Organic electrochemical transistors (OECTs) exhibit significant potential for applications in healthcare and human-machine interfaces, due to their tunable synthesis, facile deposition, and excellent biocompatibility. Expanding OECTs to the flexible devices will significantly facilitate stable contact with the skin and enable more possible bioelectronic applications. In this work, we summarize the device physics of flexible OECTs, aiming to offer a foundational understanding and guidelines for material selection and device architecture. Particular attention is paid to the advanced manufacturing approaches, including photolithography and printing techniques, which establish a robust foundation for the commercialization and large-scale fabrication. And abundantly demonstrated examples ranging from biosensors, artificial synapses/neurons, to bioinspired nervous systems are summarized to highlight the considerable prospects of smart healthcare. In the end, the challenges and opportunities are proposed for flexible OECTs. The purpose of this review is not only to elaborate on the basic design principles of flexible OECTs, but also to act as a roadmap for further exploration of wearable OECTs in advanced bio-applications.

Neuromorphic computing targets realizing biomimetic or intelligence systems capable of processing abundant tasks in parallel analogously to our brain, and organic electrochemical transistors (OECTs) that rely on the mixed ionic–electronic synergistic couple possess significant similarity to biological systems for implementing synaptic functions. However, the lack of reliable stretchability for synaptic OECTs, where mechanical deformation occurs, leads to consequent degradation of electrical performance. Herein, we demonstrate stretchable synaptic OECTs by adopting a three-dimensional poly(3-hexylthiophene) (P3HT)/styrene-ethylene-butylene-styrene (SEBS) blend porous elastic film for neuromorphic computing. Such architecture shows the full capability to emulate biological synaptic behaviors. Adjusting the accumulated layer numbers of porous film enables tunable OECT output and hysteresis, resulting in transition in plasticity. Especially, with a trilayer porous film, large-scale conductance and hysteresis are endorsed for efficient mimicking of memory-dependent synapse behavior. Benefitted from the interconnected three-dimensional porous structures, corresponding stretchable synaptic OECTs exhibit excellent mechanical robustness when stretched at a 30% strain, and maintain reliable electrical characteristics after 500 stretching cycles. Furthermore, near-ideal weight updates with near-zero nonlinearities, symmetricity in long-term potentiation (LTP) and depression, and applications for image simulation are validated. This work paves a universal design strategy toward high-performance stretchable neuromorphic computing architecture and could be extended to other flexible/stretchable electronics.

Non-fullerene organic solar cell (NFOSC) has attracted tremendous attention due to their great potential for commercial applications. To improve its power conversion efficiency (PCE), generally, sequential solution deposition (SSD) methods have been employed to construct the graded vertical phase separation (VPS) of the bulk-heterojunction (BHJ) active layer for efficient exciton separation and charge transition. However, a variety of orthogonal solvents used in the SSD may lead to the unpredicted change in the BHJ morphology and introduce additional defects inside the BHJ bulk thus complicate the fabrication process. Here, a simple oscillating stratification preprocessing (OSP) is developed to facilitate the formation of graded VPS among the BHJ layer. As a result, a significant improvement is obtained in PCE from 10.96% to 12.03%, which is the highest value reported among PBDB-T: ITIC based NFOSC.