Why Commercial solar panels are overwhelmingly built from crystalline silicon, either single-crystal or polycrystalline wafers doped to form a large-area PN junction. Silicon is cheap, abundant, non-toxic, and its bandgap of about 1.1 eV is well matched to the solar spectrum, giving a typical cell output around 0.5 V in sunlight. The same semiconductor technology used for transistors and ICs scales up nicely to wafer-sized power cells.
Watch out Selenium and cadmium sulfide were used in early photocells and light meters, and cadmium telluride and indium compounds appear in specialty or thin-film cells, but none of them dominate power generation the way silicon does.
Solar panels are just big silicon junctions: about 0.5 V per cell, 1.1 eV bandgap.