CONICET | Buscador de Institutos y Recursos Humanos

Nanostructured porous Silicon (PS) is a form of silicon obtained by electrochemicalanodization of monocrystalline silicon in a fluor containing electrolyte. The porosity andmorphology of the material depend on preparation conditions such as the currentdensity. The anodization process is self-limited, i.e. the porosity of the layer beingetched changes when the current density changes, but the previous layers remainunchanged. Therefore a current density-time profile results in an in-depth porosityprofile. This effect can be used to make multilayers. Besides, pulses of large currentdensities are used to separate the PS multilayer from the substrate.Since the nanostructure sizes are much smaller than the wavelength of the lightradiation used in solar cells, it behaves as a continuous medium with optical propertiesdependent on the porosity. Effects of light interference can be used to maximize thetransmittance of the multilayers deposited onto solar cells, enhancing its efficiency.Since the extinction coefficient of PS is not negligible, the total multilayers thicknessmust be optimized in order to prevent absorption. In this work we present numericalsimulations results of optimized multilayers used as antireflection coatings with differentnumber of layers.We demonstrate that a negligible increase in the performance is obtained for a numberof layers larger than three. Moreover, we found an optimal configuration with threelayers that transmits 95.3% of the whole usable power.We fabricate this optimal multilayer onto a monocrystalline silicon wafer obtaining up to95.2% of transmittance.In addition, we transfer a self sustained multilayer with specific optical response on to asolar cell. A multilayer with sharp optical response was successfully deposited on acrystalline silicon solar cell obtaining a tunable spectral response.

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