The rim keeps the sunlight and the shadow keeps the cold, so three mirrors hand the one down into the other.
An artistic imagining, not existing hardware: solar collectors standing in the permanent shadow of a crater at Mercury's pole, fed by mirrors that reach up over the rim into sunlight and hand it down into the cold. Sunlight at Mercury's perihelion is roughly ten times as intense as at Earth's distance while the floors of some polar craters never see the sun at all, so the fiercest light in the inner solar system and a place cold enough to hold water ice sit a few kilometres apart.Image: poweringspace.com. Artistic imagining.