Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs : a combined effect of substitution position and strength of the donors
Abstract
The 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.
Citation
Si , C , Sun , D , Matulaitis , T , Cordes , D B , Slawin , A M Z & Zysman-Colman , E 2024 , ' Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs : a combined effect of substitution position and strength of the donors ' , Science China Chemistry , vol. First Online . https://doi.org/10.1007/s11426-023-1945-8
Publication
Science China Chemistry
Status
Peer reviewed
ISSN
1674-7291Type
Journal article
Description
Funding: Changfeng Si thanks the China Scholarship Council (201806890001). Dianming Sun acknowledges support from the Royal Academy of Engineering Enterprise Fellowship (EF2122-13106). We thank EPSRC (EP/W015137/1, EP/W524505/1) for financial support. Open Access funding enabled and organized by Projekt DEAL.Collections
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