Molecular core–shell structure design: Facilitating delayed fluorescence in aggregates toward highly efficient solution-processed OLEDs

Light has been sought and explored by human since ancient times. As the most important form of light, fluorescence is significant to applications in bioimaging and optoelectronic devices. However, fluorescence quenching problem constitutes a serious bottleneck in materials creation. Inspired from the core–shell structure in nature, we report an effective strategy to overcome this long-standing problem by utilizing a molecular core–shell structure. With an emissive core and multifunctional shell fragments, these compounds show aggregation-induced delayed fluorescence (AIDF) properties by restricting singlet oxygen (¹O₂) generation and suppressing the triplet–triplet annihilation (TTA). Protected by the functional shell, the aggregation-induced emission luminogens (AIEgens) exhibit strong emission with high photoluminescent quantum yield and exciton utilization. Furthermore, because the shell materials can form exciplex with electron-transport materials, the fully solution-processed organic light-emitting diodes (OLEDs) based on these core–shell materials show low turn-on voltages, excellent device performance with current efficiency of 61.4 cd A^–1 and power efficiency of 42.8 lm W^–1, which is a record-breaking efficiency based on all-solution processed organic multilayer systems among the AIE-OLEDs so far. This simple visualization strategy based on molecular core–shell structure provides a promising platform for AIEgens used in the fully wet-processed optoelectronic field.