Excitonics for Organic Electronics

Organic semiconductors have immense potential as replacements for traditional inorganic materials in optoelectronics applications, in particular for organic light-emitting diodes (OLEDs). At the core of the device physics governing the stability and efficiency of OLEDs are tightly bound electron-hole pairs known as excitons. Here, the link between OLED excitonics and operational stability is studied in active OLEDs. First, the exciton distribution is investigated in active OLEDs with doped and undoped emissive layers. In both types of OLEDs, a surprisingly narrow exciton formation zone was measured given the bipolar nature of the materials used. Next, the influence of defects on exciton diffusion is investigated. The effective singlet exciton diffusion length is measured as a function of defect concentration and operational conditions and described in a unified model. Exciton-defect interactions are central to the efficiency and stability of OLEDs; consequently, quantifying these interactions under realistic operating conditions is a major step towards a comprehensive understanding of OLED excitonics. Finally, building on these results, a simple model for singlet exciton driven degradation in OLEDs in presented. This model accounts for the time and current density dependence of the host and defect emission in degrading OLEDs and is thoroughly validated using new experimental data, as well as literature data from leading academic and industrial research groups. Results of a first look at applying these conclusions to photovoltaic devices are also included. There exists an abundance of evidence in the literature suggesting singlet exciton driven degradation is a major degradation mechanism. Undoubtedly, providing mathematical tools to quantify this process will be invaluable.

Department dc:contributor.department

Materials Science and Engineering

Year dc:date.issued

2018

Author dc:creator

• Ingram, Grayson Lee

Advisor dc:contributor.advisor

• Lu, Zheng-Hong

• Degradation
• Diffusion
• Exciton
• OLED
• Organic Electronics

Handle dc:identifier.uri

http://hdl.handle.net/1807/89751

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/89751