Abstract
Thermally activated delayed fluorescence (TADF) materials emerged as promising light sources in third generation organic light-emitting diodes (OLED). Much effort has been invested for the development of small molecular TADF materials and vacuum process-based efficient TADF-OLEDs. In contrast, a limited number of solution processable high-molecular weight TADF materials toward low cost, large area, and scalable manufacturing of solution processed TADF-OLEDs have been reported so far. In this context, we report benzophenone-core carbazole dendrimers (GnB, n = generation) showing TADF and aggregation-induced emission enhancement (AIEE) properties along with alcohol resistance enabling further solution-based lamination of organic materials. The dendritic structure was found to play an important role for both TADF and AIEE activities in the neat films. By using these multifunctional dendritic emitters as non-doped emissive layers, OLED devices with fully solution processed organic multilayers were successfully fabricated and achieved maximum external quantum efficiency of 5.7%.
Highlights
Emissive molecules show weaker photoluminescence (PL) in neat films than in solutions due to concentration quenching
These materials have been utilized for conventional fluorescence OLEDs10–14, though only singlet excitons can be utilized for electroluminescence (EL) in fluorescence organic light-emitting diodes (OLED)
We report benzophenone-core carbazole dendrimers (GnB, n =generation) as aggregation-induced emission enhancement (AIEE) and thermally activated delayed fluorescence (TADF) active emitters for non-doped EMLs in OLED devices with fully solution processed organic multilayer fabricated by OS approach
Summary
ΦTADF of G1B at 300 K was calculated to be only 0.004% and no delayed components were detectable at lower temperatures, indicating that the TADF activity of G1B was significantly deactivated in the aggregated state presumably due to intermolecular interaction These results illustrate the importance of dendritic structure to exhibit TADF activity in GnB neat films. G1B was tested as a control experiment (Fig. 4(a)) In this case, PL spectra of G1B-PMMA composite films showed spectral redshifts as the G1B content increased, but the degree of redshift was small as compared to G2B and G3B. The results indicate that solid aromatic media (including G2B and G3B themselves) could help to increase PLQY by restricting intramolecular motions (such as rotation) through π-πinteraction These observations exemplify that the optical property of GnB is influenced by the surrounding matrix. Thick G2B film (35 nm) was found to mitigate EQE roll-off at high current density, likely due to lowered probability
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