EFFICIENT COMBINATION OF SURFACE AND BULK PASSIVATION SCHEMES OF HIGH-EFFICIENCY MULTICRYSTALLINE SILICON SOLAR-CELLS

Conventional and electromagnetically casted multicrystalline silicon solar cells are fabricated following different passivation schemes. Thin layers (similar to 100 Angstrom) of thermal dry and plasma-enhanced chemical-vapor-deposition (PECVD) SiO2 are implemented for surface oxide passivation of multicrystalline silicon solar cells and compared. ft 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 low-temperature forming gas anneal, postdeposition, in order to observe the surface passivation effect. In addition, hydrogen plasma passivation has been optimized for achieving deep penetration of atomic hydrogen in the material (>30 mu m) and as a consequence very effective bulk passivation of multicrystalline silicon solar cells. By combining front and back thermal dry SiO2 passivation with hydrogen remote plasma treatment, a cell efficiency of 17% (independently confirmed) on 4 cm(2) area and 180 mu m thickness is realized without any Al gettering. On the other hand, the 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 provided that PECVD Si3N4/SiO2 are used as a double-layer antireflection coating. (C) 1995 American Institute of Physics.