Abstract
We report on light-emitting electrochemical cells, comprising a solution-processed single-layer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated delayed fluorescence. Our optimized devices delivers a luminance of 120 cd m−2 at an external quantum efficiency of 7.0%. As such, it outperforms the combined luminance/efficiency state-of-the art for thermally activated delayed fluorescence light-emitting electrochemical cells by one order of magnitude. For this end, we employed a polymeric blend host for balanced electrochemical doping and electronic transport as well as uniform film formation, an optimized concentration (<1 mass%) of guest for complete host-to-guest energy transfer at minimized aggregation and efficient emission, and an appropriate concentration of an electrochemically stabile electrolyte for desired doping effects. The generic nature of our approach is manifested in the attainment of bright and efficient thermally activated delayed fluorescence emission from three different light-emitting electrochemical cells with invariant host:guest:electrolyte number ratio.
Highlights
We report on light-emitting electrochemical cells, comprising a solution-processed singlelayer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated delayed fluorescence
For several of the projected high-volume applications it is further desirable if the constituent device materials are sustainable[16,17,18], and it is unfortunate that current efficient light-emitting electrochemical cell (LEC) and organic lightemitting diodes (OLEDs) commonly employ emitters that comprise very rare and expensive metals from the platinum group in the periodic table[19,20,21]
We demonstrate that a yellowemitting thermally activated delayed fluorescence (TADF)-LEC, with the optimized single-layer active material sandwiched between two air-stabile electrodes and with 2-[4-(diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9one (TXO-TPA) as the guest emitter, delivers a record-high external quantum efficiencies (EQEs) of 7.0% at a significant luminance of 120 cd m−2
Summary
We report on light-emitting electrochemical cells, comprising a solution-processed singlelayer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated delayed fluorescence. TADF-active emitters are increasingly being implemented in OLEDs23, and current state-of-the-art TADF-OLEDs feature luminance values well above 1000 cd m−2 for a wide range of emission colors, as well as high efficiencies, as quantified by reported external quantum efficiencies (EQEs) exceeding 30%23–27 It should, be noted that the roll-off for TADF-OLEDs commonly is significant[28], and that TADF-OLEDs typically comprise a vacuum-deposited multilayer active material and a cathode that is unstable under ambient air, with the latter translating into a relatively expensive fabrication process
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