Modulating the peripheral large steric hindrance of iridium complexes for achieving narrowband emission and pure red OLEDs with an EQE up to 32.0%

Iridium (Ir)(iii) complexes with sufficient luminous efficiency and narrow full width at half maxima (FWHM) are required urgently for realizing organic light-emitting diodes (OLEDs) simultaneously with high electroluminescence efficiency and good color purity. In this work, three novel main ligands incorporating the peripheral large steric hindrance units and rigid structures for efficiently suppressing the intermolecular stacking effect, restricting the intramolecular relaxation and reducing the concentration quenching are developed. The corresponding Ir(iii) complexes exhibit emission peaks at 618, 609 and 621 nm, short phosphorescence lifetimes around 1 mu s, high photoluminescence quantum yields of 80-90% and a narrow FWHM of 40 nm in solution. Moreover, the devices based on these Ir(iii) complexes show superior performances with the Commission Internationale de L'Eclairage color coordinates of (x = 0.63-0.64 and y = 0.32-0.35), close to the standard red emission required by the National Television System Committee. In particular, the device using Ir-2CF(3) exhibits the best performances with a maximum luminance of 38 277 cd m(-2), a maximum current efficiency of 47.85 cd A(-1), and a maximum external quantum efficiency (EQE(max)) up to 32.0% as well as extremely low efficiency roll-off with an EQE of 30.8% at 1000 cd m(-2), which are among the best results ever reported for pure red OLEDs using Ir(iii) complexes. Therefore, the design of main ligands by modulating the peripheral large steric hindrance provides an effective strategy for realizing efficient Ir(iii) complex-based OLEDs simultaneously with narrow emission and high efficiency.

Automated summary

In this study, three novel main ligands were developed, which effectively suppressed the intermolecular stacking effect, restricted the intramolecular relaxation, and reduced the concentration quenching. The corresponding Ir(iii) complexes exhibited emission peaks at 618, 609, and 621 nm, short phosphorescence lifetimes, high photoluminescence quantum yields, and a narrow full width at half maxima. The devices based on these complexes showed superior performances, with Commission Internationale de L'Eclairage color coordinates close to the standard red emission and high luminance, current efficiency, and external quantum efficiency.