Comparison of Band Alignments at Various CdS/Cu(In,Ga)(S,Se)2 Inter-Faces in Thin Film Solar Cells

Electronic structure of the Zn(O,S)/Cu(In,Ga)Se2thin-film solar cell interface

“…As mentioned in the introduction, we have consistently found flat conduction alignments in optimized CIG(S)Sebased devices [12][13][14], with the exception of CdS/Cu(In, Ga)S 2 , for which a cliff was found [15]. Given the fact that the O/S ratio of the Zn(O,S) layer gives an additional optimization parameter for this alternative buffer layer, it is not necessarily to be expected that a flat conduction band alignment is found.…”

“…In other words: the (expected) downward band bending at the absorber surface is slightly reduced by the interface formation. This needs to be compared with the CdS/CIG(S)Se system, where we either find a negligible impact on the band edge positions or a small additional downward shift (unpublished). The here‐observed (small) upward shift could have several origins, including a small change in the CIGSe surface dipole upon becoming an interface dipole to the Zn(O,S) layer, and a possible charge transfer across the interface to influence the space‐charge region.…”

“…In other words: the (expected) downward band bending at the absorber surface is slightly reduced by the interface formation. This needs to be compared with the CdS/CIG(S)Se system, where we either find a negligible impact on the band edge positions [12][13][14] or a Table I (bottom). As the buffer layer thickness increases, the Zn, O, and S core-level peaks from the thin Zn(O,S)/CIGSe sample also shift toward lower BE.…”

“…Note that the S and O core levels all shift in unison, suggesting that these shifts are because of band bending in the buffer layer, rather than to chemical shifts because of an altered S/(S The full band alignment of the Zn(O,S)/CIGSe interface, including the band bending correction, is depicted in Figure 3. A small conduction band offset (CBO = 0.09 ± 0.20 eV) is found, indicating that the conduction band alignment at the Zn(O,S)/CIGSe interface is essentially flat (small spike), as in [12][13][14]27]. Likewise, a considerable valence band offset (VBO = 1.15 ± 0.15 eV) is formed, creating a hole barrier and decreasing interfacial recombination.…”

From 20.9 to 22.3% Cu(In,Ga)(S,Se)2solar cell: Reduced recombination rate at the heterojunction and the depletion region due to K-treatment

“…3(b). For the buffer layers, we assume there is no defects with the following material properties for CdS (ZnO): [28][29][30] E g of 2.42 eV (3.37 eV), dielectric constant of 10 (8.5), electron affinity of 4.2 eV (4.5 eV) and a donor concentration at the order of 10 18 cm −3 .…”