Controlling Nanostructure in Inkjet Printed Organic Transistors for Pressure Sensing Applications.

This work reports the development of a highly sensitive pressure detector prepared by inkjet printing of electroactive organic semiconducting materials. The pressure sensing is achieved by incorporating a quantum tunnelling composite material composed of graphite nanoparticles in a rubber matrix into the multilayer nanostructure of a printed organic thin film transistor. This printed device was able to convert shock wave inputs rapidly and reproducibly into an inherently amplified electronic output signal. Variation of the organic ink material, solvents, and printing speeds were shown to modulate the multilayer nanostructure of the organic semiconducting and dielectric layers, enabling tuneable optimisation of the transistor response. The optimised printed device exhibits rapid switching from a non-conductive to a conductive state upon application of low pressures whilst operating at very low source-drain voltages (0-5 V), a feature that is often required in applications sensitive to stray electromagnetic signals but is not provided by conventional inorganic transistors and switches. The printed sensor also operates without the need for any gate voltage bias, further reducing the electronics required for operation. The printable low-voltage sensing and signalling system offers a route to simple low-cost assemblies for secure detection of stimuli in highly energetic systems including combustible or chemically sensitive materials.

Manipulating nanoscale structure to control functionality in printed organic photovoltaic, transistor and bioelectronic devices.

Printed electronics is simultaneously one of the most intensely studied emerging research areas in science and technology and one of the fastest growing commercial markets in the world today. For the past decade the potential for organic electronic (OE) materials to revolutionize this printed electronics space has been widely promoted. Such conviction in the potential of these carbon-based semiconducting materials arises from their ability to be dissolved in solution, and thus the exciting possibility of simply printing a range of multifunctional devices onto flexible substrates at high speeds for very low cost using standard roll-to-roll printing techniques. However, the transition from promising laboratory innovations to large scale prototypes requires precise control of nanoscale material and device structure across large areas during printing fabrication. Maintaining this nanoscale material control during printing presents a significant new challenge that demands the coupling of OE materials and devices with clever nanoscience fabrication approaches that are adapted to the limited thermodynamic levers available. In this review we present an update on the strategies and capabilities that are required in order to manipulate the nanoscale structure of large area printed organic photovoltaic (OPV), transistor and bioelectronics devices in order to control their device functionality. This discussion covers a range of efforts to manipulate the electroactive ink materials and their nanostructured assembly into devices, and also device processing strategies to tune the nanoscale material properties and assembly routes through printing fabrication. The review finishes by highlighting progress in printed OE devices that provide a feedback loop between laboratory nanoscience innovations and their feasibility in adapting to large scale printing fabrication. The ability to control material properties on the nanoscale whilst simultaneously printing functional devices on the square metre scale is prompting innovative developments in the targeted nanoscience required for OPV, transistor and biofunctional devices.

Role of Stabilizing Surfactants on Capacitance, Charge, and Ion Transport in Organic Nanoparticle-Based Electronic Devices.

Deposition of functionalized nanoparticles onto solid surfaces has created a new revolution in electronic devices. Surface adsorbates such as ionic surfactants or additives are often used to stabilize such nanoparticle suspensions; however, little is presently known about the influence of such surfactants and additives on specific electronic and chemical functionality of nanoparticulate electronic devices. This work combines experimental measurements and theoretical models to probe the role of an ionic surfactant in the fundamental physical chemistry and electronic charge carrier behavior of photodiode devices prepared using multicomponent organic electronic nanoparticles. A large capacitance was detected, which could be subsequently manipulated using the external stimuli of light, temperature, and electric fields. It was demonstrated that analyzing this capacitance through the framework of classical semiconductor analysis produced substantially misleading information on the electronic trap density of the nanoparticles. Electrochemical impedance measurements demonstrated that it is actually the stabilizing surfactant that creates capacitance through two distinct mechanisms, each of which influenced charge carrier behavior differently. The first mechanism involved a dipole layer created at the contact interfaces by mobile ions, a mechanism that could be replicated by addition of ions to solution-cast devices and was shown to be the major origin of restricted electronic performance. The second mechanism consisted of immobile ionic shells around individual nanoparticles and was shown to have a minor impact on device performance as it could be removed upon addition of electronic charge in the photodiodes through either illumination or external bias. The results confirmed that the surfactant ions do not create a significantly increased level of charge carrier traps as has been previously suspected, but rather, preventing the diffusion of mobile ions through the nanoparticulate film and their accumulation at contacts is critical to optimize the performance.