Cadmium telluride CdTe is used for cells that absorb multiple frequencies. Electrochemical impedance spectroscopy EIS was used to investigate the quality of interfaces. The dots can be grown over a range of sizes, allowing them to express a variety of bandgaps without changing the underlying material or construction techniques. As shown in Supplementary Fig. In , Los Alamos National Laboratory reported spectroscopic evidence that several excitons could be efficiently generated upon absorption of a single, energetic photon in a quantum dot.