This study investigates the optoelectronic properties of van der Waals (vdW) heterostructures composed of single-layer transition metal dichalcogenides (TMDCs), specifically WSe₂ and MoS₂. The research focuses on the interlayer coupling and band alignment in these heterostructures, which are built by assembling individual single-layer TMDCs with atomically sharp interfaces and no interdiffusion. The study reveals that the optical transitions in these heterostructures are spatially indirect, with a large Stokes-like shift of ~100 meV between the photoluminescence peak and the lowest absorption peak. This shift is consistent with a type II band alignment, where spatially direct absorption occurs but spatially indirect emission dominates. The strong interlayer coupling of charge carriers is evident from the strong photoluminescence intensity of the spatially indirect transition, suggesting a significant degree of interlayer interaction. The heterostructures were fabricated by stacking single-layer WSe₂ and MoS₂ on a Si/SiO₂ substrate. The resulting heterostructures exhibit a moiré pattern due to the 3.8% lattice mismatch and angular alignment between the layers. The electronic structure of the heterostructures was analyzed using X-ray photoelectron spectroscopy (XPS), revealing a shift in the binding energy of W 4f and Mo 3d core levels, indicating a negative net charge on the WSe₂ layer and a positive net charge on the MoS₂ layer. This charge transfer results in a built-in potential of up to 400 mV, forming a two-dimensional dipole or atomically thin parallel plate capacitor. The optoelectronic properties of the heterostructures were further investigated using photoluminescence (PL) and absorption spectroscopy. The PL spectra showed a peak at 1.55 eV for the WSe₂/MoS₂ hetero-bilayer, lower than the peaks of the individual single layers, indicating a type II band alignment. The large Stokes-like shift is consistent with spatially indirect transitions in a staggered gap heterostructure. The study also demonstrates that the interlayer coupling can be tuned by inserting hexagonal boron nitride (h-BN) layers into the vdW gap, which significantly reduces the interlayer interaction. The research highlights the potential of vdW heterostructures for next-generation optoelectronic devices, with tunable optoelectronic properties and customizable composite layers. The findings suggest that these heterostructures can be used to create new families of semiconductor heterostructures with enhanced performance and functionality. The study also emphasizes the importance of interlayer coupling in determining the electronic and optoelectronic properties of these materials, offering a new degree of freedom in band engineering. The results provide a foundation for further research into the bottom-up creation of new heterostructures with tailored properties.This study investigates the optoelectronic properties of van der Waals (vdW) heterostructures composed of single-layer transition metal dichalcogenides (TMDCs), specifically WSe₂ and MoS₂. The research focuses on the interlayer coupling and band alignment in these heterostructures, which are built by assembling individual single-layer TMDCs with atomically sharp interfaces and no interdiffusion. The study reveals that the optical transitions in these heterostructures are spatially indirect, with a large Stokes-like shift of ~100 meV between the photoluminescence peak and the lowest absorption peak. This shift is consistent with a type II band alignment, where spatially direct absorption occurs but spatially indirect emission dominates. The strong interlayer coupling of charge carriers is evident from the strong photoluminescence intensity of the spatially indirect transition, suggesting a significant degree of interlayer interaction. The heterostructures were fabricated by stacking single-layer WSe₂ and MoS₂ on a Si/SiO₂ substrate. The resulting heterostructures exhibit a moiré pattern due to the 3.8% lattice mismatch and angular alignment between the layers. The electronic structure of the heterostructures was analyzed using X-ray photoelectron spectroscopy (XPS), revealing a shift in the binding energy of W 4f and Mo 3d core levels, indicating a negative net charge on the WSe₂ layer and a positive net charge on the MoS₂ layer. This charge transfer results in a built-in potential of up to 400 mV, forming a two-dimensional dipole or atomically thin parallel plate capacitor. The optoelectronic properties of the heterostructures were further investigated using photoluminescence (PL) and absorption spectroscopy. The PL spectra showed a peak at 1.55 eV for the WSe₂/MoS₂ hetero-bilayer, lower than the peaks of the individual single layers, indicating a type II band alignment. The large Stokes-like shift is consistent with spatially indirect transitions in a staggered gap heterostructure. The study also demonstrates that the interlayer coupling can be tuned by inserting hexagonal boron nitride (h-BN) layers into the vdW gap, which significantly reduces the interlayer interaction. The research highlights the potential of vdW heterostructures for next-generation optoelectronic devices, with tunable optoelectronic properties and customizable composite layers. The findings suggest that these heterostructures can be used to create new families of semiconductor heterostructures with enhanced performance and functionality. The study also emphasizes the importance of interlayer coupling in determining the electronic and optoelectronic properties of these materials, offering a new degree of freedom in band engineering. The results provide a foundation for further research into the bottom-up creation of new heterostructures with tailored properties.