Blue-green phosphorescent imidazole-based iridium(III) complex with a broad full width at half maximum for solution-processed organic light-emitting diodes

Abstract

We designed and synthesized a blue-green phosphorescent iridium(III) complex for solution-processed organic light-emitting diodes (OLEDs), (DMDPI)2Ir(tftap), that contains 1,2-dimethyl-4,5-diphenyl-1H-imidazole (DMDPI) as the main ligand and 2-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl) pyridine (tftap) as an ancillary ligand. (DMDPI)2Ir(tftap) showed good solubility in common organic solvents such as dichloromethane, chloroform, toluene, and chlorobenzene. The photoluminescence (PL) spectra of (DMDPI)2Ir(tftap) showed a maximum emission peak (λmax) of 532nm in dichloromethane solution. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of (DMDPI)2Ir(tftap) were measured to be −5.36 and −2.76eV, respectively. Solution-processed blue-green OLEDs were fabricated based on (DMDPI)2Ir(tftap) with an ITO/PEDOT:PSS (30nm)/26DCzPPy:(DMDPI)2Ir(tftap) (11%) (40nm)/TPBi (60nm)/CsF (1nm)/Al structure. The electroluminescent (EL) spectra of (DMDPI)2Ir(tftap) exhibited a maximum emission peak at 522nm with a broad full-width at half-maximum (FWHM) of 115nm and Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.54) at 1000cdm−2. The device with 11% doping concentration of (DMDPI)2Ir(tftap) exhibited a maximum luminance of 6304cdm−2, a maximum luminous efficiency of 7.14cdA−1, a power efficiency of 3.63lmW−1, and an external quantum efficiency of 2.59%. Moreover, white-light-emitting devices containing a single emissive layer consisting of PVK as a polymer host, (DMDPI)2Ir(tftap) as a blue-green dopant, and (PIQ)2Ir(acac) as a red dopant were fabricated. These devices exhibited CIE coordinates of (0.42, 0.48) at 1000cdm−2, which are close to the standard warm white-light CIE coordinates of (0.44, 0.40).