Aluminum nanoparticles for improved OPV devices

Abstract

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.