Size-tunable band alignment and optoelectronic properties of transition metal dichalcogenide van der Waals heterostructures

2D transition metal dichalcogenide (TMDC)-based heterostructures exhibit several fascinating properties that can address the emerging market of energy conversion and storage devices. Current achievements show that the vertical stacked TMDC heterostructures can form type II band alignment and possess significant optoelectronic properties. However, a detailed analytical understanding of how to quantify the band alignment and band offset as well as the optimized power conversion efficiency (PCE) is still lacking. Herein, we propose an analytical model to exhibit the PCEs of TMDC van der Waals (vdW) heterostructures and explore the intrinsic mechanism of photovoltaic conversion based on the detailed balance principle and atomic-bond-relaxation correlation mechanism. We find that the PCE of monolayer MoS2/WSe2 can be up to 1.70%, and that of the MoS2/WSe2 vdW heterostructures increases with thickness, owing to increasing optical absorption. Moreover, the results are validated by comparing them with the available evidence, providing realistic efficiency targets and design principles. Highlights Both electronic and optoelectronic models are developed for vertical stacked MoS2/WSe2 heterostructures. The underlying mechanism on size effect of electronic and optoelectronic properties for vertical stacked MoS2/WSe2 heterostructures is clarified. The macroscopically measurable quantities and the microscopical bond identities are connected.