Size Control Over Semiconducting Materials for Organic Electronics Collen Leng 1, Jeffrey M. Mativetsky 1, John E. Anthony 2, Yueh-Lin Loo 1 1.Chemical and Biological Engineering, Princeton University 2.Chemistry, University of Kentucky

Why Organic Electronics? Low cost solution processing Mechanical flexibility Lightweight

Increasing Efficiencies of Organic Solar Cells Increase charge transport –molecular packing and orientation Increase surface area between donor and acceptor materials

Make organic semiconducting nanowires –Size control of electron acceptors and donors –Increase interfacial surface area –Wire-like structures for efficient charge transport Method: templating using aluminum oxide membranes Project Goal Scanning electron micrographs of aluminum oxide membrane Cross-section of membrane Top view of membrane Cross-section (zoomed in) 300 μm 2 μm

Set-up -Allow solution to penetrate membrane from I-tube -Cap off I-tube to sustain internal pressure and prevent the solution from completely flowing through membrane I-tube membrane Viton O-rings Teflon gasket solution closed air rubber stopper Electron donor: ethyl-TES-ADT

Nanowires Inside Porous Membrane Cross-sectional views 15 μm 2 μm 10 μm 15 μm

Extracting Nanowires NaOH: dissolve membrane, free nanowires Options for removing NaOH and alumina: 1.Vacuum filtration 2. Centrifuge Nanowire mixtureViton O-rings Air out Polycarbonate filter Fritted glass

Extracted Nanowires 10 μm Bundles of ethyl-TES-ADT nanowires Close-up of ethyl-TES-ADT nanowires 1 μm

Nanowires on Glass High-density nanowires on glass: Close-up of wires: 30 μm 100 μm

TEM & Electron Diffraction Occasional polycrystalline structures Bundle of ethyl-TES-ADT nanowires in a transmission electron microscope (TEM) Electron diffraction of nanowires to the left shows some polycrystallinity

PCBM and P3HT Nanowires? Nanowires of other materials can be made. [6,6]phenyl-C61-butyric acid methyl ester (PCBM) nanowires: - the most commonly used electron acceptor 3 μm

Future Plans -Structural studies: -Thinner nanowires ( nm diameters) to better match exciton diffusion lengths -Crystallization to help electron transport -Structural characterization (Grazing Incidence X-ray Diffraction) -Photovoltaic studies: -Map photoexcited charge generation at donor-acceptor nanowire interfaces (Kelvin Probe Force Microscopy, Photoluminescence) -Nanowire-based solar cells

Acknowledgements Professor Loo Jeff Mativetsky Gerry Poirier Loo Lab PEI/Siebel Energy Grand Challenge