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Thin crystalline silicon solar cell with back surface gate electrode

Solar cells made from a thin layer of crystalline silicon have potential to achieve high efficiency and lower costs when compared to conventional thick crystalline silicon solar cells. The high efficiency potential is due to reduction in bulk minority carrier recombination assuming the thickness is less than the minority carrier diffusion length. Before this benefit can be realized however, carrier recombination at surfaces must be suppressed. It is the purpose of this paper to demonstrate how this can be achieved in a way compatible with thin layer silicon growth techniques. One difficulty with the thin layer silicon approach is handling the thickness required. For typical crystalline silicon minority carrier diffusion lengths, a thickness near 50 /spl mu/m is considered optimal. At this thickness, silicon needs mechanical support. This leads to the concept of growing the silicon to the desired thickness on a foreign substrate. This substrate would need to possess several different attributes. One of the most important is that it be compatible with passivation of the silicon back surface. Although all surfaces of the solar cell need to be passivated, the back surface is the most critical since the exposed surfaces could possibly be passivated with the growth of a thermal oxide layer after growth. The back surface, however, can not be manipulated after growth. This makes the prospect of a passivation layer built into the substrate appealing.