1. Potential of Solar Cell Technology
• Earth receives enough solar energy in 1 hour to
satisfy the world’s energy needs for a year
• Most energy sources are derived from the sun
(wind, hydroelectric, fossil fuels)
Fabrication of All-Aluminum p-Type Silicon Solar Cells
Raul Flores, Chemical Engineering, University of Kansas
REU Site: Arizona State University
PI: Meng Tao, Electrical Engineering, Arizona State University
Mentors: Laidong Wang, Electrical Engineering, Arizona State University
Wen-cheng Sun, Electrical Engineering, Arizona State University
World-Wide Implementation
• Implementing solar cell technology at a global
scale is a difficult challenge
• Solar cell technology must be engineered to
facilitate mass production and adoption
The problem being addressed
Materials: Cheap and Abundant
• Solar cells must be built from cheap and
abundant natural resources
• Expensive cells are not economically feasible
• Scarce materials will bottleneck cell production
The scope of this study
Climate and the Energy Crisis
• 80% of the world’s energy is made from fossil
fuels, which pose a threat to the climate
• Fossil fuel supply is limited, therefore a
replacement energy source is needed
Replacing Silver With Aluminum:
• This project aimed to design a solar cell which
uses aluminum instead of silver as the front
contact material (see figure below)
• Aluminum is orders of magnitude cheaper and
more abundant than silver
Solar Cell Structure and Fabrication Steps Aluminum
Front-Contact
Results:
Solar Cell Parameters:
Our Lab’s
Cell
Reference
Cell
Percent
Difference
Efficiency [%] 12.4 16.8 35
JSC [mA/cm2] 31.8 35.5 12
VOC [V] 0.60 0.61 2
RShunt [mΩ-cm2] 183 808 342
RSeries [mΩ-cm2] 1030 393 62
Table 1. Parameters for 2 p-type solar cells with an aluminum
backside contact, SiNx ARC layer; and either an aluminum
(our labs cell) or silver (reference cell) front finger electrode
Analysis of Table 1.
• Reference cell: made by another group; structure and
fabrication almost identical to ours; silver front contact
instead of our aluminum front contact
1. Our cell’s efficiency is lower than the reference’s
2. Our cell’s current (JSC) and voltage (VOC) are reasonably
similar to the reference’s
3. Our cell’s resistances (RShunt and RSeries) are much worse
than the reference’s (especially RShunt)
4. Therefore, it’s likely that 3 is the cause for 1
5. Poor resistances are likely due to fabrication defects,
poorly optimized cell specifications, and poor contact
resistance between the cell’s different layers
Project Summary
• To fabricate a solar cell that can readily be implemented at a large scale
• To this end, a solar cell which utilized an aluminum front contact (instead of the traditional
silver one) was studied
• The fabricated solar cell performed poorly relative to a similar cell with a silver front contact
• Non-optimized fabrication procedures and cell specifications are the likely main culprits for
low cell performance
• The solar cell’s efficiency can be improved by refining the fabrication procedure and
optimizing the cell structure
Conclusion: Quick Summary and Future Work
Future Work
• Improve cell efficiency by: improving the fabrication process, minimizing contamination of
the device, and optimizing the cell’s specifications
I want to show my gratitude to my principal investigator, Dr. Meng Tao. I would also like to thank my mentors, Laidong Wang and Wen-cheng Sun for their support and guidance. I would also
like to thank the National Nanotechnology Infrastructure Network Research Experience for Undergraduates, the Center for Solid State Electronics Research, and Arizona State University for
their support and funding. This research was supported by the National Science Foundation under Grant No. ECCS-0335765.
n-type Silicon
p-type Silicon
n-type Silicon
p-type Silicon
Al Back Contact
n-type Silicon
p-type Silicon
SiNX
n-type Silicon
p-type Silicon
Al Back Contact
SiNXNi
n-type Silicon
p-type Silicon
Al Back Contact
SiNXNi
1. Start with p-type silicon
2. Texture both back and front
surface with an alkaline
solution for 1 hour
3. Form the n-type layer by
diffusing phosphorus into
the top surface (.5 microns)
4. Apply the Silicon Nitride
(SiNX) layer by PECVD
SiNX
5. Screen print the back-side
aluminum contact
6. Fire at a temperature >800 C
to diffuse aluminum into p-
type silicon and create a
back surface field (BSF)
7. Etch the SiNX into the front
contact finger pattern
(photoresist, UV exposure,
developing, HF etch)
8. Apply nickel to the etching
pattern by sputter
deposition
9. Apply the front contact
aluminum layer via
electroplating
Topside view of finished solar
cell. The grey colored pattern
shown is the front contact and is
made of aluminum.
Solar Simulator:
Equipment used to
measure the
parameters listed in
table 1.
Apparatus uses a
lamp to replicate
the suns
electromagnetic
spectrum.
Close up of the
solar simulator
with a solar cell
on it. The metal
backside makes
conductive
contact with cell’s
back, and a small
needle makes
contact with the
front.
Research Motivation Flowchart: From Macroscopic Problem To Lab-Scale Solutions