Novel Cation-substituted Quarternary Chalcogenide Nanocrystals Cu2XSnS4 (X = Zn, Ni, Fe, Co): Properties and Potential Applications

Cu_2ZnSn（S，Se）_4（CZTSSe）作为一种新型的光致发光材料，在近十年来得到了广泛的研究。然而，将其应用于实际生活中面临着对非化学计量，缺陷和第二阶段的高耐受性的挑战。CZTSSe结构中阳离子的取代在克服这些挑战和实现新性能方面显示出巨大的前景。Ag和Ba是迄今为止研究最多的取代基，但它们仅引起光伏和其他性质的部分修正。非常有趣的铁族元素（Fe，Ni，Co）在这方面尚未探索。系统的调查特别缺乏胶体纳米晶体（NC）的Cu 2XSnS 4（X = Zn，Ni，Fe，Co）的化合物，虽然这样的NC是一个有前途的选择，形成能量转换和存储设备上的故意基板和区域通过印刷。已经报道了CZTSSe NC的成功合成，以及在较小程度上其他I2-II-IV-VI 4 NC的成功合成。将这些NC推进到太阳能电池、热电、催化和其他具有竞争力的应用需要填补关于其结构和电子性质的知识的差距。该项目的目的是建立Cu 2XSnS 4（X = Zn，Ni，Fe，Co）NC的晶格结构（包括缺陷）、电子态分布和光谱之间的关系。我们期望在该项目中提出的阳离子取代可以（i）由于某些缺陷的钝化而导致主体材料的性质的改善，（ii）有助于建立CZTS本身中的某些原生缺陷或电子状态的起源，以及（iii）诱导CZTS晶体和NC中不存在的新性质，特别是磁性。将进行计算筛选，以促进合成部分，使我们能够专注于最有前途的CXTS组合物，并了解阳离子取代引起的电子，光学和声子实验光谱的变化。此外，我们将调查的材料性能的演变，从合成的单个NC的合奏，通过退火形成的多晶薄膜。基于所获得的结果，我们将在简单的光伏或热电器件中对所获得的材料进行初步研究。在申请人之间16年的成功合作中，正如100多份联合出版物所证实的那样，其中大部分与胶体硫属化物NC有关，我们已经获得了足够的经验和工具，成功完成了当前项目。除了为该项目选择的已建立的表征技术外，乌克兰合作伙伴可使用的深能级光谱和电子顺磁共振的独特方法对于构建Cu 2XSnS 4 NC等复杂材料中电子状态的完整图像是不可或缺的。

Cu2ZnSn(S,Se)4 (CZTSSe) has been intensively studied over the last decade as a promising alternative material for photovoltaics. However, bringing it to real-life applications is challenged by its high tolerance to non-stoichiometry, defects, and secondary phases. Substitution of cations in the CZTSSe structure showed great promise in overcoming these challenges and enabling new properties. Ag and Ba are the substituents mostly studied so far, but they cause only a partial amendment of the photovoltaic and other properties. The very interesting iron group of elements (Fe, Ni, Co) are rather unexplored in this respect yet. Systematic investigations are especially lacking for colloidal nanocrystals (NCs) of the Cu2XSnS4 (X = Zn, Ni, Fe, Co) compounds, although such NCs are a promising option for forming energy conversion and storage devices on deliberate substrates and areas by printing. The successful synthesis of CZTSSe NCs, and to a lesser extent of other I2-II-IV-VI4 NCs, has been reported. Advancing these NCs to solar cells, thermoelectrics, catalysis, and other application at a competitive level demands filling the gap in the knowledge about their structure and electronic properties. The aim of the project is to establish the relation between the lattice structure (including defects), distribution of electronic states, and optical spectra of Cu2XSnS4 (X = Zn, Ni, Fe, Co) NCs. We expect that the cation substitutions proposed in this project can (i) lead to an improvement of the properties of the host material due to the passivation of certain defects, (ii) help to establish the origin of certain native defects or electronic states in CZTS itself, and (iii) induce new properties, not existing in CZTS crystals and NCs, in particular magnetic properties. Computational screening will be performed to facilitate the synthetic part, enabling us to focus on the most promising CXTS compositions and to understand the changes in the electronic, optical, and phonon experimental spectra caused by cationic substitution. Furthermore, we will investigate the evolution of the material properties from the ensembles of as-synthesized individual NCs to polycrystalline films formed by annealing. Based on the results obtained, we will perform a preliminary investigation of the obtained material in simple photovoltaic or thermoelectric devices. In 16 years of successful collaboration between the applicants, as confirmed by more than 100 joint publications and most of them related to colloidal chalcogenide NCs, we have acquired sufficient experience and instrumental tools for the successful fulfillment of the current project. Besides established characterisation techniques, selected for the project, rather exclusive methods of deep level spectroscopies and electron paramagnetic resonance, which are available for the Ukrainian partners, are indispensable for building the complete picture of electronic states in such a complex materials as Cu2XSnS4 NCs.