Constructing Intramolecular Locks in the Backbones of TADF Conjugated Polymers for High-Performance...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Designing thermally activated delayed fluorescence (TADF) conjugated polymers for solution-processed OLEDs is challenging due to efficiency roll-off.
• Non-radiative transitions and small energy differences between singlet and triplet states (ΔE_ST) limit device performance.

Purpose of the Study:

• To develop TADF conjugated polymers for solution-processed OLEDs with high efficiency and low efficiency roll-off.
• To suppress non-radiative transitions and optimize excited states for enhanced OLED performance.

Main Methods:

• Introduction of an intramolecular lock into polymeric backbones to restrict bond rotation in the benzophenone acceptor.
• Incorporation of pyrimidine into the acceptor to induce steric hindrance and increase the dihedral angle between donor and acceptor units.
• Synthesis of the polymer (p-2PXZ-XN) based on the designed strategy.

Main Results:

• The intramolecular lock effectively suppresses non-radiative transitions caused by molecular relaxation.
• Pyrimidine incorporation minimizes ΔE_ST and optimizes excited states, enhancing reverse intersystem crossing.
• The synthesized polymer (p-2PXZ-XN) shows a high photoluminescence quantum yield (PLQY) of 93 ± 2%.
• Solution-processed OLEDs using p-2PXZ-XN achieve a record maximum external quantum efficiency (EQE_max) of 25.6% and maintain 23.1% EQE at 1000 cd m^-2.

Conclusions:

• The developed strategy significantly improves the efficiency and stability of TADF polymers for OLED applications.
• The achieved EQE_max and sustained EQE represent state-of-the-art performance for conjugated polymers in OLEDs without sensitization.
• This work provides a promising pathway for high-performance, solution-processed OLEDs.