title: 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) 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.
authors.affiliation: State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (P.R. China).
authors.forename: Liang
authors.initials: L
authors.lastname: Zhou
authors.forename: Chun-Lam
authors.initials: CL
authors.lastname: Kwong
authors.forename: Chi-Chung
authors.initials: CC
authors.lastname: Kwok
authors.forename: Gang
authors.initials: G
authors.lastname: Cheng
authors.forename: Hongjie
authors.initials: H
authors.lastname: Zhang
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
keywords: Schiff bases; doping; electroluminescence; energy transfer; platinum