p-BaSi 2 /n-Si heterojunction solar cells consisting of a 20 nm thick B-doped p-BaSi 2 epitaxial layer (p ¼ 2.2 Â 10 18 cm À3) on n-Si(111) (q ¼ 1-4 X cm) were formed by molecular beam epitaxy. The separation of photogenerated minority carriers is promoted at the heterointerface in this structure. Under AM1.5 illumination, the conversion efficiency g reached 9.0%, which is the highest ever reported for solar cells with semiconducting silicides. An open-circuit voltage of 0.46 V, a short-circuit current density of 31.9 mA/cm 2 , and a fill factor of 0.60 were obtained. These results demonstrate the high potential of BaSi 2 for solar cell applications. V

Fabrication of p-BaSi2(20nm)/n-Si heterojunction solar cells was performed with different a-Si capping layer thicknesses (da-Si) and varying air exposure durations (tair) prior to the formation of a 70-nm-thick indium-tin-oxide electrode. The conversion efficiencies (η) reached approximately 4.7% regardless of tair (varying from 12–150 h) for solar cells with da-Si = 5 nm. In contrast, η increased from 5.3 to 6.6% with increasing tair for those with da-Si = 2 nm, in contrast to our prediction. For this sample, the reverse saturation current density (J0) and diode ideality factor decreased with tair, resulting in the enhancement of η. The effects of the variation of da-Si (0.7, 2, 3, and 5 nm) upon the solar cell performance were examined while keeping tair = 150 h. The η reached a maximum of 9.0% when da-Si was 3 nm, wherein the open-circuit voltage and fill factor also reached a maximum. The series resistance, shunt resistance, and J0 exhibited a tendency to decrease as da-Si increased. These results demonstrate that a moderate oxidation of BaSi2 is a very effective means to enhance the η of BaSi2 solar cells.

Hard x-ray photoelectron spectroscopy study on valence band structure of semiconducting BaSi2

Investigations on residual strains and the cathodoluminescence and electron beam induced current signal of grain boundaries in silicon J. Appl. Phys. 115, 163511 (2014) Potential variations across the grain boundaries (GBs) in a 100 nm thick undoped n-BaSi 2 film on a cast-grown multicrystalline Si (mc-Si) substrate are evaluated using Kelvin probe force microscopy (KFM). The h-2h X-ray diffraction pattern reveals diffraction peaks, such as (201), (301), (410), and (411) of BaSi 2 . Local-area electron backscatter diffraction reveals that the a-axis of BaSi 2 is tilted slightly from the surface normal, depending on the local crystal plane of the mc-Si. KFM measurements show that the potentials are not significantly disordered in the grown BaSi 2 , even around the GBs of mc-Si. The potentials are higher at GBs of BaSi 2 around Si GBs that are formed by grains with a Si(111) face and those with faces that deviate slightly from Si(111). Thus, downward band bending occurs at these BaSi 2 GBs. Minority carriers (holes) undergo a repelling force near the GBs, which may suppress recombination as in the case of undoped n-BaSi 2 epitaxial films on a single crystal Si (111)

We grow a boron (B)-doped BaSi2 (0.7 µm)/undoped n-BaSi2 (1.7 µm) layered structure on a p-Si(111) substrate by molecular beam epitaxy, and observe the cross-sectional potential profile across the junction by Kelvin probe force microscopy (KFM). The potential increases when the KFM tip is moved from the B-doped BaSi2 to the n-BaSi2, and decreases in the p-Si. Inflection points are clearly observed in the potential profile at the B-doped BaSi2/n-BaSi2 and n-BaSi2/p-Si interfaces. Secondary ion mass spectrometry reveals that B atoms scarcely diffuse to the n-BaSi2 layer. These results show the formation of a pn junction at the B-doped BaSi2/n-BaSi2.