Energy Making Solar Cells with Pure Pyrite Cyrus Wadia is using abundant materials to grow nanocrystals for cheaper photovoltaics. by Katherine Bourzac October 20, 2009 Sponsored by Iron salts are mixed with sulfide salts inside the metal autoclave container at left and heated in an oven for four hours. The result: a black suspension of pyrite nanocrystals. Wadia sets a glass chip on the circular pedestal in the center of a spin-coating machine and then drips the pyrite suspension onto it. A minute of spinning coats the chip with a thin film of pyrite. He uses tweezers to set the chip on a hot plate; 10 to 15 minutes of heat will fix the nanocrystals to the surface. Wadia places a glass chip with eight pyrite solar cells on its surface inside a solar simulator. The aluminum lines are the cells’ top electrical contacts; the line across the top of the chip is a strip of conductive indium tin oxide. Inside the solar simulator, the chip is illuminated with light in a mixture of wavelengths simulating the distribution found in sunlight. Electrical connections to the manifold read the current and voltage across each cell, helping Wadia to calculate its efficiency.