Continuous tuning of the mechanical sensitivity of Pentacene OTFTs on flexible substrates: From strain sensors to deformable transistors

The aim of this work is to contribute to establish whether morphological properties prevail over crystal lattice organization in determining the cause for the observed sensitivity of organic semiconductors to mechanical deformations in Organic Thin Film Transistors (OTFTs). To this aim, the morphology of the active layer (made by Pentacene) of OTFTs fabricated on flexible substrates was intentionally modified by properly changing the deposition rate. By comparing Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) investigations and the electrical characterization of the devices, we can conclude that sensitivity is clearly dominated by morphological rather than lattice effects. In addition, these results suggest a simple method for obtaining, in devices based on evaporated small molecules, a fine tuning of the sensitivity to mechanical deformation that could be predictably adjusted in a range that goes from a minimum, practically negligible, value, desirable for applications in flexible electronic circuitry, to a maximum extent, useful for mechanical sensing applications.