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

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) 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 Pt-Ag complex 3 with dibenzo[b,d]thiophene 5,5-dioxide-3-acetylide show extremely narrow emission with the 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 is 26 nm for 4 and 28 nm for 5 in CH2Cl2 solutions. TD-DFT studies suggest that the involvement of intra-ligand transition within electron-deficient acetylide ligand is likely responsible for the narrow-band emission. Solution-processed OLEDs based on complex 4 exhibit excellent device performance with the FWHM of 37 nm in 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 of 31 and 40 nm, respectively, which represent the narrowest electroluminescence for multinuclear metal complexes. The strategy by introducing electron-transport moieties not only improves device performance but also narrows the emission width and thus enhances the color purity.