Thin-Film Deposition and Characterization of a Sn-Deficient Perovskite Derivative Cs₂SnI₆

Abstract

In this work, we describe details of a two-step deposition approach that enables the preparation of continuous and well-structured thin films of Cs 2 SnI 6 , which is a one-half Sndeficient 0-D perovskite derivative (i.e., the compound can also be written as CsSn 0.5 I 3 , with a structure consisting of isolated SnI 6 4− octahedra). The films were characterized using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), UV−vis spectroscopy, photoluminescence (PL), photoelectron spectroscopy (UPS, IPES, XPS), and Hall effect measurements. UV−vis and PL measurements indicate that the obtained Cs 2 SnI 6 film is a semiconductor with a band gap of 1.6 eV. This band gap was further confirmed by the UPS and IPES spectra, which were well reproduced by the calculated density of states with the HSE hybrid functional. The Cs 2 SnI 6 films exhibited n-type conduction with a carrier density of 6(1) × 10 16 cm −3 and mobility of 2.9(3) cm 2 /V•s. While the computationally derived band structure for Cs 2 SnI 6 shows significant dispersion along several directions in the Brillouin zone near the band edges, the valence band is relatively flat along the Γ−X direction, indicative of a more limited hole minority carrier mobility compared to analogous values for the electrons. The ionization potential (IP) and electron affinity (EA) were determined to be 6.4 and 4.8 eV, respectively. The Cs 2 SnI 6 films show some enhanced stability under ambient air, compared to methylammonium lead(II) iodide perovskite films stored under similar conditions; however, the films do decompose slowly, yielding a CsI impurity. These findings are discussed in the context of suitability of Cs 2 SnI 6 for photovoltaic and related optoelectronic applications.

Perovskite Solar Absorbers: Materials by Design

“…The calculated band structure and DOS of Cs 2 SnI 6 with the HSE hybrid functional are shown in Figure b . The band structure of Cs 2 SnI 6 exhibits a direct bandgap of 1.26 eV at the Γ point, which is consistent with the experimental value obtained from the absorption spectrum . Although Cs 2 SnI 6 is structurally similar to CsSnI 3 by removing half of the Sn atoms from alternating sites, it has a distinct electronic structure, which is schematically illuminated in Figure c .…”

From Lead Halide Perovskites to Lead‐Free Metal Halide Perovskites and Perovskite Derivatives

“…As shown in Figure 9a-c, [101,110,112] the VBMs of these compounds consist of nonbonding X p orbitals, rather than the cation lonepair s-X p antibonding states for ABX 3 (B = Pb, Sn, and Ge) halide perovskites. [102,109,113,115] Despite the general similarity, there are some differences in the optoelectronic properties of these compounds. The CBMs are derived from the antibonding states of cation s or d and X p orbitals.…”

Organic–inorganic metal halide hybrids beyond perovskites

“…LEDs (Figure 2(c)), optically pumped lasers (Figure 2(d)), etc [32][33][34]. To address the toxicity issue of Pb, 3D tin halide perovskites have been developed [35][36][37][38][39]. However, bivalent Sn 2+ could be easily oxidized to Sn 4+ , resulting in the instability of the material itself and morphological change into other species [40].…”