Efficient and stable organic light-emitting devices employing phosphorescent molecular aggregates

Stable and efficient organic light-emitting diodes (OLEDs) operating at high brightness are desirable for future high-resolution displays and lighting products. Here, we report a tetradentate Pd(ii) complex called Pd3O8-P, which has attractive optoelectronics properties. At room temperature, aggregates of Pd3O8-P exhibited a close-to-unity photoluminescent quantum yield and a short transient lifetime of 0.62 μs. A host-free Pd3O8-P yellow-orange OLED emitted light with a peak at 588 nm, a half-bandwidth of 84 nm and CIE coordinates of (0.52, 0.47), and achieved a peak external quantum efficiency (EQE) of 34.8%. The device had reduced efficiency roll-off, retaining high EQEs of 33.5% at 1,000 cd m⁻² and 29.5% at 10,000 cd m⁻². The estimated operational half-lifetime was 9.59 million hours at 1,000 cd m⁻². The fact that the tetradentate metal complex has a triplet in the blue-emitting region may also assist the development of efficient and long-lived blue OLEDs in the future.