Contact Selectivity and Efficiency in Crystalline Silicon Photovoltaics

Highly doped junctions of a Si solar cell function as membranes that block minority carriers and, at the same time, provide a high conductivity for transporting majority carriers to the contacts. They are thus said to be selective contacts. We propose a quantitative definition for the selectivity of contacts. The selectivity provides a figure of merit for electron and hole contacts that is helpful in designing solar cells and in identifying the efficiency limiting components. Applying the definition of selectivity to poly-Si junctions reveals that the root cause of their high selectivity is the highly asymmetric carrier concentration rather than a specific contact geometry.