High Temperature Solar Cells based on Defect Engineered Diamond

Photon-enhanced Thermionic Emission (PETE) is a novel and very attractive concept for the exploitation of concentrated solar radiation with a promising conversion efficiency higher than 50%. PETE converters rely on the concept that engineered semiconductor structures can obtain a thermionic emission significantly enhanced by hot electrons generated by photons with sufficient energy to produce charge couples and sustained with the high temperatures induced by the absorption of photons with lower energy (i.e. IR. III-V semiconductors have been already used for the fabrication of a "proof-of-concept", but their unstable high temperature operations and the intrinsic high work-function are limiting conditions. We propose a radically new and efficient PETE cathode based on surface-hydrogenated chemical vapour deposited (CVD) diamond, one of the few semiconductors to show negative electron affinity and a work function as low as 1.7 eV if nitrogen-doped. This characteristics assure an efficient thermionic emission at moderate temperatures (up to 780 °C). CVD diamond is transparent to solar radiation due to its wide bandgap of 5.47 eV, so advanced and novel techniques are needed for preparing an efficient sunlight absorbing diamond. Surface texturing by fs-laser, boron-implantation, buried graphitic contact structures and other technological steps allow the fabrication of an innovative defect engineered diamond cathode to be efficiently exploited for the conversion of concentrated solar light.