Enhancing the Efficiency of Ultrathin-EML OLEDs via a Double-Emitter Configuration

High Resolution Image Download MS PowerPoint Slide Organic light-emitting diodes (OLEDs) employing undoped ultrathin emitting layers (UEMLs) have attracted considerable interest because they enable simplified device architectures, straightforward fabrication, and low material consumption. However, confining charge recombination and excitons to a sub-nanometer region can intensify exciton−polaron quenching and exciton−exciton annihilation, causing efficiency losses at high luminance and potentially shortening operational lifetimes. Here, we introduce a ν-DABNA-based deep-blue UEML OLED that combines an interfacial ultrathin emitter with a second ultrathin ν-DABNA layer embedded a few nanometers away in the transport layer (double-emitter architecture), providing an additional exciton-harvesting channel while preserving a minimal, nondoped device structure. The optimized double-emitter OLED reaches a maximum external quantum efficiency (EQE max ) of 14.2%, compared with 9.6% for the single-emitter reference, and exhibits higher EQE across the operating current density range. Using systematic device characterization, control structures with varied donor−acceptor separation, and electro-optical device simulations, we rationalize the efficiency enhancement with an experiment-supported energy-transfer picture consistent with Förster-type exciton redistribution between the interfacial donor/exciplex region and the two ultrathin emitter layers. These results establish double-emitter UEML placement as a practical strategy to increase efficiency in simplified, nondoped OLED stacks and suggest broader applicability to other emitter materials and device architectures.