Doping graphene with trifluoromethanesulfonyl-amide (TFSA) has enabled researchers at the University of Florida (UF) to set a new efficiency record for graphene solar cells. While the record-breaking efficiency of 8.6 percent is well short of the efficiencies seen in other types of solar cells, it is a big improvement over previous graphene solar cells that saw efficiencies ranging up to 2.9 percent. The development provides hope for cheaper, durable graphene solar cells in the future.

The prototype solar cell created in the UF’s physics department consists of a 5 mm square (0.2 in square) rigid wafer of silicon coated with a single layer of graphene that has been chemically treated with TFSA. Where the graphene and silicon come together they form what is known as a Schottky barrier – a one way barrier for electrons at a metal-semiconductor junction that acts as a power conversion zone in the solar cell when illuminated with light.

While Schotty barriers are usually formed when a metal is layered on top of a semiconductor, it was discovered in 2011 that graphene, which is a semi-metal, was a suitable metal substitute in creating the junction. According to graduate student Xiaochang Miao, doping the graphene with TFSA makes it more conductive and increases the electric field potential inside the cell to make it more efficient at converting sunlight into electricity. The TFSA is also more stable and its effects more long lasting than other dopants that have been tried in the past.

While the rigid silicon base used to create the prototype graphene solar isn’t considered an economical material for mass production, Arthur Hebard, distinguished professor of physics at UF, sees possibilities in using the doped graphene in combination with less expensive, more flexible substrates currently being developed.

The researchers believe that, if production costs are kept down, graphene solar cells could be a viable contender in the marketplace if they were to reach 10 percent power conversion efficiency.

The UF team’s results are published in the online edition of Nano Letters.