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Structural Characterization and Room Temperature Low Frequency Raman Scattering from MAPbI3 Halide Perovskite Films Rigidized by Cesium Incorporation
摘要： The structural instability of organometal halide perovskites (OHP) is one of the major issues concerning commercialization of perovskite solar cells. Probing this intrinsic instability is one of the major milestones and challenging tasks towards enhancing the lifespan of the material. Here we have incorporated Cs ions into methylammonium lead iodide (MAPbI3) films and studied the thin film structural and optical properties. Incorporation of Cs into MAPbI3 leads to formation of both α-CsPbI3 and ?-CsPbI3 phases, black and yellow respectively, as indicated by the evolution of the optical band edge and X-Ray diffraction (XRD) spectrum. At a concentration of 20% Cs ions, we observe existence of a stable α-CsPbI3 phase. Incorporating 59% or more Cs ions yields the yellow phase of CsPbI3, due to alloying of Cs with the MAPbI3 matrix. The structural transformations observed in absorption spectra and XRD are confirmed by Low Frequency Raman Spectroscopy. The thermally induced structural fluctuations in pure MAPbI3 films are damped upon Cs incorporation, thus bringing long range stabilized order to the perovskite structure and enabling for the first time observation of Low Frequency Raman Scattering at room temperature for OHPs. In addition to this, Cs incorporation rigidizes the perovskite film and sharpens all low frequency vibrational peaks.
关键词： Cesium incorporation,Low Frequency Raman,Perovskite Stability,Phonon Damping,Hybrid Perovskite
更新于2025-09-04 15:30:14
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Crystal growth, structural phase transitions and optical gap evolution of CH3NH3Pb(Br1-xClx)3 powders
摘要： Chemically tuned inorganic-organic hybrid halide perovskites based on bromide and chloride anions CH3NH3Pb(Br1-xClx)3 have been crystallized and investigated by synchrotron X-ray diffraction (SXRD), scanning electron microscopy and UV-vis spectroscopy. CH3NH3PbBr3 and CH3NH3PbCl3 experience successive phase transitions upon cooling, which are suppressed for intermediate compositions probably due to compositional disorder. For CH3NH3PbCl3 a transient phase, formerly described as tetragonal, was identified at 167.5 K; the analysis of SXRD data demonstrated that it is indeed orthorhombic, with space group Pnma, and a ≈ √2ap; b ≈ 2ap; c ≈ √2ap (ap is the ideal cubic perovskite unit-cell parameter). The band gap engineering brought about by the chemical management of CH3NH3Pb(Br1-xClx)3 perovskites can be controllably tuned: the gap progressively increases with the concentration of Cl ions from 2.2 to 2.9 eV, and shows a concomitant variation with the unit-cell parameters of the cubic phases at 295 K. This study provides an improved understanding of the structural and optical properties of the mixed CH3NH3Pb(Br1-xClx)3 perovskites.
关键词： hybrid perovskite,mixed halide,chlorine,bromine,solar cells
更新于2025-09-04 15:30:14