  The theoretical analysis of photovoltaic conversion efficiency of highly
effective silicon solar cells (SC) is performed for n-type and p-type bases.
The case is considered when the Shockley-Read-Hall recombination in the silicon
bulk is determined by the deep level of Fe. It is shown that due to the
asymmetry of the recombination parameters of this level the photovoltaic
conversion efficiency is increasing in the SC with the n-type base and
decreasing in the SC with the p-type base with the increase in doping. Two
approximations for the band-to-band Auger recombination lifetime dependence on
the base doping level are considered when performing the analysis. The
experimental results are presented for the key characteristics of the solar
cells based on $\alpha-Si:H-n-Si$ heterojunctions with intrinsic thin layer
(HIT). A comparison between the experimental and calculated values of the HIT
cells characteristics is made. The surface recombination velocity and series
resistance are determined from it with a complete coincidence of the
experimental and calculated SC parameters' values.
