Vibrational and Structural Properties of Two-Dimensional Tin Mixed-Halide Perovskites

The emergence of two-dimensional (2D) hybrid metal-halide perovskites has garnered significant attentions for optoelectronic devices and light-emitting applications. Since the toxicity of lead-based perovskites could potentially be harmful to the environment, several works have attempted to change the active metal to tin (Sn). Here, we investigate the characterization of (PEA)2SnBrxI4-x mixed halide perovskites using X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Qualitative XRF analysis suggests the presence of tin, bromine and iodine emissions under the mid-Z and high-Z ranges. In mid-Z range, Br-Kα peak appeared on 11.96 keV and Br-Kβ was detected on 13.3 keV. Meanwhile Sn-Kα, I-Kα, I-Kβ1, and I-Kβ2 peaks were detected in high-Z range on 25.24 keV, 28.6 keV, 32.35 keV and 33.11 keV, respectively. Thus, the elemental composition of mixed halide components exhibits an indicative control that bromine-rich or iodine-rich can be synthesized via rational chemical design. XRD pattern display a systematic progression at the peak 5.18° (corresponds to (002) plane), which unambiguously demonstrated the feasibility to tune halide composition in tin-based hybrid perovskite. It also confirms that (2D) hybrid metal-halide with tunable halide have identical structure for both bromine-rich and iodine-rich composition. Furthermore, the 2θ peaks slightly shifted to lower angle with increasing bromine composition. The presence of C−I bonding on ~500 cm-1 and C-Br bond on ~600 cm-1 in FTIR spectra highlights the functional group of organic cations. These experimental results promote a foundation to implement compositional engineering on 2D-tin mixed-halide perovskites for optoelectronics and scintillators.