Thin-film solar cells, manufacturing

Figure 1.1 illustrates the nature of the problem by summarizing the natural abundance and raw elemental costs for materials that are used in thin-film solar cells. It is important to note that a logarithmic scale has been used for both the abundance and the raw materials cost. The most expensive material by far is indium, and the availability and cost of indium have become geopolitical issues in recent months since it is used in the manufacture of liquid crystal displays and touch screens. 

Crystalline solar cells are heavy and expensive to manufacture. However, their efficiency in converting sunlight has historically been superior to thin-film. Crystalline cells are constructed with silicon semiconducting materials. 

Another area of development is in lower-cost thin- and ultrathin-film designs. One such product is made by Nanosolar of copper indium gallium selenide (CIGS), which is claimed to achieve up to 19.5% efficiency and is as thin as a newspaper. This claim is yet to be proved. The collector cost is also reduced, because the substrate material on which the ink is printed is much less expensive than the stainless steel substrates that are often used in thin-film solar panels. The manufacturer claims a five- to tenfold reduction in the collector cost (about 1/W) compared to conventional PV cells. 

Small-area thin-film CdTe solar cells have been fabricated with sunlight-to-electricity conversion efficiencies near 16%, comparable to crystalline siUcon solar cells in large-scale manufacturing. Large-area monolithic integrated CdTe modules have been fabricated with efficiencies of ca 10%, comparable to crystalline siUcon modules commercially available. 

We have already mentioned amorphous silicon solar cells. New processes have been developed to manufacture solar cells based upon deposition of very thin films of photosensitive materials. Such processes have a distinct cost advantage since once the films are deposited, little further processing is needed to form the final solar cell module. 

The chemical vapor deposition (CVD) of CdTe thin films is used in the manufacture of highly efficient solar cells. To model this deposition process, a surface reaction mechanism is needed. 

---