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

New ytterbium complexes K(Solv) x [Yb(L n ) 2 ] (Solv = ethanol and/or water) with 2-tosylaminobenzylidene-aryloylhydrazones (H 2 L 1 , aryloyl = benzoyl; H 2 L 2 , aryloyl = 2-naphthoyl) demonstrated high solubility and hole mobility ( ca. 2.6 × 10 −6 cm 2 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 −7 vs. 1.7 × 10 −6 cm 2 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(L n ) 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. An efficiency of 441 μW W −1 was obtained using a novel purposefully designed ytterbium complex as a host-free solution processable emission layer in an OLED. The value is the highest to date and was reached due to the increase of the charge mobility.