Nathan Duderstadt, Chemical Engineering, University of Cincinnati Stoney Sutton, Electrical Engineering, University of Cincinnati Kate Yoshino, Engineering Physics, Taylor University Advisors: Ms. Yan Jin and Dr. Vikram Kuppa 1 CEAS REU Project 4 Synthesis of Solar Cell Materials and Fabrication of Novel Polymer-Based Solar Cells Grant ID No.: DUE

Introduction  Why solar cells?  Why ORGANIC solar cells?  What is graphene and what role does it play? 2

In a semiconductor, the energy from the sun both moves the electron to an excited state, but also creates a hole (positive charge) in its place. Lowest Unoccupied Molecular Orbital 3 Highest Occupied Molecular Orbital Animation and concepts adapted from Dr. Vikram Kuppa’s presentation on organic photovoltaics Background Literature Review

4 Picture from: Deibel, Carsten, and Vladimir Dyakonov. (2010). " Polymer–fullerene Bulk Heterojunction Solar Cells.." Vol. 73.9, pp  Problems with Semiconductors :  Charge Separation  Charge Transfer  Solutions:  Bulk-heterojunction structured active layer  Graphene Organic Photovoltaic Devices

So, Why Graphene?  High aspect ratio  Conductivity  Enables lower concentration of graphene  Charge transport  Hole AND Electron  Drawbacks  Increase charge recombination  Difficult to control morphology 5 Atomic Force Microscopy Image of mg/ml 300 mesh graphene solution 5 μm

ITO + - Aluminum Charge Transport Via Graphene Animation adapted with permission from a presentation by Fei Yu 6 P3HT F8BT Electron Hole Graphene

Goals and Objectives We aim to determine how graphene makes solar cells more efficient.  Learn the basics of Organic Photovoltaic (OPV) research  Gain expertise in making and characterizing OPV cells  Differentiate between processing techniques and their influence on the solar cell  Evaluate graphene content on cell performance 7

1.Learn methods for making graphene solutions and fabricating solar cell devices 2.Prepare and analyze graphene solutions for use in solar cell polymers 3.Fabricate solar cell devices and perform thermal treatment 4.Characterize the cell through various testing 5.Conduct morphology and conductivity studies on the polymer films with different graphene concentrations 6.Report writing and presentations 8 Tasks

Task Training: Make Graphene Solution, Fabricate Solar Cell Conductivity Studies for Graphene Variations Solar Cell Fabrication and Testing Data Analysis Work on Deliverables: Paper, Presentation, Poster Week 9 Timeline and Schedule ✓✓ ✓✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

Progress Report 10

Methods 11 Making Graphene Solutions Blending P3HT and Graphene Spin Coating Procedure Electrode Deposition

Methods 12 Performance Testing Morphology Testing

Cell Structure 13 The thickness of the cell is approximately without the glass slide is approximately 500 nm in thickness.

14 Aluminum (Cathode) Indium Tin Oxide (Anode) Active layer Glass Slide Solar Cell Cell Structure

Conductivity Testing 15 Parameters:  Graphene concentration  Application method  Electrode configuration  Graphite type  Sonication time

Graphene vs. Conductivity 16

Conductivity Summary  Increase in graphene leads to increase in conductivity  0.1 mg/ml had the highest conductivity, but has potential for short-circuiting 17

Solar Cell Efficiency 18

Crystallization 19

X-ray Diffraction 20

Summary  Conductivity is improved with the use of graphene.  0.1 mg/ml graphene concentration allows for greatest amount charge transport and highest efficiency in cells.  More testing needs to be done for result confirmation. 21

References  Chen,Y., Liu,Q., Liu, Z., et al., (2009). "Polymer Photovoltaic Cells Based on Solution-Processable Graphene and P3HT." Advanced Functional Materials Journal, Vol. 19,No.6, pp  Deibel, C, and V. Dyakonov. (2010). "Polymer–fullerene Bulk Heterojunction Solar Cells," Reports on Progress in Physics, IOP, Vol. 73, No. 9, pp  Li,G., Yang,Y., and R. Zhu.(2012). "Polymer Solar Cells." NATURE PHOTONICS No.6, pp  McNeill, C.R., et al. (2007)., “Influence of Nanoscale Phase Separation on the Charge Generation Dynamics and Photovoltaic Performance of Conjugated Polymer Blends: Balancing Charge Generation and Separation.” Journal of Physical Chemistry C, Vol. 111, No. 51, pp

References  Saricifti, N.S. (2001). “Plastic Solar Cells.” Abstracts of Papers of the American Chemical Society, Vol. 222, pp. U281- U281.  Shin, M., H. Kim, and Y. Kim. (2011). “Effect of film and device annealing in polymer:polymer solar cells with a LiF nanolayer.” Materials Science and Engineering B- Advanced Functional Solid-state Materials, Vol. 176, No. 5, pp  Wan, X., Guiankui L., Lu H., and Y.Chen. (2011), “Graphene- A Promising Material for Organic Photovoltaic Cells.” Advanced Materials, Vol. 23, pp  Yu, D., et al. (2010), “Soluble P3HT-Grafted Graphene for Efficient Bilayer- Heterojunction Photovoltaic Devices.” ACS Nano, Vol. 4, No. 10, pp

Questions? Thank you! 24

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Short-circuiting 27