title: Substrate-induced phase of a [1]benzothieno[3,2-b]benzothiophene derivative and phase evolution by aging and solvent vapor annealing.
abstract: Substrate-induced phases (SIPs) are polymorphic phases that are found in thin films of a material and are different from the single crystal or "bulk" structure of a material. In this work, we investigate the presence of a SIP in the family of [1]benzothieno[3,2-b]benzothiophene (BTBT) organic semiconductors and the effect of aging and solvent vapor annealing on the film structure. Through extensive X-ray structural investigations of spin coated films, we find a SIP with a significantly different structure to that found in single crystals of the same material forms; the SIP has a herringbone motif while single crystals display layered π-π stacking. Over time, the structure of the film is found to slowly convert to the single crystal structure. Solvent vapor annealing initiates the same structural evolution process but at a greatly increased rate, and near complete conversion can be achieved in a short period of time. As properties such as charge transport capability are determined by the molecular structure, this work highlights the importance of understanding and controlling the structure of organic semiconductor films and presents a simple method to control the film structure by solvent vapor annealing.
authors.affiliation: Département de Physique, Faculté des Sciences, Université Libre de Bruxelles CP223, Campus de la Plaine, 1050 Brussels, Belgium.
authors.forename: Andrew O F
authors.initials: AO
authors.lastname: Jones
authors.forename: Yves H
authors.initials: YH
authors.lastname: Geerts
authors.forename: Jolanta
authors.initials: J
authors.lastname: Karpinska
authors.forename: Alan R
authors.initials: AR
authors.lastname: Kennedy
authors.forename: Roland
authors.initials: R
authors.lastname: Resel
authors.forename: Christian
authors.initials: C
authors.lastname: Röthel
authors.forename: Christian
authors.initials: C
authors.lastname: Ruzié
authors.forename: Oliver
authors.initials: O
authors.lastname: Werzer
authors.forename: Michele
authors.initials: M
authors.lastname: Sferrazza
keywords: X-ray diffraction; organic electronics; organic thin films; polymorphism; substrate-induced phase