Novel buried contact technology for advanced silicon solar cells

Increased efficiency of silicon solar cells has resulted in the increased complexity and cost of manufacture. Optical properties can be enhanced by increasing the optical path length, while minimising both bulk and surface recombination. Conventional silicon based solar cells are fabricated by a series of physical or chemical vapour deposition processes followed by photolithography and etching processes for each layer. These repeated deposition and etching cycles are not only difficult to perform but they also generate severe surface topography. This topography is a major cause of yield loss and reliability problems for advanced solar cells. These problems are especially severe for high aspect ratio contact holes. An alternative method of performing this metallisation inexpensively and reliably is by the use of electroless plating. As the plating process occurs selectively on Si and not on the surface passivation layer, thick metal films (Ni and Cu) can be deposited which depend entirely upon the depth of the trench used. The advantages of electroless plating as an alternative to standard metallisation are presented.