A fundamental challenge in energy sustainability is efficient utilization of solar energy towards energy‐neutral systems. The current solar cell technologies have been most widely employed to achieve this goal, but are limited to a single‐layer 2D surface. To harvest solar light more efficiently, a multilayer system capable of harvesting solar light in a cuboid through transparent photothermal thin films of iron oxide and a porphyrin compound is developed. Analogous to a multilayer capacitor, an array of transparent, spectral selective, photothermal thin films allows white light to penetrate them, not only collecting photon energy in a 3D space, but generating sufficient heat on each layer with significantly increased total surface area. In this fashion, thermal energy is generated via a multilayer photothermal system that functions as an efficient solar collector, energy converter and generator with high energy density. A solar‐activated thermal energy generator that can produce heat without any power supply and reach a maximum temperature of 76.1 °C is constructed. With a constant incoming white light (0.4 W cm−2), the thermal energy generated can be amplified 12‐fold via multilayers. The multilayer system extends another dimension in solar harvesting and paves a new path to energy generation for the energy‐neutral system.
3D Solar Harvesting and Energy Generation via Multilayers of Transparent Porphyrin and Iron Oxide Thin Films
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.
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- Award ID(s):
- 1953009
- NSF-PAR ID:
- 10407073
- Date Published:
- Journal Name:
- Energies
- Volume:
- 16
- Issue:
- 7
- ISSN:
- 1996-1073
- Page Range / eLocation ID:
- 3173
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
null (Ed.)The photothermal experiments on the incident light angle dependence are carried out using simulated solar light on thin films of both iron oxides (Fe3O4 and Fe3O4@Cu2-xS) and porphyrin compounds (chlorophyll and chlorophyllin). Fe3O4 and Fe3O4@Cu2-xS are synthesized using various solution methods that produce mono-dispersed nanoparticles on the order of 10 nm. Chlorophyll is extracted from fresh spinach and chlorophyllin sodium copper is a commercial product. These photothermal (PT) materials are dispersed in polymethyl methacrylate (PMMA) solutions and deposited on glass substrates via spin coating that result in clear and transparent thin films. The iron-oxide based thin films show distinctive absorption spectra; Fe3O4 exhibits a strong peak near UV and gradually decreases into the visible and NIR regions; the absorption of Fe3O4@Cu2-xS is similar in the UV region but shows a broad absorption in the NIR region. Both chlorophyll and chlorophyllin are characterized with absorption peaks near UV and NIR showing a “U”-shaped spectrum, ideally required for efficient solar harvest and high transparency in energy-efficient single-pane window applications. Upon coating of the transparent PT films on the window inner surfaces, solar irradiation induces the photothermal effect, consequently raising the film temperature. In this fashion, the thermal loss through the window can be significantly lowered by reducing the temperature difference between the window inner surface and the room interior, based on a new concept of so-called “optical thermal insulation” (OTI) without any intervention medium, such as air/argon, as required in the glazing technologies. Single-panes are therefore possible to replace double- or triple panes. As OTI is inevitably affected by seasonal and daily sunlight changes, an incident light angle dependence of the photothermal effect is crucial in both thin film and window designs. It is found that the heating curves reach their maxima at small angles of incidence while the photothermal effect is considerably reduced at large angles. This angle dependence is well explained by light reflection by the thin film surface, however, deviated from what is predicted by the Fresnel’s law, attributable to non-ideal surfaces of the substrates. The angle dependence data provides an important reference for OTI that window exposure to sun is greater at winter solstice while that is considerably reduced in the summer. This conclusion indicates much enhanced solar harvesting and heat conversion via optically insulated windows in the winter season, resulting in much lower U-factors.more » « less
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To address the critical issues in solar energy, the current research has focused on developing advanced solar harvesting materials that are low cost, lightweight, and environmentally friendly. Among many organic photovoltaics (PVs), the porphyrin compounds exhibit unique structural features that are responsible for strong ultraviolet (UV) and near infrared absorptions and high average visible transmittance, making them ideal candidates for solar-based energy applications. The porphyrin compounds have also been found to exhibit strong photothermal (PT) effects and recently applied for optical thermal insulation of building skins. These structural and optical properties of the porphyrin compounds enable them to function as a PT or a PV device upon sufficient solar harvesting. It is possible to develop a transparent porphyrin thin film with PT- and PV-dual-modality for converting sunlight to either electricity or thermal energy, which can be altered depending on energy consumption needs. A building skin can be engineered into an active device with the PT- and PV-dual modality for large-scale energy harvesting, saving, and generation. This review provides the current experimental results on the PT and PV properties of the porphyrin compounds such as chlorophyll and chlorophyllin. Their PT and PV mechanisms are discussed in correlations to their electronic structures. Also discussed are the synthesis routes, thin film deposition, and potential energy applications of the porphyrin compounds.more » « less
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Abstract Sunlight is one of the Earth's clean and sustainable natural energy resources, and extensive studies are conducted on the conversion of solar energy into electricity using photovoltaic (PV) devices. However, single‐junction PV devices cannot break the theoretical efficiency limit known as the Shockley–Queisser limit that is caused by the sub‐bandgap transmission and heat dissipation losses in semiconductors. Solar thermal conversion approaches may provide an alternative way to exceed this limit and enable more efficient use of solar light than that in PV devices. Recently, spectrally or thermally engineered metamaterials have attracted considerable attention for solar energy applications because of their excellent physical properties. The recent research progress in the development of these photothermal and thermoplasmonic metamaterials, along with their promising applications in solar thermophotovoltaics, radiative cooling, and solar desalination, is discussed.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/en16073173
