Pyrene-based non-doped blue hot-exciton OLEDs with hybrid local and charge-transfer states: achieving high efficiency and low efficiency roll-off

Abstract

Fluorescent materials utilizing the “hot exciton” pathway can realize efficient reverse intersystem crossing (RISC) from high-lying triplet states (T_n), effectively suppressing non-radiative decay and triplet–triplet annihilation. In this work, two pyrene-based blue emitters (mCPS and pCPS) with isomeric structures were designed and synthesized. These emitters possess a small S₁–T₂ energy splitting, which is beneficial for efficient T₂ → S₁ reverse intersystem crossing. Benefiting from the hot-exciton effect, the non-doped organic light-emitting diode (OLED) based on pCPS yields a maximum external quantum efficiency (EQE_max) of 12.59%, a maximum current efficiency (CE_max) of 20.08 cd A⁻¹, and an exciton utilization efficiency of 77.7%. Impressively, the device exhibits a remarkably low efficiency roll-off of only 16.60% at a practical luminance of 1000 cd m⁻². Magneto-electroluminescence and transient electroluminescence measurements confirm that the excellent device performance arises from the hot-exciton mechanism, rather than the triplet–triplet annihilation process. This high-efficiency and low-roll-off performance is among the best reported for non-doped pyrene-based blue hot-exciton OLEDs, demonstrating that the “hot exciton” pathway is a feasible and effective strategy for constructing high-performance blue fluorescent emitters.