Session:

Flexible electronic devices with optical transparency exhibit biocompatibility and increase the versatility of measurement methods, such as multimodal sensing that enables simultaneous usage in optical, electrical, and ionic methods. In this study, we develop fully transparent and flexible organic electrochemical transistors (OECTs) using transparent conductors of Ag nanowires (AgNWs) and conductive polymers. They demonstrate the feasibility of multimodal acquisition of biological signals. In addition, stretchable materials are newly developed to construct fully transparent and stretchable OECTs, which can contribute to the creation of next-generation medical sensors.
Sensors for use as personal healthcare devices that can measure biological signals continuously and for a long time for the early detection of diseases have been expected [1-2]. OECTs can be used to fabricate circuits suitable for such biological signal measurements owing to their advantages of low operating voltage, mechanical flexibility, and high mutual transconductance [3]. In particular, the high mechanical flexibility decreases the wearing discomfort because flexible biological tissues change their shape. Additionally, if the device has high transparency, it enables multimodal sensing that can utilize electronic, optical, and ionic methods simultaneously, as well as miniaturization through the stacking of devices. Therefore, stretchable and transparent conductors and semiconductor materials for electronic devices can facilitate a new electronic design.
In this study, we develop highly transparent and flexible OECTs using AgNWs and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) [4]. High bending durability and high visible transmittance (>90%) are achieved by controlling the orientations of the AgNWs used for wiring. Furthermore, additive layering techniques, such as printing and lamination processes, are employed to decrease damage to the nanomaterials constituting the OECT. In addition, these transparent and flexible OECTs exhibit properties comparable to those of conventional opaque OECTs. Consequently, low-noise measurements of brain waves and ion concentrations, as well as simultaneous optical measurements of blood flow and pulse waves, are feasible and a step toward the quantification of human stress.
Furthermore, stretchable channel materials are developed to create more flexible OECTs. A patterning process of AgNW-based conductors and semiconductors on elastomers is concurrently developed to fabricate fully stretchable and transparent OECTs. In particular, the stretchable conductors and channel materials exhibit durability under 50%–100% strain; thus, they can be used for fully transparent and stretchable sensors for the long-term and multimodal assessment using electrophysiological, optical, and ionic methods.

References
[1] S. M. A. Iqbal et al., npj Flex. Electron., 2021, 5, 9
[2] W. Heng et al., Adv. Mater., 2021, 34, 2107902
[3] J. Rivnay et al., Nat. Rev. Matt., 2018, 3, 17086
[4] A. Takemoto et al., Adv. Sci., 2022, 10, 2204746

Co-Author(s): Teppei Araki (SANKEN (The Institute of Scientific and Industrial Research)), Shoya Matsuda (SANKEN (The Institute of Scientific and Industrial Research)), Naoko Kurihira (SANKEN (The Institute of Scientific and Industrial Research)), Mihoko Akiyama (SANKEN (The Institute of Scientific and Industrial Research)), Takafumi Uemura (SANKEN (The Institute of Scientific and Industrial Research)), Tsuyoshi Sekitani (SANKEN (The Institute of Scientific and Industrial Research))

Takaaki Abe

Appearances