Monocrystalline Solar Panels contain cells that are cut from a single crystalline silicon ingot. The composition of these cells is purer because each cell is made from a single piece of silicon.
As a result, mono panels are slightly more efficient than poly panels. They also perform better in high heat and lower light environments, which means they will produce closer to their rated output in less than ideal conditions.
However, they cost more to produce and that higher cost is passed on to the buyer. Mono panels are a bit more expensive than poly panels of the same wattage.
The manufacturing process for mono panels is also more wasteful than the alternative. Mono panels are cut from square silicon wafers and the corners are shaved off to make the distinct cell shape shown in the picture below.
Lastly, mono panels have a uniform black look because the cells are made from a single piece of silicon. I personally think these look better than poly panels, but obviously, that is just a matter of preference.
JA Solar 375W Mono MBB Percium Half-Cell Black Short FrameR3,265.00 Incl Vat
100W 12 Volt Monocrystalline Semi-Flexible Bendable Solar PanelR3,528.00 Incl Vat