Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 2: Electrical, Dielectrical and Optical Properties of Thin Films I

CPP 2.2: Talk

Monday, March 12, 2018, 09:45–10:00, C 230

Investigation of Charge Carrier and Electric Field Distribution in OLEDs by Means of Photoluminescent Molecular Probes — •Thomas Ferschke¹ and Jens Pflaum^1,2 — ¹Experimental Physics VI, Julius Maximilian University, 97074 Würzburg — ²ZAE Bayern, 97074 Würzburg

Recently, it has been shown that current densities can be determined on nanometer length scales by means of photoluminescence (PL) studies on single guest dye molecules.[1] Here we transfer this concept to common Alq₃/α-NPD OLEDs by utilizing Tetraphenyldibenzoperiflanthene (DBP) entities as molecular probes. DBP is intentionally embedded as dopant (0.1 v-%) at defined depth within the Alq₃ emissive layer. Upon charge injection a reduction in dopant PL is observed which can be attributed to non-radiative electron - exciton interaction. The macroscopic current density scales related to the PL quenching with the distance from the injecting electrode in qualitative agreement with a SCLC model. The validity of this model and thus, variations in vertical charge carrier distribution are studied as a function of current density. Even at reverse bias condition PL quenching of DBP guest molecules in proximity of 5 nm to the Alq₃/α-NPD interface is observed. This can be attributed to strong localized electric fields at the interface caused by interfacial charges of Alq₃.[2] In addition to quenching measurements a comparative study on the integral interface charging is performed by means of impedance spectroscopy.

[1] Nothaft et al., ChemPhysChem, 2011, 12, 2590–2595

[2] Noguchi et al., J. Appl. Phys., 2012, 111(11):114508