Ultra-high photoelectric conversion efficiency and obvious carrier separation in photovoltaic ZnIn2X4 (X = S, Se, and Te) van der Waals heterostructures

Abstract

The need for low-carbon solar electricity production has become increasingly urgent for energy security and climate change mitigation. However, the bandgap and carrier separation critical requirements of high-efficiency solar cells are difficult to satisfy simultaneously in a single material. In this work, several van der Waals ZnIn₂X₄ (X = S, Se, and Te) heterostructures were designed based on density functional theory. Our results suggest that both ZnIn₂S₄/ZnIn₂Se₄ and ZnIn₂Se₄/ZnIn₂Te₄ heterostructures are direct bandgap semiconductors at the Γ point. Besides, obvious carrier spatial separations were observed in the ZnIn₂S₄/ZnIn₂Se₄ and ZnIn₂Se₄/ZnIn₂Te₄ heterostructures. Interestingly, the ZnIn₂S₄/ZnIn₂Se₄ heterostructure has a suitable bandgap of 1.43 eV with good optical absorption in the visible light range. The calculated maximum theoretical photoelectric conversion efficiency of ZnIn₂S₄/ZnIn₂Se₄ heterostructure was 32.1%, and it can be further enhanced to 32.9% under 2% tensile strain. Compared to single-layer ZnIn₂X₄ materials, the electron effective mass of the ZnIn₂S₄/ZnIn₂Se₄ heterostructure is relatively low, which results in high electron mobility in the heterostructure. The suitable bandgap, obvious carrier separation, high electron mobility, and excellent theoretical photoelectric conversion efficiency of the ZnIn₂S₄/ZnIn₂Se₄ heterostructure make it a promising candidate for novel 2D-based photoelectronic devices and solar cells.