# Templated Bipolar Host Materials for Blue Phosphorescent Organic Light-Emitting Devices with Negligible Efficiency Roll-Offs

## TL;DR

This paper introduces new bipolar host materials that improve the efficiency of blue light-emitting devices even at high brightness.

## Contribution

The novel CBP derivatives enable blue phosphorescent devices with minimal efficiency loss at high brightness.

## Key findings

- CBPmBI and CBPPO bipolar hosts showed high triplet energy and thermal stability.
- CBPPO-based devices achieved 28.0 cd/A current efficiency and 14.4% external quantum efficiency.
- Efficiency roll-off was negligible at 5000 cd/m² brightness.

## Abstract

Host engineering is one of the most efficient approaches to maximizing the electroluminescent performance of organic light-emitting devices. Herein, two carbazole-based N,N′-Dicarbazolyl-4,4′-biphenyl (CBP) derivatives, (9-(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-3-(3-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-9H-carbazole (CBPmBI), and (9-(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazol-3-yl)diphenylphosphine oxide (CBPPO), were designed as bipolar hosts for blue phosphorescent devices. By introducing the electron-withdrawing groups to the backbone of CBP, the bipolar hosts exhibited high triplet energy, enhanced thermal stability, and balanced charge transport. The device constructed with the blue guest emitter bis[2-(4,6-difluorophenyl) pyridinato-C2,N]iridium (III) (FIrpic) showed the excellent electroluminescence performance. For instance, the CBPPO-based devices achieved a maximum current efficiency of 28.0 cd/A, a power efficiency of 25.8 lm/W, and an external quantum efficiency of 14.4%. Notably, the external quantum efficiency retained at14.1% under the brightness of 5000 cd/m2, featuring the negligible efficiency roll-off.