Grapene based solar panels-easily the most efficient!!!

Researchers have also shown that they can make basic solar cells, light-emitting devices, touch screens, photodetectors and mode-lock ultra-fast lasers from the graphene. However, there are, of course, drawbacks: graphene's "external quantum efficiency" is low – it absorbs less than 3% of the light falling on it. Furthermore, useful electrical current can only be extracted from graphene-based devices that have electrical contacts with an optimized "asymmetry" – something that has proven difficult to achieve.

Now, researchers at the University of Cambridge and the University of Manchester may have solved both these problems by pairing up graphene with plasmonic nano structures. These are metal devices that enhance local electromagnetic fields in a material by coupling incoming light with electrons on the surface of the metal. The nano structures are fabricated on top of graphene samples to concentrate the electromagnetic field in the region of the material where light is converted to electrical current, so as to dramatically increase the generated photovoltage.

The team, which includes Manchester's Andre Geim and Kostya Novoselov, winners of the 2010 Nobel Prize for Physics for their discovery of graphene, started out by preparing samples of graphene using the now-famous "sticky tape" method. This involves mechanically shaving off single layers of graphene from a block of graphite. The researchers then made two-terminal electronic devices from the material by forming contacts made of titanium and gold on the graphene using electron-beam lithography. Next, various plasmonic nano structures were assembled close to the contacts.

The new devices have an external quantum efficiency of almost 50%, the highest value to date for graphene. This boosts the light-harvesting capacity of graphene by more than an order of magnitude compared to its non-contacted counterpart, without sacrificing it's speed.

Furthermore, the problem of creating contacts with the desired asymmetry is addressed through the use of titanium and gold in the device.