Thermionic performance of nanocrystalline diamond/silicon structures under concentrated solar radiation

Thin films of nanocrystalline diamond with thickness around 100 nm were deposited on highly doped p-type silicon substrates to evaluate the electron emission performance of these structures under illumination of concentrated sunlight in the temperature range 500-700 °C. By comparing the emitted current densities measured using a pure thermal source and a concentrated light source simulating the solar radiation spectrum (Xe lamp), an increase up to about 80 times at 600 °C was found using the concentrated light source, thus demonstrating the boost on the thermionic emission thanks to the sunlight absorption. At temperatures higher than 600 °C the action of the photon-enhanced thermionic emission (PETE) mechanism begins to vanish, starting the regime of pure thermionic emission. The opening of the quasi-Fermi levels reducing the barrier height down to 0.33 eV for electron emission is considered to explain the overall behavior of the diamond-silicon system in the PETE regime.