<p>The emergence of two-dimensional moiré superlattice has sparked intense research interest thanks to its rich correlated physics. Compared with graphene-based systems, moiré superlattices based on transitional metal dichalcogenides facilitate better access to such physical phenomena, with higher transition temperatures, more robust flat bands, and richer correlated states. However, the layer degree freedom in certain heterojunctions has remained largely unexplored due to various technical challenges. In this work, by excluding the effect of the moiré angle through a designed sample structure, we isolate, identify, and investigate the layer dependence in an MoSe₂/WS₂ moiré heterojunction, and observe striking contrasts between samples with different numbers of layers. In the monolayer MoSe₂/monolayer WS₂ moiré heterojunction, we observe an unusual alternation in the spectroscopic features of the correlated states, revealing competition between polaron and exciton dominances. In bilayer MoSe₂/monolayer WS₂ moiré heterojunction, we observe a clear signature oflayer-modulated moiré excitons, which we further use a probe to reveal the electric field tuning of the correlated states. Our study demonstrates the intriguing opportunities offered by the MoSe₂/WS₂ moiré heterojunction as an exciting playground for exploring many-body physics and engineering emerging quantum states.</p>