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

24 January 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Tin-based semiconductors are highly desirable materials for energy applications due to their low toxicity and bio-compatibility 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 to 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 Sn2SbS2I3, Sn2BiS2I3, Sn2BiSI5, and Sn2SI2. 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 utilize 119Sn 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.

Keywords

Chalcohalide
lead-free
enhanced stability
quaternary
solid-state nmr

Supplementary materials

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Supporting Information
Description
Phase evolution plots, XRD, SEM-EDS, diffuse reflectance, cyclic voltammograms, ssNMR, and TGA/DSC are provided in the supporting information.
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