1：Experimental Design and Method Selection:

The study involved the synthesis of bulk PdSe2 crystal using a standard self-flux method, fabrication of PdSe2-based photodetectors with different thicknesses, and characterization of their optoelectronic properties. First-principles calculations were performed to understand the electronic band structure of PdSe

2：Sample Selection and Data Sources:

High-quality PdSe2 flakes were mechanically exfoliated onto SiO2/Si substrates, and their thickness was determined using atomic force microscopy (AFM).

3：List of Experimental Equipment and Materials:

Equipment included a thermal furnace for crystal growth, optical microscope, AFM, electron-beam lithography system, thermal deposition system, Keithley 6430 and 2400 SourceMeters for electrical measurements, and a 532-nm laser for photocurrent measurements. Materials included Pd powder (99.99%) and Se (99.94%) from Sigma-Aldrich, h-BN flakes, and Ti/Au for electrodes.

4：99%) and Se (94%) from Sigma-Aldrich, h-BN flakes, and Ti/Au for electrodes. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: PdSe2 and h-BN flakes were exfoliated and transferred onto substrates. Electrodes were patterned and deposited. Electrical and photoresponse measurements were conducted under vacuum.

5：Data Analysis Methods:

Photoresponsivity and external quantum efficiency were calculated from measured photocurrent and incident light power. First-principles calculations were used to analyze the electronic band structure.