1：Experimental Design and Method Selection:

The precursor solution for the fabrication of CZTSSe thin films was prepared by mixing copper chloride (CuCl2), zinc chloride (ZnCl2), tin chloride (SnCl2) and thiourea (CS(NH2)2) powders into 50 ml de-ionized (DI) water as a molar ratio of

2：

3：

1 : 10 and stirred at room temperature for 1 hour to obtain a transparent solution. Then 0.5 ml of 37% concentrated hydrochloric acid added to adjust the ph and final aqueous solution was sprayed onto Mo-coated soda lime glass which was pre-heated at 330oC using a hot plate. Lastly, as-deposited thin films were annealed at 550oC for 30 min in a rectangular graphite box which contains various amounts of S and Se powder mixtures. CBD process for CdS buffer layer was performed at 76oC for 10 min with continuous stirring. No etching treatments applied before the deposition of CdS buffer layer. After the CdS buffer layer, transparent conductive top contact with intrinsic zinc oxide (i-ZnO/~50 nm) and indium tin oxide (ITO/~150 nm) was deposited by rf magnetron sputtering. In final, fabricated solar cells scribed mechanically around a total area of 0.16 ~ 0.18 cm2 and obtained without anti-reflection coating and Ni/Al grid pattern.

4：5 ml of 37% concentrated hydrochloric acid added to adjust the ph and final aqueous solution was sprayed onto Mo-coated soda lime glass which was pre-heated at 330oC using a hot plate. Lastly, as-deposited thin films were annealed at 550oC for 30 min in a rectangular graphite box which contains various amounts of S and Se powder mixtures. CBD process for CdS buffer layer was performed at 76oC for 10 min with continuous stirring. No etching treatments applied before the deposition of CdS buffer layer. After the CdS buffer layer, transparent conductive top contact with intrinsic zinc oxide (i-ZnO/~50 nm) and indium tin oxide (ITO/~150 nm) was deposited by rf magnetron sputtering. In final, fabricated solar cells scribed mechanically around a total area of 16 ~ 18 cm2 and obtained without anti-reflection coating and Ni/Al grid pattern. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The samples were selected based on the S/(S+Se) ratio, ranging from 0 to 0.99. Data sources include FESEM, EDS, XRD, Raman spectroscopy, J-V characteristics, EQE measurements, J-V-T measurements, AS measurements, and TR-PL measurements.

5：Data sources include FESEM, EDS, XRD, Raman spectroscopy, J-V characteristics, EQE measurements, J-V-T measurements, AS measurements, and TR-PL measurements. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Field emission scanning electron microscopy (FESEM, JEOL, JSM-7800F) equipped with energy dispersive X-ray spectroscopy (EDS, Oxford Co.), X-ray diffraction (XRD) system (Rigaku, Smart Lab), Raman spectroscopy system (Spectro Raman system equipped with the spectrometer (Mmac 750) and laser of excitation wavelength λ =532 nm), solar simulator, source meter (Keithley 2400), EQE system (McScience Inc), LCR meter (E4980A, Agilent), fluorescence lifetime spectrometer (Hamamatsu C12132), and MicroTime 100 (PicoQuant, Germany).

6：Experimental Procedures and Operational Workflow:

The experimental procedures include the preparation of the precursor solution, spraying onto Mo-coated soda lime glass, annealing, deposition of CdS buffer layer, deposition of i-ZnO and ITO, and characterization using various techniques.

7：Data Analysis Methods:

The data analysis methods include XRD peak analysis, Raman spectroscopy analysis, J-V curve analysis, EQE spectra analysis, temperature-dependent analysis, AS analysis, and TRPL analysis.