sam sprawls sures program mentors: dr. ina martin, prof. ken singer, physics case western reserve...
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Sam SprawlsSURES ProgramMentors: Dr. Ina Martin, Prof. Ken Singer, PhysicsCase Western Reserve UniversityUndecided MajorJuly 31, 2013
EXPLORATION OF SILANES AND POLYMERS AS
INTERFACIAL LAYERS IN ORGANIC PHOTOVOLTAICS
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Energy
• Huge part of our daily lives– American economy– American culture
• What comprises American energy?
2011 total US energy consumption by fuel type
eia.gov/totalenergy/data/annual
Renewablesources
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Photovoltaics
• Not just renewable• They do have their challenges – Materials– Disposal– Lifetime/Durability
• How can solar panels become competitive?
Efficiency
StabilityCost2011 total US energy
consumption by fuel typeeia.gov/totalenergy/data/annual
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• Electron-blocking material• PEDOT:PSS (standard) is
acidic, corrodes ITO• Research questions:
1. Can silanes be used as a substitute for PEDOT:PSS?
2. Can adding a silane layer between the PEDOT:PSS and TCO minimize the TCO degradation?
Organic Photovoltaics
TCO Layer (ITO)
Electron-blocking material
Bulk-heterojunction (P3HT:PCBM) (active layer)
Hole-blocking material (LiF)
Metal Cathode (Al)
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Silane Chemistry
• Silane hydrogen bonds with hydroxyl group• Condensation reaction leads to covalent bond• Clean transparent conductive oxide (TCO)
surface has OH (hydroxyl) groups• Water hydrolyzes the ethoxy group
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Silane Chemistry
APDMES film APTES film
4. R. Wieringa. Surface-Grafted Polyglutamate Films with Reaction-Induced Polar Order; Ph.D. Thesis: University of Groningen, 2000.
APDMES APTES
SiO2 SiO2
3-aminopropyldimethylethoxysilane 3-aminopropyltriethoxysilane
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Characterization of Silanes on Silica and TCOs
• Ellipsometry and scanning electron microscope– APTES showed rougher multilayer– APDMES showed smoother sub monolayer
• Contact angles
people.eku.edu/ritchisong/554notes1.html
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Contact Angle
0 5 10 15 20 25 30 35 40 450
10
20
30
40
50
60
70
80
Bare SilicaAPTESAPDMES
Thickness (Å)
Cont
act A
ngle
• Contact angles confirm silane modification
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Solar Cell Fabrication
• Silanize TCO (chemical bath deposition)
• (Spin coat PEDOT:PSS)• Spin coat P3HT:PCBM
absorber layer• Vapor deposit lithium
fluoride, then aluminum
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Solar Cell Characterization: IV Curves
Short circuit current (ISC)
Open circuit voltage (VOC)
Voltage at max power point (VMPP)
Current at max power point (IMPP)FF = Vmpp * Impp / (ISC * VOC)
Curr
ent (
mA)
Voltage (V)
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Solar Cells EfficienciesComparison of Silane vs. PEDOT:PSS EBL
Silane PEDOT:PSS η (% efficiency) Number of cellsNone Y 4.5 ± 0.1 9APDMES N 0.24 ± 0.01 3APTES N 0.01 ± 0.01 3None N 0.4 ± 0.3 3
• Silanes are not an effective substitute for PEDOT:PSS as an EBL
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Solar Cells EfficienciesComparison of Silane/PEDOT:PSS vs. PEDOT:PSS EBL
Silane PEDOT:PSS η (% efficiency) Number of cellsNone Y 4.5 ± 0.1 9APDMES Y 4.1 ± 0.2 6APTES Y 3.4 ± 0.5 2
• Both silanes result in decreased efficiency • APDMES (the thinner layer) has a smaller effect
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Conclusions
• APDMES had a 8 ± 6% drop from the control• APTES had a 20 ± 10 % drop from the control• Thin silane layer has moderate effects• To improve cell value, silanes need to increase
cell lifetime
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Future Work
• Lifetime/durability studies of APTES on TCOs (in progress in Prof. French’s Research Group)
• Additional silane characterization• Additional silanes (different functional groups)• Additional polymers– PVP (polyvinylpyrrolidone)
• Aging study of cell performance• Additional TCOs– Aluminum doped zinc oxide
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Acknowledgements
• My mentors, Prof. Kenneth Singer and Dr. Ina Martin
• My fellow researchers, Rosemary Bramante and Robert Minkebige
• Dominion• SURES, Sheila Pedigo and Bethany Pope
MORE Center
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SEM Images
APDMES APTES