High‐Performance Vertical Organic Transistors

Vertical organic thin‐film transistors (VOTFTs) are promising devices to overcome the transconductance and cut‐off frequency restrictions of horizontal organic thin‐film transistors. The basic physical mechanisms of VOTFT operation, however, are not well understood and VOTFTs often require complex patterning techniques using self‐assembly processes which impedes a future large‐area production. In this contribution, high‐performance vertical organic transistors comprising pentacene for p‐type operation and C₆₀ for n‐type operation are presented. The static current–voltage behavior as well as the fundamental scaling laws of such transistors are studied, disclosing a remarkable transistor operation with a behavior limited by injection of charge carriers. The transistors are manufactured by photolithography, in contrast to other VOTFT concepts using self‐assembled source electrodes. Fluorinated photoresist and solvent compounds allow for photolithographical patterning directly and strongly onto the organic materials, simplifying the fabrication protocol and making VOTFTs a prospective candidate for future high‐performance applications of organic transistors.     

Highly Stable Conjugated Polyelectrolytes for Water‐Based Hybrid Mode Electrochemical Transistors

Hydrophobic, self‐doped conjugated polyelectrolytes (CPEs) are introduced as highly stable active materials for organic electrochemical transistors (OECTs). The hydrophobicity of CPEs renders films very stable in aqueous solutions. The devices operate at gate voltages around zero and show no signs of degradation when operated for 10⁴ cycles under ambient conditions. These properties make the produced OECTs ideal devices for applications in bioelectronics.     

Fabric Organic Electrochemical Transistors for Biosensors

Flexible fabric biosensors can find promising applications in wearable electronics. However, high‐performance fabric biosensors have been rarely reported due to many special requirements in device fabrication. Here, the preparation of organic electrochemical transistors (OECTs) on Nylon fibers is reported. By introducing metal/conductive polymer multilayer electrodes on the fibers, the OECTs show very stable performance during bending tests. The devices with functionalized gates are successfully used as various biosensors with high sensitivity and selectivity. The fiber‐based OECTs are woven together with cotton yarns successfully by using a conventional weaving machine, resulting in flexible and stretchable fabric biosensors with high performance. The fabric sensors show much more stable signals in the analysis of moving aqueous solutions than planar devices due to a capillary effect in fabrics. The fabric devices are integrated in a diaper and remotely operated by using a mobile phone, offering a unique platform for convenient wearable healthcare monitoring.     

Complementary Logic Circuits Based on High‐Performance n‐Type Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) have been the subject of intense research in recent years. To date, however, most of the reported OECTs rely entirely on p‐type (hole transport) operation, while electron transporting (n‐type) OECTs are rare. The combination of efficient and stable p‐type and n‐type OECTs would allow for the development of complementary circuits, dramatically advancing the sophistication of OECT‐based technologies. Poor stability in air and aqueous electrolyte media, low electron mobility, and/or a lack of electrochemical reversibility, of available high‐electron affinity conjugated polymers, has made the development of n‐type OECTs troublesome. Here, it is shown that ladder‐type polymers such as poly(benzimidazobenzophenanthroline) (BBL) can successfully work as stable and efficient n‐channel material for OECTs. These devices can be easily fabricated by means of facile spray‐coating techniques. BBL‐based OECTs show high transconductance (up to 9.7 mS) and excellent stability in ambient and aqueous media. It is demonstrated that BBL‐based n‐type OECTs can be successfully integrated with p‐type OECTs to form electrochemical complementary inverters. The latter show high gains and large worst‐case noise margin at a supply voltage below 0.6 V.     

Microscopic Determination of Carrier Density and Mobility in Working Organic Electrochemical Transistors

A comprehensive understanding of electrochemical and physical phenomena originating the response of electrolyte‐gated transistors is crucial for improved handling and design of these devices. However, the lack of suitable tools for direct investigation of microscale effects has hindered the possibility to bridge the gap between experiments and theoretical models. In this contribution, a scanning probe setup is used to explore the operation mechanisms of organic electrochemical transistors by probing the local electrochemical potential of the organic film composing the device channel. Moreover, an interpretative model is developed in order to highlight the meaning of electrochemical doping and to show how the experimental data can give direct access to fundamental device parameters, such as local charge carrier concentration and mobility. This approach is versatile and provides insight into the organic semiconductor/electrolyte interface and useful information for materials characterization, device scaling, and sensing optimization.     

Vertical Organic Thin‐Film Transistors with an Anodized Permeable Base for Very Low Leakage Current

The organic permeable base transistor (OPBT) is currently the fastest organic transistor with a transition frequency of 40 MHz. It relies on a thin aluminum base electrode to control the transistor current. This electrode is surrounded by a native oxide layer for passivation, currently created by oxidation in air. However, this process is not reliable and leads to large performance variations between samples, slow production, and relatively high leakage currents. Here, for the first time it is demonstrated that electrochemical anodization can be conveniently employed for the fabrication of high‐performance OPBTs with vastly reduced leakage currents and more controlled process parameters. Very large transmission factors of 99.9996% are achieved, while excellent on/off ratios of 5 × 10⁵ and high on‐currents greater than 300 mA cm^?2 show that the C₆₀ semiconductor layer can withstand the electrochemical anodization. These results make anodization an intriguing option for innovative organic transistor design.