Laser for solar cell research. Spectroscopic laser (red beam) being used to measure properties of a semiconductor thin film used in solar cells. Solar cells use semiconductors to convert the energy in sunlight into electrical energy. The semiconductor thin film being investigated here, consists of a combination of the elements gallium, indium and phosphorus (GaInP). The efficiency of a solar cell is sensitive to its semiconducting properties, and these are determined by its chemical composition. Altering these properties changes a solar cell's efficiency. Photographed at the National Renewable Energy Laboratory, Golden, Colorado, USA, in 1997.