Photonic front-coatings with self-cleaning properties are presented as means to enhance the efficiency and outdoor performance of thin-film solar cells, via optical enhancement while simultaneously minimizing soiling-related losses. This was achieved by structuring parylene-C transparent encapsulants using a low-cost and highly-scalable colloidal-lithography methodology. As a result, superhydrophobic surfaces with broadband light-trapping properties were developed. The optimized parylene coatings show remarkably high water contact angles of up to 165.6° and extremely low adhesion, allowing effective surface self-cleaning.The controlled nano/micro-structuring of the surface features also generates strong anti-reflection and light scattering effects, corroborated by numeric electromagnetic modeling, which lead to pronounced photocurrent enhancement along the UV-Visible-Infrared range. The impact of these photonic-structured encapsulants is demonstrated on nanocrystalline silicon solar cells, that show short-circuit current density gains of up to 23.6%, relative to planar reference cells. Furthermore, the improvement of the devices' angular response enables an enhancement of up to 35.2% in the average daily power generation.
In recent years, the discovery of the excellent optical and electrical properties of perovskite solar cells (PSCs) made them a main focus of research in photovoltaics, with efficiency records increasing astonishingly fast since their inception. However, problems associated with the stability of these devices are hindering their market application. UV degradation is one of the most severe issues, chiefly caused by TiO2's photo-generated electrons that decompose the perovskite absorber material, coupled with the additional intrinsic degradation of this material under UV exposure. The solution presented here can minimize this effect while boosting the cells' generated photocurrent, by making use of combined light-trapping and luminescent downshifting effects capable of changing the harmful UV radiation to higher wavelengths that do not affect the stability and can be effectively "trapped" in the cell. This work focuses in the optimization of the photocurrent gains that can be attained by emulating the changed spectrum resulting from applying down-shifting media as encapsulant in photonic-enhanced PSCs, as well as the reduction in the harmful effects of UV radiation on the devices. Such optimized photonic solution allows current enhancement while reducing the harmful UV photo-carrier generation both in the TiO2 (by one order of magnitude) and in the perovskite (by 80%) relative to a standard PSC without light management.
Combined perovskite/crystalline-silicon 4-Terminal tandem solar cells promise >30% efficiencies. Here we propose all-thin-film double-junction architectures where high-bandgap perovskite top cells are coupled to ultra-thin c-Si bottom cells enhanced with light-trapping. A complete optoelectronic model of the devices was developed and applied to determine the optimal intermediate layers, which are paramount to maximize the cells' photocurrent. It was ascertained that, by replacing the transparent conductive oxides by grid-based metallic contacts in the intermediate positions, the parasitic absorption is lowered by 30%. Overall, a 29.2% efficiency is determined for ~2um thick tandems composed of the optimized interlayers and improved with Lambertian light-trapping.
The study shows the incorporation of chiral nematic photonic cellulose nanocrystal (CNC) films, well known for their adaptive character of selective reflection of circular polarized light (CPL), and silicon‐based thin‐film photodiodes, thus achieving a light sensor capable of discriminating right‐ from left‐handed CPL. The circular polarization (CP) response is maximum for specific wavelengths in the green‐to‐red region. When subjected to these wavelengths, they produce photocurrents that are over 50% distinct between the two CP states. Proper signal processing, thus, yields a binary output depending on the handedness of the light. Through the addition of monovalent salt to the initial CNC suspension, a blueshift to the photonic band gap is induced, enabling a larger wavelength gamut and application possibilities. The measured results are then used as a basis for electromagnetic simulations that show remarkable consistency with the experimental results, thus defining a new tool that can be used to efficiently optimize the devices’ response. Fast transient responses to CPL are shown with possible logic operations, as well as humidity sensing. The developed devices are, thus, applicable in areas as diverse as imaging, CPL sensing, optoelectronic counterfeiting, and information processing with logic states that depend solely on the handedness of the incident light.
In this work, a simple and innovative method is proposed to get an active glassy carbon electrode (GC) toward nitrite oxidation. The oxidation method was based on an anodic treatment, through a time-and potential-controlled electrolysis, in NaOH 0.1 M. This treatment increased the activity in all pH values that were studied, being the pH 8.0 as the best one. It was possible to calculate the kinetic parameters, where the number of transferred electrons calculated was one, and Tafel slope was 70 mV per decade. With these values, a reaction mechanism was postulated. At the best experimental conditions, the electrode has a good behavior as an amperometric sensor versus nitrite oxidation. The system follows linearity in all the range of concentrations and allowed the calculation of analytical parameters such as detection limit, quantification limit, accuracy, and exactitude. Good results were obtained at this point, so the system might be considered a good method for nitrite determination and quantification in aqueous solutions.
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