טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSarkar Tanmoy
SubjectSelf-Segregated Interlayer in Organic-Field Effect
Transistors
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Gitti Frey


Abstract

Electronic devices are becoming more compact and portable which is evident in the way cell phones, portable music players, computers, and other devices have evolved in the last two decades. With flexible electronic technologies, eventually we’ll have electronic gadgets that are so compact, they can even be folded up and tucked in our pocket. For this purpose, organic semiconductors (OSCs) and their unique combination of electrical and mechanical properties have received great interest since the first proof-of-principle device demonstration at the end of the 20th century. The advantages of organic electronics include flexibility, solution processability, printability and low-power operation, which make them a promising supplementary technology to conventional electronics. In this regard, field effect transistors based on OSC has drawn great interest as the building block for future technology.


In All organic electronic devices, charges are transferred from metal electrodes to the OSC across an interface. One of the main challenges to achieve efficient charge injection is to choose a metal electrode with a work function that is well aligned with one of the energy levels of the OSC. In many organic electronic devices, an ultra-thin layer is introduced between the OSC and the metal electrode to tune the effective work function (EWF) of the metal/organic interface. This ultra-thin interlayer, organic or inorganic, introduces dipoles that modify the EWF. However, insertion and characterization of interlayer is challenging for top contact devices where the metal/organic interface is buried under the metal. Recently, we developed a methodology to self-generate interlayers at the buried interface that is simple, versatile and compatible with large-scale processing techniques. 


This thesis investigates the formation of self-generated interlayer at the metal/organic interfaces in organic field-effect transistors (OFETs) and studies their effect on the device performances. Several interlayer forming organic molecules were studied for different metal electrodes. The molecules consist a dipole to tune the effective work function, are soluble in organic solvents so that they can blend with the OSC layer, and have functional end-groups (e.g. thiol and hydroxyl) to induce their migration to the interface during metal deposition.


The outcome of this research indicates that the self-generated interlayer is an efficient and effective technique for energy level alignment and improve both n-and p-channel OFET performance. Furthermore, this research reveals that a combining two additives with opposite behaviour can effectively improve both electron and hole injection in the same device. Balancing the injection of both carriers in one device enables ambipolar OFET performance and the fabrication of basic logic circuits.