636 mV open circuit voltage multicrystalline silicon solar cells on Polix material: trade-off between short circuit current and open circuit voltage

The trade-off between the open circuit voltage and the short circuit current i.f.o. the base resistivity of multicrystalline silicon (Polix) solar cells (4 cm²) is investigated. Very thin substrates (180 μm) with base resistivities between 0.2 Ω.cm and 2.5 Ω.cm are used in a laboratory high efficiency process (including back surface field, hydrogen and oxide passivation, selective and homogeneous emitters) to test the limits, in terms of open circuit voltage and short circuit current, that can be reached on this material. The variation of V_OC and J_SC with base doping is established for Polix multicrystalline silicon. On low resistivity substrates (0.2 Ω.cm) a record value of 636 mV is achieved for the open circuit voltage which largely compensates for the relatively small deficit in J_SC. The efficiencies of solar cells fabricated on the lower resistivity substrates tend to be greater than those achieved on the higher resistivity material