The single layers and layer systems deposited using the PVD or CVD method have a thickness in the range of µm or less. These layers have various chemical and physical functional features, such as conductivity, transparency, semiconductor properties, diffusion velocity, wear-resistance, resistance against chemicals, etc.
Silicon thin-film solar cells are based on amorphous (a-Si) or microcrystalline silicon (μc-Si). These solar cells require semiconductor layers (absorbers) of a thickness up to 2 μm. The semiconductor layers are deposited at low process temperatures on large-area, low-cost materials, primarily glass, but also on metal strip or polymer films. Sufficient absorption requires layer thicknesses of up to 2 µm. Transparent conductive layers TCO (e. g. SnO2:F, ZnO:Al) serve as front contact and for the back contact layer systems combining TCO and a metal layer take hold to an increasing extent (e. g. ZnO:Al/Al/NiV).
Micromorph thin-film solar cells combine both amorphous and microcrystalline silicon in one cell and belong to the group of the so-called multi-junction cells for which two (tandem cell) or more semiconductor layers are deposited alternately one above the other. As for micromorph silicon tandem cells, the absorption spectra of amorphous and microcrystalline silicon complement each other in such a way that a broad spectrum of sun radiation is utilized for energy production, thus reaching higher energetic efficiency.
The basis of a CIS thin-film solar cell is a compound semiconductor based on copper, indium, selenium and/or sulfur – CuIn(Ga)(Se, S)2. The p‑conducting CIS layer of up to 3 μm thickness is combined with an n‑conducting CdS‑buffer layer (up to 50 nm). Adding gallium to the semiconductor increases the energetic efficiency of the CIS-cell considerably (CIGS-cell). The absorber layer may be generated either by evaporation or sputtering and final silenization. A layer from i- ZnO/ZnO:Al serves as transparent front contact, a molybdenum layer normally as back contact. Glass is usually used as the basic substrate, but metal strip and polymer films (PI) are also applied.
