Ambipolar Charge Transport in Organic Semiconductors and Devices

Lead Research Organisation: Imperial College London
Department Name: Physics

Abstract

Recent years have seen tremendous advances in the area of organic electronics mainly motivated by their emerging applications in electronic devices. A very important electronic device that is in the heart of today's microelectronic circuits is the transistor since it represents the building block of all everyday electronics. Very recently, organic based transistors also made their debut in a number of electronic devices and can be arguably viewed as possible alternatives to silicon-based devices in a range of low-cost and high-volume applications.Although recent progress is impressive, use of organic transistors in practical applications is hampered because the minimum requirements (speed, power-dissipation, cost) presently cannot be meet. The proposed work addresses these specific problems using an entirely different approach. We will study the electronic properties of organic semiconductors that are capable of transporting both electrons and holes. These are the so-called ambipolar organic semiconductors. During this fellowship we will develop and advance the knowledge on ambipolar transport in organic semiconductors but we will also exploit and assess various technologically relevant phenomena.We will first study ambipolar transport in a number of known ambipolar organic semiconductors through a combination of electrical, structural, chemical and spectroscopic measurements. Understanding the key electronic properties of these materials is essential for the development of improved or new semiconductors that will be subsequently synthesized through collaborations with various chemistry groups. Using the obtained knowledge, we will demonstrate ambipolar organic transistors and, initially, basic logic circuits like voltage inverters. New applications such as light-emitting transistors and sensors are expected to arise as a result of this work. Moreover, understanding ambipolar transport in organic materials is of basic scientific interest and is expected to benefit other scientific disciplines including chemistry and material science.
 
Title IMPROVED OXIDE-BASED FIELD-EFFECT TRANSISTORS 
Description A field-effect transistor comprising: a source region; a drain region; a semiconductor layer disposed between the source and drain regions; a gate region; and a dielectric region disposed between the semiconductor layer and the gate region; wherein the semiconductor layer comprises a titanium dioxide film. The transistor may be light sensing, gas- or bio-sensing, or used in a visual display or in electronic circuits. Also provided is a method of forming a field-effect transistor comprising: forming a dielectric layer adjacent a gate; forming a source region and a drain region; and forming a semiconductor layer on the dielectric layer, the semiconductor layer comprising titanium dioxide. The titanium dioxide semiconductor layer may be deposited by spray pyrolysis, or alternatively mesoporous TiO2 films of nanocrystalline morphology may be formed by spin coating, doctor-blading or screen-printing techniques. 
IP Reference WO2008129238 
Protection Patent application published
Year Protection Granted 2008
Licensed No
Impact None
 
Title IMPROVEMENTS IN ORGANIC FIELD-EFFECT TRANSISTORS 
Description An organic field-effect transistor comprising: a source region; a drain region; one or more organic semiconductor layers disposed between the source and drain regions; a gate region; and a dielectric region disposed between the organic semiconductor layer(s) and the gate region; wherein the composition of the organic semiconductor layer(s) is such as to transport both electrons and holes, with the mobility of the holes being substantially equal to the mobility of the electrons such that the transistor substantially exhibits ambipolarity in its transfer characteristics. The organic field-effect transistor is preferably a light-sensing organic field-effect transistor. Numerous modifications to the composition and structure of organic field-effect transistors are also disclosed, as are examples of electro-optical switches, electro-optical logic circuits and image sensing arrays. 
IP Reference WO2008122778 
Protection Patent application published
Year Protection Granted 2008
Licensed No
Impact None