1：Experimental Design and Method Selection

The study employs a direct metal surface elemental reaction (DMSER) method for the in-situ fabrication of CuBiI4 perovskite-like films at room temperature, using bilayer metal Bi/Cu thin films as precursors. The methodology includes controlling the Bi/Cu atomic ratios to create films with a Bi gradient.

2：Sample Selection and Data Sources

Samples were prepared by depositing Bi and Cu thin films on ITO substrates, followed by reaction with elemental iodine. The thickness of the Cu layer was varied to control the Bi gradient in the resulting CuBiI4 films.

3：List of Experimental Equipment and Materials

Equipment includes magnetron sputtering for thin film deposition, XRD for structural analysis, SEM and TEM for morphological studies, UV-Vis spectrophotometer for optical properties, and TSPV for charge carrier dynamics. Materials include Bi, Cu, I2, ITO substrates, and organic semiconductors (Spiro-OMeTAD, P3HT, PTB7).

4：Experimental Procedures and Operational Workflow

The process involves depositing Bi and Cu layers on ITO, reacting with I2 to form CuBiI4, spin-coating organic semiconductors, and assembling solar cell devices. Characterization techniques were applied at each step to analyze the films and devices.

5：Data Analysis Methods

Data analysis included XRD for structural confirmation, SEM/TEM for morphology, UV-Vis for optical properties, and TSPV for charge carrier dynamics. Solar cell performance was evaluated through J-V curves and EQE measurements.