Light emitting electrochemical cells and compounds

Abstract

Charged organic thermally activated delayed fluorescence (TADF) species are described. A light-emitting electrochemical cell (LEEC) includes the charged organic thermally activated delayed fluorescence (TADF) species and sufficient counter ions to balance the charge on the charged organic thermally activated delayed fluorescence species, as emitter material. Also disclosed are OLEDSs containing the TADF species.

Description

FIELD OF THE INVENTION[0001]The present invention is directed to the provision of Light Emitting Electrochemical Cells (LEECs) and luminescent emitter compounds for use in LEECs, in particular to Thermally Activated Delayed Fluorescence (TADF) compounds for use in LEECs or other light emitting devices.BACKGROUND TO THE INVENTION[0002]Organic Light Emitting Diodes (OLEDs) have come to the fore as the state-of-the-art technology for visual displays and lighting. OLEDs are desirable as they are light weight, flexible, provide better contrast and possess large viewing angle. OLEDs are also more power efficient than traditional lighting sources and thus their wide adoption can alleviate significantly the strain on current energy demand because lighting alone constitutes about 20% of energy consumption worldwide.[0003]The “first generation” OLEDs were based on organic fluorescent emitters whose efficiency was intrinsically capped at 25% due to only being able to recruit singlet excitons. ...

AI Technical Summary

Benefits of technology

[0021]The charged organic thermally activated delayed fluorescence (TADF) species does not contain a metal, although the counter ions may be metal cations if the TADF species is negatively charged. For example alkali metal cations. This absence of metal in the organic TADF species provides benefits in terms of cost and can avoid toxicity caused by the presence of heavy metals. The TADF species can provide the benefits in terms of high efficiencies found with OLED devices but in use in a LEEC, by virtue of the charge and corresponding counter ions. The charged organic thermally activated delayed fluorescence (TADF) species and its accompanying counter ions can present the advantage of good solubility allowing solution processing, for example inkjet type printing when fabricating display devices, especially when fabricating large displays. The benefits of solution processing can be employed when fabricating OLEDs or LEECs. Other benefits of LEECs can be realised, such as the ability to fabricate the device in air and the ability to use air stable electrodes.

[0022]The emitter material of the light-emitting electrochemical cell (LEEC) may comprise, consist of, or consist essentially of a TADF species that includes a charged substituent or charged substituents. The charged substituents may be an integral part of the TADF species i.e. the charged substituent may exhibit or contribute to either acceptor or donor behaviour that provides the TADF effect.

[0067]Where used as a substituent on a donor moiety D as described herein, phosphine oxide or phosphine sulphide acts to moderate the character of the donor and can therefore alter the photo physical behaviour of a TADF compound, for example resulting in a change in colour and or intensity of emission.

Problems solved by technology

Despite their highly desirable performance characteristics, the rarity of these metals, their high cost and their toxicity are important detracting features that inhibit large-scale, worldwide adoption of OLED technology.

However, current OLEDs, including TADF-OLEDs, still employ air sensitive electrodes requiring encapsulation, are vacuum deposited limiting the size of the device, and possess a complex multi-layer architecture that add to the cost of fabrication.

As with their use in OLEDs the use of rare heavy metal complexes in LEECs presents challenges.

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