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Efforts to reduce the cost of Si-based solar cells

| By Chemical Engineering

Most of today’s solar cells are made from silicon wafers cut from blocks of crystals. The wafers are typically 0.2-0.25-mm thick, yet most of the photon-to-electricity conversion takes place in the outermost 0.02 mm of the wafer. In an effort to reduce the amount of Si required (and thus the cost) for solar cells, BP Solar (Frederick, Md; is supporting a three-year research project with the Institute for Crystal Growth (IKZ; Berlin, Germany; to develop a process to deposit Si onto low-cost supports, such as glass.

Up to now, thin deposits of Si on glass have exhibited poor conversion efficiencies because of a high density of grain boundaries. IKZ hopes to overcome this problem by a two-step process. First the glass surface will be nucleated at regularly-distributed sites with Si crystallites. The seeds will then be enlarged by crystallization from a metallic solution. The goal is to form a continuous multicrystalline layer with a thickness less than 0.05 mm, says IKZ.

Meanwhile, Ferro Electronic Material Systems (Vista, Calif.; launched (last month) a new material that will enable solar-cell manufacturers to "significantly" reduce silicon usage, says the firm. The cadmium- and lead-free system of aluminum and rear- and front-silver metallizations are said to improve the electrical performance of Si wafers that are less than 180 µm thick; the current generation of "thin" wafers are 240 µm thick, says Ferro.