Bending TIPS-pentacene single crystals: from morphology to transistor performance

Abstract

Organic single crystals, with regular molecular packing and fewer structural defects, have presented record-high carrier mobility of various organic semiconductor materials, making them ideal charge-transport media for flexible devices. However, compared with organic amorphous/polycrystalline films, organic single crystals are more fragile. To utilize high-quality organic single crystals in flexible devices, the diverse response (cracks, delamination) of single crystals to bending strain should be meticulously explored, as well as the associated effects on transistor performance. Here, flexible organic field-effect transistors (OFETs) fabricated from aligned, ribbon-like single crystals of bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) are studied in different bending scenarios. With increasing tensile or compressive bending strain, the single crystal will crack or delaminate. The cracks are prone to appear faceted with a direction along the crystal ribbons, parallel to the crystallographic planes of the dense molecular packing. While interestingly, devices exhibit negligible decline in mobility even if the crystal surface has obvious cracks, which is ascribed to the intact charge transport channel. Moreover, devices show superior stability after 1000 consecutive bending cycles or keeping bent for 20 days. As such, this work confirms the potential of organic single crystals being applied to flexible transistor devices with good stability as well as high performance.