Thermal expansion and strain on organic thin films: Unravelling the effect of thickness and intermolecular interactions

The charge transport properties of Organic Field-Effect Transistors (OFETs) are largely determined by the interface between the dielectric and the organic semiconductor (OSC), where the conducting channel forms. While high crystallinity in OSC thin films is known to enhance mobility, the impact of strain on device reliability remains underexplored and poorly understood. Strain may play a crucial role in achieving consistent high performance and morphological stability in OSCs. In prior studies of thermal annealing on Ph-BTBT-C10 thin films, a [1]benzothieno[3,2-b]benzothiophene (BTBT) derivative, we observed interfacial strain and anisotropic thermal expansion, prompting further investigation into how strain relates to molecular packing and thickness. This proposal focuses on in situ GIWAXS studies during thermal annealing aiming to: i) examine the effect of film thickness (from a few monolayers to several layers), ii) explore the influence of side groups in different BTBT derivatives on intermolecular interactions, and iii) assess the impact of thermal expansion coefficient (CTE) mismatches between the substrate and OSC by comparing results from two substrates with different CTEs. These findings will be correlated with electrical performance in OFETs, providing insights into how side groups affect thermal behavior and strain accommodation in OSC materials.