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16. Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

Author

Cai, Boyuan, Watanabe, Takashi, KAMIJO, Chikashi, SUNAHARA, Kohei, Susa, Masahiro, and Hayashi, Miyuki

Subjects
Materials science, Mechanical Engineering, Metallurgy, Metals and Alloys, 02 engineering and technology, engineering.material, 010403 inorganic & nuclear chemistry, 01 natural sciences, 020501 mining & metallurgy, 0104 chemical sciences, 0205 materials engineering, Mechanics of Materials, X-ray crystallography, Materials Chemistry, engineering, Wüstite
Published
2017
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21. Overcoming photovoltage deficit via natural amino acid passivation for efficient perovskite solar cells and modules.

Author

Hu, Jinlong, Xu, Xin, Chen, Yijun, Wu, Shaohang, Wang, Zhen, Wang, Yousheng, Jiang, Xiaofang, Cai, Boyuan, Shi, Tingting, Brabec, Christoph J., Mai, Yaohua, and Guo, Fei

Abstract

Electronic defects at grain boundaries and surfaces of perovskite crystals impair the photovoltaic performance and stability of solar devices. In this work, we report the compensation of photovoltage losses in blade-coated methylammonium lead triiodide (MAPbI3) devices via passivation with natural amino acid (NAA) molecules. We found that the optoelectronic properties of NAA-passivated perovskite films and the corresponding device performances are closely correlated with the molecular interaction strength. A side-by-side comparative study of four typical NAAs reveals that arginine (Arg) functionalized with a guanidine end group exhibits optimum passivation effects owing to the strongest coordinative bonding with the uncoordinated Pb2+, which markedly suppresses the detrimental antisite PbI deep level defects. As a result, nonradiative charge recombination is significantly reduced, resulting in a substantially increased open-circuit voltage (VOC) of 1.17 V and a high efficiency of 20.49%. A solar module with an active area of 10.08 cm2 is also fabricated, yielding an efficiency of 15.65% with negligible VOC losses. In parallel, the Arg-passivated solar devices exhibit enhanced operational stability due to the formation of a hydrophilic Arg protective layer which encapsulates the perovskite crystals. [ABSTRACT FROM AUTHOR]

Published
2021
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22. Ultra-broadband all-dielectric metamaterial thermal emitter for passive radiative cooling

Author

Cai Boyuan, Xiaocong Yuan, Peng Shi, and Kong Aru

Subjects
Materials science, Radiative cooling, business.industry, Infrared, Metamaterial, Atomic and Molecular Physics, and Optics, Optics, Thermal radiation, Thermal, Emissivity, Radiative transfer, Astrophysics::Earth and Planetary Astrophysics, business, Absorption (electromagnetic radiation)
Abstract

Passive radiative cooling, which pumps heat to outer space via thermal radiation, has been a promising energy free technology to maintain the earth surface temperature. Nighttime radiative cooling technology is quite mature, while daytime radiative cooling still poses many challenges due to the requirement of minimization of incident solar absorption and maximization of the mid-infrared emissivity in the atmospheric transparency windows. However, the mid-infrared emissivity efficiency of natural materials is usually poor, providing a low cooling efficiency and the realization of a high performance daytime radiative cooler is still quite challenge. In this work, we design and numerically investigate a three dimensional (3D) all-dielectric pyramidal multilayer metamaterial (PMM), which not only avoids the problem of high absorptivity loss of metal materials to solar, but also provide extremely high infrared absorptivity due to the attenuation effect of moth-eye structure and the electromagnetic resonant absorption in the metamaterial, achieving the purpose of both extremely low solar spectrum absorption and strong infrared emissivity within the atmospheric windows under the direct sunlight. Eventually, our designed cooler presents the potential to achieve a net radiative cooling power exceeding 156 W/m2 at ambient temperature of 300 K under direct solar irradiation, leading to a temperature reduction of 42.4°C. At nighttime, the net cooling power is more than 199 W/m2 at ambient temperature, resulting in a temperature reduction of 58.5°C. Even considering the non-radiative heat exchange conditions, this metamaterial cooler can still cool down 9.6°C at the daytime and 12.3°C at the nighttime respectively. Therefore, this work further promotes the development of all-dielectric metamaterial based passive radiative coolers and is of great significance for energy conservation.

Published
2019
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23. Improving the Photovoltage of Blade-Coated MAPbI3Perovskite Solar Cells via Surface and Grain Boundary Passivation with π-Conjugated Phenyl Boronic Acids

Author

Abbas, Mazhar, Cai, Boyuan, Hu, Jinlong, Guo, Fei, Mai, Yaohua, and Yuan, Xiao-Cong

Abstract

High-density electronic defects at the surfaces and grain boundaries (GBs) of perovskite materials are the major contributor to suppressing the power conversion efficiency (PCE) and deteriorating the long-term stability of the solar devices. Hence, the judicious selection of chemicals for the passivation of trap states has been regarded as an effective strategy to enhance and stabilize the photovoltaic performance of solar devices. Here, we systematically investigated the passivation effects of four organic π-conjugated phenylboronic acid molecules: phenylboronic acid, 2-amino phenylboronic acid (2a), 3-amino phenylboronic acid (3a), and 4-amino phenylboronic acid (4a) by adding them into the methylammonium lead iodide (MAPbI3) precursor solution. We found that solar devices with an optimized 5% (mol %) 3a treatment achieve the best passivation effect due to the strong cross-linking ability via hydrogen bonding interactions between the I of the [PbI6]4–octahedral network of perovskite films and the cross-linking terminal groups [−B(OH)2, (−NH2)] of 3a. Moreover, the lone pair of electrons on the N atom of an amino group of 3a can passivate the uncoordinated Pb2+defects at the surface/GBs. As a result, the 3a-passivated device shows a high open-circuit voltage of 1.13 V, which is a 14.1% improvement compared to the control device (0.99 V). Moreover, the reduced defect density and improved carrier lifetimes enabled a high PCE of 18.89% in our blade-coated champion inverted structure of MAPbI3solar cells, with improved long-term stability.

Published
2021
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30. Temperature-Assisted Crystal Growth of Photovoltaic α-Phase FAPbI3Thin Films by Sequential Blade Coating

Author

He, Wenxin, Hu, Jinlong, Chen, Chaoran, Chen, Yijun, Zeng, Linxiang, Zhang, Xin, Cai, Boyuan, Mai, Yaohua, and Guo, Fei

Abstract

Formamidinium lead triiodide (FAPbI3) exhibits the smallest band gap among lead halide perovskites, which is more desirable for solar cell applications compared to methylammonium-based counterparts. However, it remains a big challenge to prepare phase-pure α-FAPbI3in addition to controlling the crystal morphology during film formation. Herein, we developed a temperature-assisted crystal growth to prepare high-quality thin films of α-FAPbI3by sequential blade coating. It is found that depositing organic cation FAI at elevated temperatures facilitates the growth of α-FAPbI3, which otherwise yields mainly a yellow δ-phase at room temperature. In parallel, the crystal morphology of the perovskite films can be effectively manipulated by taking advantage of the porous structure of PbI2. Solar cells prepared with the blade-coated α-FAPbI3yield a champion efficiency of 18.41%, which is among the highest values for FAPbI3-only solar devices. These results suggest that two-step sequential blade deposition offers a viable approach to fabricate high-quality α-FAPbI3films for optoelectronic applications.

Published
2020
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33. Intrinsically core-shell plasmonic dielectric nanostructures with ultrahigh refractive index

Author

Yue, Zengji, Cai, Boyuan, Wang, Lan, Wang, Xiaolin, Gu, Min, Yue, Zengji, Cai, Boyuan, Wang, Lan, Wang, Xiaolin, and Gu, Min

Abstract

Topological insulators are a new class of quantum material s with metallic (edge) surface states and insulating bulk states. They demonstrate a variety of novel electronic and optical properties, which make them highly promising electronic, spintronic, and optoelectronic materials. We report on a novel conic plasmonic nanostructure that is made of bulk-insulating topological insulators and has an intrinsic core-shell formation. The insulating (dielectric) core of the nanocone displays an ultrahigh refractive index of up to 5.5 in the near-infrared frequency range. On the metallic shell, plasmonic response and strong backward light scattering were observed in the visible frequency range. Through in- tegrating the nanocone arrays into a-Si thin film solar cel ls, up to 15% enhancement of light absorption was predicted in the ultraviolet and visible ranges. With these unique features, the intrinsically core-shell plasmonic nanostructure paves a new way for designing low-loss and high-performance visible to infrared optical devices.

Published
2016

50. Improving the Photovoltage of Blade-Coated MAPbI 3 Perovskite Solar Cells via Surface and Grain Boundary Passivation with π-Conjugated Phenyl Boronic Acids.

Author

Abbas M, Cai B, Hu J, Guo F, Mai Y, and Yuan XC

Abstract

High-density electronic defects at the surfaces and grain boundaries (GBs) of perovskite materials are the major contributor to suppressing the power conversion efficiency (PCE) and deteriorating the long-term stability of the solar devices. Hence, the judicious selection of chemicals for the passivation of trap states has been regarded as an effective strategy to enhance and stabilize the photovoltaic performance of solar devices. Here, we systematically investigated the passivation effects of four organic π-conjugated phenylboronic acid molecules: phenylboronic acid, 2-amino phenylboronic acid (2a), 3-amino phenylboronic acid (3a), and 4-amino phenylboronic acid (4a) by adding them into the methylammonium lead iodide (MAPbI 3 ) precursor solution. We found that solar devices with an optimized 5% (mol %) 3a treatment achieve the best passivation effect due to the strong cross-linking ability via hydrogen bonding interactions between the I of the [PbI 6 ] 4- octahedral network of perovskite films and the cross-linking terminal groups [-B(OH) 2 , (-NH 2 )] of 3a. Moreover, the lone pair of electrons on the N atom of an amino group of 3a can passivate the uncoordinated Pb 2+ defects at the surface/GBs. As a result, the 3a-passivated device shows a high open-circuit voltage of 1.13 V, which is a 14.1% improvement compared to the control device (0.99 V). Moreover, the reduced defect density and improved carrier lifetimes enabled a high PCE of 18.89% in our blade-coated champion inverted structure of MAPbI 3 solar cells, with improved long-term stability.

Published
2021
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