Integrated Experimental and Density Functional Theory Study of SnS/SnSe Heterojunction Nanostructures: Synthesis, Band Alignment, and Electronic Structure Insights

Semiconductor heterojunction band alignment critically determines the optoelectronic device efficiency. SnS/SnSe nanostructures are considered promising candidates for sustainable energy conversion and production applications. However, their practical deployment is limited by issues such as impurity, charge carrier separation, recombination, and structural defects. Understanding their band alignment is essential to addressing these issues. This paper reports the successful synthesis of binary SnS/SnSe heterojunction nanostructures via a facile solution-based route. The study integrates experimental cyclic voltammetry (CV) and density functional theory (DFT) calculations to elucidate the electronic band structure, alignment, and offsets of binary SnS/SnSe heterojunction nanostructures. Cyclic voltammetry reveals a type-II band alignment with minimal offsets (0.07 eV CBO, 0.05 eV VBO) at the SnS/SnSe interfaces. The DFT calculations confirm these findings and elucidate the charge separation mechanism. Crucially, these small offsets enable a rapid carrier transfer. Our analysis establishes CV as a cost-effective alternative to Ultraviolet Photoelectron Spectroscopy or Scanning Tunneling Microscopy for band mapping. The SnS/SnSe interface design principles demonstrated here advance high-efficiency optoelectronics, particularly multijunction solar cells and photodetectors.