If you paired those materials, you could collect solar energy on the hot end, and radiate thermal energy into empty space on the cool end, and put a Stirling engine between them. Then you have a heat engine that does not dump its waste heat into the atmosphere. At the theoretical limit, that means your passively-radiating cool end can approach 3 K, instead of 300 K.
So you take a huge polished stainless steel dome, and etch the outside to be black at visible and near-infrared wavelengths, from 200 nm to 8000 nm, and you take some smaller domes, etch them to be black between 8000 nm and 14000 nm, and put them at the focal points of some parabolic reflectors, all in the shadow of the first dome, aimed at empty space. (8000 nm to 14000 nm is the "infrared window", where the atmosphere is mostly transparent to those wavelengths.)