1：Experimental Design and Method Selection:

Oxygen plasma treatment was employed to enhance the optoelectronic performance of SnS2 flakes. The treatment was conducted with low power plasma to avoid significant damage on the SnS2 crystal structure.

2：Sample Selection and Data Sources:

Multi-layer, single-crystal SnS2 flake was mechanically exfoliated onto a 300 nm thick SiO2 substrate.

3：List of Experimental Equipment and Materials:

Optical microscope (Olympus, BX51), AFM, X-ray diffractometer (D2 PHASER, Bruker), X-ray photoelectron spectroscopy equipment (ESCALab250, Thermo Fisher Scientific), confocal Raman/PL machine (Alpha 300R, WITec), laser source (LDLS, EQ-1500, Energetiq), silicon photodiode, probe station (CRX-6.5K, Lake Shore), semiconductor test system (4200-SCS and 2400, Keithley).

4：5K, Lake Shore), semiconductor test system (4200-SCS and 2400, Keithley). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The O2 plasma treatment was executed with reactive ion etcher power (15 W), plasma pressure (0.1 mbar), O2 flow rate (20 sccm), and RF frequency (40 kHz). The photodetection properties were explored under wavelength range of 350 to 900 nm.

5：1 mbar), O2 flow rate (20 sccm), and RF frequency (40 kHz). The photodetection properties were explored under wavelength range of 350 to 900 nm. Data Analysis Methods:

5. Data Analysis Methods: The responsivity (Rλ), external quantum efficiency (EQE), and detectivity (D*) of the devices were evaluated using specific relations.