Improving Luminescent Performances of Thermally Activated Delayed Fluorescence Conjugated Polymer by Inhibiting the Intra‐ and Interchain Quenching

Abstract

Suppressing emission quenching is still a real issue for thermally activated delayed fluorescence (TADF) materials as the emitters generally tend to aggregate in condensed film, leading to deteriorating performance in devices. In contrast to the TADF small molecules adopting host–guest systems, polymers possess the advantage that the TADF chromophore can be chemically dispersed into the backbone and thus the quenching process can be inhibited effectively. Here, a strategy applied to the conjugated polymer is presented, in which a TADF chromophore with controlled content is embedded into the backbone of polycarbazole through its donor moiety. The oligomeric carbazole segment acts as the role of “blocking segment,” suppressing the intra‐ and interchain interactions. The polymers therefore exhibit superior photoluminescence quantum yield of up to 92.1%. More importantly, the efficiency roll‐offs of the relevant devices are significantly reduced, offering an external quantum yield (EQE) of 15.6% even at luminance of 1000 cd m−2, corresponding to 92.3% to the maximum EQE.

Thermally Activated Delayed Fluorescent Polymers: Structures, Properties, and Applications in OLED Devices

“…A series of conjugated polymers PCzAPTx (Figure ) (x means the percentages of TADF units) was prepared and the distance between TADF chromophores was regulated through carbazole oligomer as “blocking segments.” The triplet‐quenching effect in the film can effectively be reduced by increasing the content of the blocking segment, with PLQY rising from 50.0% ( PCzAPT50 ) to 92.1% ( PCzAPT10 ). A non‐doped OLED device with the structure ITO/PEDOT:PSS (50 nm)/EML ( PCzAPT10 ) (40 nm)/TmPyPB (80 nm)/LiF (1 nm)/Al (100 nm) was fabricated with a maximum EQE of 16.9% with greenish‐yellow emission, and a reduced roll‐off . In further research, the TADF unit 9,9‐dihexal‐10‐(4‐(4,6‐di‐tert‐butyl‐1,3,5‐triazin‐2‐yl)phenyl)‐9,10‐dihydroacridine ( APT ) was replaced by a more rigid acceptor, 10‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐9,9‐dimethyl‐9,10‐dihydro‐acridine (ATD or MAC‐TRZ ), to prepare four conjugated polymers PCzATDx (Figure ) with different contents of ATD units, while the other two monomers remained unchanged.…”

Effect of a Pendant Acceptor on Thermally Activated Delayed Fluorescence Properties of Conjugated Polymers with Backbone‐Donor/Pendant‐Acceptor Architecture

“…[10] In dilute solution, only the polymer PCzAB2Py50s hows as ingle emission at 587 nm, whereas the others with 25-0.5 mol %c ontento ft he TADF unit exhibit ad ual emission profile peaked around 590 and 420 nm, of which the latter is assigned to the carbazole fragment. [57][58][59][60] In contrast, the neat films of PCzAB2Py50-PCzAB2Py5 merely display as ingle peak at 579-555 nm, whereas dual emissions are observed only in PCzAB2Py1 and PCzAB2Py0.5, implying that stronger interchaini nteraction occurs in film. These photophysicalb ehaviors are similar to the other two sets of polymers, PCzA3PyBa nd PCzAB3Py,a sw ell as PABPC.…”

“…[43] In our recent work, the differences in TADF behavior were also observed owing to using different pendant acceptors in the polymers with backbone-donor/pendant-acceptor (BDPA) architectures. [55][56][57][58][59][60][61] The solution-processed device based on the polymers with BP as the pendanta cceptora chieved the higher EQE than those with formylphenyl pendant acceptor,a lthough the devices had similar emissive wavelength with low turn-on voltages ands low efficiency roll-offs. [59,60] The results provide an incentive to further develop the TADF polymer by meanso f replacing the pendant acceptor so as to furnish improved EL performance, especially with other emission colors to supplement the numerous green TADF materials.O nthe basis of this consideration, three isomeric benzoylpyridine derivatives are selected as pendanta cceptorst oc reate three sets of conjugated polymers,P CzA3PyB, PCzAB2Py,a nd PCzAB3Py,w ithi dentical backbones.…”

Synthesis and electroluminescent performance of thermally activated delayed fluorescence‐conjugated polymers with simple formylphenyl as pendant acceptor

“…According to the unambiguous principle, a great number of TADF small molecular compounds have been designed and synthesized . By contrast, the TADF polymer, more suitable for the solution processing technology, lags behind, although a few efficient TADF polymers have been developed by means of various strategies over recent years …”

“…In the previous reports, a backbone‐donor/pendant‐acceptor (BDPA) strategy has been confirmed to be valuable for developing TADF conjugated polymers due to the excellent heritage of the intrinsic twisted D/A structure from the corresponding small molecules . The polymers exhibit high photoluminescent quantum yield (PLQY) of up to 71% and superior electroluminescent (EL) performance with the maximum external quantum efficiency (EQE) of up to 19.4% .…”