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Photovoltaic solar cells have been extensively used for various applications and are considered one of the most efficient green energy sources. However, their 2D surface area solar harvesting has limitations, and there is an increasing need to explore the possibility of multiple layer solar harvest for enhanced energy density. To address this, we have developed spectral-selective transparent thin films based on porphyrin and iron oxide compounds that allow solar light to penetrate multiple layers, significantly increasing solar harvesting surface area and energy density. These thin films are designed as photovoltaic (PV) and photothermal (PT) panels that can convert photons into either electricity or thermal energy for various green energy applications, such as smart building skins and solar desalination. The advantages of this 3D solar harvesting system include enlarged solar light collecting surface area and increased energy density. The multilayer system transforms the current 2D to 3D solar harvesting, enabling efficient energy generation. This review discusses recent developments in the synthesis and characterization of PV and PT transparent thin films for solar harvesting and energy generation using multilayers. Major applications of the 3D solar harvesting system are reviewed, including thermal energy generation, multilayered DSSC PV system, and solar desalination. Some preliminary data on transparent multilayer DSSC PVs are presented. 

A Cold Atmospheric Plasma (CAP) apparatus was designed and developed for SARS-CoV-2 killing as evaluated by pseudotyped viral infectivity assays. The reactive species generated by the plasma system was fully characterized by using Optical Emission Spectroscopy (OES) measurement under given conditions such as plasma power, flow rate, and treatment time. A variety of reactive oxygen species (ROS) and reactive nitrogen species (RNS) were identified from plasma plume with energies of 15–72 eV in the frequency range between 500–1000 nm. Systematic virus killing experiments were carried out, and the efficacy of CAP treatment in reducing SARS-CoV-2 viral infectivity was significant following treatment for 8 s, with further enhancement of killing upon longer exposures of 15–120 s. We correlated killing efficacy with the reactive species in terms of type, intensity, energy, and frequency. These experimental results demonstrate effective cold plasma virus killing via ROS and RNS under ambient conditions. 

The effects of dipole interactions on magnetic nanoparticle magnetization and relaxation dynamics were investigated using five nanoparticle (NP) systems with different surfactants, carrier liquids, size distributions, inter-particle spacing, and NP confinement. Dipole interactions were found to play a crucial role in modifying the blocking temperature behavior of the superparamagnetic nanoparticles, where stronger interactions were found to increase the blocking temperatures. Consequently, the blocking temperature of a densely packed nanoparticle system with stronger dipolar interactions was found to be substantially higher than those of the discrete nanoparticle systems. The frequencies of the dominant relaxation mechanisms were determined by magnetic susceptibility measurements in the frequency range of 100 Hz–7 GHz. The loss mechanisms were identified in terms of Brownian relaxation (1 kHz–10 kHz) and gyromagnetic resonance of Fe3O4 (~1.12 GHz). It was observed that the microwave absorption of the Fe3O4 nanoparticles depend on the local environment surrounding the NPs, as well as the long-range dipole–dipole interactions. These significant findings will be profoundly important in magnetic hyperthermia medical therapeutics and energy applications. 

The US highway system features a huge flux of energy transportation in terms of weight, speed, volume, flow density, and noise levels, with accompanying environmental effects. The adverse effects of high-volume traffic cause health concerns for nearby residential areas. Both chronic and acute exposure to PM 2.5 have detrimental effects on respiratory and cardiovascular health, and motor vehicles contribute 25–35% of direct PM 2.5 emissions. In addition to traffic-related pollutants, residing near major roadways is also associated with exposure to increased noise, and both affect the health and quality of life of residents. While regulatory and policy actions may reduce some exposures, engineering means may offer novel and significant methods to address these critical health and environmental issues. The goal of this study was to harvest highway-noise energy to induce surface charge via a piezoelectric material to entrap airborne particles, including PM 2.5. In this study, we experimentally investigated the piezoelectric effect of a polymethyl methacrylate (PMMA) sheet and ethylene propylene diene monomer (EPDM) rubber foam on the entrapment of copper (II)-2,4 pentanedione powder (Cu II powder). Appreciable voltages were induced on the surfaces of the PMMA via mechanical vibrations, leading to the effective entrapment of the Cu II powder. The EPDM rubber foam was found to attract a large amount of Cu II powder under simulated highway noise in a wide range, of 30–70 dB, and at frequencies of 700–1300 Hz, generated by using a loudspeaker. The amount of Cu II powder entrapped on the EPDM rubber-foam surfaces was found to scale with the SPL, but was independent of frequency. The experimental findings from this research provide a valuable base for the design of a robust piezoelectric system that is self-powered by harvesting the wasted sound energy from highway noise and reduces the amount of airborne particles over highways for effective environmental control. 

The temperature dependency of photovoltaic power conversion efficiency (PCE) has been a key challenge to solar applications due to intrinsic processes. Herein, an alternative strategy is developed by modulating the solar light spectrum with a series of photonic hybrids. Transparent thin films are synthesized with the solutions of porphyrin compounds and iron oxides which exhibit strong absorptions in the UV and IR regions. These spectral modulating thin films are photonically tuned via compositional optimization to absorb photons near 400 nm and above 1127 nm from solar spectrum to reduce thermalization and sub‐bandgap absorption. These spectral modulators are applied in a particular configuration above a commercial silicon panel to partially filter the simulated solar light. The PCE of the silicon panel suffers a significant decrease due to temperature increase from 22.9 to 92.9 °C after 60 min solar irradiation, resulting in a PCE decrease from 25.1% to 16.3%. With the transparent spectral modulators, upon solar irradiation for 60 min, the maximum PCE has maintained at 20.5%. The mechanisms of PCE enhancement are identified based on reduced thermalization and sub‐bandgap absorption.

 

To address critical energy issues in civic structures, we have developed a novel concept of optical thermal insulation (OTI) without relying on a conventional thermal intervention medium, such as air or argon, as often used in conventional window systems. We have synthesized the photothermal (PT) materials, such as the Fe 3 O 4 and Fe 3 O 4 @Cu 2− x S nanoparticles, that exhibit strong UV and near-infrared (NIR) absorptions but with good visible transparency. Upon coating the inner surface of the window glass with a PT film, under solar irradiation, the inner surface temperature rises due to the PT effect. Subsequently, the temperature difference, Δ T , is reduced between the single pane and room interior. This leads to lower the thermal loss through a window, reflected by the U -factor, resulting in considerable energy saving without double- or triple-glazing. Comparing with the Fe 3 O 4 coatings, Fe 3 O 4 @Cu 2− x S is spectrally characterized with a much stronger NIR absorbance, contributing to an increased PT efficiency under simulated solar irradiation (0.1 W/cm 2 ). PT experiments are carried out via both white light and monochromic NIR irradiations (785 nm). The parameters associated with the thermal performance of the PT films are calculated, including PT conversion efficiency, specific absorption rate (SAR), and U -factor. Based on the concept of OTI, we have reached an optimum U -factor of 1.46 W/m 2 K for a single pane, which is satisfactory to the DOE requirement (<1.7 W/m 2 K). 

One of the critical components of energy savings in buildings is thermal insulation, especially for windows in cold climates. The conventional approach mainly relies on a double-pane design. In this study, a new concept of “Green Window” has been designed for single-pane applications that lower the U-factor. The “Green Window” is structurally and simply composed of a thin film window coating of chlorophyll that exhibits pronounced photothermal effect, while remaining highly transparent. We demonstrate a new concept in “thermal insulation” via optical means instead of solely through thermal insulators or spectral selectivity. This concept lifts the dependence on insulating materials making single-pane window highly possible.