Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

Abstract

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular π-π distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

Low-Voltage, High-Performance Flexible Organic Field-Effect Transistors Based on Ultrathin Single-Crystal Microribbons

“…The AFM image of the device channel (Figure c) revealed no noticeable damage on the microribbon after bending tests. The bending test induces an interfacial strain on the single crystal and the dielectric layer, which may change the intermolecular spacing inside the single crystal leading to the degradation of the carrier mobility. , It is worth noticing that the negative shifts in the threshold voltage of the device after 0.88% tensile strain loading were reduced by 13.3% (−1.3 to −1.5 V) compared with the initial state (Figure d). It may have been caused by the cracking or buckling of the gold electrodes with an increased resistance of the electrodes, resulting in the need for a higher bias for transistor operation …”