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At present, the light conversion efficiencies achievable with organic photovoltaic (OPV) technology are significantly
below those seen in inorganic materials. The efficiency of OPV devices is limited by material properties; the high energy
and narrow-band absorption of organic semiconductors results in inefficient harvesting of solar radiation, while the low
charge carrier mobility in organic semiconductors limits the possible active layer thickness. Utilization of plasmonic
structures in or around the OPV active layer has been suggested as a way to achieve a higher conversion efficiency in
thin film photovoltaic devices. Our theoretical and experimental results indicate that aluminum-based plasmonic
nanostructures hold significant promise for conversion efficiency enhancement in OPV devices. The high plasma
frequency of aluminum permits a nanoparticle concentration close to the percolation threshold, which results in a
broader band of plasmonically enhanced absorbance in OPV material and better overlap between the natural absorption
bands of OPV materials and the plasmonic band of the metal nanostructure than what is achievable with gold or silver
plasmonic structures. This is demonstrated experimentally by embedding aluminum nanoparticles in P3HT:PCBM
layers, which leads to a significantly enhanced absorption over a broad range of wavelengths. While aluminum
nanoparticles are prone to oxidation, our results also indicate the path to stabilization of these particles via proper surface
functionalization.
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