Lead-Free Semiconductors: Phase-Evolution and Superior Stability of Multinary Tin Chalcohalides

Abstract

Tin-based semiconductors are highly desirable materials for energy applications due to their low toxicity and biocompatibility relative to analogous lead-based semiconductors. In particular, tin-based chalcohalides possess optoelectronic properties that are ideal for photovoltaic and photocatalytic applications. In addition, they are believed to benefit from increased stability compared with halide perovskites. However, to fully realize their potential, it is first necessary to better understand and predict the synthesis and phase evolution of these complex materials. Here, we describe a versatile solution-phase method for the preparation of the multinary tin chalcohalide semiconductors Sn 2 SbS 2 I 3 , Sn 2 BiS 2 I 3 , Sn 2 BiSI 5 , and Sn 2 SI 2 . We demonstrate how certain thiocyanate precursors are selective toward the synthesis of chalcohalides, thus preventing the formation of binary and other lower order impurities rather than the preferred multinary compositions. Critically, we utilized 119 Sn ssNMR spectroscopy to further assess the phase purity of these materials. Further, we validate that the tin chalcohalides exhibit excellent water stability under ambient conditions, as well as remarkable resistance to heat over time compared to halide perovskites. Together, this work enables the isolation of lead-free, stable, direct band gap chalcohalide compositions that will help engineer more stable and biocompatible semiconductors and devices.

High Entropy Oxides: Mapping the Landscape from Fundamentals to Future Vistas

“…A prevalent approach entails introducing a solution containing a blend of metal precursors into a heated solvent, that also act as a reducing agent, simultaneously . As elevated temperatures are generally necessary for entropy stabilization, this makes it difficult, though not impossible, to synthesize colloidal HEOs due to variations in the reduction rates of cationic precursors − and lack of comprehensive understanding of reaction intermediates. , Also, in contrast to chalcogenides , and phosphides, no universally recognized molecular precursors exist that decompose to liberate oxide anions in the reaction mixture, impeding the straightforward formation of oxides. Instead, the introduction of oxygen into oxides typically involves the use of reagents and solvents containing hydroxyl or alkoxy groups.…”

Prospective Chalcohalide Perovskites: Pursuing (and Failing) the Synthesis of CsBiSCl2 Nanocrystals

“…In addition, a partial role may be also played by the tendency of Bi­(III) not to adopting an octahedral coordination in chalcohalide compounds, in contrast to multinary chalcogenides (AgBiS 2 ) and halides (Cs 2 AgBiBr 6 ). , Nevertheless, we cannot definitely exclude the possibility of stabilizing heavy pnicotgen chalcohalide perovskites. It is in fact possible that such compounds could be accessible by heat-up, solution phase synthetic methods, exploiting, for example, the reported selectivity of metal thiocyanate precursors to obtaining quaternary heavy pnictogen chalcohalide nanomaterials, while avoiding secondary phases; by ion exchange, an intrinsically kinetically driven process, also using nanostructured metal chalcogenides and halides as precursors; , more broadly, by topotactic reactions, which may allow the replacement of atoms in a perovskite (nano)­crystal without altering the structure; , by entropic stabilization, which could be in principle be attained given the compositional complexity of quaternary compounds comprising alkali or alkaline-earth metals, heavy pnictogens, chalcogenides, and halides. , Moreover, ligands could be exploited to affect metal precursor reactivity and selectivity in the attempt to exert phase control in the Bi 2 E 3 –BiX 3 –CsX diagram. , Therefore, although our results confirm that heavy pnictogen chalcohalides are hardly prone to adopt a perovskite structure, we are open to the possibilities offered by materials chemistry at the nanoscale to providing alternative paths toward prospective, even unpredicted, mixed anion compound semiconductors.…”