Proteins as functional interlayer in organic field-effect transistor

The paper summarizes and discusses the recent advances of proteins as functional interlayers in organic field-effect transistors (OFETs). Specific focus is given on the proteins integrated into the device structure, either to act as dielectric materials or to perform as the functional interlayer between the dielectric and the organic semiconductor (OSC). The main emphasis is give to the location and the specific effect of protein layers in the structure of OFETs. Besides, the possibility of amyloid serving as useful building blocks for OFET is discussed.     

有机场效应晶体管应用于化学及生物传感的研究进展

有机场效应晶体管(OFETs)是以有机半导体材料作为有源层的晶体管器件。和传统的无机半导体器件相比,由于其具有成本低、易加工、柔性好和生物相容性而被人们广泛研究,在多种化学和生物传感器领域具有潜在而广泛的应用前景。本文简单介绍了OFETs的结构和工作原理,总结了近几年来OFETs在化学及生物传感方面的研究进展,最后对OFETs的发展方向做了归纳和展望。     

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.     

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

Photoresponsive OFETs were fabricated based on a tri-component active layer (NDI2OD-DTYM2, spiropyran and polystyrene). The results demonstrated that these OFETs displayed photoresponsive feature to alternate UV and vis light due to the photoisomerization of spiropyran between the closed-ring state and ionic open-ring state.     

Perfluoropentacene: high-performance p-n junctions and complementary circuits with pentacene

We report the synthesis and characterization of perfluoropentacene as an n-type semiconductor for organic field-effect transistors (OFETs). Perfluoropentacene is a planar and crystalline material that adopts a herringbone structure as observed for pentacene. OFETs with perfluoropentacene were constructed using top-contact geometry, and an electron mobility of 0.11 cm2 V-1 s-1 was observed. Bipolar OFETs with perfluoropentacene and pentacene function at both negative and positive gate voltages. The improved p-n junctions are probably due to the similar d-spacings of both acenes. Complementary inverter circuits were fabricated, and the transfer characteristics exhibit a sharp inversion of the output signal with a high-voltage gain.     

Synthesis of new microsensor coatings and their response to test vapors 2,4,6-trisubstituted-1,3,5-triazine derivatives

Novel 1,3,5-triazine derivatives were spray-coated onto surface acoustic wave (SAW) devices and exposed to vapors of dimethyl methylphosphonate (DMMP), chloroethyl ethyl sulfide (CEES) and water. Changes in chemiresistor and SAW responses were monitored and recorded by computer-controlled data-acquisition techniques. All the derivatives tested showed little or no chemiresistor or SAW responses to water vapor. The largest reversible chemiresistor response to DMMP vapor was observed with the dicarboxylic acid derivative. The largest SAW response to DMMP was with the dithione, and the dichloro-octylthio derivative showed the largest response to CEES.     

High-performance organic field-effect transistors: molecular design, device fabrication, and physical properties

In the past decade, tremendous progress has been made in organic field-effect transistors (OFETs). Their real applications require further development of device performance. OFETs consist of organic semiconductors, dielectric layers, and electrodes. Organic semiconductors play a key role in determining the device characteristics. The properties of the organic semiconductors, such as molecular structure and packing, as well as molecular energy levels, can be properly controlled by molecular design. Therefore, we designed and synthesized a series of organic molecules. The synthesized organic semiconductors exhibit excellent field-effect properties due to strong intermolecular interactions and proper molecular energy levels. Meanwhile, the influence of the device fabrication process, organic semiconductor/dielectric layer interface, and organic layer/electrode contact on the device performance was investigated. A deep understanding of these factors is helpful to improve field-effect properties. Furthermore, single-crystal field-effect transistors are highlighted because the single-crystal-based FETs can provide an accurate conducting mechanism of organic semiconductors and higher device performance as compared with thin film FETs.     

Synthesis and response of new microsensor coatings-II Acridinium betaines and anionic surfactants

Four acridinium betaines and two ionic surfactants were synthesized, and evaluated as chemical microsensor coatings by exposure to vapors of chloroethyl ethyl sulfide (CEES) and dimethyl methylphosphonate (DMMP). Two of the acridinium betaines showed selective and reversible responses (of 9.8 and 6.8 kHz) as SAW (surface acoustic wave) coatings in the detection of CEES vapor: there appears to be a connection between the long alkyl chain (C-12 and C-14) in the acridinium molecules and the response. Response times were generally less than 30 sec but desorption was significantly slower. The ionic surfactant coatings show small SAW changes (> 0.5 kHz) in response to DMMP vapor, and somewhat greater responses (20- and 68-fold), as chemiresistors, to CEES vapor. In each case the response occurred within 3 min, with return nearly to baseline levels within 6 min of cessation of exposure to the vapor. The responses were reproducible within +/- 5%.     

Detection of trace organophosphorus vapor with a self-assembled bilayer functionalized SiO2 microcantilever piezoresistive sensor

Using piezoresistive SiO₂ microcantilever technology, we present an ultra-sensitive chemical sensor for trace organophosphorus vapor detection. A self-assembled composite layer of Cu²⁺/11-mercaptoundecanoic acid is modified on the surface of the sensing cantilever as a specific coating to capture PO containing compounds. Experimental results indicate that the sensor can be quite sensitive to DMMP vapor (well known as a simulant of nerve agent). The signal-noise-limited detection resolution of the sensor is experimentally obtained as low as several parts per billion. Besides that the sensor can yield reversible and repeatable response to DMMP vapor, adsorption of DMMP on the self-assembled composite layer is well fit to the Langmuir isotherm model.     

Effect of humidity on the interaction of dimethyl methylphosphonate (DMMP) vapor with SiO2 and Al2O3 surfaces, studied using infrared attenuated total reflection spectroscopy

Infrared attenuated total reflection spectroscopy has been used to study the interaction of DMMP vapor with SiO(2), Al(2)O(3), and AlO(OH) vs relative humidity (RH) and DMMP partial pressure (P/P(0)). For SiO(2) the growth with increasing RH of ice-like and liquid-like layers is seen in agreement with previous work. H?D exchange during exposure to H(2)O and D(2)O indicates that the ice-like layer is more resistant to exchange, consistent with stronger H-bonding than in the liquid-like layer. Exposure of nominally dry SiO(2) to D(2)O indicates the existence of adsorbed H(2)O that does not exhibit an ice-like spectrum. The ice-like layer appears only at a finite RH. Exposure of SiO(2) to DMMP in the absence of intentionally added H(2)O shows the formation of a strongly bound molecular species followed by a liquid-like layer. The strong interaction involves SiO-H···O═P bonds to surface silanols and/or HO-H···O═P bonds to preadsorbed molecular H(2)O. At a finite RH the ice-like layer forms on SiO(2) even in the presence of DMMP up to P/P(0) = 0.30. DMMP does not appear to penetrate the ice-like layer under these conditions, and the tendency to form a such a layer drives the displacement of DMMP. Amorphous Al(2)O(3) and AlO(OH) do not exhibit an ice-like H(2)O layer. Both have a higher surface OH content than does SiO(2), which leads to higher coverages of H(2)O or DMMP at equivalent RH or P/P(0). At low P/P(0), for which adsorption is dominated by Al-OH···O═P bonding, a-Al(2)O(3) interacts with DMMP more strongly than does AlO(OH) as a result of the higher acidity of OH sites on the former. Up to RH = 0.30 and P/P(0) = 0.30, DMMP appears to remain bonded to the surface rather than being displaced by H(2)O. H(2)O appears to have little or no effect on the total amount of DMMP adsorbed on any of these surfaces, up to an RH of 0.30 and a P/P(0) of 0.30. The results have implications for the transport of DMMP and related molecules on oxide surfaces in the environment.     

并五苯及其衍生物在有机场效应晶体管中的应用

有机场效应晶体管（organic field—effect transistors,OFETs）是以有机半导体材料作为有源层,通过电场控制电流的电子器件．与传统的无机半导体器件相比,由于其可应用于生产大面积、柔性、低成本电子设备而备受关注,在有机存储器件、有机太阳能电池、柔性平板显示和电子纸等众多领域具有潜在而广泛的应用前景．并苯类材料因其紧密的分子堆积及优异的半导体性能被广泛研究．其中,并五苯及其衍生物在场效应晶体管中表现出良好的性质,其效果甚至可以与非晶硅相媲美,但并五苯较差的溶解性及环境稳定性阻碍了其进一步应用．科研工作者通过对分子结构进行修饰改造设计,合成了一系列并五苯的衍生物,其不仅在稳定性、电学性能和溶解性方面有很大提高,还可以将该p-型半导体材料拓展到双极性及n-型半导体材料领域．本文对并五苯及其衍生物在有机场效应晶体管中的应用进行了较为全面的综述,期望对该领域的研究起到一定的推动作用．     

2,2']Bi[naphtho[2,3-b]furanyl]: a versatile organic semiconductor with a furan-furan junction

[2,2']Bi[naphtho[2,3-b]furanyl] was synthesized, characterized, and examined as an organic semiconductor for thin-film OFETs, bilayer OPVs, and organic light-emitting transistors (OLETs). In the devices, the material acted as a p-type semiconductor, showing moderately high mobility in OFETs, good photo conversion efficiency in OPVs, and blue-green emission in OLETs.     

Highly Sensitive NH(3) Detection Based on Organic Field-Effect Transistors with Tris(pentafluorophenyl)borane as Receptor

We have increased organic field-effect transistor (OFET) NH(3) response using tris(pentafluorophenyl)borane (TPFB) as a receptor. OFETs with this additive could detect concentrations of 450 ppb v/v, with a limit of detection of 350 ppb, the highest sensitivity reported to date for semiconductor films; in comparison, when triphenylmethane (TPM) or triphenylborane (TFB) was used as an additive, no obvious improvement in the sensitivity was observed. These OFETs also showed considerable selectivity with respect to common organic vapors and stability toward storage. Furthermore, excellent memory of exposure was achieved by keeping the exposed devices in a sealed container stored at -30 °C, the first such capability demonstrated with OFETs.     

High-performance low-cost organic field-effect transistors with chemically modified bottom electrodes

The characteristics of organic field-effect transistors (OFETs) were dramatically improved by chemically modifying the surface of the bottom-contact Ag or Cu source-drain (D-S) electrodes with a simple solution method. The contact resistance and energetic mismatch typically observed with Ag D-S electrodes in pentacene bottom-contact OFETs can be properly eliminated when modified by the Ag-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane). The pentacene transistors with low-cost Ag-TCNQ-modified Ag bottom-contact electrodes exhibit outstanding electrical properties, which are comparable with that of the Au top-contact devices. It thus provides a novel way toward high-performance low-cost bottom-contact OFETs.     

Tailoring and patterning of dielectric interfaces for the development of advanced organic field-effect transistors

The progress of organic field-effect transistors (OFETs) has led to the advent of a new area of printed and/or flexible electronics. In organic transistors and circuits, the interface between a gate insulator (GI) and an organic semiconductor (OS) plays a critical role on the electrical performance together with the functionality, the reliability and the long-term stability. In this review, we describe the basic principles of engineering a variety of the GI/OS interfaces for the development of advanced OFETs from the framework of the surface morphology and the physico-chemical surface interactions. We also discuss the dielectric interface modification and the resultant device performance of the OFETs.     

Strongly Correlated Alignment of Fluorinated 5,11‐Bis(triethylgermylethynyl)anthradithiophene Crystallites in Solution‐Processed Field‐Effect Transistors

The crystallinity of an organic semiconductor film determines the efficiency of charge transport in electronic devices. This report presents a micro‐to‐nanoscale investigation on the crystal growth of fluorinated 5,11‐bis(triethylgermylethynyl)anthradithiophene (diF‐TEG‐ADT) and its implication for the electrical behavior of organic field‐effect transistors (OFETs). diF‐TEG‐ADT exhibits remarkable self‐assembly through spin‐cast preparation, with highly aligned edge‐on stacking creating a fast hole‐conducting channel for OFETs.     

Electron transporting semiconducting polymers in organic electronics

Significant progress has been achieved in the preparation of semiconducting polymers over the past two decades, and successful commercial devices based on them are slowly beginning to enter the market. However, most of the conjugated polymers are hole transporting, or p-type, semiconductors that have seen a dramatic rise in performance over the last decade. Much less attention has been devoted to electron transporting, or n-type, materials that have lagged behind their p-type counterparts. Organic electron transporting materials are essential for the fabrication of organic p-n junctions, organic photovoltaic cells (OPVs), n-channel organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs) and complementary logic circuits. In this critical review we focus upon recent developments in several classes of electron transporting semiconducting polymers used in OLEDs, OFETs and OPVs, and survey and analyze what is currently known concerning electron transporting semiconductor architecture, electronic structure, and device performance relationships (87 references).     

Recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells

Organic semiconductor materials, especially donor–acceptor (D–A) polymers, have been increasingly applied in organic optoelectronic devices, such as organic field-effect transistors (OFETs) and organic solar cells (OSCs). Plenty of high-performance OFETs and OSCs have been achieved based on varieties of structurally modified D–A polymers. As the basic building block of D–A polymers, acceptor moieties have drawn much attention. Among the numerous types, lactam- and imide-functionalized electron-deficient building blocks have been widely investigated. In this review, the structural evolution of lactam- or imide-containing acceptors (for instance, diketopyrrolopyrrole, isoindigo, naphthalene diimide, and perylene diimide) is covered and their representative polymers applied in OFETs and OSCs are also discussed, with a focus on the effect of varied structurally modified acceptor moieties on the physicochemical and photoelectrical properties of polymers. Additionally, this review discusses the current issues that need to be settled down and the further development of new types of acceptors. It is hoped that this review could help design new electron-deficient building blocks, find a more valid method to modify already reported acceptor units, and achieve high-performance semiconductor materials eventually.

This review highlights the recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells.     

Efficient modification of Cu electrode with nanometer-sized copper tetracyanoquinodimethane for high performance organic field-effect transistors

We report high performance organic field-effect transistors (OFETs) with the modified Cu bottom-contact electrodes. Efficient modification of the Cu electrodes with nanometer-size copper tetracyanoquinodimethane (Cu-TCNQ) increases the electrode/organic layer contact area and reduces contact resistance. We investigated the effect of the Cu-TCNQ morphology on the device performance. The pentacene-based OFETs with the modified Cu bottom-contact electrodes exhibited high device performance. The field-effect mobility up to 0.31 cm(2)/V s was achieved. To the best of our knowledge, this is the highest device performance for the OFETs with the bottom Cu electrodes ever reported. Consequently, our results provide an effective approach to fabricate high performance and low-cost OFETs.     

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.