We present a versatile mechanism utilizing time-varying metasurfaces for achieving linear frequency conversion, historically governed by nonlinear interactions. Our approach, rooted in invoking linear equations, demonstrates the feasibility of single-frequency conversion through a metasurface, likened to parametric processes found in time-varying systems. Leveraging a generalized time-inhomogeneous convolution product, we introduce an effective nonlinearity furnished by external memory effects, which presents a path that provably adheres to the principles of causality and energy conservation. We explicit the double time-variable electric and magnetic susceptibilities which allow frequency conversion from one frequency to another. The approach can be extended to accommodate multi-frequency conversion by reflection or transmission, as well as full coherence for each monochromatic input. As we anticipate exploring numerical solutions and extension into the quantum regime, we believe this introductory result prepares the ground for future work.
Photon management of perovskite solar cells (PSCs) is studied by the use of nanohole front contact, which allows improving the JSC of the PSC by providing an improved light incoupling. The front contact integrated with spherical nanocone shaped holes represent a refractive index grating allowing for light incoupling approaching unity while minimizing reflection losses. Besides, the front contact has a comparable refractive index (n~2.5) with the perovskite absorber, which minimizes the front reflections in PSC. Optics and optimization of front contact and solar cell are investigated by three-dimensional (3D) finite-difference time-domain (FDTD) simulations whereas finite element method simulations are used to study the electrical response of the device. Investigations reveal a maximum light incoupling enhancement of 10~12% for the optimized PSC, leading to 10 to 27% JSC enhancement with respect to the planar reference PSC.
We present a comprehensive investigation of resonant all-dielectric multi-layers. We first introduce a numerical as well as analytical optimization based on admittance recurrence law. We then address the technological aspects of the fabrication using dual-ion-beam sputter deposition. Using the optimally fabricated structures, we carry out experiments to optically characterize their responses in the near and far fields. Previously, our optimization strategy had been based on maximizing the absorption within the dielectric stack [1] for any illumination conditions without altering the field enhancement. Recently, we have improved this process by introducing a single zero-admittance layer that allows defining the field enhancement localization within the multi-layer [2]. Similarly to the Kretschmann configuration for surface plasmon resonances (SPR), these resonant all-dielectric components work under total internal reflection but they can support field enhancements up to 104-105. From a theoretical point of view, the enhancement is not intrinsically limited (except for nonlinear phenomena or material damages under high flux), and it is therefore the illumination bandwidths (angular divergence and spectral range), which mainly limit the resulting field enhancement [3]. We will introduce the resonant all-dielectric components, demonstrate their potential for sensing applications and give a brief comparison with SPR [4].
The authors acknowledge the PSA group for financial support of this work, the ANRT for their support through the CIFRE program and the RCMO Group of the Institut Fresnel for the realization of the coatings. This work is part of the OpenLab PSA/AMU: Automotive Motion Lab through the StelLab network.
1- Appl. Phys. Lett. 103, 131102 (2013)
2- Phys. Rev. A 97, 023819 (2018)
3- Opt. Express 25, 14883 (2017)
4- Appl. Phys. Lett. 111, 011107 (2017)
We study light absorption in ZnO nanorod arrays sensitized with CdSe quantum dots as one of the factors affecting solar cell performance in need of improvement given their current performance well below expectations. Light trapping in nanorod arrays (NRAs) as it relates to array density and length as well as quantum dot (QD) loading is studied using the Finite Difference Time Domain model. It is shown that light absorption in such solar cell architecture is a sensitive function of the morphological dimensions and that a higher NRA density does not necessarily correspond to large absorption in the solar cell. Instead, light trapping efficiency depends significantly on the array density, QD axial distribution and refractive index contrast between NR and QDs thus suggesting strategies for improved quantum dot solar cell (QDSC) fabrication. In addition, we present experimental data showing dramatic improvement in photo conversion efficiency performance for relatively short ZnO NRAs (~1 μm) of low NRA density, but whose efficiency improvement can not be solely explained based on our current light trapping estimates from the numerical simulations.
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