Comparing Morphology in Dip-Coated and Spin-Coated Polyfluorene: Fullerene Films

When preparing the active layer film for organic optoelectronic devices, e.g., solar cells, spin-coating is often used for the deposition of the solution of electron donor and acceptor molecules. An alternative, among others, is to use dip-coating, where the substrate is dipped into the solution and subsequently withdrawn, all at coordinated speeds and times. In order to develop knowledge on how the final active layer morphology is influenced by preparation parameters, different coating methods are compared. In this contribution, we report on a comparative study of thin deposited films from a model system. The investigated model system is poly(9,9-dioctylfluorene) (F8, also referred to as PFO) as donor and [6,6]-phenyl-C-61-butyric acid methyl ester (PC60BM) as acceptor. Combining fluorescence and absorption spectroscopy with atomic force microscopy allows us to conclude that dipcoating offers increased possibilities to manipulate the film morphology, that the transition of the glassy F8 alpha-phase to the more ordered beta-phase is influenced by the dipping speed as well as by the blend ratio, and that the long-wavelength emission of F8 cannot stem from the oxidized keto-F8 only.