Efficient Near-Infrared Organic Light-Emitting Diodes with Emission Peak Above 900 nm Enabled by Enhanced Photoluminescence Quantum Yields and Out-Coupling Efficiencies

Near-infrared organic light-emitting diodes (NIR OLEDs) with emission peak above 900 nm are attractive for many emerging applications, spanning from bioimaging to light detection and ranging. However, the device performance of NIR OLEDs is generally limited by the low quantum efficiency of emitters because of the fast nonradiative transition process imposed by energy-gap law and aggregation quenching. So far, only a few Pt(II) complexes delivering external quantum efficiency (EQE) over 1% are reported, while there is no comparable electroluminescence in heavy-metal-free fluorescent organic emitters. Here, NIR OLEDs centered at 934 nm by blending an acceptor-donor-acceptor type molecule Y11 into a polymer host poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4 '-(N-(4-sec-butylphenyl)diphenylamine) (TFB) are reported. The OLEDs show a remarkably high EQE of 1.72%. Moreover, owing to a low turn-on voltage (approximate to 0.9 V), the resultant NIR OLEDs have an electricity-to-light power efficiency surpassing 20 mW W-1. The improved device performance can be attributed to enhanced photoluminescence quantum yields (PLQYs) of the blends owing to suppressed aggregation quenching, and favorable light extraction from the emissive layer. Such values are the highest among fluorescent OLEDs with electroluminescence above 900 nm. Incorporating a hole-transporting polymer (TFB) into emissive fluorescent organic emitter Y11 strongly boosts the photoluminescence quantum yields (PLQY) of the film, as well as enhances the light out-coupling efficiency of the device, giving rise to efficient near-infrared OLEDs peaked at 934 nm with external quantum efficiency (EQE) over 1.7%.image