New solar cell production process may improve efficiency and reduce cost

Abstract

Photovoltaics is a renewable energy that can reduce pollution and climate change effects. A serious alternative to fossil energy, the solar industry is showing exponential growth in production. Currently about 90% of fabricated solar modules are made of crystalline silicon. Materials costs represent about 45% of the total module price. One way to make the photovoltaic industry more competitive is to reduce the consumption of silicon and increase the efficiency of solar cells. Approaches to trimming materials costs include replacing crystalline silicon with silicon thin films deposited on cheap substrates at low temperatures. However, the efficiency of solar cells made using this technique is limited by the low quality of the material. Cutting thinner wafers of crystalline silicon from the ingot can also decrease costs, but mechanical problems limit this method. We are developing silicon thin films that are epitaxially grown on a sacrificial layer and transferred to a cheap foreign substrate.1 To maximize the potential of this material, we combine it with rear contact solar cell technology. Figure 1 illustrates the process we use to create these solar cells. First, we create a sacrificial porous silicon layer on top of a monocrystalline silicon substrate. A high-quality single-crystal silicon film is then grown by epitaxy on this surface. The rear contact solar cell is created on this film. All metallic contacts are deposited on the rear side of the cell to avoid shadowing effects and to allow high efficiencies. A low-cost substrate (glass or ceramic) is then stuck on the back side of the cell. Using the sacrificial layer, the cell is separated from the initial wafer, which can be recycled several times.2 Figure 1. Process to create solar cells with lower cost and higher efficiency.