This study investigated key factors affecting the stability of photovoltaic (PV) slopes using finite element models and an orthogonal experimental design. Slope height, slope gradient, and soil cohesion were evaluated based on safety factor (Fs) assessments. The results indicate that soil cohesion exerts the dominant influence—more than 2.4 times the combined effect of slope height and gradient—followed by slope height and gradient. The optimal parameter combination (a1b3c5) achieved an Fs of 3.172. Increasing slope height from 8 m to 20 m reduced Fs by 33.45%–42.29%, while flattening the slope gradient from 45° to 26.57° improved Fs by 45.9%, with steeper slopes exhibiting greater optimization potential. Although soil cohesion is positively correlated with Fs, its incremental benefit diminishes at higher values. PV system weight had minimal influence; PV loads accounted for only 7% of the soil’s self-weight, and doubling module density from 400 to 800 kg/m3 increased Fs by merely 0.06 for 45° slopes. In addition, increasing bracket foundation depth significantly improved the stability of steep slopes, albeit with diminishing returns at excessive depths. These findings underscore the critical role of soil cohesion management in PV slope design, with geometric optimization and foundation depth adjustments serving as secondary stabilization strategies.