Boosted solar light absorbance in PdS2/PtS2 vertical heterostructures for ultrathin photovoltaic devices

Transition-metal dichalcogenides (TMDs) represent a class of materials whose archetypes, such as MoS2 and WS2, possess exceptional electronic and optical properties and have been massively exploited in optoelectronic applications. The layered structure allows for their exfoliation to two-dimensional samples with atomic thickness (≲ 1 nm), promising for ultrathin, ultralight devices. In this work, by means of state-of-the-art ab initio many-body perturbation theory techniques, we focus on single-layer PdS2 and PtS2 and propose a novel van der Waals heterostructure with outstanding light absorbance, reaching up to 50% in the visible spectrum and yielding a maximum short-circuit current of 7.2 mA/cm2 under solar irradiation. The computed excitonic landscape predicts a partial charge separation between the two layers and the momentum-forbidden lowest-energy state increases the carrier diffusion length. Our results show that the employment of vertical heterostructures with less conventional TMDs, such as PdS2/PtS2, can greatly boost light absorbance and favor the development of more efficient, atomic-thin photovoltaic devices.