improving the stability of hydrogenated amorphous silicon solar cells sd may 2012-09 ecpe dept.,...
TRANSCRIPT
![Page 1: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/1.jpg)
Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells
SD May 2012-09
ECpE Dept., Iowa State University
Advisor/Client – Dr. Vikram Dalal
Anthony Arrett, Wei Chen, William Elliott, Brian Modtland, and David Rincon
![Page 2: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/2.jpg)
Problem Statement
• Amorphous Silicon Solar Cells are inherently unstable - we want to improve that
• Investigate the instability of a-Si Solar Cells
• Use Stradins’ research to design a baseline a-Si solar cell with less defects over time
• Determine new fabrication recipes that produce more stable a-Si with the best efficiency
![Page 3: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/3.jpg)
Background of PV Cells
-EHP are created in the depleted intrinsic layer-PIN junction allows us have a bigger depletion layer over PN Junction-Electric field within junction allows faster transport of carriers, and reduces likelihood of recombination
![Page 4: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/4.jpg)
Background to Amorphous Si• Same tetrahedral bonding as crystalline Si, but does not
have long range crystalline structure
• Random structure leads to dangling bonds in the material, these are considered defects
• Dangling bonds lead to midband gap states
• Hydrogen is used to fill those dangling bonds
![Page 5: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/5.jpg)
Light-Induced Instability• Discovered that defect density increases with exposure to
light, not necessarily time
![Page 6: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/6.jpg)
Staebler-Wronski Effect
-Dramatic drop in efficiency after just a few hours of exposure to light-Stable efficiency is the most important attribute-Theorized that light breaks the H-Si bonds, creating dangling bonds in material-Self annealing
![Page 7: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/7.jpg)
Overview of Plan• Build a device with a higher stable efficiency than is
currently available
• Working off Stradins’ breakthrough to reducing defect density of intrinsic layer
• Experiment with anneal temperatures
• Add graded Boron doping to improve internal field
![Page 8: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/8.jpg)
High Temperature Anneal
• High temp annealing shows promise in reducing Li-DB
![Page 9: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/9.jpg)
Boron Doping• Graded Boron doping will create an electric field in the
intrinsic layer
• 10ppm-100ppm
• Electric field will speed up collection process and lower recombination
• Lower recombination leads to higher efficiency
![Page 10: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/10.jpg)
Functional Requirements
• Photoconductivity > 1*10-5 Ω-1 cm-1
• Dark Conductivity < 1*10-10 Ω-1 cm-1
• Tauc Band Gap < 1.8eV
• Defect density after light soaking < 1*1016 cm-3
• Fill Factor > 60%
• Efficiency > 5%
• Drop in Efficiency after light soaking of no more than 10%
![Page 11: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/11.jpg)
Non-functional Requirements
• Ability to be reproduced time after time of similar quality
• Ability to convert recipe to mass-production with little
changes
• Samples that are easily measured and tested with devices
at the MRC
• Size of the cell
![Page 12: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/12.jpg)
Market Overview• The firm projects $1.3 billion in revenues from a-Si based
photovoltaic in the year 2009• Will grow to $4.1 billion in the year 2014
the market share of different PV technology
![Page 13: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/13.jpg)
Testing of the Solar Cells• Quantum Efficiency
• Indicates a solar cells capability to convert energy
• Current vs. Voltage• Power Efficiency, Fill Factor
• Capacitance vs. Voltage• Used to measure defect density and intrinsic layer thickness
• Capacitance vs. Frequency• Defect Density vs. Energy
• Thickness• Serves a prerequisite to calculating properties of the device
• Photoconductivity• Used to determine the film’s ability to conduct a current with
exposure to light
![Page 14: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/14.jpg)
Automated I-V Setup
• Automated I-V measurement of a-Si solar cells
• Find ISC, VOC, Fill Factor, Efficiency, RSHUNT, and RSERIES
• Extended Light Soaking up to 100 hours• Simulated solar exposure to study Staebler-Wronski
instability
• AM1.5 Solar spectrum standard
• Capability for 1x, 2x, 3x, and 4x Solar Irradiance
• LabView software programming
![Page 15: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/15.jpg)
Specifications of Auto I-V Setup
• Easy-to-use software interface
• NI LabView
• AM1.5 Spectrum for solar simulation
• 100 hour measurements w/ adjustable intervals
• I-V taken every 1 to 5 minutes
• 1x, 2x, 3x, and 4x Suns with the use of lenses
• Reference cell for tracking intensity of the light source
![Page 16: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/16.jpg)
Detailed Design• Concept Diagram
TOP VIEWSIDE VIEW
![Page 17: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/17.jpg)
Cost EstimateItem Cost Status
Keithley 236 $3000 (already purchased)
Shipped and Done
Keithley 485 $1000 Ships Early January
ABET 10500 $4300$325 for beam turner
Ships Mid-January
USB GPIB Adapter $0 (In Stock) Done
Dell Desktop Optiplex 790 w/ 20” Monitor
$784 Ships in ~2 Weeks
Reference Solar Cell $0 (In Stock) Done
NI LabView Software $0 (CSG Install)
TOTAL $9084 w/ Software (no beam turner)
Completed by mid-Feb
![Page 18: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/18.jpg)
Status Report• Design has been completed for automated IV
measurements
• A proposal has been written up, submitted to our client, and accepted• Now ordering parts and materials for the setup
• Beginning measurements have been taken for different recipes.• QE, I-V, and C-V
![Page 19: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/19.jpg)
Task Responsibilities• We all did our own separate research and reading to
become acquainted with amorphous silicon.• Measurement Research & Auto I-V:
- Tony - QE & LabView setup for auto I-V
- William - Light soaking & LabView setup
- David - Conductivity & Hardware Research
- Chen - Tauc Band gap & Hardware
- Brian - Defect Density & Team Leader
![Page 20: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/20.jpg)
Plan for the Upcoming Semester
• I-V hardware ordered by end of December
• Software implemented by end of January
• Have everything up and running and tested by middle of
February
• Once this this done, continue with device measurements
• Finalize device recipe based on results
![Page 21: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/21.jpg)
Summary• Our goal is to determine new fabrication recipes that
produce more stable a-Si solar cells• Dangling Bonds cause defects in the structure
• Leads to loss of efficiency
• Can combat this with high temp annealing and graded Boron doping
• Automated I-V measurements will save time (added feature)
• Automated I-V tool should be up and running by the end of February
• Finalized device recipe by next April
![Page 22: Improving the Stability of Hydrogenated Amorphous Silicon Solar Cells SD May 2012-09 ECpE Dept., Iowa State University Advisor/Client – Dr. Vikram Dalal](https://reader033.vdocuments.site/reader033/viewer/2022051412/55174888550346a3338b477a/html5/thumbnails/22.jpg)
QUESTIONS?Comments, Concerns, or Donations?