werent iron plates in sunlight used to prove some of Einsteins throeirs about photovoltaic effect? light wont penetrate iron very far, if at all.Light has such a short wavelength that it doesn't penetrate a conductor so can't induce a current in them.
To generate a current you need a material that can absorb the light short wavelength and generate a current, such as a doped semiconductor junction, thus giving us solar cells.
The nominal point where standard electrical conductors don't work well for inducing electrical currents is somewhere in the terrahertz region. That's why there is little practical electronics in this region although much experimental work is being done there.
For comparison visible light goes from 470THz to 790THz.