The Photophysical Properties of Squaraine Derivatives and Their Impact upon Photovoltaic Efficiencies

Squaraine dyes provide potential on improving the efficiency of Organic photovoltaic OPV solar cell. Characterization of the photophysical properties of squaraine dyes is going to help us find the best material for our device. A series of squaraines (DESQ(OH)2, DiBSQ(OH)2, and novel DiPSQ(OH)2) in which side chains length increasing were characterized in this paper. The material photophysical properties of these squaraines were systematically characterized using various tools. Our research showed that the length of side chain plays an important role in aggregation properties of squaraines, longer side chains result in smaller exciton splitting and hence less broadened absorbance spectrum. Interestingly, DiPSQ(OH)2 which has the longest side chains unexpectedly gave the most broadened absorbance spectrum in aggregation. The impact of aggregation on fluorescence was also studied, we demonstrated that the squaraines lost fluorescence before a pure solid state was reached. We attribute this to the formation of some kind long range aggregate