1. Sam Sprawls SURES Program Mentors: Dr. Ina Martin, Prof. Ken Singer, Physics Case Western Reserve University Undecided Major July 31, 2013 EXPLORATION OF SILANES AND POLYMERS AS INTERFACIAL LAYERS IN ORGANIC PHOTOVOLTAICS 1

2. 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 Renewable sources 2

3. Photovoltaics Not just renewable They do have their challenges – Materials – Disposal – Lifetime/Durability How can solar panels become competitive? Efficiency StabilityCost 2011 total US energy consumption by fuel type eia.gov/totalenergy/data/annual 3

4. 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 4

5. 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 5

6. 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. APDMESAPTES SiO 2 3-aminopropyldimethylethoxysilane 3-aminopropyltriethoxysilane 6

7. 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 7

8. Contact Angle 8 Contact angles confirm silane modification

9. Solar Cell Fabrication Silanize TCO (chemical bath deposition) (Spin coat PEDOT:PSS) Spin coat P3HT:PCBM absorber layer Vapor deposit lithium fluoride, then aluminum 9

10. Solar Cell Characterization: IV Curves Short circuit current (I SC ) Open circuit voltage (V OC ) Voltage at max power point (V MPP ) Current at max power point (I MPP ) 10 FF = V mpp * I mpp / (I SC * V OC ) Current (mA) Voltage (V)

11. SilanePEDOT:PSSη (% efficiency)Number of cells NoneY4.5 ± 0.19 APDMESN0.24 ± 0.013 APTESN0.01 ± 0.013 NoneN0.4 ± 0.33 11 Silanes are not an effective substitute for PEDOT:PSS as an EBL

12. SilanePEDOT:PSSη (% efficiency)Number of cells NoneY4.5 ± 0.19 APDMESY4.1 ± 0.26 APTESY3.4 ± 0.52 12 Both silanes result in decreased efficiency APDMES (the thinner layer) has a smaller effect

13. 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 13

14. 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 14

15. 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 15

16. SEM Images APDMESAPTES 16