We need a variety of cell that is transparent to wavelengths plants use, so they could be used above farmland and pasturage. Many plants could probably be grown under them in places where it would otherwise be too hot, maybe even needing less water.
Best be making green absorbing panels. The plants ain't using that part of the spectrum.
Conversion efficiency of the part they do use can't be more than a few percent, so they probably radiate in IR. Converting IR radiating from plants, as suggested in TFA, thus seems like a good idea.