Multicrystalline silicon solar cells with low rear surface recombination

Improvements in the manufacture of multicrystalline silicon (mc-Si) and processing induced impurity gettering have enabled the demonstration of diffusion lengths in mc-Si much greater than the substrate thickness. High recombination velocities at the rear surface, rather than bulk recombination, can then limit cell efficiency. The traditional n⁺/p/p⁺ cell structure (produced with aluminum alloying) is therefore less suitable for high lifetime material due to high effective rear surface recombination velocities. Rear surface recombination can be reduced by reducing the rear metal contact area and passivating most of the rear with thermal oxides. Record open circuit voltages (654 mV) and high efficiencies (18.2%) are demonstrated with 4 cm² cells on 0.5 Ωcm Eurosil substrates. Cells with local boron diffusions under the rear contacts also demonstrate high efficiencies.