Superbly Efficient and Stable Ultrapure Blue Phosphorescent Organic Light-Emitting Diodes with Tetradentate Pt(II) Complex with Vibration Suppression Effect

Abstract

Blue phosphorescent organic light-emitting diodes (PHOLEDs) are on the brink of commercialization for decades. However, the external quantum efficiency (EQE) and operational lifetime of PHOLEDs are not yet reached industrial standards. Here, a novel tetradentate Pt(II) emitter with a spirofluorene onto the carbazole unit that minimizes the vibration modes, corresponding to the structural relaxation during the de-excitation, called the vibration suppression effect is reported. This modification reduces the intensity of the second peak in the spectrum and Shockley-Read-Hall recombination by blocking direct hole injection into the emitter while enhancing Förster resonance energy transfer, resulting in 451 h of LT₅₀ (the time until a 50% decrease in initial luminance at 1000 cd m^-2) and 25.1% of the maximum EQE (EQE_max). Thanks to the vibration suppression effect, an extremely narrow full width at half a maximum of 22 nm is obtained. In phosphor-sensitized thermally activated delayed fluorescent OLED, ultra-pure blue emission with Commission internationale de l'Eclairage (CIE) coordinates of (0.136, 0.096) is obtained with 28.1% of EQE_max. Furthermore, 50.3% of the EQE_max and 589 h of LT₇₀ are simultaneously recorded with the two-stack tandem PHOLED, which is the highest EQE_max among 2-tandem and bottom-emission PHOLEDs with CIEy < 0.15.

Keywords: Long lifetime; Phosphorescent organic light‐emitting diodes; Tandem structure; Ultrapure blue.