Thin-film solar cells are basically thin layers of semiconductor materials applied to a solid backing material. Thin films greatly reduce the amount of semiconductor material required for each cell when compared to silicon wafers and hence lowers the cost of production of photovoltaic cells. Amorphous (uncrystallized) sili- con is the most popular thin-film technology with cell efficiencies of 5–7% and double- and triple-junction designs raising it to 8–
10%.