Influence of Processing Solvents on Optical Properties and Morphology of a Semicrystalline Low Bandgap Polymer in the Neutral and Charged States

We present a systematic study of the morphology and absorption properties of a typical donor-acceptor polymer (PCPDTBT) with semicrystalline behavior in solution and in thin films. In-situ spectroelectrochemical data give information about the evolution of the absorption spectra from neutral to charged species. The experimental data are supported by theoretical calculations in the framework of the density functional theory (DFT). Regarding thin film structures, we show that the choice of the solvent has significant influence on the morphology in thin films: whereas CS2 and CHCl3 give rather structureless (amorphous) morphologies, films from 1-CN exhibit a clear crystalline nanofiber morphology. Accompanying UV/vis/NIR spectra of films are highly dependent on the morphology and therefore on the choice of the processing solvent. The absorption of fiber morphologies is strongly red-shifted compared to the structureless films.