Solution-processed inorganic solar cells based on nontoxic and abundant AgBiS2 nanocrystals could be a low-cost alternative to first-generation solar cells. A semitransparent solar cell based on AgBiS2 nanocrystals. Courtesy of ICFO. The most-common inorganic solar cells for rooftop installation are made of silicon. The production of silicon solar cells can be expensive and energy demanding, and the modules are heavy and bulky. Many lower-cost thin-film solar cells, alternatives to silicon, are composed of toxic elements such as lead or cadmium, or contain scarce elements such as indium or tellurium. The AgBiS2-based cells were fabricated under ambient conditions at low temperatures of 100 °C. Researchers from The Institute of Photonic Sciences (ICFO) demonstrated devices with a certified power conversion efficiency of 6.3 percent, with no hysteresis and a short-circuit current density of about 22 mA cm−2 for an active layer thickness of only about 35 nm. Researchers Nicky Miller and Maria Bernechea hold a semitransparent solar cell. Courtesy of ICFO. The temperature required for synthesis is an order of magnitude lower than that required for production of silicon-based solar cells, the researchers said. Their hot-injection synthetic procedure involved first dispersing AgBiS2 nanocrystals into organic solvents, where the solutions showed to be stable for months without any losses in the device performance. Then, the nanocrystals were deposited onto a thin film of ZnO and ITO, the most commonly used transparent conductive oxide, in a layer-by-layer deposition process until a thickness of approximately 35 nm was achieved. The solar cell material meets demands for nontoxicity, abundance and low-temperature solution processing, and the researchers are working toward a milestone efficiency of greater than 12 percent. The research was published in Nature Photonics (doi: 10.1038/nphoton.2016.108).