Dresden 2011 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Poster: Organic Semiconductors

CPP 8.36: Poster

Monday, March 14, 2011, 17:30–19:30, P2

White top-emitting OLEDs using organic colour-conversion layers for improved colour-stability — •Tobias Schwab, Simone Hofmann, Michael Thomschke, Björn Lüssem, and Karl Leo — Institut für Angewandte Photophysik, Technische Universität Dresden, D-01069 Dresden

In contrast to white organic light-emitting diodes (OLEDs) using several vertical stacked emitters [1], the principle of down-conversion gives the chance to achieve white light with a simplified layer structure and enhanced colour stability by preventing a colour shift over lifetime due to differential aging of dyes. We investigate an approach where the conversion material is integrated into a top-emitting OLED structure in a way, that only electrons can pass this layer. This assures optical excitation and avoids unwanted electrical recombination inside the conversion layer. The emission spectra, CIE-coordinates, efficiencies, and IV-characteristics depending on the conversion layer thickness have been determined and were compared to the non-emitting host-material with similar optical properties. Lifetime measurements show that these OLEDs have almost no colour change over an investigated period up to 2200 hours. It is shown that the external quantum efficiency of the OLED does not necessarily decrease with an increased conversion layer thickness, even if the photoluminescence quantum yield of these materials is below unity. This indicates that the efficiency is improved by out-coupling of isotropic re-emitted wave-guided modes.

[1] Reineke, S et al.: White organic light-emitting diodes with fluorescent tube efficiency, Nature, 2009, 459: 234-238