We simulated the optical absorptance of BaSi₂-based heterojunction solar cells with transition metal oxides as hole transport layer (HTL) using GenPro4 software and optimized the device structures. The complex refractive index of each layer was used as an input in the optical simulations. We adopted ITO (80 nm) / HTL / a-Si (3 nm) / n-BaSi₂(500 nm) / TiN (250 nm) / glass substrates (200µm) structures. First, the implied photocurrent density (Jph) loss caused by parasitic absorption in 20-nm-thick p⁺-BaSi₂ layer was calculated to be 7.9 mA cm^-2, The Jph increased to 29.1 mA cm^-2 by substituting p⁺-BaSi₂ with 2-nm-thick MoO₃. To figure out the optimal HTL materials and the structures for BaSi₂ solar cells, we simulated the absorption spectra as function of materials such as NiO, Cu₂O, MoO₃, V₂O₅, and WO₃, which have already demonstrated the HTL functionality, and their thicknesses. The highest Jph was obtained with MoO₃, V₂O₅, or WO₃, meaning that these oxides are optically suitable HTL materials. By increasing the n-BaSi₂ absorber layer thickness to 2 µm and importing 3D random pyramidal texture structure with the height of 4 µm, the Jph reached a maximum of 33.1mA cm^-2, This is the largest value of all BaS_i2 solar cells ever reported.

We formed phosphorous(P)-ion-implanted n-BaSi₂ films on p-Si(111) substrates and demonstrated solar-cell functionality of the n-BaSi₂/p-Si heterojunction under AM1.5 illumination. The BaSi₂ films were grown by molecular beam epitaxy, followed by implantation of P ions to the BaSi₂ films using PF₃ gas at an energy of 10 keV and a dose of 1 × 10¹⁴ cm⁻². Subsequent postannealing was conducted at 500°C in Ar for different durations (t = 30–480 s) to activate the P atoms. The diffusion coefficient for P atoms in BaSi₂ was evaluated from the depth profiles of P atoms by secondary-ion mass spectrometry. The activation energies of lattice and grain boundary diffusion were found to be 1.1 ± 0.6 and 2.5 ± 0.6 eV, respectively. From the analysis of Raman and photoluminescence spectra, the ion implantation damage was recovered by the postannealing. For one treated sample with t = 120 s, the internal quantum efficiency reached 67% at a wavelength of 870 nm. This is the highest ever achieved for n-BaSi₂/p-Si heterojunction solar cells. Ion implantation is thus applicable to BaSi₂ films grown by any other method. This achievement thereby opens a new route for the formation of BaSi₂ solar cells.