3. Research Motivations and Objectives:
Need for an environmentally responsible energy source
• 80% of energy produced from fossil fuels
4. Need for an environmentally responsible energy source
Solar cells are a promising energy technology
• 165,000 terawatts of sunlight
Research Motivations and Objectives:
5. Need for an environmentally responsible energy source
Solar cells are a promising energy technology
Challenge of global implementation
• 500,000 km2 (~ size of Spain)
Research Motivations and Objectives:
6. Need for an environmentally responsible energy source
Solar cells are a promising energy technology
Challenge of global implementation
Use cheap and abundant materials
• Cost prohibiting and Resource prohibiting
• Silver currently used as front contact material
Research Motivations and Objectives:
7. Need for an environmentally responsible energy source
Solar cells are a promising energy technology
Challenge of global implementation
Use cheap and abundant materials
• Cost prohibiting
• Resource prohibiting
Research Motivations and Objectives:
Our lab’s objective
• Replace silver with aluminum
9. P-type Si
N-type Si
Rear Contact (Aluminum)
Solar Cell Basics: Basic Solar Cell Structure
• Simplest functional silicon (Si) solar cell
• 4 Parts: n-type Si, p-type Si, 2 electrodes
Front Contact (Silver)
10. P-type Si
N-type Si
Rear Contact (Aluminum)
Solar Cell Basics: Basic Solar Cell Structure
• Simplest functional silicon (Si) solar cell
• 4 Parts: n-type Si, p-type Si, 2 electrodes
Front Contact (Silver)
11. P-type Si
N-type Si
Rear Contact (Aluminum)
Solar Cell Basics: Basic Solar Cell Structure
• p-n junction formed at boundary
• Permanent electric field formed
Front Contact (Silver)
Electric
Field
12. P-type Si
N-type Si
Solar Cell Basics: Interaction With Sunlight
• Photons absorbed—electron-hole pairs created
• Charges separated by p-n junction
• Charge separation induces current
Electric
Field
14. Solar Cell Fabrication and Structure:
• Our cell’s structure is similar to the model cell
• 2 additional features
Front Contacts
Ni
Al
SiNx Passivation and
ARC Layer
Ag
15. Solar Cell Fabrication and Structure:
Silicon Substrate
P-type Silicon
N-type Silicon
• P-type silicon wafer (200 microns)
• N-type layer made by diffusing phosphorus (0.5 microns)
Phosphorus Diffusion
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
16. Solar Cell Fabrication and Structure:
SiNx PassivationandAnti-ReflectionCoating
P-type Silicon
N-type Silicon
• Applied by PECVD (75 nm)
• Passivation effect:
• Minimizes surface recombination
• Anti-reflection coating
SiNx Passivation and
ARC Layer
Phosphorus Diffusion
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
17. Solar Cell Fabrication and Structure:
Aluminum Back Contact
P-type Silicon
N-type Silicon
• Screen printed aluminum (10 microns)
Rear Contact (Aluminum)
Phosphorus Diffusion
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
18. Solar Cell Fabrication and Structure:
Nickel Seed Layer
P-type Silicon
N-type Silicon
• SiNx etched into front finger pattern
• Nickel layer applied (250 nm)
• Helps adhesion of aluminum
SiNx Passivation and
ARC LayerNi
Rear Contact (Aluminum)
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
Phosphorus Diffusion
19. Solar Cell Fabrication and Structure:
Aluminum Front Contact
P-type Silicon
N-type Silicon
• Aluminum electroplated onto nickel
Ni
Al
Rear Contact (Aluminum)
Phosphorus Diffusion
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
SiNx Passivation and
ARC Layer
21. Parameter Descriptions:
First, we need to define some parameters
• Efficiency
• Ratio of energy extracted to energy input
• Short-circuit current (JSC):
• Upper-limit to actual current
• Open-circuit voltage (VOC):
• Upper-limit to actual voltage
• Series resistance (RSeries):
• Shunt resistance (RShunt):
23. Parameter Descriptions: RShunt
• RShunt : Resistance to current flow around device
• Example: Current leaking around edges of device, not
through p-n junction
25. PV Cell Performance:Parameter Summary
• Data for another group’s cell was obtained
• Crucial difference is the front electrode material
Ni
Al
Silver
Our groups device Reference cell
28. PV Cell Performance:Parameter Summary
• The current and voltages of both cells are reasonably
close
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 [Ω-cm2] 183 808 342
RSeries [mΩ-cm2] 1030 393 62
29. PV Cell Performance:Parameter Summary
• The reference cell has a much better RShunt and RSeries
• Poor resistances might account for bad efficiency
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 [Ω-cm2] 183 808 342
RSeries [mΩ-cm2] 1030 393 62
30. PV Cell Performance:Parameter Summary:
Causes of Poor Resistances
• RShunt:
• Small wafer area
• Contamination
• RSeries:
• Nickel-Silicon and/or Aluminum-Nickel interfaces
• Problems with electroplating
31. Conclusion: Future Work
• Fixing fabrication errors
• Cell area
• Contamination
• Etc.
• Optimizing cell specifications
• SiNx thickness, front contact width/spacing,
electroplating conditions, etc.
32. Conclusion: Project Summary
Goal:
• Demonstrate solar cell with an aluminum front
contact electrode
Results:
• Device performed poorly compared to a similar
reference solar cell
Conclusion:
• Solar cell needs to be improved by optimizing
fabrication and device specifications
33. Questions?
• Study’s objective
• General solar cell operation
• Our groups device or fabrication
• Significance of results
• Miscellaneous
National Science Foundation,
Grant No. ECCS-0335765
Editor's Notes
*Over the course ________ I assisted my lab, under the direction
*First I want to introduce the problem ____ this project is focusing on _____ and how our research fits into the context of this problem
*Energy crisis and energy
*Fossil fuels provide most of the energy
*Need clean energy
*Solar is most promising
*energy factoid
*Collecting even a small fraction is huge challenge
*Spain factoid
*For this to be possible we must only
*Currently one of the more expensive materials used in photovoltaics
*Therefore, our labs goal
*Now I’ll introduce the basic structure and function of photovoltaic devices
REMEMBER TO TALK SLOWER
*Before I move on ______
*Now I’m going to briefly describe the fabrication procedure of our labs device
*Our Device is also simple
*Two additional structures
*Started with p-type
*Diffused phosphorus to make n-type
*Explain shunt resistance
*Large is good
*I found data for cell with structure similar to ours
*Key difference is in front electrode material
*Can compare data between cells to see how performance differ
*Introduce extra columns
*Shunt and series resistance for the reference cell are much better (especially shunt)
*Insinuates that resistances are keeping efficiency down
*Small wafer area: area hit by sunlight too close to edge, therefore, current leak
*Contamination due to shared facilities
*Contact resistance of the…
*We also suspect that the aluminum thickness
*General future goal is to improve cell
*Identifying and eliminating….
*Also, the group will have to play around with cell spec…..
