Some researchers at the Georgia Institute of Technology have succeeded in making a rectenna that works at light frequencies:
OPTICAL RECTENNA CONVERTS LIGHT TO DC
Using multiwall carbon nanotubes, researchers at Georgia Institute of Technology have created what they say are the first optical rectennas–antennas with rectifiers that produce DC current. The work could lead to new technology for advanced photodetectors, new ways to convert waste heat to electricity and, possibly, more efficient ways to capture solar energy.
A paper in Nature Nanotechnology describes how light striking the nanotube antennas create a charge that moves through attached rectifiers. Challenges included making the antennas small enough for optical wavelengths, and creating diodes small enough and fast enough to work at the extremely short wavelengths. The rectifiers switch on and off at petahertz speeds (something the Institute says is a record).
It takes billions of rectennas to produce significant current and the efficiency of the devices is less than one percent. However, researchers believe that a rectenna with commercial potential may be available within a year. Given that the devices are made with vapor deposition nanotechnology techniques, they might be hard to make at the local hackerspace. On the other hand, hackers are a resourceful bunch and who knows what we might see in the future?
This has great potential - commercial solar cells hit an efficiency wall at around 23% - if these arrays can be scaled up successfully and cheaply enough, the efficiency could be a lot higher and solar power could become viable without the current huge government subsidies...