RF rectennas apparently already have efficiencies up to 90%. According to this article, improving the fabrication process could lead to optical efficiencies up to 40%. That's double the efficency of any photovoltaic cell available today.
I thought they already had photo voltaic cells. I guess this is just a more efficient version of a device like that. It made it sound like they had invented a photo voltaic cell which they didn't.
Lots of dupes of this story recently, <a href="https://news.ycombinator.com/item?id=10305226" rel="nofollow">https://news.ycombinator.com/item?id=10305226</a> seems to be the oldest but there are a few more.