Physical Mechanism of the Mechanical Bending of High-Performance Organic TFTs and the Effect of Atmospheric Factors

In this paper, we investigate the electrical characteristics of organic thin-film transistors (OTFTs) after mechanical bending stress conducted in a range of different atmospheres. After 100,000 cycles of channel-width-axis compressive bending and a long-term fixed curve at a bending radius of R = 5 mm in an atmospheric environment, the threshold voltage (VT) is seen to shift in the positive direction. Following annealing after bending, the VT recovers to a value more negative than the initial VT for both dynamic and static bending tests. Performing bending tests in a vacuum, which eliminates the influence of the ambient atmosphere on the OTFTs, shows that the degradation of the device under atmospheric bending is dominated by two mechanisms. Gasses present in the ambient environment (humidity, N2, CO2, and O2) are introduced sequentially to understand their effect on the OTFTs. By studying the effects in the vacuum and atmosphere, we are able to separate the physical effects of mechanical bending on the OTFTs from the changes induced by exposure to environmental factors. Due to different mechanical bending conditions, the small molecules at the surface of the active layer cause different electrical characteristics. Finally, a physical model of mechanical bending and atmospheric factors for organic TFTs is proposed.