© 2015 American Chemical Society. Thin films of organic semiconductors have been widely studied at different length scales for improving the electrical response of devices based on them. Hitherto, a lot of knowledge has been gained about how molecular packing, morphology, grain boundaries, and defects affect the charge transport in organic thin film transistors. However, little is known about the impact of an electric field on the organic semiconductor microstructure and the consequent effect on the device performances. To fill this gap, we investigated the evolution of the structure of pentacene thin film transistors during device operation by in situ real time X-ray diffraction measurements and theoretical calculations. We observed for the first time the occurrence of a reversible structural strain taking place during the bias application mainly due to reorientation at the terrace edges of monolayer islands under the effect of electrical field. Strain exhibits the same trend of the threshold voltage hinting to the existence of a direct correlation between the phenomenon of bias stress and the structural modification.

The authors acknowledge A. Shehu for his collaboration at the early stage of the project, F. Borgatti for the fruitful discussion, J. R. Plaisier, G. Zerauschek and A. Lausi for optimizing the experimental setup at the MCX-ELETTRA beamline, and V. L.R. Jacques and P. Evans for technical support at the ID01-ESRF beamline. Financial support for this research was by the National Project N−CHEM, Flagship NANOMAX, by the DGI (Spain) with Project BE-WELL CTQ2013-40480-R, Generalitat de Catalunya (2014-SGR-17), the ERC StG 2012-306826, and by the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBERBBN).

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