Efficient Red Electroluminescent Devices with Sterically Hindered Phosphorescent Platinum(II) Schiff Base Complexes and Iridium Complex Codopant

Sterically hindered platinum(II) Schiff base complexes were prepared. Complex 4 , which displays red emission with a quantum yield of 0.29 in a thin film and a self‐quenching rate constant of 1×10 −7  dm 3  mol −1  s −1 , was used to fabricate organic light‐emitting diodes with single or double emissive layers (EMLs). An iridium(III) complex with a wide band gap was codoped into the electron‐dominant EML to act as a deep electron trapper, and red‐light‐emitting devices with the highest current, power, and external quantum efficiencies of 20.43 cd A −1 18.33 Lm W −1 , and 11.7 %, respectively, were fabricated. A high current efficiency and EQE of up to 14.69 cd A −1 and 8.3 %, respectively, were achieved at a high brightness of 1000 cd m −2 . The significant delay of efficiency roll‐off is attributed to the bulky 3D structure of the norbornene moiety at the periphery of the Schiff base ligand of 4 and to the new device design strategy. The fabricated device had a projected lifetime (LT50) of 18 000 h.