Enhancement of light harvesting in flexible photovoltaics

This talk describes a simple, low-cost technique to improve light harvesting in thin-film photovoltaics. Spontaneous surface buckling is a low-cost strategy for producing hierarchically corrugated surfaces while avoiding lithographic patterning and is attractive for use in mechanically flexible, thin-film technologies. Our studies use organic photovoltaics (OPVs) as model systems and our preliminary results suggest that thin film photovoltaic efficiencies experience improvements when prepared on corrugated topographies, which is supported by recent theories of light trapping in solar cells. Thus, understanding the origins of buckling instabilities and controlling such topographies is of importance for the engineering of functional textured surfaces. We investigate the origins of buckling instabilities in indium tin oxide (ITO) - polymer multilayer systems and explore strategies for controlling the morphology with the potential for reversibility and tunability. We identify the key processing parameters and also identify several origins of stress generation. By varying the thickness of the ITO and polymer layers we can prepare buckled topographies with characteristic wavelengths of 2-12 μm. We have deposited known absorber materials onto both buckled and planar surfaces and investigated the change in absorbance. Preliminary results of organic solar cells fabricated on buckled ITO/PS indicate a 20% greater power conversion efficiency compared to a comparable planar device.