Superficial Photovoltaic Conversion and Photoluminescence of Nanoscale Si-Layered Systems at 400 nm

A nonlinear photovoltaic conversion at 400 nm has been observed in nanoscale Si-layered systems using spectral response measurements. Normally, the UV and blue conversion is poor because of the surface recombination within the thin superficial layer. For this reason conventional solar cells need a front face electronic passivation. In multi-interface cells this conversion is always negligible within an even thicker layer. Indeed this surface layer represents a dead zone where practically no free-carriers can be collected. So any PV conversion measured in the 400 nm band in multi-interface devices is totally inconsistent with usually observed effects. This conversion is inversely proportional to the incident flux intensity: the lower the intensity, the higher the collection efficiency. Because of the device composition, the new paradoxical effects can be localized only in the superficial nanostratum. No available publication mentions such an effect despite extensive investigations on the subject of structural and optical properties of Si nanoparticles, Si nanolayers, new Si-based materials such as semiconductor silicides and the luminescence-center doped Si materials. An explanation of the effect´s origin could be particularily useful for a new generation of very highly efficient Si-based solar cells