Synthesis of Highly Monodisperse Cu₂ O Nanocrystals and Their Applications as Hole-Transporting Layers in Solution-Processed Light-Emitting Diodes

The synthesis of phase-pure, narrow-size-distributed and highly stable Cu₂ O nanocrystals is reported, which can be processed as hole-transporting layers (HTLs) in solution-processed optoelectronic devices. The synthesis is based on a thermal decomposition process with a ligand protection strategy. The reactivity of precursor can be tuned by simply modulating the concentration of oleylamine in non-coordinated solvent, resulting in effectively controlling the size and size distribution of Cu₂ O nanocrystals. Combined with ligand protection strategy of using lithium stearate and moderate reaction temperature of 170 °C, in situ aggregation of Cu₂ O nanocrystals could be inhibited, exhibiting excellent stability in hexane for several months. The resulting phase-pure colloidal Cu₂ O particles (after ozone-treatment) were applied as HTLs in polymer light-emitting diodes, the performance of which are comparable to that of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) based devices.