Two-dimensional type-II XMoSiP2/BAs (X= S, Se) van der Waals heterostructures for highly efficient excitonic solar cells

Exploiting Janus monolayers in constructing two-dimensional van der Waals (vdW) heterostructures has emerged as an effective strategy for designing highly efficient optoelectronic devices. In this paper, using first-principles calculations, we explore the stability, structural, and electronic properties of Janus XMoSiP2/BAs (X = S, Se) heterostructures in twelve possible stackings. It is shown that all twenty-four studied heterostructures are energetically stable and twenty of them possess type-II band alignment which helps the dissociation of photo-generated carriers in solar cell devices. The electronic bandstructures reveal that some stackings of XMoSiP2/BAs vdW heterostructures own proper bandgaps for maximum solar light absorption. In addition, very high carrier mobilities (up to 83000 cm2 V−1 s−1), as well as strong visible light absorption coefficients (up to 2 × 105 cm−1) are other features that suggest XMoSiP2/BAs heterostructures as promising candidates for photovoltaic applications. It is also found that the -P stackings of XMoSiP2/BAs, the configurations in which the outer P atom of XMoSiP2 faces the BAs monolayer, have high power conversion efficiency (PCE) owing to the minimal conduction band offset between their constituent monolayer. Finally, two stackings of XMoSiP2/BAs heterostructures are predicted to have excellent PCEs beyond 23% which exceeds the PCEs of many other 2D vdW heterostructures studied previously. We believe that our findings can pave the way to accomplish high-efficiency optoelectronic devices based on 2D vdW heterostructures.