Ultra-high efficiency solar cells: the path for mass penetration of solar electricity

For achieving a photovoltaic penetration above one-third of the world demand for electricity in the first half of this century, the importance of a fast manufacturing learning curve that is linked to the capacity of developing cells of increasing efficiency is stressed. Progress in multijunction cells is described as well as three novel concepts promising very high efficiency. It is explained why these concepts will probably be used in concentrator systems.