fabrication of all-aluminum p-type silicon solar cells
TRANSCRIPT
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Fabrication of All-Aluminum p-Type Silicon Solar Cells
Raul FloresPrincipal Investigator: Dr. Meng Tao
Arizona State University
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Research Motivations and Objectives:
What are we trying to do and why?
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Research Motivations and Objectives:
Need for an environmentally responsible energy source• 80% of energy produced from fossil fuels
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Need for an environmentally responsible energy source
Solar cells are a promising energy technology• 165,000 terawatts of sunlight
Research Motivations and Objectives:
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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:
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Need for an environmentally responsible energy source
Solar cells are a promising energy technology
Challenge of global implementationUse cheap and abundant materials
• Cost prohibiting and Resource prohibiting• Silver currently used as front contact material
Research Motivations and Objectives:
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Need for an environmentally responsible energy source
Solar cells are a promising energy technology
Challenge of global implementationUse cheap and abundant materials
• Cost prohibiting• Resource prohibiting
Research Motivations and Objectives:
Our lab’s objective• Replace silver with aluminum
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Solar Cell Basics:
Basic solar cell physics and structure
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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)
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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)
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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
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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
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Solar Cell Fabrication and Structure:
What our device looks like and how we made it
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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
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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
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Solar Cell Fabrication and Structure: SiNx Passivation and Anti-Reflection Coating
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
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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
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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 Layer Ni
Rear Contact (Aluminum)
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
Phosphorus Diffusion
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Solar Cell Fabrication and Structure:Aluminum Front Contact
P-type Silicon
N-type Silicon
• Aluminum electroplated onto nickel
NiAl
Rear Contact (Aluminum)
Phosphorus Diffusion
Rear Al Screen Printing
SiNx Patterning
Ni Sputtering
Front Al Electroplating
SiNx Deposition
SiNx Passivation and ARC Layer
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Results:
How well our cell performed
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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):
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Parameter Descriptions: RSeries
• RSeries : Resistance to current flow through device
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Parameter Descriptions: RShunt
• RShunt : Resistance to current flow around device• Example: Current leaking around edges of device, not
through p-n junction
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PV Cell Performance: Parameter Summary
Our Lab’s Cell
Efficiency [%] 12.4
JSC [mA/cm2] 31.8
VOC [V] 0.60
RShunt [mΩ-cm2] 183
RSeries [mΩ-cm2] 1030
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PV Cell Performance: Parameter Summary
• Data for another group’s cell was obtained• Crucial difference is the front electrode material
NiAl
Silver
Our groups device Reference cell
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PV Cell Performance: Parameter Summary
• Focus on third column (interested in difference, not absolute values)
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
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PV Cell Performance: Parameter Summary
• Reference cell has a much better 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
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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
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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
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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
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Conclusion: Future Work
• Fixing fabrication errors• Cell area• Contamination• Etc.
• Optimizing cell specifications• SiNx thickness, front contact width/spacing,
electroplating conditions, etc.
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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
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Questions?• Study’s objective
• General solar cell operation• Our groups device or fabrication
• Significance of results• Miscellaneous
National Science Foundation, Grant No. ECCS-0335765