Predicted Si 3 AlP, Si 3 GaP, and Si 3 ZnS Phases with Intrinsic Properties Relevant to Si-Based Tandem Photovoltaics

Identifying semiconductors with suitable band gaps, optical properties, and potential compatibility with Si could help address the limitations of perovskites and isovalent III–V alloys as absorbers in Si-based tandem solar cells. Using the crystalstructure prediction code SCCOP, we identified three new dynamically stable phases: Si 3 AlP (P2 1 /m), Si 3 GaP (P2 1 ), and Si 3 ZnS (P2 1 ). AIMD simulations support retention of the ordering and the principal frameworks over 15 ps at 1000 K for Si 3 AlP and Si 3 GaP and at 800 K for Si 3 ZnS. First-principles calculations further indicate the inplane lattice mismatches are below 0.4 % between Si (100) and these new compounds, anisotropic effective masses with relatively light carriers along selected crystallographic directions, and calculated absorption coefficients exceeding 10 5 cm -1 over portions of the visible spectrum. Si 3 ZnS has a direct HSE06 band gap of 1.64 eV and is therefore a candidate for further evaluation as a top-cell absorber in Si-based two-junction tandem architectures. Si 3 AlP and Si 3 GaP have indirect fundamental gaps of 1.35 and 1.33 eV and dipole-allowed transition energies of 1.56 and 1.44 eV at Z, respectively, making them candidates for further evaluation in three-junction architectures.