Optically assisted current-voltage (oa-IV) is a characterization technique for measuring both, a hot carrier (HC) population and the selectivity of an energy selective contact (ESC) in a static regime as in a HC solar cell. A HC population is generated by a concentrated photon flux from a Xenon (Xe) lamp. Its properties can be controlled further by selective wave length filtering from 1000 to 500 nm in 50 nm steps, thereby providing a narrow energy range of optical excitation up to 0.7 eV below the conduction band offset from Si to SiO₂. Measurements can be carried out down to liquid nitrogen temperature, thereby diminishing trap-assisted tunneling currents and inelastic electron scattering.
We report on the working principle, experimental setup and results of MESA samples containing a single Si-QD array as an energy selective contact below a nc-Si absorbing layer. Dark IV measurements revealed a weak resonant tunneling feature, while the massive optical excitation showed an enhancement of the resonant tunneling feature by one order of magnitude along with the bias range of the resonant tunneling feature being reduced significantly. With these experimental results, a static distribution of hot carriers being extracted by an energy selective contact was observed at room temperature.