Ligand Engineering Enables Phase Selection and Improved Crystallinity in Metastable Orthorhombic AgInSe2 Nanocrystals

AgInSe2 (AISe) nanocrystals, with their outstanding optoelectronic properties and environmentally friendly, Cd/Pb-free composition, show strong potential for applications in near-infrared luminescence and photovoltaic devices. Herein, metastable orthorhombic AISe nanocrystals were synthesized using a simplified, efficient, and environmentally friendly strategy. The results demonstrate that ligands play a decisive role in crystal-phase selection by regulating Ag+/In3+ cation exchange, while their molecular structures influence stabilization of the metastable phase. Specifically, oleylamine, characterized by its relatively soft Lewis-basic nature and long chain length, favors the formation of metastable orthorhombic AISe. In addition, introducing 1-octadecene improves the crystallinity of the products without altering the crystal phase. This work provides a practical and promising strategy for preparing high-quality metastable orthorhombic AISe nanocrystals and offers useful guidance for the controlled synthesis of other metastable materials, supporting their further integration into optoelectronic devices.