Organic Electrochemical Transistors Based on the Conjugated Polyelectrolyte PCPDTBT-SO3 K (CPE-K).

PCPDTBT-SO3 K (CPE-K), a conjugated polyelectrolyte, is presented as a mixed conductor material that can be used to fabricate high transconductance accumulation mode organic electrochemical transistors (OECTs). OECTs are utilized in a wide range of applications such as analyte detection, neural interfacing, impedance sensing, and neuromorphic computing. The use of interdigitated contacts to enable high transconductance in a relatively small device area in comparison to standard contacts is demonstrated. Such characteristics are highly desired in applications such as neural-activity sensing, where the device area must be minimized to reduce invasiveness. The physical and electrical properties of CPE-K are fully characterized to allow a direct comparison to other top performing OECT materials. CPE-K demonstrates an electrical performance that is among the best reported in the literature for OECT materials. In addition, CPE-K OECTs operate in the accumulation mode, which allows for much lower energy consumption in comparison to commonly used depletion mode devices.

High-k Fluoropolymer Gate Dielectric in Electrically Stable Organic Field-Effect Transistors.

A detailed study of a high-k fluoropolymer gate dielectric material, poly(vinylidene fluoride- co-hexafluoropropylene) [P(VDF-HFP)], is presented as a guide to achieve low operational voltage and electrically stable device performance. The large dipole moment of C-F dipoles in P(VDF-HFP) is responsible for its high dielectric constant as well as its potentially ferroelectric behavior that must be minimized to avoid hysteretic current-voltage characteristics. A range of material grades and processing conditions are explored and are shown to have a significant effect on the degree of hysteresis observed in device-transfer characteristics. The percentage of HFP monomer in the P(VDF-HFP) dielectric has an effect on gate-dependent mobility induced by disorder at the semiconductor-dielectric interface. Most importantly, we present the considerations that must be made to achieve optimal performance in multiple device architectures of organic field-effect transistors when using P(VDF-HFP) as a dielectric layer.

Solution-Processed Ion-Free Organic Ratchets with Asymmetric Contacts.

Ion-free organic ratchets with asymmetric injecting contacts (AICs) are fabricated using solution-processable organic semiconductors. Scanning Kelvin probe microscopy analysis reveals that the rectifying function is achieved via the "charge pump" mechanism. Electrical characterizations show that the device can readily operate under industrial standard radio frequency and its high-frequency performance may be enhanced through further material/device engineering. The built-in asymmetric feature exempts the devices from the complicated material design, device processing, and performance decay associated with the use of ion/semiconductor blends in ionic-organic ratchets. Thus, the AIC ratchets can deliver a persisting ratchet effect and have excellent material compatibility toward organic semiconductors.

Doping Polymer Semiconductors by Organic Salts: Toward High-Performance Solution-Processed Organic Field-Effect Transistors.

Solution-processed organic field-effect transistors (OFETs) were fabricated with the addition of an organic salt, trityl tetrakis(pentafluorophenyl)borate (TrTPFB), into thin films of donor-acceptor copolymer semiconductors. The performance of OFETs is significantly enhanced after the organic salt is incorporated. TrTPFB is confirmed to p-dope the organic semiconductors used in this study, and the doping efficiency as well as doping physics was investigated. In addition, systematic electrical and structural characterizations reveal how the doping enhances the performance of OFETs. Furthermore, it is shown that this organic salt doping method is feasible for both p- and n-doping by using different organic salts and, thus, can be utilized to achieve high-performance OFETs and organic complementary circuits.

Hole Mobility and Electron Injection Properties of D-A Conjugated Copolymers with Fluorinated Phenylene Acceptor Units.

A novel wide-gap conjugated polymer PhF2,5 (Eg = 1.9 eV) is designed to contain alternating cyclopentadithiophene and difluorophenylene unit with the goal of favoring unipolar organic field effect transistor characteristics. The higher lowest unoccupied molecular orbital energy of PhF2,5 increases the barrier to electron injection, leading to unipolar transport and higher on/off ratios, without sacrificing desirable high hole mobilities.