Alexey S. Sizov

Oligothiophene-based monolayer field-effect transistors prepared by Langmuir-Blodgett technique

Quinquethiophene-based monolayer organic field-effect transistors (OFETs) prepared by Langmuir-Blodgett (LB) technique show hole mobilities up to 10−2 cm2/Vs and On/Off ratios up to 106. Functional logic LB monolayer devices operating in air have been demonstrated. The performance of LB OFETs is comparable to self-assembled monolayer field-effect transistors (SAMFETs) devices prepared by self-assembly from solution using the same organosilicon oligothiophene despite the LB OFET monolayer is weakly bounded to the dielectric surface. Taking into account that the LB technique is a fast and rather easy process, these findings highlight a high potential of LB technique for ultrathin organic electronics.

Polymer Surface Engineering for Efficient Printing of Highly Conductive Metal Nanoparticle Inks

An approach to polymer surface modification using self-assembled layers (SALs) of functional alkoxysilanes has been developed in order to improve the printability of silver nanoparticle inks and enhance adhesion between the metal conducting layer and the flexible polymer substrate. The SALs have been fully characterized by AFM, XPS, and WCA, and the resulting printability, adhesion, and electrical conductivity of the screen-printed metal contacts have been estimated by cross-cut tape test and 4-point probe measurements. It was shown that (3-mercaptopropyl)trimethoxysilane SALs enable significant adhesion improvements for both aqueous- and organic-based silver inks, approaching nearly 100% for PEN and PDMS substrates while exhibiting relatively low sheet resistance up to 0.1 Ω/sq. It was demonstrated that SALs containing functional -SH or -NH2 end groups offer the opportunity to increase the affinity of the polymer substrates to silver inks and thus to achieve efficient patterning of highly conductive structures on flexible and stretchable substrates.

Luminescent Organic Semiconducting Langmuir Monolayers

In recent years, monolayer organic field-effect devices such as transistors and sensors have demonstrated their high potential. In contrast, monolayer electroluminescent organic field-effect devices are still in their infancy. One of the key challenges here is to create an organic material that self-organizes in a monolayer and combines efficient charge transport with luminescence. Herein, we report a novel organosilicon derivative of oligothiophene-phenylene dimer D2-Und-PTTP-TMS (D2, tetramethyldisiloxane; Und, undecylenic spacer; P, 1,4-phenylene; T, 2,5-thiophene; TMS, trimethylsilyl) that meets these requirements. The self-assembled Langmuir monolayers of the dimer were investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, X-ray reflectometry, and grazing-incidence X-ray diffraction, and their semiconducting properties were evaluated in organic field-effect transistors. We found that the best uniform, fully covered, highly ordered monolayers were semiconducting. Thus, the ordered two-dimensional (2D) packing of conjugated organic molecules in the semiconducting Langmuir monolayer is compatible with its high-yield luminescence, so that 2D molecular aggregation per se does not preclude highly luminescent properties. Our findings pave the way to the rational design of functional materials for monolayer organic light-emitting transistors and other optoelectronic devices.

Direct-write printing of reactive oligomeric alkoxysilanes as an affordable and highly efficient route for promoting local adhesion of silver inks on polymer substrates

A novel approach for improving the printability and adhesion of silver inks on flexible and stretchable polymeric substrates is reported. The method is based on polymer surface functionalisation with an organosilicon interlayer by solution processing and, more specifically, the deposition of a self-assembled layer (SAL) from thiol-containing oligomeric alkoxysilanes prepared under active medium conditions. We demonstrate the potential of SAL formation on polymer substrates by large-area uniform coating or by small feature printing. The direct-writing method, which is also referred to as reactive inkjet printing, enables the selective modification of polymer surfaces with functional thiol-containing interlayers, resulting in local adhesion enhancement of screen-printed silver nanoparticle inks. This study establishes that SALs printed from oligo(3-mercaptopropyl)(methoxy)siloxane (OMPMS) lead to significant adhesion improvements of both aqueous- and organic-based silver inks approaching approximately 100% for polyethylene naphthalate (PEN) and even polydimethylsiloxane (PDMS) substrates. Exceptional electrical and mechanical stabilities of the printed silver conductors under bending and stretching are demonstrated.

Thiophene-based monolayer OFETs prepared by Langmuir techniques

A novel fast, easily processible and highly reproducible approach to thiophene-based monolayer OFETs fabrication by Langmuir-Blodgett or Langmuir-Schaefer techniques was developed and successfully applied. It is based on selfassembly of organosilicon derivatives of oligothiophenes or benzothienobenzothiophene on the water-air interface. Influence of the conjugation length and the anchor group chemistry of the self-assembling molecules on the monolayer structure and electric performance of monolayer OFETs was systematically investigated. The efficient monolayer OFETs with the charge carrier mobilities up to 0.01 cm2/Vs and on/off ratio up to 106 were fabricated, and their functionality in integrated circuits under normal air conditions was demonstrated.

Organosilicon dimer of BTBT as a perspective semiconductor material for toxic gas detection with monolayer organic field-effect transistors

Monolayer organic field effect transistors (OFETs) provide opportunity for ultrahigh sensitivity gas sensor applications due to a strong dependence of OFET key parameters on the environment. However, an impressive combination of both high sensitivity and instantaneous response of such gas sensors can be achieved only on low-defect dense monolayers with high electrical performance. Herein, we investigated monolayer thin film formation of recently developed benzothieno[3,2-b][1]benzothiophene (BTBT) organosilicon dimer D2-Und-BTBT-Hex by Langmuir–Blodgett, Langmuir–Schaefer and spin-coating methods. For all these techniques, the conditions of uniform low-defect monolayer formation were found. These monolayers were used for preparation of OFET devices, which demonstrated excellent electrical performance with a hole mobility up to 7 × 10−2 cm2 V−1 s−1, a threshold voltage around 0 V and an on–off ratio of 105 as well as long-term stability of half-year storage under ambient conditions. Preliminary investigations demonstrated that the monolayer OFETs give an instantaneous response to ammonia at low concentrations (down to 400 ppb). These findings show a great potential of BTBT-based OFETs for large-area sensing device application.

Organosilicon derivatives of BTBT for monolayer organic field effect transistors

Synthesis of novel organosilicon derivatives of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) linked though flexible aliphatic spacers to a disiloxane anchor group is reported. They were successfully used in monolayer OFETs with the charge carrier mobilities up to 0.02 cm2 /Vs, threshold voltage close to 0 V and On/Off ratio up to 10,000. Influence of the chemical structure of the molecules synthesized on the morphology, molecular 2D ordering in the monolayers and their semiconducting properties is considered. The effect of different methods of the ultrathin semiconducting layer preparation, such as Langmuir-Blodgett, Langmuir-Schaefer, spin coating or doctor blade, on the OFET performance is discussed.

Molecular silicasol-based barrier coatings for organic electronics

A solution-processable approach to designing molecular silicasol-based barrier coatings for organic electronics has been developed. The barriers are assessed by the optical calcium test and demonstrate water-vapor permeation rates of about 10–2 g m–2 day–1. Silicasols are shown to be promising for the encapsulation of organic electronics devices, for which the resulting water-vapor permeation rates are sufficient (e.g., for organic field-effect transistors).