Large Absorption Enhancement in Ultrathin Solar Cells Patterned by Metallic Nanocavity Arrays

Improving the Efficiency of Bulk-heterojunction Solar Cells through Plasmonic Enhancement within a Silver Nanoparticle-Loaded Optical Spacer Layer

We investigate the enhancement in the efficiency of organic bulk heterojunction solar cells enabled by plasmonic excitation of Ag nanoparticles (NPs) of different diameters (10, 20, and 30 nm), randomly incorporated within an optical spacing layer of TiO2 placed between the organic medium and the Ag cathode. Such structures significantly increase the optical absorption and the photocurrent within the device system, leading to a power conversion efficiency of more than 4%, over 2.5 times that of the control bulk heterojunction cell. This corresponds to a 61% increase in J SC and a 6.3% in fill factor. 3D Finite-difference time-domain simulations were utilized to investigate the plasmonic field coupling within the nanogap medium of TiO2. They show that coupling between the Ag nanoparticle and the Ag thin film cathode extends the wavelength range of the local field enhancement beyond that obtained for isolated NPs, providing a better overlap with the absorption spectrum of the organic medium.

Gas Sensors Based on Localized Surface Plasmon Resonances: Synthesis of Oxide Films with Embedded Metal Nanoparticles, Theory and Simulation, and Sensitivity Enhancement Strategies

This work presents a comprehensive review on gas sensors based on localized surface plasmon resonance (LSPR) phenomenon, including the theory of LSPR, the synthesis of nanoparticle-embedded oxide thin films, and strategies to enhance the sensitivity of these optical sensors, supported by simulations of the electromagnetic properties. The LSPR phenomenon is known to be responsible for the unique colour effects observed in the ancient Roman Lycurgus Cup and at the windows of the medieval cathedrals. In both cases, the optical effects result from the interaction of the visible light (scattering and absorption) with the conduction band electrons of noble metal nanoparticles (gold, silver, and gold–silver alloys). These nanoparticles are dispersed in a dielectric matrix with a relatively high refractive index in order to push the resonance to the visible spectral range. At the same time, they have to be located at the surface to make LSPR sensitive to changes in the local dielectric environment, the property that is very attractive for sensing applications. Hence, an overview of gas sensors is presented, including electronic-nose systems, followed by a description of the surface plasmons that arise in noble metal thin films and nanoparticles. Afterwards, metal oxides are explored as robust and sensitive materials to host nanoparticles, followed by preparation methods of nanocomposite plasmonic thin films with sustainable techniques. Finally, several optical properties simulation methods are described, and the optical LSPR sensitivity of gold nanoparticles with different shapes, sensing volumes, and surroundings is calculated using the discrete dipole approximation method.

Enhancement in photocurrent by dual-interface period-mismatched rotating rectangle grating-based c-Si solar cells

A dual-interface period-mismatched rotating rectangular grating structure was designed for crystalline silicon thin film solar cells. The relevant parameters of the grating structures were optimized, and the absorption enhancement mechanisms were also explained by optoelectronic simulation analysis. The numerical results show that the rotating rectangular structure can improve the light-trapping performance by coupling light into the c-Si film to excite the waveguide mode and localized surface plasmon resonances. Moreover, it is found that the light-trapping effect of the rear grating rotating structure is better than that of the front grating rotating structure, because the rear interface can better excite localized surface plasmon resonances. The photocurrent density of the dual-interface period-mismatched rotating rectangular grating structure is increased to $18.01\; {\rm mA/cm}^2$, which is 76.05% higher than that of the planar 300 nm thick c-Si structure. The research results provide general guidance for the design of grating structures for thin-film solar cells.

Photonic-Plasmonic Nanostructures for Solar Energy Utilization and Emerging Biosensors

Issues related to global energy and environment as well as health crisis are currently some of the greatest challenges faced by humanity, which compel us to develop new pollution-free and sustainable energy sources, as well as next-generation biodiagnostic solutions. Optical functional nanostructures that manipulate and confine light on a nanometer scale have recently emerged as leading candidates for a wide range of applications in solar energy conversion and biosensing. In this review, recent research progress in the development of photonic and plasmonic nanostructures for various applications in solar energy conversion, such as photovoltaics, photothermal conversion, and photocatalysis, is highlighted. Furthermore, the combination of photonic and plasmonic nanostructures for developing high-efficiency solar energy conversion systems is explored and discussed. We also discuss recent applications of photonic-plasmonic-based biosensors in the rapid management of infectious diseases at point-of-care as well as terahertz biosensing and imaging for improving global health. Finally, we discuss the current challenges and future prospects associated with the existing solar energy conversion and biosensing systems.

3D structured materials and devices for artificial photosynthesis

Artificial photosynthesis is an effective way to convert solar energy into fuels, which is of great significance to energy production and reduction of atmospheric CO₂ content. In recent years, 3D structured artificial photosynthetic system has made great progress as an effective design strategy. This review first highlights several typical mechanisms for improved artificial photosynthesis with 3D structures: improved light harvesting, mass transfer and charge separation. Then, we summarize typical examples of 3D structured artificial photosynthetic systems, including bioinspired structures, photonic crystals (PC), designed photonic structures (PC coupling structure, plasmon resonance structure, optical resonance structure, metamaterials), 3D-printed systems, nanowire integrated systems and hierarchical 3D structures. Finally, we discuss the problems and challenges to the application and development of 3D artificial photosynthetic system and the possible trends of future development. We hope this review can inspire more progress in the field of artificial photosynthesis.

Light-trapping schemes for silicon thin-film solar cells via super-quadratic subwavelength gratings

We systematically investigate the light-trapping schemes of crystalline silicon thin-film solar cells (TFSCs) for three common grating layouts via one-dimensional super-quadratic subwavelength gratings. The effects of antireflective coating, absorber layer thickness, and grating geometry on the light-trapping performance of TFSCs are numerically studied using the finite-difference time-domain method. The results suggest that the conformal aluminum-doped zinc oxide (AZO) coatings have better optical properties than the plane AZO coatings. For the case of only top Si gratings, the grating geometry of degree $n={4}$n=4 can achieve a good trade-off between the shape-dependent light-trapping and antireflection properties, showing the best light-trapping effect; for the case of only bottom Ag gratings, the optical performance of TFSCs is significantly degraded as the degree $n$n increases from $n={1}$n=1 to $n\to\infty$n→∞. The above findings are analyzed and demonstrated in detail from the optical and electrical perspectives, and they can be utilized to guide the design of light-trapping structures for TFSCs.

Cavity-induced hybrid plasmon excitation for perfect infrared absorption

Photonic microcavity coupling of a subwavelength hole-disk array, a two-element metal/dielectric composite structure with enhanced extraordinary transmission, leads to 100% coupling of incident light to the cavity system and subsequent absorption. This light-funneling process arises from the temporal and spatial coupling of the broadband localized surface plasmon resonance on the coupled hole-disk array and the photonic modes of the optical cavity, which induces spectral narrowing of the perfect absorption of light. A simple nanoimprint lithography-based large-area fabrication process paves the path towards practical implementation of plasmonic cavity-based devices and sensors.

Enhanced efficiency of crystalline Si solar cells based on kerfless-thin wafers with nanohole arrays

Several techniques have been proposed for kerfless wafering of thin Si wafers, which is one of the most essential techniques for reducing Si material loss in conventional wafering methods to lower cell cost. Proton induced exfoliation is one of promising kerfless techniques due to the simplicity of the process of implantation and cleaving. However, for application to high efficiency solar cells, it is necessary to cope with some problems such as implantation damage removal and texturing of (111) oriented wafers. This study analyzes the end-of-range defects at both kerfless and donor wafers and ion cutting sites. Thermal treatment and isotropic etching processes allow nearly complete removal of implantation damages in the cleaved-thin wafers. Combining laser interference lithography and a reactive ion etch process, a facile nanoscale texturing process for the kerfless thin wafers of a (111) crystal orientation has been developed. We demonstrate that the introduction of nanohole array textures with an optimal design and complete damage removal lead to an improved efficiency of 15.2% based on the kerfless wafer of a 48 μm thickness using the standard architecture of the Al back surface field.