Self-assembly is possibly the most effective and versatile strategy for surface functionalization. Self-assembled monolayers (SAMs) can be formed on (semi-)conductor and dielectric surfaces, and have been used in a variety of technological applications. This work aims to review the strategy behind the design and use of self-assembled monolayers in organic electronics, discuss the mechanism of interaction of SAMs in a microscopic device, and highlight the applications emerging from the integration of SAMs in an organic device. The possibility of performing surface chemistry tailoring with SAMs constitutes a versatile approach towards the tuning of the electronic and morphological properties of the interfaces relevant to the response of an organic electronic device. Functionalisation with SAMs is important not only for imparting stability to the device or enhancing its performance, as sought at the early stages of development of this field. SAM-functionalised organic devices give rise to completely new types of behavior that open unprecedented applications, such as ultra-sensitive label-free biosensors and SAM/organic transistors that can be used as robust experimental gauges for studying charge tunneling across SAMs.

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There is a quest for electronic biosensors operated in water for biomedical applications and environmental monitoring. Water is an aggressive medium for standard electronics materials and devices due to its strong polarizability and electrochemical activity. Thick dielectric encapsulation provides necessary stability while it damps the sensitivity of the device to sensing events occurring in the aqueous environment. Organic electronics provides materials that exhibit stable electronic conduction in direct contact with water combined with other desirable properties like mechanical softness, biocompatibility and processability onto flexible substrates. In this review, we introduce an emerging class of organic transistors, in which the current across the organic film is gated by the electric field of the Debye–Helmholtz layer. We discuss the device physics, the sensing mechanism and the relevant electrochemical processes. Applications of water-gated transistors range from the sensing of biologically relevant molecules like DNA, proteins or hormones to non-invasive recording and stimulation of electrical activity of neurons. Materials chemistry is crucial to control properties of electrically active films and to allow the introduction of specific chemical functionalities and receptors at sensing interfaces of the device

We describe a fast and versatile method to functionalize high-quality graphene with organic molecules by exploiting the synergistic effect of supramolecular and covalent chemistry. With this goal, we designed and synthesized molecules comprising a long aliphatic chain and an aryl diazonium salt. Thanks to the long chain, these molecules physisorb from solution onto CVD graphene or bulk graphite, self-assembling in an ordered monolayer. The sample is successively transferred into an aqueous electrolyte, to block any reorganization or desorption of the monolayer. An electrochemical impulse is used to transform the diazonium group into a radical capable of grafting covalently to the substrate and transforming the physisorption into a covalent chemisorption. During covalent grafting in water, the molecules retain the ordered packing formed upon self-assembly. Our two-step approach is characterized by the independent control over the processes of immobilization of molecules on the substrate and their covalent tethering, enabling fast (t < 10 s) covalent functionalization of graphene. This strategy is highly versatile and works with many carbon-based materials including graphene deposited on silicon, plastic, and quartz as well as highly oriented pyrolytic graphite.

Antibody-antigen (Ab-Ag) recognition is the primary event at the basis of many biosensing platforms. In label-free biosensors, these events occurring at solid-liquid interfaces are complex and often difficult to control technologically across the smallest length scales down to the molecular scale. Here a molecular-scale technique, such as single-molecule force spectroscopy, is performed across areas of a real electrode functionalized for the immunodetection of an inflammatory cytokine, viz. interleukin-4 (IL4). The statistical analysis of force-distance curves allows us to quantify the probability, the characteristic length scales, the adhesion energy, and the time scales of specific recognition. These results enable us to rationalize the response of an electrolyte-gated organic field-effect transistor (EGOFET) operated as an IL4 immunosensor. Two different strategies for the immobilization of IL4 antibodies on the Au gate electrode have been compared: antibodies are bound to (i) a smooth film of His-tagged protein G (PG)/Au; (ii) a 6-aminohexanethiol (HSC6NH2) self-assembled monolayer on Au through glutaraldehyde. The most sensitive EGOFET (concentration minimum detection level down to 5 nM of IL4) is obtained with the first functionalization strategy. This result is correlated to the highest probability (30%) of specific binding events detected by force spectroscopy on Ab/PG/Au electrodes, compared to 10% probability on electrodes with the second functionalization. Specifically, this demonstrates that Ab/PG/Au yields the largest areal density of oriented antibodies available for recognition. More in general, this work shows that specific recognition events in multiscale biosensors can be assessed, quantified, and optimized by means of a nanoscale technique.

The development of low-cost printed organic electronics entails the processing of the active organic semiconductors (OSCs) by solution-based techniques. However, the preparation of large area uniform and reproducible films based on OSCs inks can be very challenging due to the low viscosity of their solutions that give dewetting problems, the low stability of OSC polymer solutions or the difficulty in achieving appropriate crystal order. To circumvent this, a promising route is the use of blends of OSCs and insulating binding polymers. This approach typically gives rise to films with an enhanced crystallinity and organic field-effect transistors (OFETs) with significantly improved device performance. In this review paper, we overview the recent progress realized in the fabrication of OFETs based on OSC/binding polymer inks highlighting the main morphological and structural features that are playing a major role in determining the final electrical properties and some future perspectives.Undoubtedly, the use of this type of blends results in more reliable and reproducible devices that can be fabricated on large areas and at low cost and, thus, this methodology brings great expectations for the implementation of OSCs in real applications.

During the last decades, small molecule organic semiconductors have been successfully used as active layer in organic field-effect transistors (OFETs). Despite the high mobility achieved so far with organic molecules, in order to progress in the field it is crucial to find techniques to process them from solution. The device reproducibility is one of the principal weak points of organic electronics for further commercialization. To achieve a high device-to-device reproducibility it is essential to control the morphology and polymorphism of the active layer for OFET application. In this work, the preparation of thin films is reported based on blends of the organic semiconductor dibenzotetrathiafulvalene (DB-TTF) and polystyrene by a solution shearing technique compatible with upscaling. Here, it is demonstrated that varying the deposition parameters (i.e., speed and temperature) or the solution formulation (i.e., semiconductor/binder polymer ratio) is possible to control the film morphology and semiconductor polymorphism and, hence, the different intermolecular interactions. It is demonstrated that the control of the thermodynamics and kinetics of the crystallization process is key for the device performance optimization. Further, this is the first time that DB-TTF thin films of the α-polymorph are reported.

Since the first demonstration, the electrolyte-gated organic field-effect transistors (EGOFETs) have immediately gained much attention for the development of cutting-edge technology and they are expected to have a strong impact in the field of (bio-)sensors. However EGOFETs directly expose their active material towards the aqueous media, hence a limited library of organic semiconductors is actually suitable. By using two mostly unexplored strategies in EGOFETs such as blended materials together with a printing technique, we have successfully widened this library. Our benchmarks were 6,13-bis(triisopropylsilylethynyl)pentacene and 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT), which have been firstly blended with polystyrene and secondly deposited by means of the bar-assisted meniscus shearing (BAMS) technique. Our approach yielded thin films (i.e. no thicker than 30 nm) suitable for organic electronics and stable in liquid environment. Up to date, these EGOFETs show unprecedented performances. Furthermore, an extremely harsh environment, like NaCl 1M, has been used in order to test the limit of operability of these electronic devices. Albeit an electrical worsening is observed, our devices can operate under different electrical stresses within the time frame of hours up to a week. In conclusion, our approach turns out to be a powerful tool for the EGOFET manufacturing.