Highly efficient luminescence from space-confined charge-transfer emitters

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Charge-transfer (CT) complexes are vital in organic semiconductors.
• Exciplexes, or excited-state CT complexes, utilize singlet and triplet excitons for light emission, making them suitable for organic light-emitting diodes (OLEDs).
• Current exciplex emitters often exhibit low photoluminescence quantum efficiencies (PLQEs) due to poor control over donor-acceptor subunit orientation, electronic coupling, and non-radiative recombination.

Purpose of the Study:

• To investigate the impact of a rigid linker on controlling donor and acceptor subunit spacing and orientation in intramolecular exciplex emitters.
• To improve photoluminescence quantum efficiencies (PLQEs) and device performance in organic light-emitting diodes (OLEDs).
• To establish design rules for enhanced exciplex emitter performance.

Main Methods:

• Synthesis of intramolecular exciplex emitters using a rigid linker to connect 10-phenyl-9,10-dihydroacridine (donor) and 2,4,6-triphenyl-1,3,5-triazine (acceptor) subunits.
• Fabrication and characterization of sky-blue OLED devices utilizing the synthesized emitters.
• Comparative analysis with devices employing less rigid, structurally related emitters.

Main Results:

• OLED devices with the rigid intramolecular exciplex emitters achieved a high external quantum efficiency (EQE) of 27.4% at 67 cd m⁻².
• The devices demonstrated minimal efficiency roll-off, maintaining an EQE of 24.4% at a higher luminous intensity of 1,000 cd m⁻².
• Control devices with less rigid emitters showed substantially lower EQEs, highlighting the effectiveness of the rigid linker design.

Conclusions:

• Employing a rigid linker is an effective strategy to control donor-acceptor subunit arrangement, leading to improved PLQE and device performance in exciplex emitters.
• The developed design principles are transferable to other donor/acceptor combinations for tuning emission color and optoelectronic properties.
• This work provides a pathway for developing high-efficiency, stable organic light-emitting diodes (OLEDs).