Scientists at Stanford University California have made the world’s first all-carbon solar cell. Their results were published Oct. 31 online edition of the journal ACS Nano. One advantage of using a carbon approach over silver and indium tin oxide (ITO) is cost. Indium is scarce and expensive and silver isn’t cheap either. Carbon on the other hand is abundant and cheap, and as our new carbon age develops, offers plenty of scope to develop carbon based solar cells along with it. The all-carbon solar cell has a photoactive layer, which absorbs sunlight, sandwiched between two electrodes producing electricity from sunlight.

The Stanford team produced a thin film prototype solar cell that replaced the silver and ITO electrodes with graphene, sheets of chicken wire like carbon that are one atom thick. The other photoactive component was one nanometer  diameter, single-walled, carbon nanotubes. “Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties,” according to senior author Zhenan Bao, a professor of chemical engineering at Stanford. Stanford’s researchers have filed for a patent for their all-carbon 21st century solar cell.

One drawback at present, the carbon solar cell isn’t yet very efficient, though the researchers believe that this deficiency will be overcome in further development. The prototype has an efficiency of less than 1% as compared to 15% for typical ITO solar cells, and about 35% reached in some of the lab models.  A big positive, however, lies in the extra flexibility of a thin film solar cell approach and a potentially much lower cost and easier manufacturing process.  Potentially this thin film carbon approach can be coated on the surface of buildings, cars, glass, trains and planes. I suspect that it will come in quite useful in shipping too, where every kilowatt hour of energy has a cost. The team at Stanford also believe that carbon solar cells have the potential to operate at much higher temperatures and greater stress. I think that we have only heard of the beginning of all-carbon solar cells.

Evaluation of Solution-Processable Carbon-Based Electrodes for All-Carbon Solar Cells
Carbon allotropes possess unique and interesting physical, chemical, and electronic properties that make them attractive for next-generation electronic devices and solar cells. In this report, we describe our efforts into the fabrication of the first reported all-carbon solar cell in which all components (the anode, active layer, and cathode) are carbon based. First, we evaluate the active layer, on standard electrodes, which is composed of a bilayer of polymer sorted semiconducting single-walled carbon nanotubes and C60. This carbon-based active layer with a standard indium tin oxide anode and metallic cathode has a maximum power conversion efficiency of 0.46% under AM1.5 Sun illumination. Next, we describe our efforts in replacing the electrodes with carbon-based electrodes, to demonstrate the first all-carbon solar cell, and discuss the remaining challenges associated with this process.

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