1. Making Solar Cells D. Venkataraman (DV) Department of Chemistry Umass Amherst dv@chem.umass.edu June 29, 2010

2. Efficiency of Photovoltaic Cells Depend on Absorption in the Solar Spectrum Charge Separation Charge Mobility Charge Collection Photovoltaic Cells Exciton Active Material

3. Source: National Renewable Energy Laboratory

4. Organic Photovoltaic Devices Stability Efficiency Cost End-User Application Konarka Home Depot/BP Solar

5. What is the Problem? Si or III-V Cells Exciton diffusion distance >100 nm Excitons loosely bound Organic/Hybrid/Dye- sensitized Exciton diffusion distance <10 nm Excitons tightly bound (Frenkel Excitons) Low dielectric constant 10 nm Gregg, B. A., Excitonic solar cells. Journal of Physical Chemistry B 2003, 107 (20), 4688-4698.

6. Active Material -conjugated molecules /polymers Active Material -conjugated molecules /polymers Stability Efficiency Cost Active Layer Morphologies Active Layer Morphologies Electrode/Active Layer Interfaces Device Fabrication/ Encapsulation Device Fabrication/ Encapsulation Intrinsic Extrinsic

7. PCBM – [6,6]-phenyl-C 61 -butyric acid methyl ester Poly(3-hexylthiophene) (P3HT) Organic Photovoltaic Cells Bulk Heterojunction Cells Efficiency ~ 5% Padinger, F.; Rittberger, R. S.; Sariciftci, N. S., Effects of postproduction treatment on plastic solar cells. Advanced Functional Materials 2003, 13 (1), 85-88. Ma, W. L.; Yang, C. Y.; Gong, X.; Lee, K.; Heeger, A. J. "Thermally stable, efficient polymer solar cells with nanoscale control of the interpenetrating network morphology," Advanced Functional Materials 2005, 15, 1617-1622. 100 nm