Record efficiency of 1000 nm electroluminescence from a solution-processable host-free OLED

New ytterbium complexes K(Solv)_x[Yb(Lⁿ)₂] (Solv = ethanol and/or water) with 2-tosylaminobenzylidene-aryloylhydrazones (H₂L¹, aryloyl = benzoyl; H₂L², aryloyl = 2-naphthoyl) demonstrated high solubility and hole mobility (ca. 2.6 × 10^-6 cm² V^-1 s^-1), while their electron mobility and PLQY were different. The substitution of a benzoyl substituent with naphthoyl resulted in a significant increase of the electron mobility (6.9 × 10^-7vs. 1.7 × 10^-6 cm² V^-1 s^-1) and a decrease of the quantum yield (1.2% vs. 0.6%). As a result, the optimized OLEDs based on the K[Yb(Lⁿ)₂] layer demonstrated efficiencies up to 385 μW W^-1 and 441 μW W^-1, indicating the superior importance of charge mobility over the quantum yield. These are the highest efficiencies of the Yb electroluminescence.