**4.1. High efficiency potential with n-type substrates**

In recent years, the growth and increase in efficiency of silicon solar cells have been observed. N-type silicon substrates have emerged as a potential material offering considerable advan‐ tages for high efficiency photovoltaic module production on the industrial scale [72]. Based upon n-type silicon substrates, SunPower and Panasonic have already presented 24.4% IBC [73] and 24.7% HIT [74] solar cells, respectively.

Ni is known to form ohmic contacts to both p-and n-type silicon surfaces [75]. However, Ni/Cu metallization schemes for n-type substrates can play an important role in cost reduction and the improvement in the efficiency of cells (improved FF, less shadowing). It has been observed that a base material of n-type against p-type silicon has improved stability in relation to thermal Ni contact formation [76]. For a boron-doped p+ emitter on n-type silicon substrates, contact resistivity of up to 0.6 mΩcm<sup>2</sup> has been achieved [77]. An efficiency of 20.5% with a FF of 79.2% has already been achieved for a n-type rear-junction cell composed of Ni/Cu/Ag metal contacts [78].
