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Title: | Phase Diagram of Methylammonium/Formamidinium Lead Iodide Perovskite Solid Solutions from Temperature-Dependent Photoluminescence and Raman Spectroscopies |
Authors: | Francisco López, Adrian; Charles, Bethan; Alonso Carmona, M. Isabel ![]() ![]() ![]() ![]() |
Keywords: | Halide perovskites Optical-properties Single-crystals Organic cations Formadinium |
Issue Date: | 13-Feb-2020 |
Publisher: | American Chemical Society |
Citation: | Journal of Physical Chemistry C 124(6): 3448-3458 (2020) |
Abstract: | The complete phase diagram of organic-cation solid solutions of lead iodide perovskites [FAxMA1–xPbI3, where MA stands for methylammonium, CH3NH3, and FA for formamidinium, CH(NH2)2] with compositions x ranging from 0 to 1 in steps of 0.1 was constructed in the temperature range from 10 to 365 K by combining Raman scattering and photoluminescence (PL) measurements. The occurrence of phase transitions was inferred from both the temperature-induced changes in the optical emission energies and/or the phonon frequencies and line widths, complementing X-ray and neutron scattering literature data. For MA-rich perovskites (x ≤ 0.2), the same structural behavior as for MAPbI3 was observed with decreasing temperature: cubic Pm3̅m → tetragonal-I I4/mcm → orthorhombic Pnma. As the FA molecule is larger and more symmetric but less polar than MA, a tetragonal crystal structure is favored at low temperatures and FA compositions x > 0.4, to the detriment of the orthorhombic phase. As a consequence, with decreasing temperature, the phase transition sequence for FA-rich compounds is cubic Pm3̅m → tetragonal-II P4/mbm → tetragonal-III. The latter presumably belongs to the P4bm symmetry group, according to neutron scattering data. Strikingly, the isostructural (tetragonal-to-tetragonal) transformation, which occurs between 200 and 150 K, exhibits a kind of critical point for x = 0.7. For intermediate FA contents, the perovskite solid solution transforms close to 250 K directly from the cubic phase to the tetragonal-III phase. The latter is characterized by a nonmonotonic dependence of the band-gap energy on temperature. We ascribe such behavior to a substantial tilting of the PbI6 octahedra in the tetragonal-III phase. In this way, we established important links between crystal-phase stability and the electronic as well as vibrational properties of mixed organic-cation halide perovskites, which might impact the current search for more stable best-performing optoelectronic materials. |
Publisher version (URL): | http://dx.doi.org/10.1021/acs.jpcc.9b10185 |
URI: | http://hdl.handle.net/10261/210417 |
ISSN: | 1932-7447 |
Appears in Collections: | (ICMAB) Artículos |
Files in This Item:
File | Description | Size | Format | |
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Francisco_JPhysChemC_2020_postprint.pdf | Artículo principal | 1,57 MB | Adobe PDF | ![]() View/Open |
Francisco_JPhysChemC_2020_suppl_postprint.pdf | Información complementaria | 5,09 MB | Adobe PDF | ![]() View/Open |
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