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High mobility organic semiconductors for microelectronic applications

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Title: High mobility organic semiconductors for microelectronic applications
Authors: Panidi, Ioulianna
Item Type: Thesis or dissertation
Abstract: The potential of organic electronic devices, over the past few years, has been proven tremendous. Flexible and transparent electronic devices will soon enter the market, but there are still some challenging aspects requiring further improvements. A generic approach to enhance the charge transport properties of the organic semiconductors is by introducing molecular additives. In particular for thin lm transistors, doping the semiconductor layer leads to higher charge carrier mobility, as well as improving several parameters of the device. The work in this thesis focuses on identifying suitable molecular additives that can dope organic semiconductors for thin lm transistors. Chapter 5 presents the application of tris(penta uorophenyl)borane B(C6F5)3 as an e ective p-type dopant. B(C6F5)3 was applied in several small molecule:polymer blends and the improvement in the charge transport properties, as measured from organic thin lm transistors (OTFTs), was remarkable. In particular the blend diF-TESADT:PTAA and the C8-BTBT:C16-IDT-BT showed hole mobility of 8 and 11 cm2/Vs, respectively. OTFT parameters, such as the threshold voltage and the contact resistance were signi cantly reduced with the addition of molecular additives. The impact of the dopant addition in the blends was studied by AFM and XRD, which revealed that long-range crystallinity was induced in certain systems. Chapter 6 presents the DMBI-BDZC as a new n-type dopant. For transistors integration into circuits balanced charge transport is required and thus extensive optimisation is still required for n-type materials. DMBI-BDZC was used to dope a small molecule (NDI3HU-DTYM2) and a polymeric (N2200) semiconductor. In both systems free electron generation was observed at an optimum dopant concentration, as measured by electron paramagnetic resonance (EPR). OTFTs with enhanced charge carrier mobility and reduced contact resistance was achieved with the dopant addition. By further analysis of the device characteristics, reduction in both activation energy and density of traps states was observed in the doped devices. The morphology studies of the organic semiconducting thin lms revealed that the dopant addition is not disrupting the structure. Furthermore, the reduction in activation energy at low voltages is in accordance with the trap density calculations as performed from the OTFTs. In chapter 7 a single organic layer light emitting transistor (OLET) is demonstrated. The key behind this device structure was the identi cation of the polymer PDITTT. This polymer combines high charge transport properties (1 cm2/Vs) as well as having green light emission. The properties of the polymer allowed the fabrication of a single layer organic semiconducting OLET. Blending the polymer with the small molecule C8-BTBT resulted in enhanced charge transport OTFTs. OTFTs and OLETs were fabricated from both the PDITTT and C8-BTBT:PDITTT.
Content Version: Open Access
Issue Date: Oct-2019
Date Awarded: Mar-2020
URI: http://hdl.handle.net/10044/1/96449
DOI: https://doi.org/10.25560/96449
Copyright Statement: Creative Commons Attribution NonCommercial Licence
Supervisor: Anthopoulos, Thomas
Heeney, Martin
Sparrowe, David
Skabara, Peter
Sponsor/Funder: Engineering and Physical Sciences Research Council (EPSRC)
Merck & Co.
Funder's Grant Number: EP/L016702/1
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses

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