Broadband Light Harvesting Research Articles

An efficient broadband and omnidirectional light-harvesting scheme employing a hierarchical structure based on a ZnO nanorod/Si3N4-coated Si microgroove on 5-inch single crystalline Si solar cells

We employ a ZnO nanorod/Si(3)N(4)-coated Si microgroove-based hierarchical structure (HS) for a light-harvesting scheme in 5 inch single crystalline Si solar cells. ZnO nanorods and Si microgrooves were fabricated by a simple and scalable aqueous process. The excellent light-harvesting characteristics of the HS, such as broadband working ranges and omnidirectionality have been demonstrated using external quantum efficiencies and reflectance measurements. The solar cells with the hierarchical surface exhibit excellent photovoltaic characteristics, i.e., a short-circuit current (J(SC)) of 38.45 mA cm(-2), open-circuit voltage of 609 mV and conversion efficiency of 14.04%. As incident angles increase from 0° to 60°, only 5.3% J(SC) loss is achieved by employing the hierarchical surface, demonstrating the enhanced omnidirectional photovoltaic performances, also confirmed by the theoretical analysis. A viable scheme for broadband and omnidirectional light harvesting using the HS employing microscale/nanoscale surface textures on single crystalline Si solar cells has been demonstrated.

Panchromatic squaraine compounds for broad band light harvesting electronic devices

Squaraine compounds are currently investigated as high performance active components in both organic and hybrid photovoltaic devices as well as in photodetectors. Their most valuable features include a particularly efficient optical absorption in the Vis-NIR region, high polarizability, and a remarkable chemical stability. Their full exploitation is somewhat limited by a negligible absorption in the UV-Vis region (prototypical squaraines basically do not absorb below 500 nm). The aim of the present paper is the design and synthesis of truly panchromatic squaraines to be effectively employed as the photoactive materials in Vis operating optoelectronic devices. Our strategy involves the design of squaraines that are both nonsymmetric and core-substituted with suitable electron-withdrawing groups. We show the effect of such a design strategy by means of UV-Vis spectroscopy, cyclic voltammetry and prototypical device performances rationalization.

Periodic Si nanopillar arrays by anodic aluminum oxide template and catalytic etching for broadband and omnidirectional light harvesting

Large-area, periodic Si nanopillar arrays (NPAs) with the periodicity of 100 nm and the diameter of 60 nm were fabricated by metal-assisted chemical etching with anodic aluminum oxide as a patterning mask. The 100-nm-periodicity NPAs serve an antireflection function especially at the wavelengths of 200~400 nm, where the reflectance is decreased to be almost tenth of the value of the polished Si (from 62.9% to 7.9%). These NPAs show very low reflectance for broadband wavelengths and omnidirectional light incidence, attributed to the small periodicity and the stepped refractive index of NPA layers. The experimental results are confirmed by theoretical calculations. Raman scattering intensity was also found to be significantly increased with Si NPAs. The introduction of this industrial-scale self-assembly methodology for light

Enhanced omnidirectional photon coupling via quasi-periodic patterning of indium-tin-oxide for organic thin-film solar cells

Enhanced optical coupling via an indium tin oxide quasi-periodic structure (ITO-QPS) as the frontal electrode for organic thin film solar cells was demonstrated. The QPS was fabricated via scalable polystyrene colloidal lithography, which effectively coupled the incident light to the photo-active layer through antireflection and light-trapping mechanisms. The cell efficiency was boosted from 2.91% to 3.26%, corresponding to a 12% enhancement after ITO patterning. Moreover, the angle-resolved absorption spectroscopy also confirmed excellent light coupling at large angles of incidence to 45°, particularly in the wavelength range between 540 and 670 nm. The ITO-QPS guarantees broadband and omnidirectional light harvesting and is widely applicable to a variety of thin film solar cells.

Enhanced angular characteristics of indium tin oxide nanowhisker-coated silicon solar cells

Omnidirectional and broadband light harvesting is critical to photovoltaics due to the sun's movement and its wide spectral range of radiation. In this work, we demonstrate distinctive indium-tin-oxide nanowhiskers that achieve superior angular and spectral characteristics for crystalline silicon solar cells using angle-resolved reflectance spectroscopy. The solar-spectrum weighted reflectance is well below 6% for incident angles of up to 70° and for the wavelength range between 400nm and 1000nm. As a result, the nanowhisker coated solar cell exhibits broadband quantum efficiency characteristics and enhanced short-circuit currents for large angles of incidence.

Broadband plasmonic device concentrating the energy at the nanoscale: The crescent-shaped cylinder

A new strategy has been proposed recently to design broadband plasmonic nanostructures capable of a significant nanofocusing of light. Applying a singular conformal transformation to a thin slab of metal, a cylinder with a crescent-shaped cross section is obtained. In this study, the corresponding theory is derived analytically and different physical insights are provided to analyze the broadband light harvesting and nanofocusing properties of this device. The optical response of the crescent is deduced by solving the metal-slab problem. The nanostructure is shown to exhibit a continuous absorption cross section which redshifts for thin crescents due to a decrease of the surface plasmon velocity. The field enhancement induced by the nanostructure is also derived analytically. The nanofocusing performance is shown to result from a balance between dissipation losses and surface-plasmons velocity. This implies a strong dependence of the field enhancement on the frequency and the crescent geometry. Numerical simulations have also been performed to investigate the effect of radiative losses when the structure dimension becomes comparable to the wavelength. Radiative damping makes the absorption cross section saturate at the level of the physical cross section. The field enhancement decreases with the size of the device. The crescent structure is shown to be quite robust to radiation losses, which opens perspectives for applications such as single-molecule detection.

Manipulating Nanoscale Light Fields with the Asymmetric Bowtie Nano-Colorsorter

We present a class of devices called Asymmetric Bowtie nano-Colorsorters. These devices are specifically engineered to not only capture and confine optical fields, but also to spectrally filter and steer them while maintaining nanoscale field distributions. We show that spectral properties and localized spatial mode distributions can be readily tuned by controlled asymmetry. Nano-Colorsorters can control light's spatial and spectral distributions at the nanoscale and thus significantly impact applications ranging from broadband light harvesting to ultrafast wavelength-selective photodetection.