Triplet harvesting in poly(9-vinylcarbazole) and poly(9-(2,3-epoxypropyl) carbazole) doped with CdSe/ZnS quantum dots encapsulated with 16-(N-carbazolyl) hexadecanoic acid ligands

Abstract

Semiconductor quantum dots (QDs) can be used as alternative for transition metal complexes to harvest the nonemissive triplet excitons in organic light-emitting diodes (OLEDs). In search for a QD-based OLED material generating blue emission, poly(9-vinylcarbazole) (PVK) and poly(9-(2,3-epoxypropyl) carbazole) (PEPK) are chosen as host for blue-emitting CdSe/ZnS core/shell QDs. The QDs are encapsulated with 16-(N-carbazolyl) hexadecanoic acid (C16), a ligand terminated by a carbazole moiety. As alternative for PVK, PEPK, where the lower molecular weight and less extensive excimer formation could promise a better film formation and more extensive exciton hopping, is explored. The efficiencies of singlet (ΦENTS) and triplet (ΦENT T) energy transfer to the C16 capped QDs are estimated by combining stationary photoluminescence spectra and fluorescence decays of pristine polymer films with those of polymer films doped with the QDs. At a loading of 30 wt % of the QDs, ΦENT S increases from 12 ± 1% in PVK to 41 ± 2% in PEPK while ΦENT T increases from 37 ± 22% in PVK to 72 ± 48% in PEPK. The investigation of the film morphology by atomic force microscopy confirms that the main factor limiting the triplet transfer efficiency in the PVK matrix is the clustering of the C16 capped QDs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 539-551 To enhance the efficiency of polymer light-emitting diodes, the polymer is often doped with a triplet emitter. In order to obtain a blue-emitting material, PVK and PEPK are chosen as fluorescent polymer matrices for blue-emitting CdSe/ZnS quantum dots (QDs), encapsulated with a carbazole-terminated ligand. The better miscibility and less extensive excimer formation enhance the efficiency of both singlet and triplet energy transfers to the QDs significantly in PEPK compared to PVK. Copyright © 2014 Wiley Periodicals, Inc.