Deep-blue organic light-emitting diodes based on a doublet d–f transition cerium(III) complex with 100% exciton utilization efficiency

Abstract

Compared to red and green organic light-emitting diodes (OLEDs), blue OLEDs are still the bottleneck due to the lack of efficient emitters with simultaneous high exciton utilization efficiency (EUE) and short excited-state lifetime. Different from the fluorescence, phosphorescence, thermally activated delayed fluorescence (TADF), and organic radical materials traditionally used in OLEDs, we demonstrate herein a new type of emitter, cerium(III) complex Ce-1 with spin-allowed and parity-allowed d–f transition of the centre Ce3+ ion. The compound exhibits a high EUE up to 100% in OLEDs and a short excited-state lifetime of 42 ns, which is considerably faster than that achieved in efficient phosphorescence and TADF emitters. The optimized OLEDs show an average maximum external quantum efficiency (EQE) of 12.4% and Commission Internationale de L’Eclairage (CIE) coordinates of (0.146, 0.078).

Exploration of Nontoxic Cs3CeBr6 for Violet Light-Emitting Diodes

“…We note that such a short excited-state lifetime potentially enhances luminous efficiency and reduces efficiency roll-off and device degradation . More importantly, the Ce element is earth-abundant and nontoxic, and the Earth’s crust abundance of Ce is 0.006 wt %, which is comparable with that of Pb (0.010 wt %) and even higher than that of Cu (0.005 wt %) …”

“…19 More importantly, the Ce element is earth-abundant and nontoxic, and the Earth's crust abundance of Ce is 0.006 wt %, which is comparable with that of Pb (0.010 wt %) and even higher than that of Cu (0.005 wt %). 20 Based on all these advantages, we may expect excellent optoelectronic properties of Ce 3+ -based perovskites or perovskite derivatives; however, they have never been investigated for electrically driven LEDs applications so far. To ensure better thermal stability, we focus on the Cs−Ce−Br ternary system with an all-inorganic nature.…”

Highly Efficient Heteroleptic Cerium(III) Complexes with a Substituted Pyrazole Ancillary Ligand and Their Application in Blue Organic Light-Emitting Diodes

“…Organic light-emitting diodes (OLEDs) have developed rapidly over the past few decades. To achieve high efficiency, fluorescence, phosphorescence, − thermally activated delayed fluorescence, − hybridized local and charge-transfer excited-state fluorescence, , radical-based luminescence, − and d-f transition-based luminescence − have been developed sequentially. As a new type of emitter in OLEDs, d-f transition Ce­(III) complexes have significant advantages, such as short excited-state lifetimes in the range of nanoseconds, ,,− up to a 100% theoretical exciton utilization efficiency due to the spin- and parity- allowed d-f transitions, , and tunable emission colors, since the 5d energy levels are sensitive to the external environment. − …”

“…Despite all these satisfying advantages, photoluminescence (PL) research on d-f transition Ce­(III) complexes is limited. Most reported Ce­(III) complexes are nonemissive due to the luminescence quenching by ligands and solvent molecules, and the electroluminescence (EL) studies on Ce­(III) complexes are more rare. , Recently, we reported two novel Ce­(III) complexes Ce-1 and Ce-2 based on the hydrotris­(3,5-dimethylpyrazolyl)­borate (Tp Me2 ) ligand. It is found that the deep blue emissive Ce-1 showed an average external quantum efficiency (EQE) of 12.4%, while the sky blue emissive Ce-2 showed a maximum EQE up to 20.8% in their prototype OLEDs.…”

Organic Light-Emitting Diodes Based on an Iron(III) Complex with Doublet Emission

“…[17] In 2020, a new kind of OLEDs with doublet emission was reported by Liu et al, in which a novel rare earth metal cerium (III) complex which possesses a doublet blue emission from the d-f transition was used as the emitter. [18] A follow-up work was carried out and a maximum external quantum efficiency (EQE) of 20.8% was obtained. [19] Apart from radicals and cerium (III) complexes, earth-abundant transition-metal complexes with low-spin d 5 electronic structure may have the doublet metal-to-ligand charge transfer ( [Fe(phtmeimb) 2 ]PF 6 , [21] where phtmeimb stands for [phenyl(tris(3-methylimidazol-1-ylidene))borate] -.…”