Inkjet‐Printed Self‐Hosted TADF Polymer Light‐Emitting Diodes

Abstract

Thermally activated delayed fluorescent (TADF) materials are extensively investigated as organic light‐emitting diodes (OLEDs) with TADF emitting layers demonstrating high efficiency without the use of heavy metal complexes. Therefore, solution‐processable and printable TADF emitters are highly desirable, moving away from expensive vacuum deposition techniques. In addition, using emissive materials not requiring an external host simplifies the fabrication process significantly. Herein, OLEDs using a solution‐processable TADF polymer that do not need an external host are introduced. The non‐conjugated TADF polymer features a TADF emitter (4‐(9H‐carbazol‐9‐yl)‐2‐(3′‐hydroxy‐[1,1′‐biphenyl]‐3‐yl)‐isoindoline‐1,3‐dione) as a side chain, as well as a hole‐transporting side chain and an electron‐transporting side chain on an inactive polymer backbone. All organic layers of the OLEDs are fabricated using solution processing methods. The OLEDs with inkjet‐printed emissive layers have comparable maximum current and external quantum efficiency as their spin‐coated counterparts, exceeding luminance of 2000 cd m−2. The herein‐explored strategy is a viable route toward self‐hosted printable TADF OLEDs.

Flexible Ink‐Jet Printed Polymer Light‐Emitting Diodes using a Self‐Hosted Non‐Conjugated TADF Polymer

“…In our earlier report on OLEDs with the self‐hosted TADF polymer, D3P‐DEH, which has the same emitting species E1, we used two unipolar hosts based on the commercial host materials, 1,3‐di(9H‐carbazol‐9‐yl)benzene (mCP). [ 16 ] Compared to ambipolar hosts, featuring a combination of two unipolar hosts within the polymer has the advantage of enabling a simpler approach to adjust the balancing of charges by varying the monomer ratios, as well as avoiding the generally low‐yielding asymmetric synthesis. [ 20 ] For D3P‐CEC, the (monomer) synthesis is further simplified through the use of carbazole and α ‐carboline units as pendant groups replacing more complex hosts such as mCP.…”

“…We recently reported the synthesis of several non-conjugated self-hosted TADF polymers and for the current work on flexible OLEDs, we have chosen the polymer D3P-CEC (Figure 1A). [16,20] It has the emitting species 4-(9H-carbazol-9-yl)-2-(3′-hydroxy-[1,1′-biphenyl]-3-yl)-isoindoline-1,3-dione (E1) and two unipolar hosts, carbazole (M2, 46.8 mol.%) and 𝛼-carboline (46.8 mol.%) (M3) as pendants in the methacrylate-based polymer chain, with a number average molecular weight of 30 kDa and a dispersity of 3.6. In our earlier report on OLEDs with the self-hosted TADF polymer, D3P-DEH, which has the same emitting species E1, we used two unipolar hosts based on the commercial host materials, 1,3-di(9H-carbazol-9-yl)benzene (mCP).…”

“…[4,[10][11][12][13][14] Although there are countless materials under development for solution-processed TADF OLEDs, only a handful have been demonstrated in TADF OLEDs with ink-jet printed emissive layers. [15][16][17][18][19] Furthermore, only a couple of reports are on fully solution-processed organic layers within the OLEDs, one being our earlier work on self-hosted TADF OLEDs. [16,17] Further research into readily processable materials and devices is necessary to further develop pathways toward the scalable fabrication of TADF OLEDs.…”

“…[15][16][17][18][19] Furthermore, only a couple of reports are on fully solution-processed organic layers within the OLEDs, one being our earlier work on self-hosted TADF OLEDs. [16,17] Further research into readily processable materials and devices is necessary to further develop pathways toward the scalable fabrication of TADF OLEDs.…”

A simplified approach to thermally activated delayed fluorescence (TADF) bipolar host polymers

“…A more-in-depth study of the performance in ink-jet printed OLEDs of the TADF copolymer P6 with two unipolar co-hosts is reported elsewhere. 28…”