Polymer Light-Emitting Diode Using a New Electrophosphorescent Cyclometalated Iridium Complex

ABSTRACT

A new iridium-based cyclometalated complex, namely bis (2-phenylpyridine–C², N′) iridium (III) picolinate [(ppy)₂Ir(pic)] is synthesized and investigated as electrophosphorescent dopant in polymer-based organic light-emitting diodes. The photoluminescence emission from this complex is observed at 501 nm, with a shoulder at 526 nm. Poly(N-vinylcarbazole) (PVK) is used as host polymer and single-layer devices of PVK doped with (ppy)₂Ir(pic) complex are fabricated. Photoluminescence (PL) spectra of PVK films doped with different concentration of iridium complex were measured to study the possible energy transfer occurring between PVK to iridium complex. A predominant blue to a completely green shifted emission is observed when the doping concentration was increased from 0% to 5 wt%. Optical and atomic force microscopic images of the doped films indicate a smooth film formation when spin coated with chlorobenzene as a solvent as compared to chloroform. Electroluminescence spectra of ITO/PEDOT:PSS/PVK:(ppy)₂Ir(pic)/Al device resembles that of the PL spectra with emission at 507 nm and Commission Internationale de l'Eclairage (CIE) coordinates (0.29, 0.57).

Keywords:

• Current–voltage characteristics
• Electroluminescence (EL)
• Electrophosphorescence
• Energy transfer
• Film morphology
• Highest occupied molecular level (HOMO)
• Lowest occupied molecular level (LUMO)
• Luminance
• Metal-organic complex
• Organic light-emitting diodes (OLED)
• Photoluminescence (PL)
• Singlet and triplet states
• Solvent effect
• Spin-orbit coupling