Suguru Yachi

p-BaSi2/n-Si heterojunction solar cells with conversion efficiency reaching 9.0%

p-BaSi2/n-Si heterojunction solar cells consisting of a 20 nm thick B-doped p-BaSi2 epitaxial layer (p = 2.2 × 1018 cm−3) on n-Si(111) (ρ = 1–4 Ω 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 η 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/cm2, and a fill factor of 0.60 were obtained. These results demonstrate the high potential of BaSi2 for solar cell applications.

Effect of amorphous Si capping layer on the hole transport properties of BaSi2 and improved conversion efficiency approaching 10% in p-BaSi2/n-Si solar cells

We investigated the effect of a 3-nm-thick amorphous Si (a-Si) capping layer on the hole transport properties of BaSi2 films. The contact resistance decreased with decreasing resistivity of p-BaSi2 and reached a minimum of 0.35 Ω·cm2. The effect of the a-Si layer was confirmed by higher photoresponsivities for n-BaSi2 films capped with the a-Si layer than for those without the a-Si layer, showing that the minority carriers (holes) were extracted efficiently across the a-Si/n-BaSi2 interface. Under AM1.5 illumination, the conversion efficiency reached 9.9% in a-Si(3 nm)/p-BaSi2(20 nm)/n-Si solar cells, the highest value ever reported for semiconducting silicides.

Influence of air exposure duration and a-Si capping layer thickness on the performance of p-BaSi2/n-Si heterojunction solar cells

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 dem...

Effect of p-BaSi2 layer thickness on the solar cell performance of p-BaSi2/n-Si heterojunction solar cells

B-doped p-BaSi2 epitaxial layers with a hole concentration of 2 × 1018 cm−3 were grown on n-Si substrates (resistivity ρ = 1–4 Ω cm) by molecular beam epitaxy to form p-BaSi2/n-Si heterojunction solar cells. We changed the p-BaSi2 layer thickness () from 10 to 50 nm and investigated its effect on solar cell performance. The open-circuit voltage almost saturated to be approximately 0.47 V at nm or higher. The short-circuit current density decreased when exceeded 20 nm. The fill factor reached a maximum of 0.60 at nm. The conversion efficiency η increased as increased, and reached a maximum of 9.9% at nm, and then decreased. On the basis of these results, the optimum was determined to be 20 nm in the present structure. The η value of 9.9% is the highest ever reported for semiconducting silicides.

Minority-carrier lifetime and photoresponse properties of B-doped p-BaSi2, a potential light absorber for solar cells

600-nm-thick B-doped p-BaSi2 layers were grown on (111)-oriented n-Si substrates by molecular beam epitaxy, and the dependences of the minority carrier lifetime τ and photoresponsivity on the hole concentration p were investigated. p was varied from 1.4 × 1016 to 3.9 × 1018 cm−3. The highest τ of 2 µs was obtained for the sample with the lowest p of 1.4 × 1016 cm−3, reaching two orders of magnitude higher than that of the sample with the highest p of 3.9 × 1018 cm−3. The low-concentration-doped sample also exhibited an excellent external quantum efficiency (EQE) as large as 80% at a wavelength of approximately 800 nm at a reverse bias voltage of 0.2 V. This value is higher than any other EQEs we have ever achieved for BaSi2, showing the great potential of p-BaSi2 as a light absorber in solar cells.

p-BaSi 2 /n-Si heterojunction solar cells with 9.0% efficiency

Summary form only given. We fabricated p-BaSi₂/n-Si solar cells by forming a 20-nm-thick B-doped p-BaSi₂ epitaxial layer (p = 2.2 × 10¹⁸ cm^-3) on an n-Si(111) substrate (ρ = 1-4 Ω·cm) by molecular beam epitaxy (MBE). 3-nm-thick amorphous-Si was deposited on the p-BaSi₂ surface to prevent the surface oxidation. According to the band alignment of p-BaSi₂/n-Si heterojunction, the separation of photogenerated minority carriers is promoted at the heterointerface. We recorded conversion efficiency of 9.0 % under AM1.5 illumination at room temperature. Short-circuit current density of 31.9 mA/cm², open-circuit voltage of 0.46 V, and fill factor of 0.60 were obtained. These results suggest the potential of BaSi₂ for solar cell application.