Revealing the Local Sn and Pb Arrangements in CsSn_xPb_1–xBr₃ Perovskites with Solid-State NMR Spectroscopy

Abstract

Mixed Sn–Pb halide perovskites are more stable at ambient conditions and can be tuned to give narrower band gaps than the all-Pb-containing counterparts (APbX3) used as photovoltaic materials. In the series CsSn x Pb1–x Br3, the crystal structure evolves from orthorhombic (space group Pnma for x = 0–0.8) to cubic (space group Pm m for x = 1), and the band gap decreases for Sn-richer compositions. It previously was unclear how the physical properties are related to structural changes entailed by the Sn–Pb mixing because the short- versus long-range arrangements have not been well characterized. Solid-state NMR spectroscopy of several NMR-active nuclei (119Sn, 133Cs, and 207Pb) supports the occurrence of complete disorder, with PbBr6 and SnBr6 octahedra distributed in random arrangements throughout the entire structure with no evidence for phase segregation. Compounds prepared by solvent-assisted vs solvent-free routes are compared and show differences in their degree of crystallinity and optical absorption properties.

Optoelectronic Properties of Low‐Bandgap Halide Perovskites for Solar Cell Applications

“…A key open question still remains as to how the Pb and Sn arrange themselves on the atomic scale, which can dictate the band structure in these mixed Pb–Sn alloys. Although the local arrangement of Pb and Sn has recently been explored in Cs‐based mixed Pb–Sn bromide perovskites using solid state nuclear magnetic resonance (NMR), [ 109 ] revealing homogeneous mixing, similar studies on hybrid Pb–Sn iodide perovskite thin films are more challenging and yet to be done. Nevertheless, the prospect of efficient CM together with the efficient charge transport properties could make Sn‐containing perovskites promising candidates to demonstrate J sc values higher than their Shockley–Queisser limits.…”

Interfaces in metal halide perovskites probed by solid-state NMR spectroscopy

“…351,352 The type of halogen atom forming the BX 6 octahedra strongly inuences the chemical shis and lineshapes of B-site cations (Pb 2+ , Sn 2+ ). 152,153,312,314,345,[353][354][355][356][357] In this context, 207 Pb and 119 Sn NMR studies have been increasingly pursued to examine the local environments of BX 6 octahedra in lead and tin halide perovskites, respectively. The subtle changes in the organicinorganic interfaces such as electrostatic interactions, cation dynamics and octahedral tilts and B-X bond distances and phase transitions may have dramatic effects on the 207 Pb and 119 Sn NMR lineshapes.…”

Synthesis of two-dimensional phenylethylamine tin–lead halide perovskites with bandgap bending behavior

“…The much higher bandgap of the 0% Sn sample should be attributed to the heavier mass of Pb than that of Sn, which agrees with previous studies. 34,36,40,[58][59][60] However, a special peak shi of the Pb-s orbital emerged when the Sn ratio was 0.25. As a result, the valence band maximum (VBM) changed from Pb-s/Br-p to Sn-s/ Br-p, while the conduction band minimum (CBM) remained mainly Pb-p. Appropriately, the dominant position of Sn-p/Br-p was replaced by Pb-p/Br-p for CBM characters, while the VBM kept Sn-s as the main composition when the Sn ratio was 0.75.…”