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

摘要

Alkali pnictogen dichalcogenides-I-V-VI2 or APnCh2-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 APnCh2 materials,including LiSbSe2,NaSbS2,NaSbSe2,NaBiS2,and NaBiSe2.Our approach utilizes alkali metal hydrides(AH) or carboxylates,A(O2CR),PnPh3,and elemental chalcogens as synthetic precursors and oleylamine or 1-octadecene as solvents.Synthetic manipulation via fine-tuning of reaction temperature enables control over the degree of ordering caused by the Sb 5s2 lone pair-induced distortions in NaSbS2.Pair distribution function analysis demonstrates that the structure of the Sb-containing 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 PnPh3) 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.