Red electroluminescent Cu₄I₄ bipyramids with external quantum efficiency beyond 40.

Area of Science:

• Materials Science
• Optoelectronics
• Chemistry

Background:

• Red cluster light-emitting devices (CLEDs) exhibit lower efficiencies compared to blue and green counterparts.
• This inefficiency stems from non-radiative decay pathways involving multiple excited states in red cluster molecules during electroluminescence.

Purpose of the Study:

• To optimize the excited states of a specific red bipyramidal cluster material, [PXZDPPQ]2Cu4I4.
• To achieve balanced dual emissions and improve the performance of red CLEDs.

Main Methods:

• Synthesized and characterized a novel red cluster material, [PXZDPPQ]2Cu4I4, featuring a ligand integrating conjugation-extended 2-diphenylphosphineylquinoline (DPPQ) and phenoxazine (PXZ).
• Accurately optimized the excited states, specifically the outer intraligand charge transfer (nLCT) and inner metal-ligand charge transfer (nMLCT) states.
• Investigated the spatial and energetic advantages of the optimized excited states for carrier capture and exciton confinement.

Main Results:

• Achieved desired excited state locations, with radiative nLCT states and protected high-lying nMLCT states.
• Realized balanced dual emissions with a 51/49 ratio due to cross transitions between nLCT states.
• Attained a record external quantum efficiency of 43.7% for planar red light-emitting devices, an eightfold increase in photoluminescence quantum yield (93.6%), and 20% improved exciton utilization efficiency.

Conclusions:

• The precise control over excited states in [PXZDPPQ]2Cu4I4 demonstrates the potential of cluster materials for advanced exciton engineering.
• This work establishes a new benchmark for red CLED performance and highlights their promise for next-generation full-color displays.