a certain frequency
at a synchronized distance away from the target
 Vibration changes can be detected by a light that is
reflected upon it, which gives data for image
 Probe station
 Uses microscope and nano-scale probe to make
contact with different shapes of arrays on target
 Probe station is utilized for contact with
conductive materials, while AFM targets regular
surfaces
The Mask
 The design and pattern
of the mask developed through
AutoCad, then sent to
specific company for
production
 Normal mask is created
with glass and
Chromium (1-2 months
for completion)
 Due to limited time,
replaced the materials
with plastic and chalk,
(only an overnight
process)
Masks
Mask Aligning
Some Measuring Equipments
Some Measuring Equipments
Finding the Optimal RPM and Time
0.2 mL HAc (hydrogen acetate) in 100 mL DI water
TiO2: 1.35±0.05 g with 40 drops of acetic acid
RPM
1
2
3
4
500
1300
1200
1100
30
30
30
Time (second) 20
Table 1: 70 Drops of Acetic Acid
RPM
Time (second) Comment
7A
1100
30
7B
1100
30
7C
1000
30
7D
900
30
not drops, painted on (corners)
7E
900
30
Less TiO2 at the corners compared to D
7F
1100
30
Less drops, not as evenly distributed
7G
1100
30
7H
1100
30
More drops at corners
Table 2: 80 Drops of Acetic Acid
RPM
Time (second)
8A
1000
30
8B
900
30
8C
700
20
8D
800
10
8E
700
40
Comment
Not evenly spread
Surfactant
Triton X 100
Surfactant
Table 3:
2 g TIO2  {60, 70, 80} drops  Triton X 100 (surfactant)
RPM
Time (second)
Comment
7XA
900
30
Good, with little bubbles
6XA
1100
30
Thicker than 7A, more bubbles
6XB
1200
30
7XB
900
30
7XC
800
30
8VC
700
30
Fabrication of DSSC
Upper Electrode (1)
 Spin-coating
 PR: AZ 5214
 Step 1: 500 RPM for 5 s
 Step 2: 3000 RPM for 30 s
 Soft bake
 90°C, 30 s
 Exposure
 Plastic mask of our design
 Duration: 4 s
Fabrication of DSSC
Upper Electrode (2)
 Reverse Bake
 110°C, 120 s
 Reverse, flood Exposure (without mask)
 15 s
 Develop
 AZ 300 developer for about 30 s
 Hard Bake
 100°C, 60 s
In order to make the photoresist negative:
REVERSE BAKE
AND
REVERSE FLOOD EXPOSURE
Fabrication of DSSC
Spacers
 Spin-coating
 PR: Su8
 Step 1: 500 RPM for 5 s
 Step 2: 3000 RPM for 30 s
 Soft bake
 90°C, 30 s
 Exposure
 Plastic mask of our design
 Duration: 15 s
Fabrication of DSSC
Spacers
No reverse bake or reverse
flood exposure
 Develop
 AZ 300 developer for about 30 s
 Hard Bake
 100°C, 60 s
Fabrication of DSSC
Final steps to putting together our DSSC cell:
Put on
electrolytes
Place the ITO glass carefully
on top of the side with the
electrolytes
Hold the ITO glass in place
with something
DSSC
How It Works and How to Test It
Electron Transfer Process
injection
regeneration
recapture
hopping
Studying Photovoltaic Performance
4. gold electrode
3. dye-sensitized
heterojunction
2. compact
TiO2 layer
1. conducting F-doped
SnO2-coated glass
Avoids direct contact
between the HTM layer
and the SnO2, which
would cause short circuit
Thin-Film Poly-Silicon
0C
0
Anneal
Induce
crystal:
at 500
500
for
Remove
Amorphous
Al layer
Si 1hr
by wet etching
a-Si 4750nm
poly-Si 5000nm
Amorphous Si
Induced metal layer
Bottom electrode
Al 250nm
a-Si
Al 250nm
poly-Si
250nm
ITO 300nm
Glass
Closeup
A Detailed Look at Our
Experiments
Photoresist Remains
50x
200x
100x
600x
TiO2
50x
100x
good contact
TIO2
]
electrode
200x
LabVIEW Portion
Measurements & Results
LabVIEW Portion
LabVIEW Portion
LabVIEW Portion
VM
4
3.5
Voltage
3
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
Time
3
3.5
4
4.5
LabVIEW Portion
I1
3.00E-03
2.50E-03
Current
2.00E-03
1.50E-03
1.00E-03
5.00E-04
0.00E+00
-5.00E-04
0
0.5
1
1.5
2
2.5
Time
3
3.5
4
4.5
The END