Fluoride-free synthesis strategy for luminescent InP cores and effective shelling processes via combinational precursor chemistry

In typical core–shell nanocrystal heterostructures, the construction of shell layers on the well-defined core surfaces can boost the intrinsic optoelectronic properties of the cores and protect them from external chemical perturbation. Manipulating the surface states of the core nanocrystals, even before shell formation is essential to enable tailored optical and electrical properties because the defects on cores surfaces can persist in the core–shell structures. However, utilizing the reported HF to fabricate InP-based core–shell NCs may pose potential safety and environmental concerns. Here, we demonstrate a fluoride-free synthesis strategy that can remove the InP cores' surface defects, and eventually enhance the luminescent properties of the cores as well as the resultant core–shell structures. We investigated the combinational effect of chemical precursors, by means of liquid coordination complexes including typical shelling precursors, on the surface properties of InP cores. Through the addition of ZnCl2-TOP complex, the InP cores, with their surface oxide and defects effectively removed, demonstrated a photoluminescence quantum yield (PLQY) of up to 60% without the need for a shell. Neat InP surfaces persisted even after the shell growth process of ZnSeS and ZnS, exhibiting high PLQYs exceeding 95%. Ultimately, when we fabricated electroluminescent devices, ZnCl2-TOP treated InP with ZnSeS/ZnS shells exhibited significantly higher EL efficiency with a maximum current efficiency of 39.0 cd/A and a maximum EQE of 14.3%, compared to untreated InP. Consequently, we have demonstrated the potential of synthetic additives that can remove oxide on the InP surface and benefit ZnSeS/ZnS shell formation without using HF.