1：Experimental Design and Method Selection

The study employed a solvothermal synthesis method to prepare nickel sulfide (NiS) with various sulfur contents. The influence of sulfur content on the morphological changes of NiS was examined, and the resultant NiS was used as hole-transport layers (HTLs) in organic solar cells (OSCs).

2：Sample Selection and Data Sources

The samples were prepared by varying the amount of thioacetamide (sulfur source) in the synthesis process, resulting in NiS_1.0, NiS_1.5, NiS_2.0, and NiS_2.5. These samples were then used as HTLs in OSCs to evaluate their photovoltaic performance.

3：List of Experimental Equipment and Materials

Field emission scanning electron spectroscopy (FESEM, JEOL-7610F-Plus), field emission transmission electron spectroscopy (FE-TEM, Tecnai G2 F20 USA), X-ray diffraction (PANalytical, X'Pert-PRO MPD), X-ray photoelectron spectroscopy (ESCALAB 250 XPS system, Thermo Fisher Scientific, UK), Bio-Logic SP-150 potentiostat, AFM with an XE-100 advanced scanning probe microscope, T60 UV–visible spectrophotometer, Kelvin probe S and Kelvin control 07.

4：Experimental Procedures and Operational Workflow

The synthesis involved dissolving nickel chloride hexahydrate in acetic acid, adding ethanol and thioacetamide, stirring, and then transferring the solution to a Teflon-lined steel autoclave for reaction at 160 °C for 5 h. The precipitate was washed and dried. The NiS samples were then used to fabricate OSCs, with the photovoltaic characteristics under illumination recorded for each device.

5：Data Analysis Methods

The photovoltaic characteristics were analyzed to determine the power conversion efficiency (PCE), short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF). The stability and reproducibility of the devices were also evaluated.