20‐2: Invited Paper: High‐Efficiency, Long‐Lifetime, Deep‐Blue Organic Light‐Emitting Diodes

Simultaneously achieving a high efficiency and long lifetime in deep‐blue organic light‐emitting diodes (OLEDs) is challenging because most high‐efficiency blue OLEDs suffer from a short device lifetime. We describe high‐efficiency, long‐lifetime deep‐blue thermally activated delayed fluorescence (TADF) OLEDs by designing new blue TADF materials and developing a triplet‐exciton‐recycling device protocol. A new deep‐blue TADF emitter that harvests the singlet excitons of the fluorescent emitter was embedded in the device structure of the triplet‐exciton‐distributed (TED) TADF devices built on a new device protocol. Two TADF materials, one distributing and one emitting, were doped into a host with a triplet energy between those of these two materials. Codoping the TADF materials to realize TED‐TADF in the low‐triplet‐energy host achieved a high external quantum efficiency of 28.3% and almost quadrupled the device lifetime relative to that of the reference device with only the emitting TADF material. Recycling the triplet excitons of the distributing TADF material that were quenched by the host and the singlet‐exciton‐harvested TADF emission of the emitting TADF material were the main mechanisms realizing simultaneous high efficiency and extended lifetime. The TADF devices based on this new approach combined with an optically optimized device stack demonstrated >30% efficiency, a lifetime of >6,000 h, and a y color coordinate