Nanotubes could boost organic PV cell efficiency, NREL finds

Researchers at the US Energy Department's National Renewable Energy Laboratory (NREL) have discovered that nanotube semiconductors could boost the efficiency of organic PV cells.

The scientists, building upon the work of Nobel laureate chemist Rudolph Marcus, have found that single-walled carbon nanotubes (SWCNT) are ideal for PV systems because they can convert sunlight to electricity with little loss of so-called "reorganisation energy".

"What we find in our study is this particular system – nanotubes with fullerenes – have an exceptionally low reorganisation energy and the nanotubes themselves probably have very, very low reorganisation energy," says NREL senior scientist Jeffrey Blackburn.

In a PV cell, once a photon is absorbed, the charge needs to be separated across an interface so that they can "live long enough" to be captured as electrical current.

The electron transfer that produces these separated charges comes with a potential energy loss – reorganisation energy. But NREL's research suggests that such energy losses were low when pairing SWCNT semiconductors with fullerene molecules.

"Organic PV devices involve an interface between a donor and an acceptor. In this case, the SWCNT served as the donor, as it donated an electron to the acceptor – here, the fullerene," explains Blackburn.

"The electron transfer event didn't come with a large energy loss associated with reorganisation, meaning solar energy can be harvested more efficiently. For this reason, SWCNT semiconductors could be favourable for PV applications."