What Is TADF?

TADF stands for Thermally Activated Delayed Fluorescence: a photophysical mechanism where non-emissive triplet excitons (T₁) are thermally up-converted to an emissive singlet state (S₁) via reverse intersystem crossing (RISC), producing delayed fluorescence (typically microseconds).

Why it matters in OLEDs

In OLEDs, electrical excitation creates both singlet and triplet excitons. Conventional fluorescent emitters mainly use singlets, but TADF materials can “harvest” triplets by converting them back to singlets, enabling near-unity internal quantum efficiency (≈100% in principle) without precious-metal phosphors.

Key engineering requirement (what enables TADF)

• Small singlet–triplet energy gap (ΔE_ST) so that room-temperature thermal energy can drive RISC efficiently.

Common practical challenges

• Efficiency roll-off at high brightness and stability/lifetime limits (especially for deep blue) due to exciton–exciton and exciton–polaron interactions and triplet management.

If you tell me your context (OLED emissive layer material choice, blue vs green vs red, mobile vs TV luminance targets), I can translate TADF into design knobs (ΔE_ST target range, PLQY, RISC rate, host selection, and roll-off mitigation strategies).