Influence of solvent and solvent additive on the morphology of PTB7 films probed via X-ray scattering.

Films of the semiconducting polymer poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] with 40% fluorinated monomers, denoted PTB7-F40, are spin coated out of different solvents onto PEDOT:PSS films. The influence of the used solvents chlorobenzene, 1,2-dichlorobenzene, and 1,2,4-trichlorobenzene as well as the influence of the additive 1,8-diiodooctane (DIO) is probed with grazing incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS). As seen with GISAXS, without DIO, the films are homogeneous and show roughness correlation with the PEDOT:PSS film surface. With DIO, an inner film structure with a size of 50-75 nm is found and the roughness correlations weaken. In addition, as seen in GIWAXS, the crystalline part of the films is influenced by the used solvent if DIO is added.