Variation of Crystalline Polymorphs of Dinaphthothienothiophene—From Monolayer to Bulk

Dinaphthothienothiophene (DNTT) derivatives have attracted considerable attention as an active layer for organic thin-film transistors (OTFTs) due to their high carrier mobility and high stability in air. Since the charge transport in OTFTs occurs mainly in the first few monolayers on the dielectric layer, analysis of the submonolayer structure is crucial for understanding the relationship between structure and properties. Nevertheless, the thin-film structure of DNTT has long been believed to be identical to the single-crystal structure [1]. In the present study, the thickness-dependent structural evolution of this compound on silicon is revealed by high-resolution measurements of X-ray diffraction and infrared spectroscopy. These techniques apparently identify several polymorphs depending on the thickness. The most important finding is that the compound exhibits a unique molecular structure in the first monolayer at the substrate interface. This study is believed to provide an in-depth understanding of the structure-property relationship in OFETs.<br/>[1] Shioya, N. et al., Appl. Phys. Express 2020, 13, 095505.