Editorial

3 pages, 170 KiB

Open AccessEditorial

Special Issue: “Thin Films for Energy Harvesting, Conversion, and Storage”

by Zhong Chen, Xin Zhao and Yuxin Tang

Coatings 2019, 9(10), 608; https://doi.org/10.3390/coatings9100608 - 25 Sep 2019

Cited by 2 | Viewed by 1729

Efficient clean energy harvesting, conversion, and storage technologies are of immense importance for the sustainable development of human society. To this end, scientists have made significant advances in recent years regarding new materials and devices for improving the energy conversion efficiency for photovoltaics, [...] Read more.

Efficient clean energy harvesting, conversion, and storage technologies are of immense importance for the sustainable development of human society. To this end, scientists have made significant advances in recent years regarding new materials and devices for improving the energy conversion efficiency for photovoltaics, thermoelectric generation, photoelectrochemical/electrolytic hydrogen generation, and rechargeable metal ion batteries. The aim of this Special Issue is to provide a platform for research scientists and engineers in these areas to demonstrate and exchange their latest research findings. This thematic topic undoubtedly represents an extremely important technological direction, covering materials processing, characterization, simulation, and performance evaluation of thin films used in energy harvesting, conversion, and storage. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

Research

Jump to: Editorial, Review

10 pages, 2056 KiB

Open AccessArticle

Compositional and Morphological Changes in Water-Induced Early-Stage Degradation in Lead Halide Perovskites

by Shi Chen, Ankur Solanki, Jisheng Pan and Tze Chein Sum

Coatings 2019, 9(9), 535; https://doi.org/10.3390/coatings9090535 - 22 Aug 2019

Cited by 23 | Viewed by 5147

Abstract

With tremendous improvements in lead halide perovskite-based optoelectronic devices ranging from photovoltaics to light-emitting diodes, the instability problem stands as the primary challenge in their development. Among all factors, water is considered as one of the major culprits to the degradation of halide [...] Read more.

With tremendous improvements in lead halide perovskite-based optoelectronic devices ranging from photovoltaics to light-emitting diodes, the instability problem stands as the primary challenge in their development. Among all factors, water is considered as one of the major culprits to the degradation of halide perovskite materials. For example, CH₃NH₃PbI₃ (MAPbI₃) and CH(NH₂)₂PbI₃ (FAPbI₃) decompose into PbI₂ in days under ambient conditions. However, the intermediate changes of this degradation process are still not fully understood, especially the changes in early stage. Here we perform an in-situ investigation of the early-stage MAPbI₃ and FAPbI₃ degradation under high water vapor pressure. By probing the surface and bulk of perovskite samples using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and XRD, our findings clearly show that PbI₂ formation surprisingly initiates below the top surface or at grain boundaries, thus offering no protection as a water-blocking layer on surface or grain boundaries to slow down the degradation process. Meanwhile, significant morphological changes are observed in both samples after water vapor exposure. In comparison, the integrity of MAPbI₃ film degrades much faster than the FAPbI₃ film against water vapor. Pinholes and large voids are found in MAPbI₃ film while only small number of pinholes can be found in FAPbI₃ film. However, the FAPbI₃ film suffers from its phase instability, showing a fast α-to-δ phase transition. Our results highlight the importance of the compositional and morphological changes in the early stage degradation in perovskite materials. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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11 pages, 6063 KiB

Open AccessArticle

Tunable Perfect Narrow-Band Absorber Based on a Metal-Dielectric-Metal Structure

by Qiang Li, Zizheng Li, Xiangjun Xiang, Tongtong Wang, Haigui Yang, Xiaoyi Wang, Yan Gong and Jinsong Gao

Coatings 2019, 9(6), 393; https://doi.org/10.3390/coatings9060393 - 18 Jun 2019

Cited by 21 | Viewed by 4353

Abstract

In this paper, a metal-dielectric-metal structure based on a Fabry–Perot cavity was proposed, which can provide near 100% perfect narrow-band absorption. The lossy ultrathin silver film was used as the top layer spaced by a lossless silicon oxide layer from the bottom silver [...] Read more.

In this paper, a metal-dielectric-metal structure based on a Fabry–Perot cavity was proposed, which can provide near 100% perfect narrow-band absorption. The lossy ultrathin silver film was used as the top layer spaced by a lossless silicon oxide layer from the bottom silver mirror. We demonstrated a narrow bandwidth of 20 nm with 99.37% maximum absorption and the absorption peaks can be tuned by altering the thickness of the middle SiO₂ layer. In addition, we established a deep understanding of the physics mechanism, which provides a new perspective in designing such a narrow-band perfect absorber. The proposed absorber can be easily fabricated by the mature thin film technology independent of any nano structure, which make it an appropriate candidate for photodetectors, sensing, and spectroscopy. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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12 pages, 2306 KiB

Open AccessArticle

Ultrathin Al₂O₃ Coating on LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material for Enhanced Cycleability at Extended Voltage Ranges

by Wenchang Zhu, Xue Huang, Tingting Liu, Zhiqiang Xie, Ying Wang, Kai Tian, Liangming Bu, Haibo Wang, Lijun Gao and Jianqing Zhao

Coatings 2019, 9(2), 92; https://doi.org/10.3390/coatings9020092 - 03 Feb 2019

Cited by 104 | Viewed by 9469

Abstract

Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ oxide has been modified by ultrathin Al₂O₃ coatings via atomic layer deposition (ALD) at a growth rate of 1.12 Å/cycle. All characterizations results including TEM, SEM, XRD and XPS together confirm [...] Read more.

Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ oxide has been modified by ultrathin Al₂O₃ coatings via atomic layer deposition (ALD) at a growth rate of 1.12 Å/cycle. All characterizations results including TEM, SEM, XRD and XPS together confirm high conformality and uniformity of the resultant Al₂O₃ layer on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ particles. Coating thickness of the Al₂O₃ layer is optimized at ~2 nm, corresponding to 20 ALD cycles to enhance the electrochemical performance of Ni-rich cathode materials at extended voltage ranges. As a result, 20 Al₂O₃ ALD-coated LiNi_0.8Co_0.1Mn_0.1O₂ cathode material can deliver an initial discharge capacity of 212.8 mAh/g, and an associated coulombic efficiency of 84.0% at 0.1 C in a broad voltage range of 2.7–4.6 V vs. Li⁺/Li in the first cycle, which were both higher than 198.2 mAh/g and 76.1% of the pristine LiNi_0.8Co_0.1Mn_0.1O₂ without the Al₂O₃ protection. Comparative differential capacity (dQ/dV) profiles and electrochemical impedance spectra (EIS) recorded in the first and 100th cycles indicated significant Al₂O₃ ALD coating effects on suppressing phase transitions and electrochemical polarity of the Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ core during reversible lithiation/delithiation. This work offers oxide-based surface modifications with precise thickness control at an atomic level for enhanced electrochemical performance of Ni-rich cathode materials at extended voltage ranges. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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10 pages, 2643 KiB

Open AccessArticle

Rational Construction of LaFeO₃ Perovskite Nanoparticle-Modified TiO₂ Nanotube Arrays for Visible-Light Driven Photocatalytic Activity

by Jiangdong Yu, Siwan Xiang, Mingzheng Ge, Zeyang Zhang, Jianying Huang, Yuxin Tang, Lan Sun, Changjian Lin and Yuekun Lai

Coatings 2018, 8(11), 374; https://doi.org/10.3390/coatings8110374 - 23 Oct 2018

Cited by 19 | Viewed by 4014

Abstract

LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays were fabricated through facile hydrothermal growth. The absorption edge of LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays displaying a red shift to ~540 nm was indicated by the results of diffuse reflectance spectroscopy (DRS) when compared [...] Read more.

LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays were fabricated through facile hydrothermal growth. The absorption edge of LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays displaying a red shift to ~540 nm was indicated by the results of diffuse reflectance spectroscopy (DRS) when compared to TiO₂ nanotube arrays, which means that the sample of LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays had enhanced visible light response. Photoluminescence (PL) spectra showed that the LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays efficiently separated the photoinduced electron–hole pairs and effectively prolonged the endurance of photogenerated carriers. The results of methylene blue (MB) degeneration under simulated visible light illumination showed that the photocatalytic activity of LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays is obviously increased. LaFeO₃ nanoparticle-modified TiO₂ nanotube arrays with 12 h hydrothermal reaction time showed the highest degradation rate with a 2-fold enhancement compared with that of pristine TiO₂ nanotube arrays. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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12 pages, 3365 KiB

Open AccessArticle

Mixed Nickel-Cobalt-Molybdenum Metal Oxide Nanosheet Arrays for Hybrid Supercapacitor Applications

by Yin She, Bin Tang, Dongling Li, Xiaosheng Tang, Jing Qiu, Zhengguo Shang and Wei Hu

Coatings 2018, 8(10), 340; https://doi.org/10.3390/coatings8100340 - 25 Sep 2018

Cited by 39 | Viewed by 4648

Abstract

Mixed metal oxide nanomaterials have been demonstrated to be promising positive electrodes for energy storage applications because of the synergistic enhancement effects. In this work, nickel-cobalt-molybdenum metal oxide (NCMO) nanosheets with hierarchical, porous structures were directly developed on nickel foam (NF) through a [...] Read more.

Mixed metal oxide nanomaterials have been demonstrated to be promising positive electrodes for energy storage applications because of the synergistic enhancement effects. In this work, nickel-cobalt-molybdenum metal oxide (NCMO) nanosheets with hierarchical, porous structures were directly developed on nickel foam (NF) through a hydrothermal method and ensuing annealing treatment. Electrochemical tests in three-electrode configurations revealed that the as-prepared NCMO nanosheets possessed high specific capacitance (1366 F g⁻¹ at the current density of 2 A g⁻¹), good rate capability (71.3% at the current density of 40 A g⁻¹), as well as excellent cycling stability (89.75% retention after 5000 cycles). Additionally, a hybrid supercapacitor was assembled and achieved an energy density of 46.2 Wh kg⁻¹ at a power density of 713 W kg⁻¹. Based on the systematic analysis of microstructure, morphology, and element compositions, the excellent electrochemical performance of the NCMO nanosheets could be attributed to the mesoporous feature, desirable compositions, excellent mechanical and electrical contacts, and fast ion/electron transportation rates. This study shows that the NCMO nanosheets offer great potentials for application in supercapacitors. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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Graphical abstract

9 pages, 1947 KiB

Open AccessArticle

Influence of Ge Incorporation from GeSe₂ Vapor on the Properties of Cu₂ZnSn(S,Se)₄ Material and Solar Cells

by Chao Gao, Yali Sun and Wei Yu

Coatings 2018, 8(9), 304; https://doi.org/10.3390/coatings8090304 - 28 Aug 2018

Cited by 6 | Viewed by 3671

Abstract

Cu₂ZnSn(S,Se)₄ (CZTSSe) and Cu₂Zn(Sn,Ge)(S,Se)₄ (CZTGSSe) thin films were prepared based on a non-vacuum solution method. The CZTSSe films were obtained by annealing the solution-deposited precursor films with Se, while the CZTGSSe films were obtained by annealing the [...] Read more.

Cu₂ZnSn(S,Se)₄ (CZTSSe) and Cu₂Zn(Sn,Ge)(S,Se)₄ (CZTGSSe) thin films were prepared based on a non-vacuum solution method. The CZTSSe films were obtained by annealing the solution-deposited precursor films with Se, while the CZTGSSe films were obtained by annealing the similar precursor films with Se and GeSe₂. We found that Ge could be incorporated into the annealed films when GeSe₂ was present during the annealing process. The Ge incorporation obviously enlarged the sizes of the crystalline grains in the annealed films. However, the energy dispersive spectrometry (EDS) measurements revealed that the element distribution was not uniform in the CZTGSSe films. We fabricated solar cells based on the CZTSSe and CZTGSSe films. It was found the Ge incorporation decreases the E_u energy of the absorber material. The solar cell efficiency was increased from 5.61% (CZTSSe solar cell) to 7.14% (CZTGSSe solar cell) by the Ge incorporation. Compared to CZTSSe solar cells, the CZTGSSe solar cells exhibited a lower diode ideality factor and lower reverse saturation current density. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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20 pages, 10512 KiB

Open AccessArticle

Electrochemical Performance of Few-Layer Graphene Nano-Flake Supercapacitors Prepared by the Vacuum Kinetic Spray Method

by Mohaned Mohammed Mahmoud Mohammed and Doo-Man Chun

Coatings 2018, 8(9), 302; https://doi.org/10.3390/coatings8090302 - 27 Aug 2018

Cited by 25 | Viewed by 5689

Abstract

A few-layer graphene nano-flake thin film was prepared by an affordable vacuum kinetic spray method at room temperature and modest low vacuum conditions. In this economical approach, graphite microparticles, a few layers thick, are deposited on a stainless-steel substrate to form few-layer graphene [...] Read more.

A few-layer graphene nano-flake thin film was prepared by an affordable vacuum kinetic spray method at room temperature and modest low vacuum conditions. In this economical approach, graphite microparticles, a few layers thick, are deposited on a stainless-steel substrate to form few-layer graphene nano-flakes using a nanoparticle deposition system (NPDS). The NPDS allows for a large area deposition at a low cost and can deposit various metal oxides at room temperature and low vacuum conditions. The morphology and structure of the deposited thin films are alterable by changing the scan speed of the deposition. These changes were verified by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The electrochemical performances of the supercapacitors, fabricated using the deposited films and H₃PO₄–PVA gel electrolytes with different concentrations, were measured using a 2-electrode cell. The electrochemical performance was evaluated by cyclic voltammetry, galvanostatic Charge–discharge, and electrochemical impedance spectroscopy. The proposed affordable fabricated supercapacitors show a high areal capacitance and a small equivalent series resistance. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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18 pages, 3924 KiB

Open AccessArticle

Effect of Sensitization on the Electrochemical Properties of Nanostructured NiO

by Matteo Bonomo, Daniele Gatti, Claudia Barolo and Danilo Dini

Coatings 2018, 8(7), 232; https://doi.org/10.3390/coatings8070232 - 29 Jun 2018

Cited by 6 | Viewed by 4291

Abstract

Screen-printed NiO electrodes were sensitized with 11 different dyes and the respective electrochemical properties were analyzed in a three-electrode cell with the techniques of cyclic voltammetry and electrochemical impedance spectroscopy. The dye sensitizers of NiO were organic molecules of different types (e.g., squaraines, [...] Read more.

Screen-printed NiO electrodes were sensitized with 11 different dyes and the respective electrochemical properties were analyzed in a three-electrode cell with the techniques of cyclic voltammetry and electrochemical impedance spectroscopy. The dye sensitizers of NiO were organic molecules of different types (e.g., squaraines, coumarins, and derivatives of triphenyl-amines and erythrosine B), which were previously employed as sensitizers of the same oxide in dye-sensitized solar cells of p-type (p-DSCs). Depending on the nature of the sensitizer, diverse types of interactions occurred between the immobilized sensitizer and the screen-printed NiO electrode at rest and under polarization. The impedance data recorded at open circuit potential were interpreted in terms of two different equivalent circuits, depending on the eventual presence of the dye sensitizer on the mesoporous electrode. The fitting parameter of the charge transfer resistance through the electrode/electrolyte interface varied in accordance to the differences of the passivation action exerted by the various dyes against the electrochemical oxidation of NiO. Moreover, it has been observed that the resistive term R_CT associated with the process of dark electron transfer between the dye and NiO substrate is strictly correlated to the overall efficiency of the photoconversion (η) of the corresponding p-DSC, which employs the same dye-sensitized electrode as photocathode. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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8 pages, 3479 KiB

Open AccessArticle

A DFT-Based Model on the Adsorption Behavior of H₂O, H⁺, Cl⁻, and OH⁻ on Clean and Cr-Doped Fe(110) Planes

by Jun Hu, Chaoming Wang, Shijun He, Jianbo Zhu, Liping Wei and Shunli Zheng

Coatings 2018, 8(2), 51; https://doi.org/10.3390/coatings8020051 - 29 Jan 2018

Cited by 10 | Viewed by 4541

Abstract

The impact of four typical adsorbates, namely H₂O, H⁺, Cl⁻, and OH⁻, on three different planes, namely, Fe(110), Cr(110) and Cr-doped Fe(110), was investigated by using a density functional theory (DFT)-based model. It is verified [...] Read more.

The impact of four typical adsorbates, namely H₂O, H⁺, Cl⁻, and OH⁻, on three different planes, namely, Fe(110), Cr(110) and Cr-doped Fe(110), was investigated by using a density functional theory (DFT)-based model. It is verified by the adsorption mechanism of the abovementioned four adsorbates that the Cr-doped Fe(110) plane is the most stable facet out of the three. As confirmed by the adsorption energy and electronic structure, Cr doping will greatly enhance the electron donor ability of neighboring Fe atoms, which in turn prompts the adsorption of the positively charged H⁺. Meanwhile, the affinity of Cr to negatively charged adsorbates (e.g., Cl⁻ and O of H₂O, OH⁻) is improved due to the weakening of its electron donor ability. On the other hand, the strong bond between surface atoms and the adsorbates can also weaken the bond between metal atoms, which results in a structure deformation and charge redistribution among the native crystal structure. In this way, the crystal becomes more vulnerable to corrosion. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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Review

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19 pages, 9237 KiB

Open AccessFeature PaperReview

Strategies of Anode Materials Design towards Improved Photoelectrochemical Water Splitting Efficiency

by Jun Hu, Shuo Zhao, Xin Zhao and Zhong Chen

Coatings 2019, 9(5), 309; https://doi.org/10.3390/coatings9050309 - 09 May 2019

Cited by 13 | Viewed by 5435

Abstract

This review presents the latest processes for designing anode materials to improve the efficiency of water photolysis. Based on different contributions towards the solar-to-hydrogen efficiency, we mainly review the strategies to enhance the light absorption, facilitate the charge separation, and enhance the surface [...] Read more.

This review presents the latest processes for designing anode materials to improve the efficiency of water photolysis. Based on different contributions towards the solar-to-hydrogen efficiency, we mainly review the strategies to enhance the light absorption, facilitate the charge separation, and enhance the surface charge injection. Although great achievements have been obtained, the challenges faced in the development of anode materials for solar energy to make water splitting remain significant. In this review, the major challenges to improve the conversion efficiency of photoelectrochemical water splitting reactions are presented. We hope that this review helps researchers in or coming to the field to better appreciate the state-of-the-art, and to make a better choice when they embark on new research in photocatalytic water splitting. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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29 pages, 6451 KiB

Open AccessReview

Recent Studies of Semitransparent Solar Cells

by Dong Hee Shin and Suk-Ho Choi

Coatings 2018, 8(10), 329; https://doi.org/10.3390/coatings8100329 - 20 Sep 2018

Cited by 39 | Viewed by 6537

Abstract

It is necessary to develop semitransparent photovoltaic cell for increasing the energy density from sunlight, useful for harvesting solar energy through the windows and roofs of buildings and vehicles. Current semitransparent photovoltaics are mostly based on Si, but it is difficult to adjust [...] Read more.

It is necessary to develop semitransparent photovoltaic cell for increasing the energy density from sunlight, useful for harvesting solar energy through the windows and roofs of buildings and vehicles. Current semitransparent photovoltaics are mostly based on Si, but it is difficult to adjust the color transmitted through Si cells intrinsically for enhancing the visual comfort for human. Recent intensive studies on translucent polymer- and perovskite-based photovoltaic cells offer considerable opportunities to escape from Si-oriented photovoltaics because their electrical and optical properties can be easily controlled by adjusting the material composition. Here, we review recent progress in materials fabrication, design of cell structure, and device engineering/characterization for high-performance/semitransparent organic and perovskite solar cells, and discuss major problems to overcome for commercialization of these solar cells. Full article

(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)

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