Highly Stable Flexible Organic Electrochemical Transistors with Natural Rubber Latex Additives

Abstract

Organic electrochemical transistors (OECTs) have attracted considerable interest in the context of wearable and implantable biosensors due to their remarkable signal amplification combined with seamless integration into biological systems. These properties underlie OECTs' potential utility across a range of bioelectronic applications. One of the main challenges to their practical applications is the mechanical limitation of PEDOT:PSS, the most typical conductive polymer used as a channel layer, when the OECTs are applied to implantable and stretchable bioelectronics. In this work, we address this critical issue by employing natural rubber latex (NRL) as an additive in PEDOT:PSS to improve flexibility and stretchability of the OECT channels. Although the inclusion of NRL leads to a decrease in transconductance, mainly due to a reduced carrier mobility from 0.3 to 0.1 cm²/V·s, the OECTs maintain satisfactory transconductance, exceeding 5 mS. Furthermore, it is demonstrated that the OECTs exhibit excellent mechanical stability while maintaining their performance even after 100 repetitive bending cycles. This work, therefore, suggests that the NRL/PEDOT:PSS composite film can be deployed for wearable/implantable applications, where high mechanical stability is needed. This finding opens up new avenues for practical use of OECTs in more robust and versatile wearable and implantable biosensors.

Keywords: PEDOT:PSS; elastomer; flexible OECTs; natural rubber latex; stretchable.

Figure 1

Schematics of (a) latex/PEDOT:PSS film preparation and (b) an OECT structure.

Figure 2

(a) Optical microscope images of the OECT channels (10× magnification). Geometry of the channels: W/L = 9.5. (b) Transfer and (c) transconductance curves of the flexible OECTs. (d) Carrier mobility and (e) channel capacitance of all samples. All the measurements were performed by an Ag/AgCl gate at V_D = −0.8 V, and in (d,e), the data were obtained by applying AC modulation at the gate electrode.

Figure 3

(a) Schematic of the repetitive bending test of the flexible OECTs. (b) Transconductance curves of all samples at V_D = −0.8 V before and after bending stress. Output curves of (c) PEDOT:PSS and (d) 8% NRL/PEDOT:PSS before and after bending stress. V_G step of +0.2 V.

Figure 4

(a) Current degradation (I/I₀) as a function of elongation percentage. (b) Real-time current response when the 6% NRL/PEDOT:PSS thin film was elongated up to 70% and then returned to its original size. (c) Microscope images of samples (i) before and (ii) after stretching. Samples: PEDOT:PSS and 6% NRL/PEDOT:PSS thin films spin-coated on latex substrates.