Conceptual Comparison between Standard Si Solar Cells and back Contacted Cells

It is often stated that one of the main advantages of back-contacted (BC) Si solar cells over standard cells is that shading due to the front-finger metallization is avoided – while it is also often stated that BC cells are prone to “electronic shadowing”, which means that the carrier collection efficiency in front of the back-surface-field (BSF) may be reduced. We compare these two cell concepts in two ways: by means of an extensive collection of measured IV data from literature, and by interpreting as well as quantifying the differences with the aid of numerical device simulation. Both literature data and simulations indicate that BC cells have a Jsc-advantage of maximally about 1 mA/cm2, but in Voc and FF there is no clear advantage or disadvantage over standard cells. With a parameter study, we reveal the main design advantages and weaknesses in each cell type. Our numerical device modeling indicates that one of the most crucial design advantages of BC over standard cells is that the collection of minority carriers in the emitter is rather unimportant, which leaves greater flexibility in emitter design than in standard cells.