Synthesis of Two-Dimensional CsPb₂X₅ (X = Br and I) with a Stable Structure and Tunable Bandgap by CsPbX₃ Phase Separation

Abstract

Perovskite-related materials with various dimensionalities have attracted sustained attention owing to their extraordinary electronic and optoelectronic properties, but it is still challenging in the synthesis of compounds with desired compositions and structures. Herein, a two-dimensional (2D) CsPb 2 I 5 perovskite has been synthesized by the conversion of CsPbI 3 at high-pressure and high-temperature (high P−T) conditions, which is quenchable at ambient conditions. In situ synchrotron X-ray diffraction shows that high-pressure monoclinic CsPbI 3 converts into tetragonal CsPb 2 I 5 and cubic CsI at 8.7 GPa upon heating from 644 to 666 K. Keeping the tetragonal structure stable, CsPb 2 I 5 exhibits tunable optical properties with the bandgap changing from ∼2.4 eV at ambient pressure to ∼1.4 eV at 36.9 GPa. Further experiments demonstrate similar structural evolution in the typical three-dimensional CsPbBr 3 perovskite into 2D CsPb 2 Br 5 at high P−T conditions, indicating that the conversion of CsPbX 3 (X = Br and I) into CsPb 2 X 5 is ubiquitous.

Synthesis of Edge-Shared Octahedral MAPbBr3 via Pressure- and Temperature-Induced Multiple-Stage Processes

“…The pressure calibration was determined utilizing the ruby fluorescence method . The generation of high P – T conditions is similar to that previously reported in CsPbI 3 …”

“…In inorganic MHPs, for instance, CsPbI 3 and CsPbBr 3 have been reported to undergo the conversion from the Pm3m perovskite structure with cornershared BX 6 octahedra to the Pnma structure with double chains of edge-shared PbX 6 under pressure; 22,23 2D CsPb 2 X 5 (X = Br and I) with face-shared BX 6 octahedra (space group I4/mcm) was synthesized by the direct phase separation of 1D CsPbI 3 with edge-shared PbX 6 octahedra (space group C2/m) at high-pressure and temperature (P−T) conditions. 24 The tunable connectivity modes of BX 6 octahedra observed in inorganic MHPs under high P−T conditions provide a new possibility for the design and synthesis of more perovskiterelated structures, but the underlying mechanisms remain unclear in organic MHPs due to the limitation of the pressureinduced amorphization and temperature-induced decomposition. In this work, we control the thermodynamic parameters of both pressure and temperature and select MAPbBr 3 as an example to explore the new structures and physical properties.…”

“…In the last few decades, increasing numbers of research on MHPs under high pressure have been reported, − adding numerous new structures with novel physical properties to the family of perovskite materials. In inorganic MHPs, for instance, CsPbI 3 and CsPbBr 3 have been reported to undergo the conversion from the Pm 3̅ m perovskite structure with corner-shared BX 6 octahedra to the Pnma structure with double chains of edge-shared PbX 6 under pressure; , 2D CsPb 2 X 5 (X = Br and I) with face-shared BX 6 octahedra (space group I 4/ mcm ) was synthesized by the direct phase separation of 1D CsPbI 3 with edge-shared PbX 6 octahedra (space group C 2/ m ) at high-pressure and temperature ( P – T ) conditions . The tunable connectivity modes of BX 6 octahedra observed in inorganic MHPs under high P – T conditions provide a new possibility for the design and synthesis of more perovskite-related structures, but the underlying mechanisms remain unclear in organic MHPs due to the limitation of the pressure-induced amorphization and temperature-induced decomposition.…”

Photoelectrochemical performance of ligand-free CsPb2Br5 perovskites

“…13 However, to date, no one has reported the photoelectrochemical properties of CsPb 2 X 5 perovskite synthesized in a pure water phase. 14,15 Thus, it is imperative to develop new strategies for the synthesis of water-stable perovskites that allow them to maintain their good charge transportability while extending their applicability to photoelectronics and related applications. In this study, we developed a pure-water-phase synthesis strategy for ligand-free 2D cesium lead halide perovskite CsPb 2 X 5 nanoplatelets, and the photoelectrochemical performance of CsPb 2 Br 5 nanoplatelets was evaluated and preliminarily explored.…”

“…13 However, to date, no one has reported the photoelectrochemical properties of CsPb 2 X 5 perovskite synthesized in a pure water phase. 14,15…”