Organic Photovoltaics Developing the science and technology of organic bulk heterojunction (BHJ) photovoltaic devices can lead to a new breed of cheap, lightweight, and flexible power sources. While tremendous progress in their power conversion efficiency has been demonstrated ( ηp ˜5% is reported for a single BHJ layer), obtaining an efficiency of ~10% (comparable to amorphous silicon) has been elusive. Yet it should be attainable if organic materials with the right absorbance can be found. As shown in the figure below, we have fabricated P3HT-C60 devices with a fill-factor that is comparable to that of a single crystalline silicon solar cell. The difference in their power conversion efficiencies (and short circuit currents) is due to the much narrower optical absorption in the organic photovoltaic device, which can be widened by the addition of other polymer(s) that are absorbing in the needed spectral range.
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 Glove box with integrated spincoater and evaporator for fabricating organic solar cells and photodetectors in an inert environment. |
 Figure 1. Characteristics of a P3HT:PCBM-C60 BHJ organic PV device (blue) and a single-crystalline silicon solar cell (red). Fill factors are nearly identical. The biggest difference is in their short-circuit current which is due to the much wider spectral range of the optical absorption in silicon, as indicated by their quantum efficiencies shown in the inset. |
“F8T2 Copolymer / C60 Bulk Heterojunction Photovoltaic Devices”, M. Ballarotto, S.S. Manoharan, W.N. Herman, and D.B. Romero, Frontiers in Optics: Organic Thin Films for Photonic Applications Symposium, San Jose, California, September 2007.
“Organic Photovoltaic Devices Based on a Block Copolymer / Fullerene Blend,” R. P. Barber, Jr., R. D. Gomez, W. N. Herman, D. B. Romero, Organic Electronics 7, 508(2006).