Dr. A. J. Gillett: "Spin-triplet exited states in organic semiconductors"

Young Investigator Seminar

Das Institut für Organische Chemie lädt ein zum Vortrag von

Dr. Alexander J. Gillett, Cavendish Laboratory der University of Cambridge

mit dem Titel:

"Spin-triplet exited states in organic semiconductors"

Abstract:

Electronic excited states with spin-triplet character play a key role in the operation of optoelectronic devices fabricated from organic semiconductors, including organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). In general, spin-triplet excitations are optically dark and lie deeper in energy than their bright spin-singlet counterparts and can thus be considered low energy trap states that are detrimental to device performance. Therefore, it is important that we develop an experimental toolkit to probe triplet states, understand their formation mechanisms, and mitigate against their detrimental effects.

In the first part of my talk, I will present some of our recent work exploring the role of triplet excited states in OPVs. I will discuss the three possible triplet exciton formation mechanisms in OPVs and how we probe them, before examining the impact of electron-hole recombination via triplet excitons on device performance. Two possible strategies to overcome the negative impact of triplet exciton recombination on OPV device performance will be demonstrated. In the second part, I will turn to OLED systems, focusing on a new class of multiple-resonance thermally-activated delayed fluorescence (MR-TADF) materials that can combine desirable narrowband blue emission with the efficient upconversion of dark spin-triplet excited states into bright singlet states via a reverse intersystem crossing (rISC) process. I will show how combining ultrafast Impulsive Vibrational Spectroscopy with quantum-chemical calculations and magnetic resonance techniques can provide a complete picture of the ISC processes in these model MR-TADF systems.