February 14, 2013
Rochester Institute of Technology
Squaraines for mechanistic studies and improved efficiency
of bulk heterojunction organic photovoltaic devices
Organic photovoltaic devices promise low-cost, flexible options for future renewable energy. Yet their efficiencies are currently too low compared to other solar cell technologies. In order to improve device efficiency we must understand the mechanism of operation of these "bulk heterojunction" photovoltaics. A brief overview of the mechanism for operation will be provided. I will then talk about one strategy to increase device efficiency through a broader spectral overlap between the device absorbance and the solar spectrum. I will describe a number of characterization techniques (e.g. cyclic voltammetry, Fluorescence lifetime) of potential new Squaraine materials such that their candidacy for effective use can be properly determined. Squaraines can be chemically modified such that their electronic properties remain more or less intact while their solid state packing properties can be substantially and systematically modified.
I will describe in more detail one particularly interesting Squaraine, whose aggregation properties in the solid state offer us the ability to understand how the electron transfer process at the bulk heterojunction may be a critical bottleneck that ultimately stifles power conversion efficiencies.
One approach to replacing ITO as the transmissive conducting layer is to use thin films made of single-walled carbon nanotubes (SWCNT). SWCNT also offer options for the active layers of bulk heterojunction devices. Yet SWCNT cannot be easily spin- or spray-coated because their dispersions in a variety of solvents are unstable. I will present fluorescence quenching measurements used to investigate the fundamental understanding of interactions between organic materials and SWCNT. The goal is to find more appropriate surfactants such that SWCNT dispersion limits are increased and hence SWNCT manipulation is improved.