Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors

With the aim of understanding the relationships between organic small molecule field-effect transistors （FETs） and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly （3-hexylthiophene） （RR-P3HT） field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is largely related to the morphology of the organic active layer. We observe that the change trends of the surface morphologies （average size and average roughness） of pentacene and RR-P3HT thin films are mutually opposite, as the thickness of the organic layer increases. Further, we demonstrate that the change trends of the field-effect mobilities of pentacene and RR-P3HT FETs are also opposite to each other, as the thickness of the organic layer increases within its limit.

High performance pentacene organic field-effect transistors consisting of biocompatible PMMA/silk fibroin bilayer dielectric

Pentacene organic field-effect transistors （OFETs） based on single- or double-layer biocompatible dielectrics of poly（methyl methacrylate） （PMMA） and/or silk fibroin （SF） are fabricated. Compared with those devices based on sin- gle PMMA or SF dielectric or SF/PMMA bilayer dielectric, the OFETs with biocompatible PMMA/SF bilayer dielectric exhibit optimal performance with a high field-effect mobility of 0.21 cm2/Vs and a current on/off ratio of 1.5 × 104. By investigating the surface morphology of the pentacene active layer through atom force microscopy and analyzing the elec- trical properties, the performance enhancement is mainly attributed to the crystallization improvement of the pentacene and the smaller interface trap density at the dielectric/organic interface. Meanwhile, a low contact resistance also indicates that a good electrode/organic contact is formed, thereby assisting the performance improvement of the OFET.

Methylthio side-chain modified quinoidal benzo-[1,2-b:4,5-b']dithiophene derivatives for high-performance ambipolar organic field-effect transistors

Quinoidal small molecule semiconductors hold huge potential in ambipolar organic field-effect transistors(OFETs)and organic spintronic devices.Here,two quinoidal molecules with methylthio side chains were synthesized to develop molecular semiconductors with high ambipolar mobility,designated QBDTS and QTBDTS.The theoretical calculation results reveal that QBDTS has a closed-shell structure while QTBDTS showed an open-shell structure with a biradical character(y0)of 0.46 and its magnetic properties were further investigated using electron paramagnetic resonance(EPR)and superconducting quantum interference device(SQUID)methods.The methyl side chains showed a large impact on the molecular orbital levels.The HOMO/LUMO levels of QBDTS and QTBDTS were measured to be-5.66/-4.56 and-5.27/-4.48 eV,respectively,which are favorable for ambipolar charge transport in OFETs.Importantly,the spin-coated QBDTS displayed hole and electron mobilities of 0.01 and 0.5 cm^(2)V^(-1)s^(-1)while QTBDTS showed a record high hole mobility of 1.8 cm^(2)V^(-1)s^(-1)and electron mobility of 0.3 cm^(2)V^(-1)s^(-1).Moreover,comparative studies of the thin film morphologies also manifested the beneficial influence of methyl side chains on film crystallinity and molecule orientation.These results strongly proved that methyl side chain engineering can be a simple but efficient strategy for modulating electronic properties and molecular stacking behaviors.This work also represents a big advancement for quinoidal molecular semiconductors in ambipolar OFET applications.

Interfacial molecular screening of polyimide dielectric towards high-performance organic field-effect transistors

The compatibility of the gate dielectrics with semiconductors is vital for constructing efficient conducting channel for high charge transport.However,it is still a highly challenging mission to clearly clarify the relationship between the dielectric layers and the chemical structure of semiconductors,especially vacuum-deposited small molecules.Here,interfacial molecular screening of polyimide(Kapton)dielectric in organic field-effect transistors(OFETs)is comprehensively studied.It is found that the semiconducting small molecules with alkyl side chains prefer to form a high-quality charge transport layer on polyimide(PI)dielectrics compared with the molecules without alkyl side chains.On this basis,the fabricated transistors could reach the mobility of 1.2 cm^(2) V^(−1)s^(−1) the molecule with alkyl side chains on bare PI dielectric.What is more,the compatible semiconductor and dielectric would further produce a low activation energy(E_(A))of 3.01 meV towards efficient charge transport even at low temperature(e.g.,100 K,0.9 cm^(2) V^(−1)s^(−1)).Our research provides a guiding scheme for the construction of high-performance thin-film field-effect transistors based on PI dielectric layer at room and low temperatures.

Sensitive sensors based on bilayer organic field-effect transistors for detecting lithium-ion battery electrolyte leakage

The leakage of flammable and explosive lithiumion battery(LIB) electrolytes can be one of the early symptoms of battery malfunction and can even lead to spontaneous battery combustion or electric car explosion. Therefore, it is necessary to find a rapid and simple method to monitor any leakage of LIB electrolytes. However, LIB electrolytes are generally composed of volatile and redox neutral carbonate solvents. Trace amounts of electrolyte leakage are difficult to detect effectively and rapidly by existing compact sensors.Here, for the first time, we propose a strategy that cooperatively combines the sensitivity of organic field-effect transistors(OFETs) and the selectivity of biurea receptors to detect LIB electrolyte leakage. The fabricated sensors show much higher sensitivity than the pristine sensor without receptors, and the detection limit of the sensor toward diethyl carbonate was 1.4 ppm. Trace amounts of LIB electrolyte leakage could be detected effectively in seconds, with 200 n L electrolyte leakage leading to a 3% response. We also demonstrate the real-time detection of LIB electrolyte leakage by our OFET sensors. The excellent performance of the receptorcoated OFET sensor makes it a good candidate for LIB safety monitoring and provides a promising platform for the development of sensing technologies.

Organic Field-effect Transistors Based on Tetrathiafulvalene Derivatives

1 Restults Tetrathiafulvalene (TTF) and its derivatives have been extensively investigated in the field of organic conductors and superconductors since 1973. Recently, their application in organic field-effect transistors (OFETs) has attracted considerable attention. So far, on the one hand, the fabrication techniques of the TTF-based FETs have been primarily limited to high vacuum evaporation, which is a relatively expensive process. On the other hand, low FET performances, such as the low on/off ratio...

A Facile Photo-cross-linking Method for Polymer Gate Dielectrics and Their Applications in Fully Solution Processed Low Voltage Organic Field-effect Transistors on Plastic Substrate

A simple and effective photochemical method was developed for cross-linking of polymer gate dielectrics. Laborious synthetic processes for functionalizing polymer dielectrics with photo-cross-linkable groups were avoided. The photo-cross-linker, BBP-4, was added into host polymers by simple solution blending process, which was capable of abstracting hydrogen atoms from polymers containing active C--H groups upon exposure to ultraviolet （UV） radiation. The cross-linking can be completed with a relatively long wavelength UV light （365 nm）. The approach has been applied to methacrylate and styrenic polymers such as commercial poly（methylmethacrylate） （PMMA）, poly（iso-butylmethacrylate） （PiBMA） and poly（4-methylstyrene） （PMS）. The cross-linked networks enhanced dielectric properties and solvent resistance of the thin films. The bottom-gate organic field-effect transistors （OFETs） through all solution processes on plastic substrate were fabricated. The OFET devices showed low voltage operation and steep subthreshold swing at relatively small gate dielectric capacitance.

Dual-function surfactant strategy for two-dimensional organic semiconductor crystals towards high-performance organic field-effect transistors

Two-dimensional(2D)organic semiconductor crystals(OSCs)are ideal platforms for investigating fundament materials as well as achieving high-performance organic field-effect transistors(OFETs).The surfactants played an important role in the 2DOSCs growth in previous studies.However,residual surfactants may cause performance degradation of devices.Herein,a simple and effective dual-function surfactant strategy is used to control the growth of large-area few-molecular-layer 2DOSCs.The introduction of phosphatidylcholine decreases the interfacial tension and improves the crystal growth dynamics,resulting in high-quality and large-area few-molecular-layer 2,6-bis(4-hexylphenyl)anthracene(C_6–DPA)2DOSC.The additive also passivates charge traps,boosting the mobility of 2DOSC-based OFETs by almost threefold.This method is also suitable for the growth of various high-quality 2DOSCs,opening up a new avenue for high-quality 2DOSCs towards high-performance OFETs.

Enhanced performance of C_(60) N-type organic field-effect transistors using a pentacene passivation layer

We investigated the properties of C_（60）-based organic field-enect transistors（OFETs）（？） a pentacene passivation layer inserted between the C_（60） active layer and the gate dielectric.After modification of the pentacene passivation layer,the performance of the devices was considerably improved compared to C_（60）-based OFETs with only a PMMA dielectric.The peak field-effect mobility was up to 1.01 cm^2/（V·s） and the on/off ratio shifted to 10~4.This result indicates that using a pentacene passivation layer is an effective way to improve the performance of N-type OFETs.

Tetramethylammonium Iodide Additive for Enhancing the Charge Carrier Mobilities of Diketopyrrolopyrrole-Based Conju-gated Polymer in Ambipolar Organic Field-Effect Transistors

Diketopyrrolopyrrole(DPP)is one of the most promising building blocks for constructing polymer semiconductors with high charge-carrier mobilities in organic field-effect transistors(OFETs).In this study,a novel DPP-based conjugated polymer,PDPPy-BDD,was designed and synthesized.The ambipolar field-effect transistor characteristics were realized with the average hole and electron mobilities of 3.5×10^(-3)and 3.07×10^(-2)cm^(2)V^(-1)s^(-1),respectively.Both the hole and electron mobilities could be successfully en-hanced by using a tetramethylammonium iodide(NMe4l)additive.Such an enhancement was attributed to the formation of stronger interchainπ-πstackings,the weakening of the face-on packing orientation in the thin film state,and the higher channel conductivi-ties in the OFETs.

Photoresponsive organic field-effect transistors involving photochromic molecules

In recent years,organic field-effect transistors（OFETs） with high performance and novel multifunctionalities have attracted considerable attention.Meanwhile,featured with reversible photoisomerization and the corresponding variation in color,chemical/physical properties,photochromic molecules have been applied in sensors,photo-switches and memories.Incorporation of photochromic molecules to blend in the device functional layers or to modify the interfaces of OFETs is common way to build photo-transistors.In this review,we focus on the recent advantages on the study of photoresponsive transistors involving one of three typical photochromic compounds spiropyran,diarylethene and azobenzene.Three main strategies are demonstrated in detail.Firstly,photochromic molecules are doped in active layers or combined with semiconductor structure thus forming photoreversible active layers.Secondly,the modification of dielectric layer/active layer interface is mainly carried out by bilayer dielectric.Thirdly,the photo-isomerization of self-assembled monolayer（SAM） on the electrode/active layer interface can reversibly modulate the work functions and charge injection barrier,result in bifunctional OFETs.All in all,the combination of photochromic molecules and OFETs is an efficient way for the fabrication of organic photoelectric devices.Photoresponsive transistors consisted of photochromic molecules are potential candidate for real applications in the future.

Highly responsive biosensors based on organic field-effect transistors under light irradiation

High responsivity and sensitivity play essential roles in the development of organic field-effect transistors(OFETs)-based biosensors with regard to biological detections,particularly for disease diagnosis.Nonetheless,how to design a biosensor which improves these two outstanding properties while achieving low cost,easy processing,and time saving is a daunting challenge.Herein,a novel biosensor based on OFET with copolymer thin film,whose surface is illuminated with a suitable light beam is reported.This film can be used as both an organic semiconductor material and as a photoelectric active material.Due to amplification of signals as a result of the film’s strong response to light,the biosensor possesses higher responsivity and sensitivity compared to dark condition and even realizes a maximum responsivity of up to 10^(3)for alpha-fetoprotein(AFP)detection.The simple combination of light and transistor builds a bridge between photoelectric effect and biological system.In addition,the emergence of more excellent photoelectric active materials is expected to pave a way for ultrasensitive bio-chemical diagnostic tools.

Recent Progress in Donor-Acceptor Type Conjugated Polymers for Organic Field-effect Transistors

The recent progress in the design and synthesis of high-performance donor-acceptor conjugated polymeric semiconducting materials is reviewed from the perspective of multiscale structures.The multiscale of conjugated polymers is from the primary one-dimensional polymer molecular scale to the secondary polymer-chains interaction scale,and then to the tertiary polymer aggregate scale.This review focuses on the design and synthesis of polymer molecules,proposes new classification rules,and rationally summarizes the design strategies and modulation methods of polymers.We describe the recent progress from these three aspects:(1)the modification ofπ-conjugated backbone,(2)the evolution of the polymerization methods,and(3)the regulation of aggregate-state structure.

Effects of gate dielectric thickness and semiconductor thickness on device performance of organic field-effect transistors based on pentacene

In this paper,the pentacene-based organic field-effect transistors(OFETs)with poly(methyl methacrylate)(PMMA)as gate dielectrics were fabricated,and the effects of gate dielectric thickness and semiconductor thickness on the device performance were investigated.The optimal PMMA thickness is in the range of 350–400 nm to sustain a considerable current density and stable performance.The device performance depends on the thicknesses of the active layer non-monotonically,which can be explained by the morphology of the pentacene film and the position of the conducting channel in the active layer.The device with a pentacene thickness of 50 nm shows the best performance,which has a maximum hole mobility of 1.12 cm2/V·s.In addition,the introduction of a thin layer of tris-(8-hydroxyquinolinato)aluminum(Alq3)to the OFETs as a light-emitting material greatly decreases the device performance.

Device design principles and bioelectronic applications for flexible organic electrochemical transistors

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 fexible devices will significantly facilitate stable contact with the skin and enable more possible bioelectronic applications. In this work,we summarize the device physics of fexible 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 fexible OECTs. The purpose of this review is not only to elaborate on the basic design principles of fexible OECTs, but also to act as a roadmap for further exploration of wearable OECTs in advanced bio-applications.

Transient Response and Ionic Dynamics in Organic Electrochemical Transistors

The rapid development of organic electrochemical transistors(OECTs)has ushered in a new era in organic electronics,distinguishing itself through its application in a variety of domains,from high-speed logic circuits to sensitive biosensors,and neuromorphic devices like artificial synapses and organic electrochemical random-access memories.Despite recent strides in enhancing OECT performance,driven by the demand for superior transient response capabilities,a comprehensive understanding of the complex interplay between charge and ion transport,alongside electron–ion interactions,as well as the optimization strategies,remains elusive.This review aims to bridge this gap by providing a systematic overview on the fundamental working principles of OECT transient responses,emphasizing advancements in device physics and optimization approaches.We review the critical aspect of transient ion dynamics in both volatile and non-volatile applications,as well as the impact of materials,morphology,device structure strategies on optimizing transient responses.This paper not only offers a detailed overview of the current state of the art,but also identifies promising avenues for future research,aiming to drive future performance advancements in diversified applications.

Photoresponsive n-channel organic field-effect transistors based on a tri-component active layer

Introducing photochromic molecules into the active layer of organic field-effect transistors （OFETs） is a direct way to implement a photoresponse nature in OFETs. However, active layer blended photo- responsive transistors based on n-type semiconductors are challenging and rarely studied, which are crucial for multifunctional organic-based logic applications. Herein, we fabricated n-channel photo- responsive OFETs based on a tri-component active layer spin-coated from the mixed solution of an n-type semiconductor （NDI2OD-DTYM2）, spiropyran and polystyrene with a weight ratio of 1：1：1. The morphology of the blended films was improved by the introduction of the polymer matrix. Photochromic spiropyran molecules dispersed in the semiconductor layer could switch between the closed-ring state and ionic open-ring state flexibly under the irradiation of different wavelengths of light, and thus change the channel conductivity reversibly and modulate the OFET characteristics. Therefore, under the irradiation of alternate UV and vis light, both the device carrier mobility and current on and off ratio successfully realized a reversible switch.

Monolayer organic field-effect transistors

Monolayer organic field-effect transistors(OFETs) are attracting worldwide interest in device physics and novel applications due to their ultrathin active layer for two-dimensional charge transport. The monolayer films are generally prepared by thermal evaporation, the Langmuir technique or self-assembly process, etc., but their electrical performance is relatively lower than corresponding thick films. From 2011, the performance of monolayer OFETs has been boosted by using the monolayer molecular crystals(MMCs) as active channels, which opened up a new era for monolayer OFETs. In this review, recent progress of monolayer OFETs, including the preparation of monolayer films, their OFET performance and applications are summarized.Finally, perspectives of monolayer OFETs in the near future are also discussed.

Advances in organic field-effect transistors and integrated circuits

Organic field-effect transistors (OFETs) have received significant research interest because of their promising applications in low cast, lager area, plastic circuits, and tremendous progress has been made in materials, device performance, OFETs based circuits in recent years. In this article we introduce the advances in organic semiconductor materials, OFETs based integrating techniques, and in particular highlight the recent progress. Finally, the prospects and problems of OFETs are discussed.

Tuning crystal polymorphs of a π-extended tetrathiafulvalene-based cruciform molecule towards high-performance organic field-effect transistors

It is a common phenomenon for organic semi- conductors to crystallize in two or more polymorphs, leading to various molecular packings and different charge transport properties. Therefore, it is a crucial issue of tuning molec- ular crystal polymorphs （i.e., adjusting the same molecule with different packing arrangements in solid state） towards efficient charge transport and high performance devices. Here, the choice of solvent had a marked effect on con- trolling the growth of a-phase ribbon and β-phase platelet during crystallization for an indenofluorene （IF） π-extended tetrathiafulvalene （TTF）-based cruciform molecule, named as IF-TTF. The charge carrier mobility of the a-phase IF-TTF crystals was more than one order of magnitude higher than that of β-phase crystals, suggesting the importance of reasonably tuning molecular packing in solid state for the improvement of charge transport in organic semiconductors.