Regensburg 2022 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 12: Poster 1
CPP 12.79: Poster
Montag, 5. September 2022, 18:00–20:00, P1
Photoinduced metastable and trapped charge-carrier pairs in neat amorphous films of OLED host materials — Sebastian Lulei1, Jeannine Grüne1, Andreas Sperlich1, •Vladimir Dyakonov1, Andrei Stankevych2, Andrey Kadasshchuk2, and Anna Köhler2 — 1Experimental Physics 6, Julius Maximilian University of Würzburg, 97074 Würzburg — 2Soft Matter Optoelectronics and Bavarian Polymer Institute (BPS), 95448 Bayreuth
We discuss light-induced ESR (LESR) transients, PL-detected magnetic resonance (PLDMR), and thermally-stimulated luminescence (TSL) in neat amorphous thin films of 3’,5-di(9H-carbazol-9-yl)-[1,1’-biphenyl]-3-carbonitrile (mCBP-CN), which is commonly used as a host material for blue emitters based on thermally activated delayed fluorescence (TADF) in OLED devices. While the half-field LESR signal associated with triplet excitations shows fast saturation being comparable with the triplet lifetime, the full-field LESR featured extremely slow kinetics of both growth and decay at T=10K. The latter implies very slow accumulation and subsequent recombination of the photogenerated charge carriers due to shallow charge trapping at such low temperatures. These results are in good agreement with the observation of a long isothermal afterglow lasting up to thousands of seconds at 5K. Further, the persistent LESR signal is detected in the same temperature range as the TSL emission, implying that both are caused by the same trapped carriers. Finally, PLDMR showed signals from closed-by triplet states, emitting through fluorescence.