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 can convert triplet excitons from high-lying excited states (T₂) to singlet excitons (S₁) via the "hot exciton" pathway. Characterized by a small S₁-T₂ energy splitting and a relatively large T₂-T₁ energy gap, this mechanism facilitates reverse intersystem crossing (RISC) from high-lying triplet states (T, n≥2) to singlet states (S, m≥1) while suppressing T₂-to-T₁ internal conversion. Thus, the S₁ state can maintain high luminescence efficiency as a locally excited state, theoretically enabling simultaneous achievement of high exciton utilization and fluorescence efficiency. Since intersystem crossing occurs at high-energy excited states, RISC proceeds extremely rapidly, avoiding triplet-triplet annihilation induced by long-lived T₁ exciton accumulation and endowing organic light-emitting diodes (OLEDs) with excellent stability. Herein, two pyrene-based blue hot exciton materials (mCPS and pCPS) were designed and synthesized.The pCPS-based device achieved a maximum external quantum efficiency (EQEmax) of 12.59%, a maximum current efficiency of 20.08 cd A⁻¹, an exciton utilization efficiency of 77.7%, and a remarkably low efficiency roll-off of 16.60% at 1000 cd m⁻². This EQE ranks among the highest reported for non-doped pyrene-based blue hot exciton materials, confirming the "hot exciton" pathway as a promising strategy for high-efficiency, low-roll-off non-doped blue OLEDs.