Photovoltaic effect with high open circuit voltage observed in electrochemically prepared nanocrystalline silicon membranes

We have investigated photovoltaic effect in electrochemically etched nanocrystalline porous silicon (nc-PSi) thin layer for potential application as a wide-gap absorber for solar cells. The free-standing nc-PSi layer with a pn junction structure shows a photovoltaic effect with a large open circuit voltage in excess of 0.87 V. Comparison with single doped material in different top contact configurations clearly indicates that the original junction remains in the porosified material and plays a major role in the observed photovoltaic effect, while the contributions from the contacts are negligible. The effects of additional processing of the material including chemical etching as well as annealing of the material in an inert atmosphere suggests a strong contribution from the hydrogenated surface in the observed photoconductive characteristics. Replacement of interfacial hydrogen by more stable organic molecules appears to be a promising approach toward stabilization of the material for practical application.