Stable and Narrowband Blue Phosphorescent OLEDs Based on Tetradentate Pt(II) Complexes Achieving EQE Close to 35% with Improved Device Lifetime

Blue organic light-emitting diode (OLED) with high efficiency, good color purity and long operational lifetime is still in demand. Tetradentate cyclometalating Pt(II) complexes hold a great promise to fulfill these criteria. Herein a modulation of the electronic structure through cyano-functionalization is reported towards a robust blue phosphor. The blue Pt(II) complexes exhibit near unity photoluminescence quantum yields, narrow full-width-at-half-maxima and enhanced stability. The devices utilizing PtON-TBBI-p-CN achieve a maximum external quantum efficiency (EQE) of 34.9% and a peak luminance up to 67384 cd m^-2 with CIE coordinates of (0.13, 0.18). The operational lifetimes of the devices are improved with LT₉₀ reaching 146 h, which represents a 2.7-fold increase over the reference complex PtON-TBBI (54 h) in the same device setting. Theoretical studies reveal that CN-functionalization simultaneously increases bond-dissociation energies for the susceptible Pt─N and C─N bonds and the energy difference between ³MC and T₁ states, which are conceived to account for the enhanced stability. This study suggests that the modulation of electronic structure through simple functionalization can be further explored for the development of robust blue phosphorescent Pt(II) emitters based on the most promising tetradentate ligand skeleton.