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Title: Solution-processable n-type organic semiconductors for electronics and energy harvesting systems
Author: Rossbauer, Stephan
ISNI:       0000 0004 6423 1414
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Organic semiconductors provide a wealth of interesting properties like tailor made electrical characteristics, cost effective large area fabrication and mechanical flexibility which can be difficult to achieve with crystalline inorganic semiconductors. However, their advance into applications such as logic circuits is hindered by the limited availability of high performance air-stable n-type materials, which limits organics to unipolar circuits. This thesis explores three different routes to improve the performance of n-type organic semiconductors. Firstly a novel air-stable small molecule with mobilities of up to 0.6 cm2/Vs in TFTs is presented. We blend the small molecule with a polymer to improve the thin film smoothness and homogeneity. In combination with an established p-type small molecule:polymer blend semiconductor we demonstrate an air-stable, solution processed, complementary inverter with gains above 5. Secondly we use doping to enhance the properties of Fullerene semiconductors. The efficiency of the doping process is found to depend strongly on the Fullerene derivative used as matrix material, but where it is effective, we see an increase in charge carrier mobility by the filling of shallow trap states and enhanced bias stress stability. Thirdly we investigate a new patterning process called adhesion lithography for metal electrodes, which is compatible with high throughput fabrication. We use the process to manufacture asymmetric electrodes with a distance below 15 nm. Taking advantage of the short distance and the small parasitic capacitance of the structure we fabricate Schottky diodes based on Fullerenes with operating frequencies exceeding 20 MHz. These diodes can be used in wireless communication or energy harvesting systems. The findings may help to develop new materials and processes for the next generation of organic semiconductors.
Supervisor: Anthopoulos, Thomas D. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral