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

Abstract

Designing thermally activated delayed fluorescence (TADF) conjugated polymers for solution-processed OLEDs that achieve high efficiency with low efficiency roll-off remains a significant challenge. Here, an intramolecular lock is introduced into the polymeric backbones to restrict the rotation of flexible single bonds in the benzophenone acceptor, thereby significantly suppressing non-radiative transitions caused by molecular relaxation. Additionally, pyrimidine is incorporated into the acceptor to introduce steric hindrance, which synergistically increases the dihedral angle between the acceptor and donor, minimizing the energy difference between singlet and triplet states (ΔE_ST). This acceptor modification also optimizes the excited states, thus enhancing spin-orbit coupling between singlet and triplet states to accelerate the reverse intersystem crossing process. As a result, the polymer (p-2PXZ-XN) synthesized based on this strategy exhibits an elevated photoluminescence quantum yield up to 93 ± 2%. Furthermore, the solution-processed OLED employing p-2PXZ-XN achieves a record maximum external quantum efficiency (EQE_max) of 25.6% and maintain an EQE of 23.1% at 1000 cd m^-2. To our knowledge, both EQE_max and EQE at 1000 cd m^-2 of p-2PXZ-XN represent the highest values among the reported conjugated polymers without sensitization.