This idea has been kicking around for close to a decade but this is
apparently the first time it's been demonstrated with actual solar cells
and actual sunlight.
The idea seems to be that you put a collector made of nanotubes and
nanophotonic crystals in front of the cell and it "transforms" the
incoming sunlight from a mishmosh of frequencies into a nearly
monochromatic beam, whose frequency is centered on the band the cell can
convert.
This is supposed to allow the cells to break the 32% barrier, which is
the theoretical limit for a single-layer cell, or so they say (I sure
don't know enough semiconductor physics to critique that statement).
('Course the whole system needs to be operated at about 1000 C which
might impose some limitations on where you could deploy it.)
Brief article here (original paper was in /Nature Energy/):
http://news.mit.edu/2016/hot-new-solar-cell-0523
