Sterically-Locked Donor-Acceptor Conjugated Polymers Showing Efficient Thermally Activated Delayed Fluorescence

Area of Science:

• Organic Electronics
• Materials Science
• Photophysics

Background:

• Donor-acceptor (D-A) conjugated polymers often exhibit large singlet-triplet energy splitting (ΔE_ST) due to conjugation elongation, hindering efficient thermally activated delayed fluorescence (TADF).
• Minimizing ΔE_ST is crucial for developing high-performance TADF materials.

Purpose of the Study:

• To introduce a novel steric locking strategy to tune torsion in D-A polymers and reduce ΔE_ST.
• To enable efficient TADF in D-A conjugated polymers through controlled molecular conformation.

Main Methods:

• Incorporation of methyl groups into D-A conjugated polymers to create steric hindrance.
• Tuning the torsion between donor and acceptor units to achieve a sterically-locked conformation.
• Fabrication of doped and non-doped organic light-emitting devices (OLEDs) via solution processing.

Main Results:

• Achieved an extremely low ΔE_ST of 0.09 eV, facilitating efficient TADF.
• Demonstrated a record-high external quantum efficiency (EQE) of 24.0% in doped devices.
• Obtained high performance in non-doped devices with an EQE of 15.3%.

Conclusions:

• The steric locking strategy effectively prevents planarization and conjugation elongation, enhancing charge separation.
• The developed D-A polymer exhibits excellent potential for high-efficiency, solution-processed OLEDs.
• This approach offers a promising pathway for designing advanced TADF materials.