Optimal surface and bulk passivation of high efficiency multicrystalline silicon solar cells

Conventional (CC) and electromagnetically cast (EMC) multicrystalline silicon solar cells are fabricated following different passivation schemes. Thin layers (~100 Å) of thermal dry and PECVD SiO₂ are implemented for providing oxide surface passivation for multicrystalline silicon solar cells. It is found that growing thin layers of thermal dry oxide results in efficient surface passivation. However, for thin PECVD SiO₂ layers it is necessary to perform, post deposition, low temperature (~350°C) forming gas anneal in order to observe the surface passivation effect. In addition, hydrogen plasma passivation has been optimized for achieving very deep penetration of atomic hydrogen in the material (>30 μm) and as a consequence very effective bulk passivation of multicrystalline silicon solar cells. By combining the thermal dry surface oxide passivation with the hydrogen plasma treatment from the front and the back sides, efficiency of 17% on 4 cm² (independently confirmed by NREL as 16.93%) is realized without any Al gettering. On the other hand, the solar cell efficiencies obtained using thin layers of PECVD SiO₂ are found to be very comparable to the efficiency of the cells fabricated with thermal dry SiO₂ layers