For wearable and implantable electronics applications, developing intrinsically stretchable polymer semiconductor is advantageous, especially in the manufacturing of large-area and high-density devices. A major challenge is to simultaneously achieve good electrical and mechanical properties for these semiconductor devices. While crystalline domains are generally needed to achieve high mobility, amorphous domains are necessary to impart stretchability. Recent progresses in the design of high-performance donor-acceptor polymers which exhibited low degrees of energetic disorder, while having high fraction of amorphous domains, appears promising for polymer semiconductors. Here, a low crystalline, i.e. near-amorphous, indacenodithiophene-co-benzothiadiazole (IDTBT) polymer and a semi-crystalline thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTT) are compared, for mechanical properties and electrical performance under strain. It is observed that IDTBT is able to achieve both high modulus and high fracture strain, and to preserve electrical functionality under high strain. Next, fully stretchable transistors are fabricated using the IDTBT polymer, and observed mobility ~0.6 cm2 V-1 s-1 at 100% strain along stretching direction. In addition, the morphological evolution of the stretched IDTBT films is investigated by polarized UV-Vis and GIXD to elucidate the molecular origins of high ductility. This work represents the first study to show the usefulness of low crystallinity microstructures of polymer semiconductor to stable device performances under strain. Our results underscored the following molecular design guidelines toward achieving intrinsically stretchable high-performance polymer semiconductor, which are: (i) low crystallinity could be achieved with long, bulky side chain attached on a tetrahedral carbon along polymer backbone, which may interrupt π-π stacking and reduce degree of crystallinity, and (ii) rigid backbone configuration is desirable to minimize energetic disorder, thus facilitating more efficient intrachain charge transport. These understanding will facilitate further improvement of next-generation low crystallinity polymer system to possess both higher charge carrier mobility and stretchability.

An intrinsically stretchable high-performance polymer semiconductor with low-crystallinity

ACS Spring Meeting 2021

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