1：Experimental Design and Method Selection:

The study uses solid-state reaction route at room temperature in ambient air to synthesize CsxMA(1-x)PbI3 powders with x from 0 to 0.4 in steps of 0.1. Rietveld refinement, thermodynamic analysis, Raman spectroscopy, and optical absorption are employed to characterize the samples.

2：4 in steps of Rietveld refinement, thermodynamic analysis, Raman spectroscopy, and optical absorption are employed to characterize the samples. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Precursors include Methyl Ammonium Iodide (CH3NH3I) and Cesium Iodide (CsI) from Sigma Aldrich (purity >99.9%), and lab-synthesized PbI2. Samples are prepared by grinding stoichiometric mixtures in a mortar pestle.

3：9%), and lab-synthesized PbISamples are prepared by grinding stoichiometric mixtures in a mortar pestle. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes Rigaku Miniflex for XRD, JASCO V-770 UV-visible spectrometer for optical absorption, EVO-SEM MA15/18 and TECHNAI G2 20G TWIN TEM for morphology, DXRxi Raman imaging microscope for Raman spectra, SHIMADZU DSC-60 plus for thermodynamics, and Wayne Kerr LCR meter for impedance studies.

4：Experimental Procedures and Operational Workflow:

Precursors are mixed and ground at room temperature. Characterization involves XRD for structural analysis, UV-visible for optical properties, SEM/TEM for morphology, Raman for vibrational modes, DSC for thermal analysis, and impedance spectroscopy for electrical properties.

5：Data Analysis Methods:

Rietveld refinement using FULLPROF suite, Tauc's plot for band gap calculation, Urbach energy analysis from absorption spectra, and impedance data interpretation for microstructure.