Towards high-performance organic semiconductor devices: Microstructure, interlayers, and emerging applications

Thesis

The field of organic electronics mainly focuses on the lightweight, flexible, and low-cost organic semiconductors, with ultimate goals of competing with or even substituting for the conventional silicon industries, and expanding the established success in xerography and displays to more fields. As a response to the persistent pursuit of high-performance organic semiconductor devices, in this thesis we exemplify three case studies from different perspectives, namely microstructure control, interlayer engineering, and emerging applications. First, the conformation of a light-emitting copolymer, 90F8:10BT, is regulated so that the β-phase, in which the intermonomer torsion angle of a fraction of chain segments is 180°, is generated. Recognised from its characteristic absorption peak, this typical microstructure shows significant impacts on charge transport, injection, and trapping in 90F8:10BT-based light-emitting diodes, leading to pronounced enhancements in device luminance, efficiencies, and lifetime. Second, we investigate a solution-processable hole injection/transport material, copper(I) thiocyanate (CuSCN), highlighting the effect of different solvents on its properties and applications. With a set of characterisation on thin-film topography, roughness, polymorphism, composition, and chemical bonding, as well as two critical hole-injection/transport-related properties, i.e. the surface energy and the ionisation potential, we demonstrate how CuSCN interlayers processed from six different solvents can be used in various organic semiconductor devices for improved performance. Third, we explore the possibility of using organic semiconductors to facilitate the Internet of Things, and a golden opportunity comes from organic rectifiers that can play an essential role in radio-frequency identification tags. Guided by simulation results thanks to our improved device model, we fabricate and optimise three organic rectifiers using different semiconducting materials, among which the best exhibits the potential of operating at a frequency towards the ultrahigh-frequency regime. We hope that these strategies of seeking high-performance organic semiconductor devices can make some contribution to the community of organic electronics, enriching the knowledge database and opening opportunities for the upcoming research.

Authors: Wang, B

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: organic semiconductor devices; copolymer chain conformation; hole injection/transport materials; organic high-frequency rectifiers; organic semiconductors
• Subjects: Organic electronics