Guanidinium and Mixed Cesium–Guanidinium Tin(II) Bromides: Effects of Quantum Confinement and Out-of-Plane Octahedral Tilting

Abstract

Hybrid organic–inorganic main-group metal halide compounds are the subject of intense research owing to their unique optoelectronic characteristics. In this work, we report the synthesis, structure, and electronic and optical properties of a family of hybrid tin (II) bromide compounds comprising guanidinium [G, C(NH 2 ) 3 + ] and mixed cesium–guanidinium cations: G 2 SnBr 4 , CsGSnBr 4 , and Cs 2 GSn 2 Br 7 . G 2 SnBr 4 has a one-dimensional structure that consists of chains of corner-sharing [SnBr 5 ] 2– square pyramids and G cations situated in between the chains. Cs + exhibits a pronounced structure-directing effect where a mixture of Cs + and G cations forms mono- and bilayered two-dimensional perovskites: CsGSnBr 4 and Cs 2 GSn 2 Br 7 . Furthermore, the flat shapes of the guanidinium cations induce anisotropic out-of-plane tilts of the [SnBr 6 ] 4– octahedra in the CsGSnBr 4 and Cs 2 GSn 2 Br 7 compounds. In G 2 SnBr 4 , the Sn lone pair is highly stereoactive and favors non-octahedral, that is, square pyramidal coordination of Sn(II). G 2 SnBr 4 exhibits bright broad-band emission from self-trapped excitonic states, owing to its soft lattice and electronic localization. This emission in G 2 SnBr 4 is characterized by a photoluminescence (PL) quantum yield of 2% at room temperature (RT; 75 ± 5% at 77 K) and a fast PL lifetime of 18 ns at room temperature.

Enhanced Light Emission Performance of Mixed Cation Perovskite Films—The Effect of Solution Stoichiometry on Crystallization

“…It has been noted that the reflection corresponding to d-spacing ≈1.0 nm appears also in the "small spacer cation" type of RP n = 1 perovskite structures where small guanidinium (GA) cations, typically present exclusively within the octahedral voids, act as spacer cations. [44] Similarly in our case, we might expect the formation of such a special type of RP phase with Cs or FA cations acting as very small spacer cations. Indeed, all-inorganic Ruddlesden-Popper phases Cs n+1 Pb n Br 3n+1 have been previously observed in HRTEM, [45] while similarly they could not be detected in XRD, but the structure details have not been reported.…”

Tin Halide Perovskites: From Fundamental Properties to Solar Cells

“…1D zigzag chains are also observed in (GA) 2 SnBr 4 and (GA) 2 SnCl 4 , however, square pyramidal tin halide cages are formed instead of octahedral tin halide cages. [ 121,122 ] These structures are highly different compared to the iodine variant and illustrate the profound impact of the halides on the structure. An exotic 〈330〉‐type structure could be obtained by using pentanediammonium as the organic cation.…”

(1-C5H14N2Br)2MnBr4: A Lead-Free Zero-Dimensional Organic-Metal Halide With Intense Green Photoluminescence

“…In addition to modifying the length of the organic components, the diverse structural dimensionality, referring to three-dimensional (3D), two-dimensional (2D), one-dimensional (1D) and zerodimensional (0D) structures, can also be achieved by tuning the inorganic frameworks, which results in fascinating properties. In the first place, the most obvious alternative substitution to Pb 2+ , should be the elements in the same group in the periodic table, namely Sn 2+ and Ge 2+ (Zhumekenov et al, 2017;Fu et al, 2018;Ju et al, 2018a;Nazarenko et al, 2019). In addition, heterovalent elements in Group 15 (Bi 3+ and Sb 3+ ) (Abulikemu et al, 2016;Sun et al, 2016;Ji et al, 2017Ji et al, , 2018Ju et al, 2018b;Zhang et al, 2018;Tao et al, 2019) and in Group 13 (In 3+ ) (Zhou et al, 2019) have also been demonstrated as the alternative metals.…”