Single-molecule studies of OLED emitters: towards a comprehensive understanding of disorder in host-guest organic semiconductor systems

• Applicant: Dr. Francisco Tenopala Carmona
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 548649522

Organic semiconductor light-emitting molecules are promising carbon-based materials that can efficiently convert electronic excitations into light and thus allow the realization of organic light-emitting diodes (OLEDs). These molecules can be deposited from solution or via thermal evaporation in vacuum to form macroscopically homogeneous thin films that enable the fabrication of versatile, flexible, and light-weight devices. However, these materials have an intrinsic level of disorder at the microscopic scale. This means that variations between the specific configurations of the individual molecules within these films can significantly impact the performance of devices, and our current understanding of the effect of such disorder is limited by the sensitivity of state-of-the-art measuring methods.In this project, I will apply single-molecule microscopy and spectroscopy tools to measure distributions in the orientation and the conformation of individual electroluminescent molecules used in OLEDs. The outstanding sensitivity and resolution provided by these techniques will allow me to obtain unprecedented information about how the orientation, conformation, and luminescence of emitter molecules are influenced by their molecular structure and their microscopic environment. At an initial stage, I will aim at understanding how the chemical structure of these molecules influences their orientation distributions in different host materials. Then, I will study changes in these distributions across different positions in films with thicknesses relevant to the individual layers of OLEDs (around 20 to 50 nm thick), which I will relate to changes in the configuration of host molecules across the film. In a following stage, I will study the effect of the electronic and optical properties of different host molecules through changes in the photoluminescence of individual emitter molecules. Finally, I will use the knowledge gained in the first two stages to study how the conformation and electronic properties of individual molecules are influenced by different host materials. The information provided by this project will allow me to provide guidelines for the design and processing of OLED emitters, as well as to improve current theoretical models of these systems.

• DFG Programme: Research Grants
• International Connection: Belgium, Italy, United Kingdom
• Cooperation Partners: Dr. Gordon Hedley; Professor Dr. Yoann Olivier; Professorin Dr. Anna Painelli