Monocrystalline Panels
Monocrystalline solar panels are made from cells using a single silicon crystal and do not have the multiple grain boundaries which you can sometimes see in polycrystalline cells. The cells are black, but have small areas of white at the corners of each cell.
Monocrystalline solar panels used to be both more expensive and more powerful than polycrystalline panels. However, due to advanced manufacturing techniques that is no longer the case and some polycrystalline solar panels are now just as efficient as their monocrystalline alternatives.