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

Abstract

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 dm3 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.