Electronic structure and stability of Ti- and Zr-based vacancy ordered double perovskites
Creators: name: Cucco, Bruno
name: Bouder, Gaelle
name: Pedesseau, Laurent
name: Katan, Claudine
name: Even, Jacky
name: Kepenekian, Mikaël
name: Volonakis, George
Publisher: name: Zenodo
Year: 2021
Subjects: Lead Free
optoelectronic applications
solar cell
electronic structure

description: Along the past few years, the vacancy-ordered halide double perovskites (VOHDP) have been extensively<br> investigated as promising candidates for various optoelectronic applications [1]. Among these compounds,<br> Cs2TiBr6 and Cs2TiI6 are VOHDP that have been successfully synthesised, and are reported to be interesting photoactive<br> materials with band-gaps well within the visible range (1.02-2.00 eV) and potentially good carrier transport<br> properties [2–4]. Photovoltaic devices using Cs2TiBr6 achieved a 3.3% power-conversion efficiency [3], though their<br> actual potential has been recently questioned [5]. In this work, we perform a thorough computational analysis of<br> the electronic structure, the mechanical and chemical stability, and the optical properties, of the entire family of<br> VOHDP that have the same B’-site electronic valence as Ti4+ (i.e., d10). By doing so, we probe the potential tuning<br> limits of their opto-electronic properties, extend the existing understanding on the well-established Ti-based<br> materials, and propose the less-known Zr-based compounds (i.e., Cs2ZrX6; X=Br, I) as potential prominent<br> alternatives. In particular, we employ three levels of calculations: DFT-PBE, hybrid functionals, and state-of-the-art<br> GW, to calculate their electronic structure, and perform a complete symmetry analysis of the electronic bands to<br> reveal its consequences of the exhibited band-gaps and charge carrier effective masses. We also show the<br> importance of spin-orbit coupling effects, highlight the limitations when calculating quasi-particle corrections, and<br> demonstrate how a simple crystal field theory can be used to describe the observed electronic structure.<br> Furthermore, we investigate all possible decomposition reaction pathways to competing compounds, and further<br> assess their mechanical stability by means of phonon calculations. Overall, our findings unveil the fundamental<br> electronic and optical properties of Cs2TiBr6, establish the stability and tunability limits of electronic band-gaps and<br> effective mass within the family of VOHDP materials with a d10 electronic configuration, but most importantly<br> propose a novel composition for the next generation of optoelectronic devices, namely Cs2ZrI6 that has been<br> practically unexplored to date.<br> Acknowledgments<br> The research leading to these results has received funding from the European Union’s Horizon 2020 program,<br> through a FET Open research and innovation action under the grant agreement No 862656 (DROP-IT). <br> References<br> [1] A. E. Maughan et al., Chem. of Mater. 31, 1184 (2019).<br> [2] M.-G. Ju et al., ACS Energy Lett. 3, 297 (2018).<br> [3] M. Chen et al, Joule 2, 558 (2018).<br> [4] D. Kong et al., J. Mater. Chem. C 8, 1591 (2020).<br> [5] J. Euvrard et al., J. Mater. Chem. A 8, 4049 (2020).