Absorption optimization in nano-structured optical thin films: Application to photovoltaic solar cells

Nowadays, the search for giant amplifications of the electromagnetic field in a confined structure is a major challenge for applications such as photovoltaic solar, nonlinear optics, microcavities, microscopy and optical sensors. It is in this context that this work consists of optimizing absorption in nano-structured optical thin films for applications related to photovoltaic solar cells. In other words, the aim is to couple these planar resonant structures to the solar cell in order to maximize the field intensity collected by the latter. Therefore, a synthesis method allowing to reach arbitrary exaltations in plasmonic and/or multi-dielectric resonant structures has been developed. The component is an interferential filter, or a one-dimensional photonic crystal, whose geometry is calculated with respect to the desired exaltation and the desired resonance frequency. The calculation technique is based on the complex admittance method widely used to synthesize optical functions. The expected result is a resonance in total absorption in free space whose sharpness is adjustable during the synthesis. This resonance is accompanied by a giant amplification of the confined field inherent to the low imaginary indices of dielectric materials (a few 10
^-5
in practice). Numerical results, obtained with the Matlab/Simulink software, from the mathematical modelling allowed to validate this synthesis method. Taking into account the modest over-intensification of the field for the plasmonic type structures, an optimization of the absorption has been proposed via a transition from metallic structures to multi-dielectric structures. Thus, a final model has been retained for applications related to solar photovoltaic.