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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.

Organic Light Emitting Diodes (OLEDs) are a critical part of current consumer electronics, from mobile device displays to solid-state lighting. Thus demand for the development of industrially compatible OLED materials continues to increase. Herein, we introduce a series of solution-processible polymers incorporating a Thermally Activated Delayed Fluorescence (TADF) emitter and a host species in the side chain to finely adjust the charge transport properties. For balanced charge transport, a bipolar host polymer based on carbazole and alpha-carboline was investigated in addition to the commonly employed unipolar host mCP and an electron transporting version thereof. We demonstrate that the combination of unipolar co-hosts on one polymer chain can generate, with less synthetic effort, the same optoelectronic properties as a polymer carrying the corresponding bipolar host molecule as a pendant.

Amongst emissive materials for organic light emitting diodes (OLEDs), thermally activated delayed fluorescence (TADF) materials have shown substantial promise in the last few years. For OLEDs, solution processable and printable emissive materials are highly desirable as printing allows for precise patterning without masks, enables deposition of nanometer scale thicknesses and results in minimal wastage of material. Herein, we introduce a solution processable TADF emitting polymer as an emissive material for OLEDs. The bespoke polymer structure features the TADF emitter 4-(9H-carbazol9-yl)-2-(3′-hydroxy-[1,1′-biphenyl]-3-yl)isoindoline-1,3-dione as a pendant group on a poly(methyl methacrylate) based polymer chain. The resulting OLEDs have a peak emission wavelength of 520 nm with a maximum luminance of around 4700 cd m−2. The peak emission wavelength can be blue-shifted by exciplex management to achieve a peak wavelength of 494 nm. Critically, we employed the TADF-containing polymer system to ink-jet print OLEDs, demonstrating that such polymers are viable for printable OLEDs.