High-Performance Transistor Based on Individual Single-Crystalline Micrometer Wire of Perylo[1,12-b,c,d]thiophene

Abstract

Over the past 20 years, organic field-effect transistors (OFETs) based on soluble polymers and conjugated oligomers have attracted enormous interest for the realization of organic electronic devices. 1 Pentacene as the benchmark material with a mobility beyond 1.0 cm 2 V -1 s -1 has been reported. 2 Despite the great progress in the exploration of functional organic materials for OFETs, 3 fundamental aspects of carrier transport, especially the role of solid-state packing, still remain unclear. 4 From the standpoint of bandwidth and the hopping theory of carrier conduction, a cofacial π stacking structure is expected to facilitate carrier transport. 4,5 However, most of the organic semiconductors with high mobilities have a herringbone structure which reduces the overlap. 6 On the other hand, the research work for OFETs has mainly focused on thin-film and bulk singlecrystal state. Study of micro-and nanomaterials, including fibers, ribbons, and wires, has only been recently reported because of the potential applications in integrated (opto) electronic devices due to many unique properties, such as flexibility, high photoconductivity, and nonlinear optical effects, etc. 7 Herein we present our studies of a new class of a high-performance OFET semiconductor based on perylo [1,12-b,c,d]thiophene (PET, Figure 1). The integration of a S atom into the polycyclic aromatic hydrocarbon (PAH) skeleton induces an extraordinary solid-state packing arrangement with the likelihood of double-channel superstructure, which is expected to permit effective charge transporting. Furthermore, we have grown its micrometer single-crystal wires by physical vapor transport and successfully applied them to transistors. The devices exhibit excellent performance with a high mobility up to 0.8 cm 2 V -1 s -1 .The oligothiophene and PAHs are among the most versatile and effective molecular scaffolds for organic functional materials. It is thus surprising that little effort has been devoted to exploiting sulfur heterocyclic PAHs in OFETs. We choose PET as an ideal system for investigating structure-property relationships among organic semiconductors because of its unique packing in single crystals ( Figure 1). Although its synthesis was first reported by Rogovik, 8 its electrical property is rarely studied. The crystal structure contains almost planar PET molecules stacked along the b-axis with interplanar distances of 3.47 Å, 9 in contrast to the sandwich herringbone packing of perylene crystals. Remarkably, marked S‚ ‚‚S short contacts (3.51 Å) were found between the neighboring columns related by an inversion center. The double-channel fashion is envisioned to be transformed into the facile establishment of a high-performance charge transport system.As a control result, we have first investigated the thin-film fieldeffect behavior of PET. Transistors have been fabricated on SiO 2 / Si substrate with octadecyltrichlorosilane (OTS) treatment, adopting a top-contact configuration. Only p-channel activity is observed for the device. It exhibits...

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