According to the forecast of Allied Market Research, the flexible electronics market is projected to reach $42.48 billion by 2027. It is estimated to revolutionize the lighting technology, power integration displays, and health monitoring systems. The popularity of flexible electronics is mainly due to the unique benefits of organic materials and devices that offer cost-effectiveness, low-temperature processability, mechanical softness, and shape adaptability, [5][6][7] which are difficult to obtain with traditional, complementary-metal-oxide-semiconductor (CMOS)-based rigid systems. [8] Over the past two decades, research interest in flexible electronic systems has grown exponentially, driven by the requirements of interface softness and shape adaptability for electronics used in Internet-of-Things (IoT), [9] human-machine interfaces, [10] and advanced healthcare. [11] Although significant progress has been made in academia, the practical application of flexible electronics in the industry is limited. Presently, thin-film photovoltaics and flexible displays mainly contribute to the flexible electronics market, with a noticeable presence held by radio frequency identification (RFID) tags and medical X-ray imagers. [12] Indeed, much of the success of present flexible electronic systems rely on the performance and reliability of thin-film The development of flexible and conformable devices, whose performance can be maintained while being continuously deformed, provides a significant step toward the realization of next-generation wearable and e-textile applications. Organic field-effect transistors (OFETs) are particularly interesting for flexible and lightweight products, because of their low-temperature solution processability, and the mechanical flexibility of organic materials that endows OFETs the natural compatibility with plastic and biodegradable substrates. Here, an in-depth review of two competing flexible OFET technologies, planar and vertical OFETs (POFETs and VOFETs, respectively) is provided. The electrical, mechanical, and physical properties of POFETs and VOFETs are critically discussed, with a focus on four pivotal applications (integrated logic circuits, light-emitting devices, memories, and sensors). It is pointed out that the flexible function of the relatively newer VOFET technology, along with its perspective on advancing the applicability of flexible POFETs, has not been reviewed so far, and the direct comparison regarding the performance of POFET-and VOFET-based flexible applications is most likely absent. With discussions spanning printed and wearable electronics, materials science, biotechnology, and environmental monitoring, this contribution is a clear stimulus to researchers working in these fields to engage toward the plentiful possibilities that POFETs and VOFETs offer to flexible electronics.

Organic electrochemical transistors (OECTs) are technologically relevant devices presenting high susceptibility to physical stimulus, chemical functionalization, and shape changes—jointly to versatility and low production costs. The OECT capability of liquid‐gating addresses both electrochemical sensing and signal amplification within a single integrated device unit. However, given the organic semiconductor time‐consuming doping process and their usual low field‐effect mobility, OECTs are frequently considered low‐end category devices. Toward high‐performance OECTs, microtubular electrochemical devices based on strain‐engineering are presented here by taking advantage of the exclusive shape features of self‐curled nanomembranes. Such novel OECTs outperform the state‐of‐the‐art organic liquid‐gated transistors, reaching lower operating voltage, improved ion doping, and a signal amplification with a >104 intrinsic gain. The multipurpose OECT concept is validated with different electrolytes and distinct nanometer‐thick molecular films, namely, phthalocyanine and thiophene derivatives. The OECTs are also applied as transducers to detect a biomarker related to neurological diseases, the neurotransmitter dopamine. The self‐curled OECTs update the premises of electrochemical energy conversion in liquid‐gated transistors, yielding a substantial performance improvement and new chemical sensing capabilities within picoliter sampling volumes.