Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
DOI: https://doi.org/10.29363/nanoge.matsus.2023.068
Publication date: 22nd December 2022
Aliovalent I-V-VI semiconductor nanocrystals represent promising candidates for non-toxic and earth-abundant thermoelectric and infrared optoelectronic applications. Among them, famatite Cu3SbSe4 material stands out due to high absorption coefficients and narrow band gap in the mid-infrared spectral range. In this presentation we combine experiments and theory calculations to study the effects of composition and defects on optical properties of Cu3SbSe4 nanocrystals. Using fast and modular hot-injection colloidal synthesis approach, we achieve size-uniform and stoichiometric Cu3SbSe4 nanocrystals and study the influence of reaction parameters such as reaction temperature, growth time, and precursor concentrations. While a reduced activity of the Cu precursor induces the formation of Cu-deficient Cu3SbSe4 nanocrystals, an increased anion concentration or a balancing of cation precursor concentrations result in stoichiometric Cu3SbSe4 products with an absorption onset of 0.2 eV. Characterizing the products, we discover a broad solid solution for nanocrystals (nominally, CuxSbSe4, where x is 2.4–3.0), which is significantly larger than for the bulk Cu3SbSe4 phase. Within this CuxSbSe4 solid solution, the optical band gap widens to 0.35 eV as the amount of Cu decreases. Tight-binding simulations point to the existence of large amount of Cu vacancies, which are non-harmful for the optical performance of CuxSbSe4 nanocrystals. In contrast, even a small amount of CuSb and SbCu antisite defects creates intrinsic doping states, which are detrimental for Cu3SbSe4 properties. We affirm tunable band gaps by infrared spectroscopy and observe a good agreement to the theory calculations. We further report the energy-resolved photoelectric response of Cu3SbSe4 nanocrystals and show their excellent resilience towards oxidation. Our results will provide a launch platform for Cu3SbSe4 nanocrystals as one of very few non-toxic alternatives for mid-infrared applications.
The authors thank Mario Mücklich for technical lab assistance. TEM, STEM and EDX measurements are performed at the Scientific Center for Optical and Electron Microscopy (ScopeM) of the Swiss Federal Institute of Technology, Zurich.
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