Realizing Highly Efficient Solution-Processed Homojunction-Like Sky-Blue OLEDs by Using Thermally Activated Delayed Fluorescent Emitters Featuring an Aggregation-Induced Emission Property

Two new blue emitters, i.e., bis-­[2-(9,9-dimethyl-9,10-dihydroacridine)-­phenyl]-­sulfone (<i><b>o</b></i><b>-ACSO2</b>) and bis-­[3-(9,9-dimethyl-9,10-dihydroacridine)-­phenyl]-­sulfone (<i><b>m</b></i><b>-ACSO2</b>), with reserved fine thermally activated delayed fluorescent (TADF) nature and simply tuned thermal and optoelectronic properties, were synthesized by isomer engineering. The <i>meta</i>-linking compound, i.e., <i><b>m</b></i><b>-ACSO2</b>, obtains the highest photoluminescence quantum yield with a small singlet–triplet energy gap, a moderate delayed fluorescent lifetime, excellent solubility, and neat film homogeneity. Due to its unique aggregation-induced emission (AIE) character, neat film-based heterojunction-like organic light-emitting diodes (OLEDs) are achievable. By inserting an excitonic inert exciton-blocking layer, the PN heterojunction-like emission accompanied by intefacial exciplex was shifted to a homojunction-like channel mainly from the AIE emitter itself, providing a new tactic to generate efficient blue color from neat films. The solution-processed nondoped sky-blue OLED employing <i><b>m</b></i><b>-ACSO2</b> as emitter with homojunction-like emission achieved a maximum external quantum efficiency of 17.2%. The design strategies presented herein provide practical methods to construct efficient blue TADF dyes and realize high-performance blue TADF devices.