Highly efficient single-layer organic light-emitting devices using cationic iridium complex as host

Highly efficient single-layer organic light-emitting devices (OLEDs) based on blended cationic Ir complexes as emitting layer have been demonstrated using narrow band gap cationic Ir complex [Ir(Meppy)2(pybm)](PF6) (C1) as guest and wide band gap cationic Ir complex [Ir(dfppy)2(tzpy-cn)](PF6) (C2) as host. As compared with single cationic Ir complex emitting layer, these host–guest systems exhibit highly enhanced efficiencies, with maximum luminous efficiency of 25.7 cd/A, external quantum efficiency of 8.6%, which are nearly 3-folds of those of pure C1-based device. Compared with a multilayer host-free device containing C1 as emitting layer and TPBI as electron-transporting and hole-blocking layer, the above single-layer devices also show 2-folds enhancement efficiencies. The high efficiencies achieved in these host–guest systems are among the highest values reported for ionic Ir complexes-based solid-state light-emitting devices. In addition, a white-similar emission with CIE of (0.36, 0.47) has also been achieved with luminous efficiency of 4.2 cd/A as the C1 concentration is 0.1 wt.%. The results demonstrate that the ionic Ir complexes-based host–guest system provides a new approach to achieve highly efficient OLEDs upon single-layer device structure and solution-processing technique.

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► We report highly efficient single-layer OLEDs based on blended cationic Ir complexes.
► Use narrow band gap cationic Ir complex C1 as guest and wide band gap C2 as host.
► The resulted device exhibit highly enhanced efficiency of 25.7 cd/A.
► The high efficiency is nearly 3 folds of that of pure C1-based device.