Modulating the carrier transport of PtAg2 heteronuclear complexes to attain highly efficient OLEDs with narrow-band emission

Abstract

High color purity with narrow-band emission is a key factor for full-color displays. However, phosphorescent metal complexes typically exhibit broad emission with a full width at half maxima (FWHM) in the range of 80–100 nm. Here, we demonstrate a facile approach to achieve narrow-band emission by introducing electron-deficient moieties with electron-transport character into PtAg₂ heteronuclear complexes. The as-synthesized PtAg₂ complex 3 with dibenzo[b,d]thiophene 5,5-dioxide-3-acetylide shows extremely narrow emission with an FWHM of 25 nm in CH₂Cl₂ solution. The narrow-band emission is further verified by another two PtAg₂ complexes containing electron-transport units such as oxadiazole (complex 4) and triphenyl-triazine (complex 5), in which the FWHM values are 26 nm for 4 and 28 nm for 5 in CH₂Cl₂ solution. TD-DFT studies suggest that the involvement of intra-ligand transition within an electron-deficient acetylide ligand is likely responsible for the narrow-band emission. Solution-processed OLEDs based on complex 4 exhibit excellent device performance with an FWHM of 37 nm in the electroluminescent spectrum and the highest current efficiency (CE) of 69.5 cd A⁻¹, power efficiency (PE) of 50.5 lm W⁻¹ and external quantum efficiency (EQE) of 18.2%. The narrow-band electroluminescence is also attained in complexes 3 and 5 with the FWHM values of 31 and 40 nm, respectively, which represent the narrowest electroluminescence for multinuclear metal complexes. This strategy of introducing electron-transport moieties not only improves the device performance but also narrows the emission width and thus enhances the color purity.