Electric field and strain tunable optoelectronic properties of X ₂ Te ₃ /WSe ₂ (X = Bi, Sb) vertical heterostructures for high-efficiency photovoltaics

Abstract In recent years, two-dimensional heterojunctions have attracted widespread attention due to their atomic-scale thickness and tunable electronic properties, showing great potential for next-generation optoelectronic devices. Monolayer WSe 2 possesses a direct bandgap and high carrier mobility, while monolayer X 2 Te 3 (X = Bi, Sb) exhibits a moderate bandgap and favorable semiconductor characteristics, rendering both materials ideal building blocks for high-performance heterostructures. Here, we systematically investigate the electronic and optical properties of vertically stacked X 2 Te 3 /WSe 2 van der Waals heterostructures using first-principles calculations, considering applied electric fields (-0.45 to 0.45 V/Å) and biaxial strain (-5% to 5%). Our results demonstrate that biaxial strain enables continuous bandgap tuning across the visible spectrum for both Bi 2 Te 3 /WSe 2 and Sb 2 Te 3 /WSe 2 heterostructures, offering superior tunability compared to electric fields. At the same time, both Bi 2 Te 3 /WSe 2 and Sb 2 Te 3 /WSe 2 heterostructures maintain an indirect bandgap, while exhibiting predicted power conversion efficiencies of nearly 20% for Bi 2 Te 3 /WSe 2 under -3% strain and 16% for Sb 2 Te 3 /WSe 2 under -5% strain. Moreover, both heterostructures exhibit significantly enhanced and precisely tunable optical absorption compared to their constituent monolayers. This work not only reveals the key interfacial electronic coupling mechanisms, but also provides a theoretical foundation for the design of tunable, high-efficiency two-dimensional optoelectronic devices.