2D layered BP/group-IV monochalcogenide van der Waals heterostructures for photovoltaics: electronic structure, band alignment, and carrier dynamics

van der Waals heterostructures, composed of two-dimensional materials, have emerged as a promising platform for optoelectronic and photovoltaic applications. In this study, we constructed four vdW heterostructures, including BP/GeS, BP/GeSe, BP/SnS, and BP/SnSe, using BP and group-IV monochalcogenides as building blocks and investigated their potential for photovoltaic applications. First-principles calculations reveal that BP forms type II heterostructures with GeSe, SnS, and SnSe, while the BP/GeS system exhibits type I band alignment due to interfacial charge transfer. The structural stability of these heterostructures is confirmed by binding energy calculations, with the experimental synthesis of BP/SnSe providing additional validation. These heterostructures exhibit strong absorption in the infrared and visible regions, with predicted power conversion efficiencies ranging from 9.53% to 11.40%. Time-dependent density functional theory coupled with molecular dynamics simulations demonstrates ultrafast charge transfer in BP/GeSe, with electron transfer times (<i>τ</i> ≈ 147 fs) and hole transfer times (<i>τ</i> ≈ 839 fs), and the slower hole transfer rate is attributed to the limited mixing of higher energy levels and a coherent coupling mechanism. This work advances the fundamental understanding of BP/group-IV monochalcogenide van der Waals heterostructures and provides a robust theoretical foundation for their application in next-generation photovoltaic devices. Future research should focus on experimental validation, strain and stacking effects, and detailed device integration studies to fully harness their potential.