Investigation of Solvent-Dependent Properties of Donor and Acceptor Materials for Photovoltaic Applications

The choice of solvent and additive has been shown to affect efficiency of organic solar cell devices. To gain a basic understanding of the role of solvents in influencing overall device performance, we present a comparative study on the physical properties of donor: acceptor mixtures in different solvents. Investigations have been carried out for P3HT (poly(3-hexylthiophene-2,5-diyl)), PTB7 (poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b\u27]-dithiophene-2,6-diyl][3-fluro-2-[2-ethylhexyl)carbonyl[thieno[3,4-b]thiophenediyl]]), PC61BM ([6,6]-phenyl-C60-butyric acid methyl ester), and PC71BM ([6,6]-phenyl-C70-butyric acid methyl ester). The physical properties reported are based on UV-Vis absorption spectroscopy, resistance measurements, cyclic voltammetry measurements, and surface energy characterizations of the organic films. The solvents used to prepare the organic films are chlorobenzene and 1,2-dichlorobenzene, with and without 1,8-diiodooctane as an additive. The use of different solvents affects the intensity of absorption in the UV-Vis region and the extent of conjugation of the polymers. The surface energy measurements suggest corresponding modifications on the surface morphology of the films