Lone-pair driven ferroelectric and piezoelectric response of germanium halide perovskites CsGeX 3 (X = Cl, Br, and I) Jiwoo Lee, Young-Kwang Jung, Zhenzhu Li, Aron Walsh Imperial College London, United Kingdom Computational screening via density-functional-theory calculations reports Ge as a candidate element for substituting Pb in halide perovskite compounds suitable for light harvesting; and clarifying the existence of ferroelectricity and piezoelectricity in halide perovskites have important technological consequences as ferroelectric nanodomains can reduce the recombination of light-excited electron-hole pairs and extend the carrier lifetime [1,2]. The explanation for the origin of spontaneous polarization in germanium halide perovskites in terms of an on-site second-order Jahn-Teller effect has not been hitherto investigated [3]. In this work, we report the interaction between Ge and the anion mainly derives the magnitude of the spontaneous polarization. The role of the anion p atomic orbital in chemical bonding is key to explain why CsGeCl 3 has the largest spontaneous polarization value of 19 μ C/cm 2 [4]. We expect that the computational exploration of lone pair systems offers a key insight to design novel photoelectric devices. References 1. Lead-free germanium iodide perovskite materials for photovoltaic applications. J. Mater. Chem. A , 3, 23829-23832(2015) ; https://doi.org/10.1039/C5TA05741H 2. F erroelectric Alignment of Organic Cations Inhibits Nonradiative Electron–Hole Recombination in Hybrid Perovskites: Ab Initio Nonadiabatic Molecular Dynamics. J. Phys. Chem. Lett. 8, 4, 812–818 (2017) ; https://doi.org/10.1021/acs. jpclett.7b00008 3. Resolving the Physical Origin of Octahedral Tilting in Halide Perovskites. Chem. Mater. 28, 12, 4259–4266 (2016) ; https:// doi.org/10.1021/acs.chemmater.6b00968 4. Stereochemistry of post-transition metal oxides: revision of the classical lone pair model. Chem. Soc. Rev. 40 , 4455-4463 (2011) ; https://doi.org/10.1039/C1CS15098G
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