There are mainly three different types of solar cells: monocrystalline, polycrystalline and amorphous ones.
Crystalline means that silicon is present in crystallised form: all atoms are aligned in a strictly arranged specific pattern. This contrasts with amorphous cells (Greek amorphous = formless), in which atoms are arranged irregularly.
Crystallised solar cells are classed into two different types:
Monocrystalline (mono: one) means that the silicon block, the disks are cut out from, is made up of one single crystal. This block is drawn from silicon melt. The manufacturing process is similar to candle dipping. Visually, monocrystalline cells can be discerned by their consistent blue or black surface.
Polycrystalline solar cells (poly: several) are derived from a cast silicon block, which consists of several crystals. Visually, polycrystalline cells can be discerned by their marble-like structure.
For amorphous solar panels, a thin layer of silicon is vapour-deposited to glass. This cell type requires less materials and energy in production and thus bears enormous future potential. However, currently their efficiency is below the one featured by crystalline solar cells. Thus, most applications are still based on high-performance crystalline solar cells today.