High Irradiance, Low Turn-On Voltage NIR Organic Light–Emitting Diodes with Emission Peaks Centered Around 1000 nm by Introducing [Yb(DPPDA)2](DIEA) as Emitter and Regulating Carriers’ Recombination

Development of near-infrared (NIR) organic light–emitting diodes (OLEDs) with emission peaks ≈1000 nm has been restricted due to the limitation of the energy gap law. Ytterbium [bis(4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylate)](N-ethyl-N,N-diisopropyl aminium) [Yb(DPPDA)₂](DIEA) exhibits high photoluminescence quantum yield (PLQY) (6.25%) in solid state, while its emission peaks are centered ≈972 nm. The solid structure of [Yb(DPPDA)₂](DIEA) demonstrates that the high-energy oscillators have been blocked out of the inner coordination sphere of Yb³⁺, and thus the quenching effect has been alleviated. Furthermore, due to its decent physical properties, [Yb(DPPDA)₂](DIEA) is suitable to be utilized as emitter to fabricate NIR OLEDs by selecting host material to balance carriers’ distribution. Subsequently, the doping concentration of emitter, the selection of electron transporting layer (ETL), and the thickness of ETL are optimized to enhance the performances. Ultimately, the maximum NIR irradiance of 162 µW cm⁻² and the external quantum efficiency (EQE) of 0.30%, which are considerable values, are achieved. Eventually, the night vision application of NIR OLEDs based on ytterbium complexes is successfully proceeded for the first time to broaden the application prospects of ytterbium complexes.