Dielectric Surface Energy-Tuned Growth and Functionality of Thin Active Layers of Molecular-Engineered Dinaphthothienothiophene

Abstract

Dinaphthothienothiophene (DNTT), being a highly π-extended heteroarene, is a promising active material for organic field-effect transistors (OFETs). However, the performance of such OFETs strongly depends on the structure and morphology (more specifically, molecular arrangement and wettability) of the active layer, especially near the active-layer/gate-dielectric interface, and thus, their improvement is of prime importance. Focusing on these aspects, a systematic investigation was carried out for low-thickness active layers of such a material by molecular engineering and dielectric surface energy (DSE) tuning. Although DSE modification creates a minor impact on the Volmer–Weber (V–W)-type growth mode of DNTT thin layers, it produces a subtle difference in the morphology of the islands, namely, more columnar (i.e., better out-of-plane crystalline coherency) islands on the lower DSE substrate. Additionally, a strong 3D herringbone packing of DNTT molecules and a weak dielectric interfacial interaction lead to a dewetted island-like structure, restricting in-plane connectivity and hole mobility within layers of low thickness. On the other hand, DSE modification (from high to low) leads to a transition in the growth mode (from V–W to nearly Stranski–Krastanov type), a major change (improvement) in the morphology (wettability) of molecular-engineered S-DNTT-C10 thin layers, and a 3-fold improvement in the hole mobility, which is the maximum observed mobility for this molecule in such a low-thickness regime. Essentially, cofacial packing of S-DNTT-C10 molecules and the relatively strong interfacial interaction lead to wetted and better π-overlapped 2D layers, which improve the hole mobility and demonstrate that a synergistic approach of molecular engineering and DSE tuning is essential to improve the performance of DNTT-based OFETs, especially in the low-thickness regime.