Correlation of Controllable Aggregation with Light-Emitting Property in Polymer Blend Optoelectronic Devices

The control of solution-processed emitting layers in organic-based optoelectronic devices enables cost-effective processing and highly efficient properties. However, a solution-based protocol for emitter fabrication is highly complex, and the link between the device performance and internal nanoscale features as well as three associated fabricating parameters (e.g., the employed solvents, annealing temperatures, and molecular concentration) needs to be understood. Here, this study investigates the influence of the solution-processing parameters on the nanostructure-property relationship in light emitters that consist of iridium complexes doped in polymer. The boiling points and evaporation rates of the selected solvents govern the nanomorphology of molecular aggregation in the as-processed state, and the aggregation is either needle-like, spherical, or even a mixture of needles and spheres. Furthermore, a direct observation via in situ heating microscopy indicates that annealing of emitters containing a needle-type aggregation promotes the associated molecular transport, leading to a substantial reduction in the surface roughness. Consequently, a nearly threefold increase in the current efficiency of the device is induced. These findings have important implications for the tuning of the aggregation of iridium complexes for emitters used in the new evolution of high-performance organic-based optoelectronic devices.