Solution-Processed Conducting Films for Organic Field-Effect Transistors (OFETs)

Abstract

Transparent conducting materials are widely used as contact electrodes in optoelectronic applications such as liquid crystal displays (LCDs), solar cells, light emitting diodes (LEDs) and Thin Film Transistors (TFTs). Future bendable optoelectronic devices will require suitable fabrication methods for flexible transparent electrodes to be formed at low cost on large areas. The most used materials among these applications, are doped metal oxides (mainly indium tin oxide, ITO) because of their high electrical conductivity and high optical transparency. However, doped metal oxides have many disadvantages: they are expensive, some require high vacuum during thin film fabrication processes and are prone to cracking on flexible substrates. Alternatives to Indium Tin Oxide (ITO) have been developed in recent years to replace it. The aim of this project was to develop novel organic-inorganic nanocomposite materials that combine high conductivity and transparency intrinsic to doped semiconducting metal oxides with low-cost and ease of processing characteristic for polymers that will pave the way towards low cost fabrication and integration of transparent conducting materials for high performance electronic components (e.g. Thin Film Transistors, Photovoltaic cells, Light Emitting Diodes) and circuits on flexible substrates. This involved formulation of polymer/nanowire nanocomposite solutions, as well as fabrication and electrical characterisation of thin conductive films and Organic Field-Effect Transistors (OFETs) for applications such as driving circuits for displays and sensors that require low switching speed, as well as low voltage and power operation. In this work, solution-processed silver nanowire (AgNW) electrodes to be used as transparent contacts for thin film transistors have been developed by demonstrating low sheet resistance and high transmittance. The performance of the electrodes depends on the properties of the silver nanowires (AgNWs), their roughness, as well as thin film sheet resistance and transparency. A transparent insulating polymer (polyvinyl alcohol, PVA) was used as both a high-k dielectric (k = 7.8) and as the top layer of the silver nanowire electrodes to form a composite during the fabrication of Organic Field-Effect Transistors (OFETs). It is shown that using this approach, low threshold voltage Organic Field-Effect Transistors (OFETs) operating with gate voltages |VG| ≤ 5 V can be successfully realized.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Mohamed Missous (Supervisor) & Leszek Majewski (Supervisor)