1：Experimental Design and Method Selection:

The study used the successive ionic layer absorption and reaction (SILAR) method for synthesizing CdS quantum dots on fluorine doped tin oxide (FTO) substrate. A polysulfide electrolyte was used as a redox mediator. The combination of ZnO/TiO2 was used as a photoanode, and a low-cost CuS counter electrode replaced the conventional Pt counter electrode.

2：Sample Selection and Data Sources:

Precursor solutions of CdS quantum dots with concentrations of 0.1 M, 0.2 M, 0.5 M, and 0.8 M were synthesized on FTO substrate.

3：1 M, 2 M, 5 M, and 8 M were synthesized on FTO substrate. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Field-emission scanning electron microscope (FESEM) and X-ray diffractometer for morphological and structural characterizations, ultraviolet–visible (UV–Vis) spectroscopy for optical characterizations, and a solar simulator for evaluating J-V characteristics and performance under AM 1.5G spectrum illumination.

4：5G spectrum illumination. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The ZnO/TiO2 layers were deposited onto the FTO glass substrate, followed by the deposition of CdS QDs using the SILAR method. The CuS counter electrodes were fabricated onto the FTO glass substrate by the doctor blade method. The polysulfide electrolyte solution was prepared and used in the solar cell device fabrication.

5：Data Analysis Methods:

The degree of porosity was determined by ImageJ Software. The efficiencies and the fill factors of the solar cell were calculated from J-V measurements.