Exceptional Dewetting of Organic Semiconductor Films: The Case of Dinaphthothienothiophene (DNTT) at Dielectric Interfaces

The novel organic semiconductor dinaphthothienothiophene (DNTT) has gained considerable interest because its large charge carrier mobility and distinct chemical robustness enable the fabrication of organic field effect transistors with remarkable long-term stability under ambient conditions. Structural aspects of DNTT films and their control, however, remain so far largely unexplored. Interestingly, the crystalline structure of DNTT is rather similar to that of the prototypical pentacene, for which the molecular orientation in crystalline thin films can be controlled by means of interface-mediated growth. Combining atomic force microscopy, near-edge X-ray absorption fine structure, photoelectron emission microscopy, and X-ray diffraction, we compare substrate-mediated control of molecular orientation, morphology, and wetting behavior of DNTT films on the prototypical substrates SiO₂ and graphene as well as technologically relevant dielectric surfaces (SiO₂ and metal oxides that were pretreated with self-assembled monolayers (SAMs)). We found an immediate three-dimensional growth on graphene substrates, while an interfacial wetting layer is formed on the other substrates. Rather surprisingly, we observe distinct temporal changes of DNTT thin films on SiO₂ and the SAM-treated dielectric substrates, which exhibit a pronounced dewetting and island formation on time scales of minutes to hours, even under ambient conditions, leading to a breakup of the initially closed wetting layer. These findings are unexpected in view of the reported long-time stability of DNTT-based devices. Therefore, their future consideration is expected to enable the further improvement of such applications, especially since these structural modifications are equivalently observed also on the SAM-treated dielectric surfaces, which are commonly used in device processing.