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Abstract

Abstract

In this paper, using a deep neural network and a genetic algorithm, an optimized digital metasurface is designed to trap sunlight in thin-film solar cells. The deep neural network is trained using full-wave numerical simulation results as the training dataset, and it is designed to predict the electromagnetic response of thin-film solar cells whose active layers are shaped as a digital metasurface. The developed neural network can predict the results much faster than full-wave solvers and therefore can be used for optimization purposes. Using the results generated by the trained neural network, an evolutionary procedure based on the genetic algorithm is developed to find the optimum structure for the digital metasurface, which provides the highest short circuit current inside the thin-film solar cell. The performance of the resultant optimum design is validated using full-wave numerical simulation illustrating a short circuit current of 15.39mA/cm215.39mA/cm2 and 13.30mA/cm213.30mA/cm2 for TE and TM polarization of the incident light, respectively. The resultant short circuit current is 2.47 and 2.13 times higher than a simple thin-film solar cell with the same amount of silicon inside, for TE and TM polarization of the incident light, respectively. To have a more comprehensive comparison, the designed optimum structure is compared with several standard shapes for the metasurface, such as star and plus sign. This comparison showed that the optimum structure provides a short circuit current which is much higher than the current achieved by standard shapes.

link:

https://opg.optica.org/josab/abstract.cfm?uri=josab-38-9-2728

Abstract

In this paper, a new architecture comprising silicon nanoparticles inside a hole transport layer laid on a thin silicon layer is proposed to develop ultrathin film solar cells. Using generalized Mie theory, a fast analytical approach is developed to evaluate the optical absorption of the proposed structure for various geometries, polarizations and angles of incidence. The analytical results are verified through comparison with full-wave simulations, illustrating a reasonable agreement. The electrical performance of a distributed silicon nanoparticle solar cell is determined for selected configurations. To be able to predict the light-trapping in a solar cell comprising randomly distributed nanospheres, a new technique based on probability theory is developed and validated through comparison with the simulation results. Both analytical and numerical results show that the excited Mie resonant modes in the proposed structure lead to a significant enhancement in both absorption and the photo-generated current, in comparison to a conventional silicon solar cell with an equivalent volume of the active layer. In the case of random distributions, other advantages, including the simple fabrication process, indicate that the cell is a promising structure for ultrathin photovoltaics.

link:

https://opg.optica.org/oe/fulltext.cfm?uri=oe-29-18-28037&id=457250

Abstract

Abstract

Losing the information contained in evanescent waves scattered from an object limits the best achievable resolution in far-field optical imaging systems to about half of the wavelength. This limitation is known as the diffraction limit. In this paper, we propose a new holography-based far-field imaging technique to go beyond the diffraction limit and achieve super-resolution images. In the proposed method, after the recording process, multiple reconstruction processes with appropriate reconstruction waves are performed to extract information about sub-wavelength features of a target object encoded in the evanescent waves scattered from it. It is analytically proved that in the proposed method, by increasing the number of reconstruction steps, the resolution increases. The performance of the method is numerically validated. In numerical analysis, by performing two reconstruction steps, a resolution of 1/14 of the working wavelength is achieved. This resolution can be further improved by increasing the number of reconstruction steps.

link:

https://opg.optica.org/josab/abstract.cfm?uri=josab-38-3-670

Abstract
With the advances in the field of plasmonics, techniques for trapping and localizing light have become more feasible at the nanoscale. Several works have shown that plasmonics-based photovoltaic devices have yielded an improved absorption capability, enabling the design of thin-layered photovoltaic absorbers. In this review, we shed light on recent advances that employ plasmonics and nano-sized structures and thin-film technologies intended to increase solar cell efficiency. In this work, we provide an overview of the challenges associated with developing high-efficiency solar cells. Despite significant efforts by numerous groups to improve the efficiency of solar cells, practical realization of these concepts has yet to materialize. The conclusions made here hope to encourage researchers to re-examine the factors and challenges that could have created barriers to full realization of all concepts proposed over the past 15 years. In fact, because of the immense impact of improving the efficiency of solar cells on the environment and economy, it is hoped that this review encourages new technology paradigms that can be translated into commercially viable products.

link:

https://opg.optica.org/josab/abstract.cfm?uri=josab-38-2-638

Mr. Pooria Salami successfully defended his Ph.D. thesis titled “Sub-Wavelength Imaging using Optical Hyperbolic Metamaterials”.

Abstract:
Tunable metasurfaces enable us to dynamically control light at subwavelength scales. Here, using phase change materials and transparent graphene heaters, a new structure is proposed to develop tunable metasurfaces which support first-order Mie-type resonance in the near-IR regime. In the proposed structure, by adjusting the bias voltages applied to transparent graphene heaters, the crystallization levels of the phase change materials are controlled, which in turn modifies the response of the metasurface. The proposed metasurface is able to modulate the phase of the reflected wave in the range of 0° to −270° at the telecommunication wavelength of λ = 1.55 µm. A comprehensive Joule heating analysis is performed to investigate the thermal characterizations of the proposed structure. The results of this analysis show that there is a suitable thermal isolation between adjacent unit cells, making individual control on unit cells possible. The potential ability of the proposed metasurface as a beam steering device is also demonstrated. By using the proposed unit cells, a beam-steering device is designed and numerically studied. This study shows that the device can reflect a light normally incident on it in the range of ±65° with reasonably low sidelobe levels. The proposed structure can be used in developing low-cost integrated LiDARs.

Link:

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-23-33876&id=441947

Mr. Hadi Mohajerani successfully defended his Master’s thesis titled “Absorption Enhancement in Solar Cells using Traveling Wave Nano-Antennas” with excellent grade.