Dresden 2020 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 86: Organic Electronics and Photovoltaics III

CPP 86.12: Talk

Thursday, March 19, 2020, 12:30–12:45, ZEU 260

Increasing the triplet-to-singlet ratio in photoluminescence of TADF emitters using phosphorescent sensitizers: a pathway to study non-linear effects — •Paulius Imbrasas, Simone Lenk, and Sebastian Reineke — Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, 01187 Dresden, Germany

Organic emitters based on thermally activated delayed fluorescence (TADF) have been extensively investigated in the past decade. The main appeal of TADF is that it allows excited triplet state up-conversion to the singlet manifold, leading to increased light generation efficiencies. However, due to comparably long lifetimes of triplet states in TADF emitters, non-linear quenching mechanisms as triplet-triplet annihilation (TTA) or triplet-polaron quenching (TPQ) start playing a role. Adding to that, due to the nature of exciton generation in organic light-emitting diodes (OLEDs), 75% of created excitons are triplet states, which is different in the case of photophysical emitter studies. This typically leads to a high mismatch between triplet densities in photoluminescence (PL) and electroluminescence (EL). In this work, we introduce phosphorescent sensitizer molecules to TADF based emission layers to increase the triplet-to-singlet exciton density ratio under optical excitation to close the gap to EL exciton distributions. This allows us to investigate triplet-related detrimental effects under practical lab conditions. This simple and versatile approach represents a powerful toolbox to thoroughly probe unfavorable high brightness effects.