Making Solar Cells D. Venkataraman (DV) Department of Chemistry Umass Amherst June 29, 2010

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

Source: National Renewable Energy Laboratory

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

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),

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

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), 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, nm