'Darker Than Black' Metamaterial Promises Better Solar Cells - Technology Review: These guys created a hyperbolic metamaterial by growing silver nanowires grown in a membrane of aluminium oxide to create a flat light-absorbing slab. This absorbs some 80 per cent of the light that hit it.
That's fairly black but then they had an idea. By roughening the surface of the slab, any light that is still reflected gets absorbed in the peaks and troughs of the surface. In effect, the photons are "sucked" into the material, say the team. The result is a substance that absorbs up to 99 per cent of the light that hits it.