Designing a strain-tunable hydrogenated GeCH/Janus HfSO van der Waals heterostructure for solar-energy conversion

The rational integration of complementary two-dimensional (2D) semiconductors into van der Waals (vdW) heterostructures provides an effective route for engineering interfacial electronic and optoelectronic properties. Herein, we systematically investigate the GeCH/HfSO vdW heterostructure by first-principles calculations, with particular emphasis on the roles of interfacial stacking, Janus polarization, and biaxial strain. The optimized heterostructure exhibits weak vdW interlayer coupling, together with dynamical and thermal stability. The electronic structure reveals a type-II band alignment, with the valence-band maximum predominantly localized on GeCH and the conduction-band minimum on HfSO. The heterostructure also exhibits enhanced broadband optical absorption with coefficients on the order of 10⁵ cm^-1. More importantly, biaxial strain enables effective control of the band alignment, inducing a transition from type-I to type-II, while tensile strain continuously enhances the theoretical estimated photovoltaic conversion efficiency from 2.23% at zero strain to 28.60% at ε = +10%. These results establish GeCH/HfSO as a mechanically tunable vdW heterostructure with strong interfacial charge-separation capability and promising potential for next-generation optoelectronic and solar-energy conversion applications.