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Title: Solution-processable organic blend semiconductors for next generation thin-film transistor applications
Author: Hunter, Simon
ISNI:       0000 0004 5989 8214
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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Organic semiconductors display a wide array of enticing properties for the fabrication of novel electronic devices. Mechanical flexibility provides the potential for robust, conformable devices; while wide-area and low-temperature deposition enables the manufacture of low-cost, disposable electronics. This means that the commercial applications should be wide-ranging, as long as the performance and stability of devices based on organic semiconductors are sufficient. One of the most promising organic thin-film transistor (OTFT) systems that have been demonstrated in recent years involves the blending of small molecule and polymer organic semiconductors. A blend of the high hole mobility small molecule 2,8-difluoro 5,11 triethylsilylethynyl anthradithiophene (diF-TES ADT) with the amorphous semiconducting polymer poly(triarylamine) (PTAA) is investigated in this thesis. This blend system has been shown to allow considerable control over processing from solution and charge carrier mobilities of up to 3 cm^2/Vs. The aim of this thesis is to provide a deeper understanding of the critical charge transport and stability characteristics of this blend system, while also investigating the system's suitability to a high-throughput spray-deposition technique. In the first part of this thesis the fundamental charge transport characteristics of the diF-TES ADT:PTAA blend system are investigated. The densities of band-gap tail states in blend films of differing composition are found to be exhibit considerable thermal broadening at low temperatures, and at high temperatures are controlled by the concentration of the small molecule component in the blend. In the second part of the work the electrical and environmental stability of blend OTFTs is studied. The devices exhibit state-of-the-art bias stability in an inert environment, however exposure to air and elevated temperatures highlights some interesting degradation pathways which are investigated. Finally, the blend system was used with a high-throughput spray deposition technique. Subsequent spray deposition of semiconductor and ultra-thin dielectric layers was demonstrated, resulting in the fabrication of low-power OTFTs operating at -4 V and exhibiting hole mobilities on the order of 1 cm^2/Vs.
Supervisor: Anthopoulos, Thomas Sponsor: Engineering and Physical Sciences Research Council ; Plastic Logic
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral