Chinese Academy of Sciences tests multi-spiro emitter for 32.1% efficient blue OLEDs
Chemists synthesized a rigid TADF molecule that suppresses concentration quenching and achieves a 99.5% quantum yield at high doping levels in lab tests.
Researchers from the Fujian Institute of Research on the Structure of Matter at the Chinese Academy of Sciences developed a blue thermally activated delayed fluorescence emitter designated SAF-BO, as reported by EurekAlert eurekalert.org
EurekAlerteurekalert.orgOpen source ↗. The experimental material relies on a multi-spiro molecular configuration designed to mitigate exciton annihilation and concentration quenching in organic light-emitting diodes. Vacuum-deposited prototype devices based on this emitter reached a maximum external quantum efficiency of 32.1% at an electroluminescence peak of 476 nm.
Molecular packing and photophysics
The team incorporated several sp3-hybridized spiro units into a framework combining an oxygen-bridged triarylboron acceptor with a spiroacridine donor. Single-crystal analysis showed that the architecture expands the intermolecular stacking distance beyond 4.4 Å, which restricts π–π interactions and diminishes detrimental Dexter exchange interactions without degrading electronic properties. At a 50 wt% doping concentration, SAF-BO films demonstrated a photoluminescence quantum yield of 99.5%, maintaining an emission peak at 477 nm with a full width at half maximum of around 50 nm. The compound also exhibited a delayed fluorescence lifetime of 1.29 μs and a reverse intersystem crossing rate constant of 1.78 × 10⁶ s⁻¹.
Device efficiency and sensitization
During electroluminescence testing, the SAF-BO diode retained 23.0% external quantum efficiency at an operating luminance of 1000 cd/m². Under identical brightness conditions, control devices using SA-BO and PAF-BO molecules without the full multi-spiro architecture retained 13.6% and 12.0% efficiency, indicating a 1.7- to 1.9-fold improvement in high-brightness stability for the new structure.
The authors further deployed SAF-BO as a sensitizer for the deep-blue multiple-resonance TADF emitter v-DABNA in a sensitized fluorescence configuration. This system exhibited Förster resonance energy transfer with a rate constant of 5.38 × 10⁸ s⁻¹ and an efficiency of 90.4%, while keeping the Dexter transfer rate down to 1.86 × 10⁴ s⁻¹ eurekalert.org
EurekAlerteurekalert.orgOpen source ↗. The resulting sensitized device achieved a peak external quantum efficiency of 35.2%, sustained 27.1% efficiency at 1000 cd/m², and registered a deep-blue color coordinate of CIEy = 0.130.
