Well, isn't this new device essentially a multijunction organic solar cell? That's what I gathered from the BBC article.

I guess the hope is that they will command less of a relative premium compared to multijunction silicon cells?

Inorganic multijunction devices are very difficult and costly to make, because the materials have to be evaporated into place. Organics in principle can be printed using standard solvents.

Let’s not forget that many thin-film amorphous silicon devices use multiple junctions as well.