Black diamond for solar energy conversion

Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, able to drastically modify the interaction with solar radiation from optical transparency up to solar absorptance values even >90%. Surface texturing, performed by the use of an ultra-short pulse laser, is demonstrated to induce an intermediate band within the diamond bandgap supporting an efficient photoelectronic conversion of sub-bandgap photons (<5.5 eV). The intermediate band introduction results in an external quantum efficiency enhanced up to 800 nm wavelengths (and up two orders of magnitude larger than the starting transparent diamond film), without affecting the film transport capabilities. The optical and photoelectronic outstanding results open the path for future application of black diamond as a photon-enhanced thermionic emission cathode for solar concentrating systems, with advantages of excellent electronic properties combined with a potentially very low work function and high thermal stability.