Solution-Grown Ternary Semiconductors: Nanostructuring and Stereoelectronic Lone Pair Distortions in I–V–VI₂ Materials

Alkali pnictogen dichalcogenides-I-V-VI2 or APnCh(2)- have been identified as promising semiconducting materials for energy conversion devices. However, the controlled nanoscale synthesis and our understanding of the effects of cation ordering and stereochemically active lone pairs on the structures of these ternary compounds remain underdeveloped. Here, we use solution-phase chemistry to synthesize a family of APnCh(2) materials, including LiSbSe2, NaSbS2, NaSbSe2, NaBiS2, and NaBiSe2. Our approach utilizes alkali metal hydrides (AH) or carboxylates, A(O2CR), PnPh(3), and elemental chalcogens as synthetic precursors and oleylamine or 1-octadecene as solvents. Synthetic manipulation via finetuning of reaction temperature enables control over the degree of ordering caused by the Sb 5s(2) lone pair-induced distortions in NaSbS2. Pair distribution function analysis demonstrates that the structure of the Sbcontaining phases deviates much more from a disordered rock salt structure than that of the Bi-containing phases. This local distortion, induced by the Sb lone pair, leads to a previously unreported noncentrosymmetric NaSbS2 crystal structure, which is additionally supported by second-harmonic generation measurements. Infrared and multinuclear solid-state NMR spectroscopies show that oleylamine or chelating carboxylates and, in some cases, unreacted precursors (LiH and PnPh(3)) remain bound to the nanocrystalline surfaces. A deeper understanding of the local atomic environment, long-range ordering, surface chemistry, and optoelectronic properties of these materials may speed up their fundamental study and application.