Exploring the potential of semiconducting BaSi₂for thin-film solar cell applications

Abstract

Semiconducting barium disilicide (BaSi2), which is composed of earth-abundant elements, has attractive features for thin-film solar cell applications; both a large absorption coefficient comparable to copper indium gallium diselenide and a minority-carrier diffusion length much larger than the grain size of BaSi2 can be used to improve solar cells properties. In this review article, we explore the potential of semiconducting BaSi2 films for thin-film solar cell applications. We start by describing its crystal and energy band structure, followed by discussing thin-film growth techniques and the optical and electrical properties of BaSi2 films. We used a first-principle calculation based on density-functional theory to calculate the position of the Fermi level to predict the carrier type of impurity-doped BaSi2 films using either a Group 13 or 15 element, and compare the calculated results with the experimental ones. Special attention was paid to the minority-carrier properties, such as minority-carrier lifetime, minority-carrier diffusion length, and surface passivation. The potential variations across the grain boundaries measured by Kelvin-probe force microscopy allowed us to detect a larger minority-carrier diffusion length in BaSi2 on Si(111) compared with in BaSi2 on Si(001). Finally, we demonstrate the operation of p-BaSi2/n-Si heterojunction solar cells and discuss prospects for future development.

Design and Simulation of FeSi2‐Based Novel Heterojunction Solar Cells for Harnessing Visible and Near‐Infrared Light

“…With significant reduction in parasitic absorptions by CdS, i.e., assisting in more photon absorption by the absorber in cell 5, CdS contributes to enhancing V OC more with respect to Si in cell 4. The dark saturation current density ( J 0 ) and the light‐induced current density ( J SC ) are mathematically related to V OC by Equation where K B is Boltzmann's constant (1.3807 × 10 −23 J K −1 ), q is the elemental charge of an electron (1.602 × 10 −19 C), and T is the absolute temperature (300 K). Thus, V OC has a direct dependence on the ratio of J SC to J 0 .…”

“…[34] With significant reduction in parasitic absorptions by CdS, i.e., assisting in more photon absorption by the absorber in cell 5, CdS contributes to enhancing V OC more with respect to Si in cell 4. The dark saturation current density ( J 0 ) and the light-induced current density ( J SC ) are mathematically related to V OC by Equation (1) [29]…”

“…[23] The potential of BaSi 2 for solar cell applications has also been reported by many groups. [23][24][25][26][27][28][29] In this work, we introduce and numerically assess three novel npp þ heterojunction solar cells based on an FeSi 2 absorber that incorporate heavily doped c-Si, or BaSi 2 , as the BSF layer. We also use cadmium sulphide (CdS) instead of Si as a window material for the first time in this type of solar cells.…”

Investigation of defect levels in BaSi2 epitaxial films by photoluminescence and the effect of atomic hydrogen passivation

“…Thus, exploring alternative materials for thin film solar cells is very important. We have paid considerable attention to barium disilicide (BaSi 2 ), which is a new alternative for next generation solar cell applications [12]. The unit cell of BaSi 2 , shown in figure 1, contains eight barium atoms (Ba) and 16 silicon atoms (Si).…”

Reduction in interface defect density in p-BaSi2/n-Si heterojunction solar cells by a modified pretreatment of the Si substrate

“…However, these solar cells are based on expensive materials and so there has been renewed interest in high-efficiency solar cells using inexpensive Si substrates. BaSi2 is a semiconductor material that shows great promise for use in solar cells [9] as it has a suitable band gap (Eg = 1.3 eV), large optical absorption coefficients that exceed those of chalcopyrites [10][11][12][13], and a large minority carrier lifetime (~10 μs) [14][15][16], which leads to a minority carrier diffusion length (L =10 µm) that is larger than the grain size of BaSi2 [17]. A η beyond 25% is expected for a 2-μm-thick BaSi2 homojunction solar cell [18].…”