In single-crystal silicon, the molecular structure of the material is uniform because the entire structure is grown from the same or a "single" crystal. This uniformity is ideal for efficiently transferring electrons through the material. To make an effective PV cell, silicon is "doped" to make it n-type and p-type. Semicrystalline silicon, on the other hand, consists of several smaller crystals or "grains," which introduce "boundaries." These boundaries impede the flow of electrons and encourage them to recombine with holes and thereby reduce the power output of the cell. However, semicrystalline silicon is much cheaper to produce than single-crystalline silicon, so researchers are working on other ways of minimizing the effects of grain boundaries.