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Guoyan Zhang1

1, Georgia Institute of Technology, Atlanta, Georgia, United States

Interest in stretchable organic semiconductors stems from its competence in depositing elastic semiconducting films onto soft substrates such as silicones or artificial skin. Some promising applications of stretchable semiconductor systems are developing flexible displays, elastic sensors, artificial electronic skins (E-skins), and then integrating them together for creating intelligent electronics, such as soft robotics. Besides stretchable electrodes, the key challenge for fabricating good E-skins and other soft circuits that achieve their full potential is to obtain robust organic semiconductor components with desired mechanical properties while retaining good electronic performance under bend and stretch with high curvatures.Three typical approaches for the stretchable semiconducting films have been engineered during the last decades. The first approach based on geometric designs. This strategy demonstrates the possibility of imparting stretchability to brittle semiconducting films while maintaining their electrical properties under certain strain. However, it is still a challenge to retain electrical performance under large strains or deformations using this approach owing to the limit of the dimensions of the semiconductors and its adhesion to the elastic substrate. The second approach is directly synthesizing new semiconductors through incorporating modified side-chains or dynamic non-covalent molecular units into polymer chains. Nevertheless, the elaborate synthesis process of the intrinsically elastic semiconductor polymers and limited stretchability because of the structure hindered their further application. The third route is blending semiconductor polymers with dissimilar insulating elastomeric polymer toward stretchable semiconductor nanocomposite via continues semiconducting network. The resulting network structure in the film will enhance the polymer chain dynamics and is necessary to achieve good charge transport. These researchers have mainly focused on this nanocomposite as a strategy to obtain the stretchable devices. The understanding and control of such network formation in semiconducting films are few studies, even though the microstructure in the semiconducting films is crucially important for fabrication of stretchable electronics.
In this study, we systematically examined the morphology of the semiconducting films with different blends and its role in the mechanical and electronic performance. We found that it is extremely beneficial to use low weight fractions of the semiconducting materials to achieve both excellent stretchability and charge-transport properties in the bicomponent semiconductor-dielectric active layers of polymer transistors. The film morphology can be controlled by adjusting the ratio of the semiconducting materials and insulating materials. Correlation between microstructure and charge-transport performance has also been investigated.

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