Only problem with that theory is that you have a very large aperture with the radiotelescopes, whereas a molecular antenna would have a very small aperture.
Remember that the solar flux at all wavelengths is about 1300 watts/square meter. As hot as a small volume of air can get, like between a storm door and a regular door, in sunlight, makes you wonder if direct conversion to electricity is barking up the wrong tree. Leaving it as heat and light may be a better answer.
My thoughts exactly. Build a solar oven and line it with thermocouples. Much cheaper too.
The other thought that bothers me is that this idea falls into what I refer to as "California thinking". Even if those optical rectennas were efficient, they aren't well suited for many areas that aren't graced with long periods of fair weather. There isn't much useable direct or ambient infrared on a cold and cloudy day in the midwest.
"California thinking"... like when heat pumps were all the rage until people in states where Winter is a reality discovered that they weren't very practical. "California thinking".... like expecting your Toyota Prius to run on battery power when you turn the heat on when it's -10 outside.