Acceptor modification of diindolocarbazole embedded multiple-resonance emitters for efficient narrowband deep-blue OLEDs with CIEy ≤ 0.08 and alleviated efficiency roll-off

Abstract

Diindolocarbazole embedded multiple-resonance emitters have shown unique advantages in achieving narrowband deep-blue organic lighting emitting diodes (OLEDs). However, the severe efficiency roll-off still challenges their further applications. Herein, two efficient narrowband deep-blue emitters, pICz-PPO and pICz-2PPO, are designed and synthesized via an acceptor modification strategy to optimize the charge carrier mobility and thus the efficiency roll-off issue is addressed. Both emitters show narrowband deep-blue emission with narrow full width at half maximum (FWHM), high efficiency, and excellent color purity. The pICz-2PPO device exhibits a high maximum external quantum efficiency (EQE_max) of 17.7% and pure deep-blue emission peaking at 441 nm with a narrow FWHM of 24 nm and CIE coordinates of (0.16, 0.07). More importantly, the significantly alleviated efficiency roll-off is achieved by taking advantage of the balanced charge carrier mobility introduced by the PPO unit with excellent electron-transporting ability, manifesting that the appropriate charge carrier mobility modification can validly suppress the efficiency roll-off without the sacrifice of the efficiency and color purity. Surprisingly, the pICz-2PPO device exhibits the highest EQE of 12.8% amongst all the reported deep-blue devices based on pICz derivatives (below 10%) at an equivalent brightness of 100 cd m⁻². This work provides guidance to develop efficient multiple-resonance materials for OLEDs with low efficiency roll-off.