SP3 Thin-film wafer equivalents

An important approach in CRYSTALCLEAR towards cost reduction (as well as efficiency improvement) is the use of thin silicon wafers made by sawing or ribbon growth, see SP2. The basis for cost reduction here is the smaller consumption of silicon per unit of module power.

Another research line pursued in the project is that of the use of so-called thin-film "wafer equivalents". In this case a thin (typically 10-20 µm), high-quality silicon layer is deposited onto a cheap substrate such as low grade silicon or ceramic material. Depending on the method used, the silicon layer needs to be recrystallized after deposition to obtain a sufficiently high crystal quality.

An alternative route is the preparation of thin free-standing films by a "lift-off" method. Here the silicon films are formed on a high-quality silicon substrate, but they are subsequently removed and the substrate may be reused. The lift-off films may be processed and used as such for special applications, but for power modules they are most likely attached to a cheap substrate.

If well designed, the cell properties determined by the thin active layer can be very good, while the costs may be reduced both because of the small amount of high-grade silicon used and because no wire sawing is needed. Obviously, the costs of film deposition or formation should also be low to obtain the desired result.

There are many different concepts for thin-film silicon-based solar cells. The wafer alternatives investigated in CRYSTALCLEAR have an important short and medium term potential since they can be processed in standard crystalline silicon cell fabrication lines, employing basically the same processes as used today. The work in this subproject is aimed at achieving efficiencies comparable to those of solar cells based on cut wafers or ribbons, but at lower manufacturing cost.