Impact of Mechanical Stress on Shellac-Based Organic Field-Effect Transistors Fabricated on Paper Substrates

Recent advancements in the development of organic electronics have led to the investigation of natural, biodegradable materials to achieve greener alternatives to current electronics. Shellac, a natural resin material, has recently shown great potential as a dielectric and substrate in greener organic electronics. With this material, the evaluation of other properties, such as mechanical compatibility, is necessary to explore the avenue of naturally sourced materials in the development of biodegradable, flexible electronics. This work investigates the effects of mechanical strains on the performance of functional paper-based organic field-effect transistors through compressive and tensile cyclic bending to examine the stability of the devices. Bottom-gate top-contact organic field-effect transistors were fabricated on paper using a DPP-based polymer (semiconductor) and shellac (dielectric). Finite element simulation was performed to provide a better understanding of the low and high areas of strain on the devices. Based on repetitive bending results, the devices undergoing compressive bending proved to be more stable over a period of 1000 cycles compared with the devices undergoing tensile bending. Our work confirms that the difference in Young's modulus in these multilayered device structures significantly affects morphological changes during bending, with the presence of a layer of conjugated polymer mitigating these changes compared to shellac alone. Tensile bending in bilayer systems led to nanoscale crack formation, while compressive bending resulted in consistent microscale ridge formation, maintaining both consistent depth and height over 1000 cycles. Compressive bending exhibited superior electrical performance and stability, with devices experiencing slower declines in charge mobility and threshold voltages compared to those subjected to tensile bending, while repetitive bending perpendicular to the channel pathway hindered charge carrier movement due to the formation of cracks and ridges. The direction of bending, in relation to the direction of charge transport, also influenced the performance, exhibiting anisotropic properties due to mechanical stress. Through this study, we evaluate the electrical and mechanical capabilities of paper-based organic electronics in order to continue the optimization of these environmentally friendlier devices with the objective to highlight the potential of organic electronics as greener alternatives to current technologies.