High-field magnetic resonance spectrometer for OLEDs

• Subject Area: Condensed Matter Physics
• Term: Funded in 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431688806

In the course of this project we will acquire and install a new high-field magnetic resonance spectrometer system in order to investigate effects relating to the intrinsic spin-orbit coupling (SOC) in organic semiconductors within working organic light-emitting diodes (OLEDs). Under magnetic resonance, the spin dependent recombination of electrically injected electrons and holes within an OLED is modified, which can be detected in the device current or in the electroluminescence. The SOC gives rise to a shift of the electronic g factor of the recombinant species from that of the free electron. Because of disorder, this shift gives rise to an additional spectral broadening mechanism of the magnetic resonance which becomes relevant at large Zeeman splitting energies and therefore at high resonant frequencies and magnetic fields. These operating conditions are necessary because, at low frequencies, the resonance is inhomogeneously broadened by the local hyperfine fields present in the material. The goal of the project within the framework of the Collaborative Research Centre 1277 “Emergent relativistic effects in condensed matter” is to identify microscopic material properties such as the intra- and intermolecular morphology, which exhibit an impact on the SOC and therefore enable a controlled tuning thereof. A central aspect of the project lies in the application of dual OLED emitter materials developed in the group, which show simultaneous luminescence from the singlet (fluorescence) and triplet (phosphorescence) states and therefore offer direct insight into the spin statistics of the electron-hole recombination process. To enable such studies, the spectrometer must allow optical access to the sample volume.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Spezial-Hochfeld-EPR-Spektrometer für OLEDs
• Instrumentation Group: 1770 Elektronenspinresonanz-Spektrometer (EPR, ESR)
• Applicant Institution: Universität Regensburg
• Leader: Professor Dr. John Lupton