1：Experimental Design and Method Selection

The study involved fabricating mixed-halide perovskites (FAPbI3)x(MAPbBr3)1-x and FA0.85MA0.15Pb(IxBr1-x)3 for bandgap tuning. The optical properties were measured using ultraviolet-visible absorption spectra, and the bandgap was determined using Tauc’s law for direct bandgap semiconductors.

2：Sample Selection and Data Sources

Perovskite films were deposited on ITO/glass substrates. The samples were prepared with varying ratios of bromine to iodine to explore the range of bandgap tunability.

3：List of Experimental Equipment and Materials

Materials included FAI, MABr, PbI2, PbBr2, DMF:DMSO solvent, TiO2 nanocrystal colloidal solution, spiro-OMeTAD, and Au for electrodes. Equipment included a spectrophotometer for UV-vis absorption spectra, SEM for imaging, and a source meter for J-V measurements.

4：Experimental Procedures and Operational Workflow

Perovskite precursor solutions were spin-coated onto substrates, followed by annealing. The spiro-OMeTAD solution was then spin-coated onto the perovskite surface, and Au electrodes were deposited by thermal evaporation. Characterization included SEM imaging, UV-vis absorption spectra, and J-V measurements under laser illumination.

5：Data Analysis Methods

Bandgap values were calculated from (αhν)2 versus hν plots. EQE measurements and J-V curves were used to evaluate photovoltaic performance.