I've read in some statements here that one of the applications of copper oxide is that it can be used for solar energy transformation, but how exactly is a nano particle used in such way?
Adding to what is said by Manohar, The copper oxide behaves as a wide gap semiconductor material. It i able to absorb part of the incident solar radiation and produce superconductive effect. It can be used with relatively narrow energy gap semiconductor such as silicon to form a hetero junction solar cell as indicated in details by the papers mentioned by Manohar. The cupperoxide a a windo materials absorbs the UV light and the silicon absorbs the rest till about 1.1 um.
However, these cells are still of low efficiency because of the high density of interface state at the hetero junction.