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

Abstract

Alkali pnictogen dichalcogenides�I−V−VI 2 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 LiSbSe 2 , NaSbS 2 , NaSbSe 2 , NaBiS 2 , and NaBiSe 2 . Our approach utilizes alkali metal hydrides (AH) or carboxylates, A(O 2 CR), 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 NaSbS 2 . 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 NaSbS 2 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.

Colloidal Synthesis of Multinary Alkali-Metal Chalcogenides Containing Bi and Sb: An Emerging Class of I–V–VI2 Nanocrystals with Tunable Composition and Interesting Properties

“…Further, from the XPS analysis of NaBiSe 2 , NaBi 0.5 Sb 0.5 Se 2 , and NaSbSe 2 NCs, the elemental composition and surface chemistry of the NCs are corroborated (Figure ). The low energy peaks of Sb (Sb 3d at ∼540 eV, Figure a), Bi (4f 5/2 at ∼163 eV and Bi 4f 7/2 at ∼158 eV, Figure b), and Se (Se 3d 5/2 at ∼53 eV and Se 3d 3/2 at∼54 eV, Figure c) and the peak of Na 1s at ∼1071 eV (Figure d) correspond to the crystal bound Sb, Se, Bi, and Na for the respective NCs. , Besides, Sb, Bi, and Se all show higher energy peaks that could be associated with interaction with surface-bound ligands. , The high energy peaks of Sb 3d (green in 6a) and Bi 4f (green in 6b) possibly arise from the interaction of the Sb and Bi with the COO – group of the surface-bound oleates. Similarly, the high energy peaks in the Se 3d XPS (54.5 and 55.3 eV) can be ascribed to the surface-bound alkane thiol–selenium complex (R-CH 2 S–Se n –1 -Se – ) formed upon the thiol–amine reaction with Se as observed in the IR spectra.…”

“…However, a further increase in Sb substitution (x=0.5) becomes detrimental for electrical conductivity and increases the Seebeck coefficient. Recently, the 5S 2 LP in Sb was shown to be stereochemically more active than 6S 2 LP in Bi . The increased LP activity upon Sb substitution induces local structural distortion to disrupt phonon propagation resulting in lower thermal conductivities ( K ).…”

“…However, this type of transformation in the alkali metal-based chalcogenide system is yet to be thoroughly investigated. Very recently, using highly reactive and flammable metal hydride precursors, phase-pure ternary NaBiSe 2 and NaSbSe 2 NCs were synthesized. , The high reactivity of the metal hydrides leads to uncontrolled nucleation and growth kinetics limiting control over size, and thus, wide size distributions were obtained. The complexity further increases with compositions consisting of three or more elements with the propensity of co-formation of binary chalcogenide phases.…”

Colloidal synthesis of the mixed ionic–electronic conducting NaSbS2 nanocrystals

“…48 Vela et al recently described the preparation of I-V-VI 2 nanocrystals (NCs) with a focus on the computational studies to describe the effect of stereoelectronic lone pair in the crystal structure of I-V-VI 2 materials. 49 However, there is a missing gap in the literature for a detailed study on the impact of reaction parameters in determining the size, shape and crystal phase of NaSbS 2 NCs, as well as mechanistic insight for the synthesis of NCs and their transport properties using colloidal hot injection approach.…”

Solution-grown ternary quasi-cube AgSbTe2 and its optoelectronic performance for broadband photodetection

“…[12][13][14] Ternary silver-based I-V-VI 2 semiconductor nanocrystals (NCs) are an important class of colloidal nanocrystals for photodetection because of their relatively low toxicity and large absorption coefficients and they potentially possess tunable optoelectronic properties. [15][16][17][18][19][20] In particular, the silver antimony telluride compound (AgSbTe 2 ) has emerged as a promising candidate for optoelectronic applications due to its optical phase-change properties and tunable band gap from 0.75 to 1.34 eV. 21 Moreover, in comparison with other ternary silver-based I-V-VI 2 compounds, AgSbTe 2 exhibits a very low lattice thermal conductivity, which is beneficial for conversion efficiency in optoelectronic devices.…”