Light absorbing diamond for solar energy conversion

High-temperature solar cells are possible by exploiting the Photon-Enhanced Thermionic Emission (PETE) concept, which represents a novel and very attractive mechanism for the exploitation of solar radiation, especially if concentrated, and characterized by promisingly high conversion efficiency (>50%). PETE converters rely on the concept that engineered semiconductor photocathodes can provide a very efficient electron emission, induced by hot-electrons produced by photons with sufficient energy, combined to a thermionic emission, sustained by the high temperatures induced by every other thermalization process. Ultrashort pulse laser-assisted surface nanotexturing combined to surface-hydrogenation, aimed at achieving negative electron affinity conditions and a work function as low as 1.7 eV with a nitrogen-doping of the emitting-layer, have been proposed as a radically new and potential effective PETE cathode completely based on chemical-vapour-deposited (CVD) diamond, able to operate up to temperatures of 800 °C. CVD diamond is transparent to solar radiation due to its wide bandgap, consequently "black diamond" technology, based on ultrashort laser treatment, was developed for drastically increase its absorption coefficient and photogeneration capability under sunlight irradiation [1]. The final p/i/n structure merges the technologies of surface texturing by fs-laser [2], boron-implantation for formation of buried p-type layer [3], and laser-induced graphitic microchannels [4], to form an innovative defect-engineered black diamond cathode for the conversion of concentrated solar radiation operating at high temperature. Ongoing extension of the technology to polycrystalline films for large area scale-up and to thin single crystal films for an optimized performance has been discussed.