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Multistage PV conversion using nanostructured multi-interface Si components: experimental evidence

Completing one-step PV conversion by additional new low-energy mechanisms is one of the most important challenges of modern photovoltaics. Si is a basic PV material which is not efficient enough to convert the light into electricity in its bulk or thin-film form because of its indirect bandgap. Progress in conversion efficiency requires breakthroughs. One way has been indicated by low-dimensional or nanostructured Si materials such as, for example, nanoscale Si-layered systems combined with an active interface with its crystalline defects. We have demonstrated low-energy carrier multiplication experimentally under attenuated solar excitation in nanostructured Si in both the optical and electronic approaches. This paper gives results, among others, concerning: 1) a simulation based on previously determined parameters and 2) experiments using a reference cell. In the simulation, the nanolayer thicknesses are 5 nm for a-Si (estimation based on TEM images) and 20 nm for (estimation based on EELS data). To be simple and directly useful in the future development, the project has been limited to comparative measurements of the short-circuit currents of our test cells relative to the new generation photovoltaics. The ratio of short-circuit currents shows steps which allow estimating a characteristic energy Eδ = 0.274 eV, previously determined by us from spectral response and modeling. The effect is particularly visible under weak incident beams. Thanks to these investigations, the fabrication of a very highly efficient Si solar cell becomes more realistic. The results suggest scientific and technological prospectives.