Adam V. S. Parry

A simple method for controllable solution doping of complete polymer field-effect transistors

Controllable p-type doping of both poly(3-hexylthiophene) (P3HT) and poly(triarylamine) (PTAA) organic field effect transistors (OFETs) was achieved by immersing complete top-contact OFETs in a solution of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) in acetone. As this method is applied to complete devices, it has a greater utility than methods involving doping of the solution prior to film deposition as it allows separation of the device processing and doping steps, facilitating the use of optimal processing conditions at each stage. It was found that by varying immersion time and the concentration of the dopant solution, it was possible to vary the threshold voltage for a P3HT OFET by over 30 V. Although PTAA devices are less sensitive to oxidation by F4-TCNQ than OFETs using P3HT, they can also be controllably doped by this method up to a threshold voltage of +12 V.

Non-linear, cata-Condensed, Polycyclic Aromatic Hydrocarbon Materials: A Generic Approach and Physical Properties.

A generic approach to the regiospecific synthesis of halogenated polycyclic aromatics is made possible by the one- or two-directional benzannulation reactions of readily available (ortho-allylaryl)trichloroacetates (the “BHQ” reaction). Palladium-catalysed cross-coupling reactions of the so-formed haloaromatics enable the synthesis of functionalised polycyclic aromatic hydrocarbons (PAHs) with surgical precision. Overall, this new methodology enables the facile mining of chemical space in search of new electronic functional materials.

Submicron Patterning of Polymer Brushes: An Unexpected Discovery from Inkjet Printing of Polyelectrolyte Macroinitiators

Using an electrostatic-based super inkjet printer we report the high-resolution deposition of polyelectrolyte macroinitiators and subsequent polymer brush growth using SI-ARGET-ATRP. We go on to demonstrate for the first time a submicron patterning phenomenon through the addition of either a like charged polyelectrolyte homopolymer or through careful control of ionic strength. As a result patterning of polymer brushes down to ca. 300 nm is reported. We present a possible mechanistic model and consider how this may be applied to other polyelectrolyte-based systems as a general method for submicron patterning.

Towards solution processable air stable p-type organic semiconductors: synthesis and evaluation of mono and di-fluorinated pentacene derivatives

The synthesis of a series of mono and di-fluorinated TIPS pentacene compounds for application as organic semiconductors is reported. Namely the novel 1-fluoro-6,13-bis[triisopropylsilyl-ethynyl]pentacene (1-fluoro-TIPS-pentacene), 2-fluoro-TIPS-pentacene and the recently reported 1 : 1 syn : anti isomeric mixtures of 1,(8 : 11)-difluoro-TIPS-pentacenes and 2,(9 : 10)-difluoro-TIPS-pentacenes. For the first time these materials have been subjected to a study of the relationship between molecular structure and thermal/photochemical stability. The changes in the pentacene HOMO via alteration of fluorine substitution is studied and related to environmental stability. As predicted, it was found that increasing the number of electron-withdrawing fluorine substituents increases stability to photodegradation. It was also observed that stability increases (and HOMO decreases) when fluorine is present on the 1- and 1,(8 : 11)-positions closer to the central rings rather than in the 2- and 2,(9 : 10)-positions. Comparative transistor measurements for the fluoro-derivatives demonstrated competitive device performance in comparison to underivatised TIPS-pentacene. Full characterisation and NMR assignment of these materials has been accomplished by comparison over the series for the first time.

Switchable disposable passive RFID vapour sensors from inkjet printed electronic components integrated with PDMS as a stimulus responsive material

A route to cheap and disposable sensors for the chemical sensing market, with potential applications including monitoring of food spoilage, is reported herein. The sensor is the result of the direct integration of a stimuli-responsive material, poly(dimethylsiloxane) (PDMS), with an electronic component. The printing and sintering of colloidal silver ink solutions onto PDMS was optimized to allow the printing of conductive silver feed loops, which are the active sensing component in antennas for passive (battery-free) Radio Frequency Identification (RFID) tags. The response of these devices is related to the degree of swelling of the PDMS, which, in turn, has been shown to be correlated to the Hansen solubility parameters and the vapour pressures of the corresponding volatile organic compounds (VOCs). When exposed to solvent vapour the printed feed loop fractures, increasing resistance and ultimately breaking conductivity, leading to a change in the transmitted power and read range of the wireless device. Remarkably upon removal from the vapour, the fractured feed loops reassemble and become conductive again, making them switchable and “multi-use”. This work paves the way to a fully inkjet printed RFID substrate for vapour detection.

Extended conjugation in poly(triarylamine)s: synthesis, structure and impact on field-effect mobility

Polytriarylamines with extended fused backbones are accessible by the coupling of anilines with dibromoarenes based on substituted indenofluorenes, diindenofluorenes, carbazoles and indolocarbazoles. The optical and electrochemical properties of these polymers show an increase in the HOMO energy levels and the onset of absorption on extending the length of the fused ring segment. The polymer derived from the indenofluorene unit shows the highest reported performance for a polytriarylamine in an OFET and this observation can be rationalized by DFT calculations of model oligomers that show higher calculated reorganization energies for the more extended diindenofluorene units.