Advanced Device Architecture for Highly Efficient Organic Light-Emitting Diodes with an Orange-Emitting Crosslinkable Iridium(III) Complex

Rehmann, Nina; Ulbricht, Christoph; Köhnen, Anne; Zacharias, Philipp; Gather, Malte C.; Hertel, Dirk; Holder, Elisabeth; Meerholz, Klaus; Schubert, Ulrich S.

Abstract:

We have recently reported on solution-processed, highly efficient PHOLEDs doped with an electrophosphorescent iridium- containing triplet emitter. A key feature in these devices was the use of hole-transport layers (HTL) that were realized by the conversion of a soluble precursor into insoluble polymer films: monomeric, triarylamine-based hole-transport materials (X-HTM) with oxetanes as reactive units can be crosslinked by cationic ring-opening polymerization (CROP). Several thin films of X-HTM lead to multilayer devices with improved efficiency, partly reaching near-unity internal quantum efficiencies. However, since the matrix materials as well as the phosphorescent dopant used for the emissive layer (EML) in these devices were not crosslinked, no additional electron-conducting layer (ETL) could be added on top of the EML. Therefore, due to an imbalance of charges the recombination within the device is expected to be not optimal. Furthermore, due to the rather large amount of the triplet emitter necessary to achieve high efficiencies, phase separation and aggregation may occur during device operation. Both these problems could be overcome if the phosphorescent dopant could be co-polymerized with a crosslinkable matrix, allowing for the deposition of additional layers and introducing excellent morphological stability due to the crosslinking process.

Year:

2008

Type of Publication:

Article

Journal:

Advanced Materials

Volume:

20

Pages:

129 - 133