A crucial aspect of the fabrication of optoelectronic devices based on organic small molecules is the understanding of the growth and the postgrowth effects in thin films of these molecules. One of the factors that can negatively impact the performance of a given material despite its suitability in terms of electrical and optical properties is the dewetting of the produced film. The present work reveals the growth behavior and the postgrowth effects in thin films of dibenzoselenadiazoloquinoxaline (dbSeQ), a new organic semiconductor, thin films of which tend to dewet on Si/SiOx substrates. To overcome this limiting feature, we deposited thin films of dbSeQ in combination with well-studied organic semiconductors, namely, diindenoperylene (DIP) and pentacene (PEN) at room and low substrate temperatures (RT and LT, respectively). Using X-ray scattering techniques, i.e. grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR), we characterized the growth and the annealing of thin films in situ in real time. The combination of atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS) and UV–Vis absorption spectroscopy provides additional important information about the morphology, structure and optical properties of the deposited films ex situ. We found that in thin films grown at RT, dbSeQ molecules predominantly adopt an edge-on orientation, which leads to formation of pronounced islands on the substrate. This growth mode of dbSeQ was also observed in bilayer and codeposited films with DIP and PEN. In case of LT growth, dbSeQ molecules adopt a lying orientation that in turn results in a very smooth dbSeQ layer. Further findings reveal pronounced structural and morphological changes in LT-grown films during their annealing to RT. These results are of great importance for understanding the growth of organic semiconductors incorporating fused 1,2,5-selenadiazoles and the factors that influence it, which can be used for the future development of thin film-based devices.
Pylypenko et al. (Wed,) studied this question.