Organic field-effect transistors (OFETs) represent a critical component in the evolution of flexible and wearable electronics due to their compatibility with low-temperature processing, mechanical flexibility, and tunable electronic properties. These devices rely on organic semiconductors as the active layer, which can be deposited on a variety of substrates, including plastics, paper, and textiles. The operational principle of OFETs is analogous to conventional FETs, where charge carriers are modulated by an applied gate voltage. However, the unique properties of organic materials introduce distinct charge transport mechanisms, fabrication challenges, and application opportunities.

The choice of organic semiconductor materials is central to OFET performance. Conjugated polymers and small molecules dominate this field due to their π-electron delocalization, which enables charge transport. Common polymer semiconductors include poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), which exhibit hole mobilities in the range of 0.1 to 1 cm²/Vs. Small molecules such as pentacene and rubrene demonstrate higher mobilities, often exceeding 10 cm²/Vs in single-crystal form, but face challenges in uniform thin-film deposition. Recent advancements in non-fullerene acceptors and donor-acceptor copolymers have further improved charge transport, with some materials achieving mobilities above 5 cm²/Vs in solution-processed films.

Fabrication methods for OFETs are tailored to the unique requirements of organic semiconductors. Solution processing techniques, including spin-coating, inkjet printing, and blade coating, are widely used due to their scalability and compatibility with flexible substrates. Vacuum deposition is employed for high-purity small-molecule films, particularly in top-gate or bottom-gate architectures. The dielectric layer, often composed of polymers like poly(methyl methacrylate) (PMMA) or inorganic oxides, must exhibit low leakage and high capacitance to ensure efficient gate control. Electrode materials, typically gold or conductive polymers such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), are selected for their work function compatibility with the organic semiconductor.

Charge transport in OFETs is governed by hopping mechanisms due to the localized nature of electronic states in organic materials. Unlike inorganic semiconductors with band-like transport, charge carriers in organic semiconductors move between localized sites via thermally activated hopping. Disorder in the film, including energetic and structural inhomogeneities, significantly impacts mobility. High-performance OFETs require optimized molecular packing, reduced grain boundaries, and minimized trap states. Recent studies highlight the role of side-chain engineering and post-deposition treatments, such as solvent vapor annealing, in enhancing crystallinity and charge transport.

Performance limitations in OFETs arise from several factors. Contact resistance at the semiconductor-electrode interface often dominates device performance, particularly when charge injection barriers are present. Environmental stability is another challenge, as oxygen and moisture can degrade organic semiconductors, necessitating encapsulation strategies. Bias stress effects, where prolonged gate voltage application leads to threshold voltage shifts, further limit operational stability. Advances in material design, such as the incorporation of fluorinated side chains, have improved environmental stability, while interface engineering has reduced contact resistance.

Flexible electronics represent the most promising application area for OFETs. Their compatibility with large-area, low-cost manufacturing makes them ideal for rollable displays, electronic skin, and wearable sensors. In displays, OFETs serve as backplane transistors for active-matrix organic light-emitting diode (AMOLED) arrays, enabling lightweight and bendable screens. Sensors based on OFETs exploit their sensitivity to mechanical strain, chemical vapors, or biological analytes, making them suitable for health monitoring and environmental sensing. Recent demonstrations include OFET-based pressure sensors with sub-100 Pa sensitivity and glucose sensors for non-invasive diagnostics.

Recent advancements in organic semiconductors have focused on improving mobility, stability, and processability. The development of high-k polymer dielectrics has enabled low-voltage operation, reducing power consumption. New donor-acceptor polymers with fused-ring backbones exhibit reduced energetic disorder, leading to mobilities exceeding 10 cm²/Vs in some cases. Researchers have also explored mixed ionic-electronic conduction in OFETs, enabling applications in bioelectronics where ion-to-electron transduction is critical. Another notable trend is the integration of OFETs with emerging memory technologies, such as resistive switching layers, for flexible non-volatile memory applications.

The future of OFETs lies in addressing remaining challenges while expanding their application scope. Improving environmental stability without compromising performance remains a key goal, with encapsulation techniques and intrinsically stable materials under investigation. Scalable manufacturing methods, such as roll-to-roll printing, are being refined to enable commercial production. Emerging applications in neuromorphic computing leverage the tunable synaptic behavior of OFETs, offering energy-efficient alternatives for artificial neural networks. As material design and device engineering continue to advance, OFETs will play an increasingly vital role in the next generation of flexible and wearable electronics.

In summary, OFETs represent a versatile and rapidly evolving technology with unique advantages for flexible electronics. Their performance is intrinsically linked to the properties of organic semiconductors, which continue to improve through molecular design and processing optimization. While challenges remain in stability and contact resistance, ongoing research is addressing these limitations through innovative materials and device architectures. The broad applicability of OFETs, from displays to biosensors, underscores their potential to enable new functionalities in electronics that are lightweight, conformable, and cost-effective.