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

Conventional and electromagnetically casted multicrystalline silicon s olar cells are fabricated following different passivation schemes. Thi n layers (similar to 100 Angstrom) of thermal dry and plasma-enhanced chemical-vapor-deposition (PECVD) SiO2 are implemented for surface oxi de passivation of multicrystalline silicon solar cells and compared. f t is found that growing thin layers of thermal dry oxide results in ef ficient surface passivation. However, for thin PECVD SiO2 layers it is necessary to perform low-temperature forming gas anneal, postdepositi on, in order to observe the surface passivation effect. In addition, h ydrogen plasma passivation has been optimized for achieving deep penet ration of atomic hydrogen in the material (>30 mu m) and as a conseque nce very effective bulk passivation of multicrystalline silicon solar cells. By combining front and back thermal dry SiO2 passivation with h ydrogen remote plasma treatment, a cell efficiency of 17% (independent ly confirmed) on 4 cm(2) area and 180 mu m thickness is realized witho ut any Al gettering. On the other hand, the cell efficiencies obtained using thin layers of PECVD SiO2 are found to be very comparable to th e efficiency of the cells fabricated with thermal dry SiO2 layers prov ided that PECVD Si3N4/SiO2 are used as a double-layer antireflection c oating. (C) 1995 American Institute of Physics.