Estudo da deformação de perovskitas de haleto com organometálicos através do cálculo do número de coordenação do sítio B

Abstract

The growth in energy demand, combined with the environmental impact caused by fossil fuel sources, has triggered great interest and research in alternative clean and renewable sources, particularly solar energy. In this context, the development of solar energy conversion devices seeks new materials to compose photovoltaic cells, among which perovskites have gained attention due to their diversity, low production cost, and superior optoelectronic properties, allowing for high energy conversion efficiency. The optoelectronic properties of perovskites are closely related to structural distortions, and being able to explore these distortions allows for a deeper understanding of these materials. Due to the peculiar structure of perovskites, which have the chemical formula ABX3, an ideal cubic system without distortions presents coordination 6 at the B-site, which is used as a reference value. Based on this, this work explores the coordination at the B-site as a way to quantify the structural deformations of perovskites. Specifically, three different methods for calculating the Coordination Number (CN) were implemented, namely CN, ECN, and ECNav, and their results were compared for a set of Halide Perovskites with Organometallics available in a public domain database. The results showed that CN is entirely dependent and sensitive to the cutoff factor p, making it unsuitable for comparing different systems, as there is no way to define this factor univocally. In contrast, ECN and ECNav provide close and compatible results. However, the ECNav method has a slight tendency to yield results closer to the ideal value (6). On the other hand, ECN results in a more homogeneous distribution. These differences are justified by the specific algebraic formulation of each implementation. Indeed, ECNav proved to be a superior method as it is free from external parameters, meaning it is not limited to the number of neighbors considered, and defines the average distance through a self-consistent calculation, unlike ECN, which is restricted to the first six neighbors.