  The transformation of the long-wavelength edge of the external quantum exit
(EQE) formation mechanisms in textured silicon solar cells (SCs) is revealed,
depending on their thickness. Expressions for experimental EQE dependences on
the long-wavelength absorption edge are obtained for a wide range of base
thicknesses (100-450 {\mu}m). The expressions allow optimal SC base thickness
values calculation from the condition of maximal photoconversion efficiency
taking into account surface recombination velocity. In particular, it was found
that optimal 100-{\mu}m base thickness corresponds to the surface recombination
velocity of about 3 cm/s.
