Determination of Bulk Minority-Carrier Lifetime in BaSi₂Earth-Abundant Absorber Films by Utilizing a Drastic Enhancement of Carrier Lifetime by Post-Growth Annealing

Abstract

We have successfully determined the bulk minority-carrier lifetime in BaSi2 epitaxial films by utilizing a drastic enhancement of lifetime by post-growth annealing at 800 °C, which is attributed to strain relaxation. From the film-thickness dependence of lifetime, we reveal that the bulk lifetime is 14 µs, which is long enough for thin-film solar cell applications. In addition, the sum of surface and interface recombination velocities is found to be as low as 8.3 cm/s presumably due to the ionic nature of BaSi2. This confirms that BaSi2 is promising as an absorption-layer material for earth-abundant thin-film solar cells.

Formation of BaSi2 heterojunction solar cells using transparent MoOx hole transport layers

“…10 lm) 17 and long minority-carrier lifetime (ca. 10 ls), 18,19 even in multidomain a-axis-oriented BaSi 2 epitaxial layers, have confirmed that BaSi 2 could be a candidate for thin-film solar cells. The six-fold symmetry of Si(111) means that a-axis-oriented BaSi 2 can be grown epitaxially on Si(111) with its three epitaxial variants rotating around the surface normal at 120 with respect to each other.…”

Improving the photoresponse spectra of BaSi2 layers by capping with hydrogenated amorphous Si layers prepared by radio-frequency hydrogen plasma

“…Semiconducting barium disilicide (BaSi 2 ), 1,2 composed of earth-abundant elements, has all these properties such as a band gap of 1.3 eV, 3 a large α of 3 × 10 4 cm -1 at 1.5 eV, [3][4][5][6] inactive grain boundaries, 7 and a large minority-carrier lifetime (τ ∼ 10 µs). 8,9 Since BaSi 2 can be grown epitaxially on a Si substrate 10 and its band gap can be increased by adding other elements such as Sr and C, 11,12 BaSi 2 is a material of choice for targeting η > 30% in Si-based tandem structure solar cells. We have achieved η approaching 10% in a p-BaSi 2 /n-Si heterojunction solar cell capped with a pure amorphous Si (a-Si) layer by an electron-beam (EB) evaporation.…”

Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

“…[1][2][3][4] Large absorption coefficients come from the band structure of BaSi 2 , where the localized Ba d-like states form flat energy bands in the conduction band. [5][6][7] Minority-carrier properties, such as a long minority-carrier diffusion length (ca.10 lm) 8,9 and a long minority-carrier lifetime (ca.10 ls), [10][11][12] in a-axis-oriented undoped n-type BaSi 2 epitaxial films spurred interest in this material. One of the striking features of this material is the fact that both large minority-carrier diffusion length and large absorption coefficient are available.…”