Solar photon energy can be better used when totally transformed on collectable free-carriers. The conversion of one
energetic photon could result in more than one free-carrier pair if a low-energy mechanism is involved. Such PV
conversion represents a multistage nonlinear process and requires especially dedicated low-energy centers. A cascade-like
progression is induced by the primary/fundamental/interband absorption. As shown by us previously, the
corresponding structure can be realized, for example, with nanostructured Si.
The experimental devices convert 400 nm photons into collectable primary and secondary free-carriers. The excess
carriers can be drawn out into the external electrical circuit even in a multiinterface architecture containing a carrier
collection limit. The superficial effect seems to be totally independent of the presence or not of a buried amorphized
layer. This is the first simple experimental evidence for low-energy generation. The performance is inversely
proportional to the incident light intensity.
The thermodynamic limit of conventional photovoltaic conversion is lower than 30%, while in the case of the
mechanism reported here, it can be propelled above 60%. An optimization of the effect by a suitable conditioning and
annealing should be possible, opening the way to different applications, especially in the areas of nanophotovoltaics and
very high efficiency solar cells.