New Material for Thin Film Solar Technology

A new advanced material used for thin film solar deposition processes may hold considerable promise for the future of thin-films said the company that developed it.

Hanau, Germany, March 11, 2003[SolarAccess.com] W. C. Heraeus GmbH & Co. KG, a subsidiary of the globally active precious metals and technology group Heraeus Holding GmbH, has developed an innovative coating material for thin film solar cells. Under the product name ZAO – for aluminum-doped zinc oxide – the “Thin Film Materials Division” of W. C. Heraeus has introduced a so-called “sputter target” to the market, a substrate used for coating, which they say effective and cost-efficient at the same time. It has been designed to pave the way for thin film solar cells into the economically attractive mass production, where it is used for the coating of a transparent conductive metal oxide. The new material has already been qualified by important producers of solar cells and modules, said the company. Today, solar modules for photovoltaics are still made by approximately 90 percent of silicon wafers. In this semiconductor material electrical energy is produced by using light. In contrast to this, thin film solar cells consist mostly of silicon-coated glass, sometimes also of other semiconductor materials. In thin film solar cells, the coated semiconductor layer is around 80 times thinner than a wafer made of high-purity silicon. Some argue the thin film solar cell is considered to be the solar cell of the future since it can be produced at a much lower price due to reduced material costs, said the company. In about ten years, it is estimated to make a significant contribution to energy production. Beyond that, thin film solar modules can be used as multi-faceted architectural elements for the design of façades. The new, ZAO sputter target from W. C. Heraeus is used for the creation of the transparent conductive “window layer”, which is positioned between the upper glass substrate and the semiconductor layer. Through this approximately one micrometer thin layer – this equals one thousandth of a millimeter – sunlight gets to the semicon-ductor layer, where an electrical current develops through charge sepa-ration. This current can be used as solar power through a metallic thin film contact at the back of the cell. In a solar module, many individual cells are connected in-line so that their currents accumulate. Since sputtering processes are used for the production of several layers in the thin film solar cell and are generally gaining importance, W. C. Heraeus expects a high future market potential in photovoltaics. “Thin film solar cells made of amorphous silicon have a lower efficiency factor, but in the long run, they are more economical than wafer-based solar cells,” said Martin Weigert, Manager R&D and Technology of the Thin Film Materials Division. “Therefore, high-quality, reliable, and cost-efficient sputter targets play an important role in the future techno-logical development of solar cells, so that solar power can become economically more and more attractive as an environmentally sound alter-native source of energy.” The extremely thin semiconductor layers, the window layer, and, most of all, the conductive contact layer in thin film solar cells are created by sputtering. “Sputtering” stands for the detachment of atoms of a coating material (sputter target) through argon ions, whereby the target material is deposited atom by atom on a substrate as a homogeneous layer.
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