High‐Efficiency Blue‐Emission Crystalline Organic Light‐Emitting Diodes by Engineering Thermally Activated Delayed Fluorescence Nanoaggregates

A crystalline host matrix (CHM) with embedded nanoaggregates (NA) is a powerful strategy to develop high‐performance crystalline OLEDs that can combine the advantages of both crystalline and high‐exciton‐utilization‐efficiency light emitting materials. Here a CHM‐NA structure blue‐emission crystalline OLED is developed, which employs a thermally activated delayed fluorescence (TADF) material. The CHM‐TADFNA OLED is proved to efficiently manage exciton distribution by engineering nanoaggregates. The device exhibits a remarkable EQE up to 10.4% and achieves the characteristics of rapid turn‐on, and fast ramping of luminance and current density, resulting in an enhanced photon output and a lower series‐resistance Joule‐heat loss ratio, indicating a competitive pathway to future blue‐emission OLEDs.