Highly Efficient Near‐Infrared Electroluminescence up to 800 nm Using Platinum(II) Phosphors
Sheng Fu Wang, Yi Yuan, Yu‐Chen Wei, Wei‐Hsiang Chan, Li‐Wen Fu, Bo‐Kang Su, I‐Yun Chen, Keh‐Jiunh Chou, Po‐Ting Chen, Hsiu‐Fu Hsu, Chang‐Lun Ko, Wen‐Yi Hung, Chun‐Sing Lee, Pi‐Tai Chou, Yün Chi
Abstract
Abstract Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes ( 1 – 4 ) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ * energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm −2 .