Tracking the dimensional conversion process of semiconducting lead bromide perovskites by mass spectroscopy, powder X-ray diffraction, microcalorimetry and crystallography

Abstract

The structural information of a material in both the solid state and solution state is essential to the in-depth understanding of the properties of inorganic–organic hybrid materials. A one-dimensional (1D) lead bromide formulated as [H][NH₃(CH₂)₂SS(CH₂)₂NH₃][H₂O][PbBr₅] (1) could be converted into a new two-dimensional (2D) complex, [NH₃(CH₂)₂SS(CH₂)₂NH₃][PbBr₄] (2), by soaking the crystals in water. The isolated 2D compound showed single-layer lead-halide perovskite structures. Electrospray ionization mass spectrometry (ESI-MS) analyses of the reaction solution revealed that the [PbBr₃]⁻ fragments are initially formed from the rapid decomposition of the 1D [PbBr₅]³⁻ chains and subsequently reassemble into 2D [PbBr₄]²⁻ layers, which was verified by powder X-ray diffraction (PXRD) and microcalorimetry. Because of the decomposition and reassembly process, complex 1 could be used as a precursor to synthesize M²⁺-doped 2D lead bromide perovskites, namely, Mn@2, Ni@2 and Cd@2. In addition, preliminary tests indicated that complex 2 exhibited a lower optical band gap (3.25 eV) and higher electrical conductivity (3.2 × 10⁻¹¹ S cm⁻¹) than complex 1 (3.38 eV, 5.4 × 10⁻¹² S cm⁻¹).