Thanks for doing some more digging. honestly the article is pretty shoddy. The reference image looks like someone labelled a jpeg of a science fair project in MS Paint. It was especially disappointing after the green battery looking image that opens the article.

So at least (if they're correct) the power is coming directly from photosynthesis rather than just some degradation of the materials used.

It's interesting at least, but it's still pretty useless if you'd have to wire up a whole plant leaf to leaf for it to become scalable as they suggested.