Achieving host-free near-ultraviolet electroluminescence via electronic state engineering with phosphine oxide

Developing near-ultraviolet (NUV) emitters with board band gap and high photoluminescence quantum efficiency (PLQY) is a formidable challenge for organic light-emitting diode (OLED) applications. Herein, two NUV emitters PhImPOCz and PhImPOtBuCz were designed on the basis of phosphine oxide (PO) modification. It is showed that based on crescent phenanthrene (Phen) fused with acceptor imidazole (Im) as NUV chromophore, carbazole (Cz) or 3,6-di-tertbutyl carbazole (tBuCz) donors make the molecule bipolar character to balance carrier recombination in emissive layer (EML). More significantly, besides steric hindrance for aggregation suppression, the introduction of triphenylphosphine enhances localized excited feature of the electronic states, and prevents the red shift induced by intra- and inter- molecular charge transfer, which establishes the basis for fabricating host-free NUV OLEDs. The non-doped devices based on the PhImPOCz and PhImPOtBuCz emitters achieved the low turn-on voltages of 4.2 V and 4.4 V, and the state-of-the-art external quantum efficiency (EQE) up to 2.81% and 3.42%, respectively. This work demonstrates the significance of electronic state engineering for high-energy OLED applications.

Automated summary

The development of near-ultraviolet (NUV) emitters with wide band gap and high photoluminescence quantum efficiency (PLQY) for organic light-emitting diode (OLED) applications is a significant challenge. By utilizing crescent phenanthrene (Phen) fused with acceptor imidazole (Im) as NUV chromophore, and introducing steric hindrance for aggregation suppression and triphenylphosphine to enhance electronic states, the designed PhImPOCz and PhImPOtBuCz emitters achieved low turn-on voltages and high external quantum efficiency. This work highlights the importance of electronic state engineering in high-energy OLED applications.