Solution-processed Red Organic Light-emitting Diodes Research Articles

Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs: a combined effect of substitution position and strength of the donors

AbstractThe development of high-performance solution-processed red organic light-emitting diodes (OLEDs) remains a challenge, particularly in terms of maintaining efficiency at high luminance. Here, we designed and synthesized four novel orange-red thermally activated delayed fluorescence (TADF) dendrimers that are solution-processable: 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz. We systematically investigated the effect of substitution position and strength of donors on the optoelectronic properties. The reverse intersystem crossing rate constant (kRISC) of the emitters having donors substituted at positions 11 and 12 of the dibenzo[a,c]phenazine (BP) is more than 10-times faster than that of compounds substituted having donors substituted at positions 3 and 6. Compound 2DPACzBP, containing stronger donors than 2GCzBP, exhibits a red-shifted emission and smaller singlet-triplet energy splitting, ΔEST, of 0.01 eV. The solution-processed OLED with 10 wt% 2DPACzBP doped in mCP emitted at 640 nm and showed a maximum external quantum efficiency (EQEmax) of 7.8%, which was effectively maintained out to a luminance of 1,000 cd m−2. Such a device∙s performance at relevant display luminance is among the highest for solution-processed red TADF OLEDs. The efficiency of the devices was improved significantly by using 4CzIPN as an assistant dopant in a hyperfluorescence (HF) configuration, where the 2DPACzBP HF device shows an EQEmax of 20.0% at λEL of 605 nm and remains high at 11.8% at a luminance of 1,000 cd m−2, which makes this device one of the highest efficiency orange-to-red HF SP-OLEDs to date.

New ionic iridium(III) complexes based on methoxyl-modified 1-phenylisoquinoline for solution-processed red organic light-emitting diodes

Three transition-metal phosphorescent iridium(Ⅲ) complexes (Ir1, Ir2, and Ir3) are designed and synthesized with 1-phenylisoquinolines modified by methoxy as the main ligands and o-phenanthroline as the auxiliary ligands. The introduction of different amounts of methoxy can change the luminescence color of the complexes, and Ir1, Ir2, and Ir3 show orange, dark red, and red phosphorescence under the excitation of 365 nm UV lamp, peaking at 588, 648, and 622 nm, respectively. Ionic complexes are conducive to the efficient solution-processed phosphorescent red organic light-emitting diodes (OLEDs). Among the three devices, the Ir2-based device achieved a relatively high external quantum efficiency, current efficiency, and power efficiency of 1.12 %, 0.75 cd/A, and 0.37 lm/W, respectively. These results indicated that polymethoxy-based ionic Ir(III) complexes have great potential for the fabrication of red OLEDs with wet method.

Two novel neutral and ionic Ir(iii) complexes based on the same bipolar main ligand: a comparative study of their photophysical properties and applications in solution-processed red organic light-emitting diodes

A bipolar ligand design for solution-processed red Ir(iii) complex OLED.

Efficient solution-processed orange-red organic light-emitting diodes based on a novel thermally activated delayed fluorescence emitter

A novel thermally activated delayed fluorescence (TADF) emitter was designed and synthesized for solution-processed red organic light-emitting diodes (OLEDs).

Power-efficient solution-processed red organic light-emitting diodes based on an exciplex host and a novel phosphorescent iridium complex

A novel red heteroleptic iridium complex, Ir(DPA-Flpy-CF3)2acac, was synthesized and whose corresponding solution-processed PhOLED shows a record power efficiency of 44.5 lm W−1 with CIE coordinates of (0.64, 0.36).

Novel Thieno-[3,4-b]-Pyrazines Cored Dendrimers with Carbazole Dendrons: Design, Synthesis, and Application in Solution-Processed Red Organic Light-Emitting Diodes

A series of novel red-emitting thieno-[3,4-b]-pyrazine-cored molecules containing oligo-carbazole dendrons (called C1-TP, C2-TP) are synthesized. Their photophysical, electrochemical, and electroluminescent properties are investigated. The peripheral carbazolyl units facilitate the hole transporting ability and inhibit the intermolecular interactions, but quench the fluorescence of the thieno-[3,4-b]-pyrazine core through Intramolecular Charge Transfer (ICT). Introduction of a polyphenyl spacer between the core and the first generation carbazole dendrons, i.e., C-DTP, decreases the ICT efficiency. In addition to providing the site-isolation effect on the planar emissive core, these bulky dendrons enable these molecules to be solution processable. As a result, efficient OLEDs with saturated red emission are fabricated by spin coating technique using these dendritic materials as nondoped emitting layer. C-DTP exhibits much better device performance than C1-TP and C2-TP, while the small molecular reference compound containing neither the spacer nor the carbazole dendrons (TP) fails to transmit pure red emission under identical conditions. A brightness of 925 cd m(-2) and a luminous efficiency of 0.53 cd A(-1) are obtained for C-DTP, which are comparable with OLEDs fabricated from thieno-[3,4-b]-pyrazine-based counterparts by the vacuum deposition method or those assembled with other red fluorescent dendrimers via the solution processing method.

Highly efficient solution-processed red organic light-emitting diodes with long-side-chained triplet emitter

Newly synthesized red Ir complexes tris[2-(4-n-hexyl-phenyl)quinoline]iridium(III) and tris[(4-n-hexylphenyl)isoquinoline)]iridium(III) with long alkyl side chains are utilized to demonstrate the high efficiency multi-layer solution-processed red organic light-emitting diodes. Solubilities of these triplet emitters are high which enable them to be uniformly dispersed in the polymer host. Blade coating method is utilized to prepare organic multi-layers without mutual dissolution between different layers. 17cd/A current efficiency, 10lm/W power efficiency, and 8.8% external quantum efficiency can be achieved for the device with CsF/Al cathode. 10,000cd/m2 is reached at 10V. Similar quantum efficiency is also achieved with an electron-transport layer and LiF/Al cathode.