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The ability to break Kirchhoff’s law is of fundamental importance in thermal radiation. Various nonreciprocal emitters have been proposed to break the balance between absorption and emission. However, the thicknesses of the nonreciprocal materials are usually larger than 1/10 times of the wavelength. Besides, the previous proposed nonreciprocal emitters are complex, thus they can hardly be fabricated in experiment to verify the Kirchhoff’s law for nonreciprocal materials. In this paper, we investigate the nonreciprocal thermal radiation of the magnetic Weyl semimetal (MWSM) film atop of the metal substrate. It is found that the strong nonreciprocal radiation at the wavelength of 9.15 µm can be achieved when the thickness of the MWSM film is 100 nm. The enhanced nonreciprocity is attributed to the Fabry-Perot resonances. The results indicate that the MWSM film is the promising candidate to engineer the ultrathin and simple nonreciprocal thermal emitters. What is perhaps most intriguing here is that the proposed structure can be more easily fabricated in experiment to verify the Kirchhoff’s law for nonreciprocal materials.

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Plasmonic nanofluids have excellent optical properties in solar energy absorption and have been widely studied in solar thermal conversion technology. The absorption of the visible region of solar energy by ordinary metal nanoparticles is usually limited to a narrow resonance band, so it is necessary to enhance the coupling effect of nanoparticles in the visible spectrum region to improve absorption efficiency. However, it is still a difficult task to improve solar energy absorption by adjusting the structure and performance of nanoparticles. In this paper, a plasma dimer Ag nanoparticle is proposed to excite localized surface plasmon resonance (LSPR). Compared with an ordinary Ag nanoparticle in the visible region, the plasmonic Ag dimer nanoparticle produces more absorption peaks and broader absorption bands, which can broaden solar energy absorption. By analyzing the electromagnetic field of the nanoparticle, the resonance mode of the plasma dimer is discussed. The effects of the geometric dimensions of the nanoparticle and the embedding of two spheres on the optical properties are studied. In addition, the effects of a trimer and its special structure on the optical properties are also analyzed. The results show that the proposed plasma dimer Ag nanoparticle has broad prospects for application in solar thermal conversion technology.

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Temperature inhomogeneity occurs frequently in the application of photovoltaic devices. In the present study, the effect of nonuniform horizontal temperature distributions on the photovoltaic output parameters of a monocrystalline silicon solar cell including short-circuit current, open-circuit voltage, output power, etc. was investigated. A laser beam irradiated on the center of the cell surface was used to obtain nonuniform temperature distributions. The results show that the higher initial temperature region of the solar cell absorbs more heat energy and achieves higher temperature than the lower initial temperature region after exposure to the same sunlight. Meanwhile, the photovoltaic parameters vary with the temperature difference between the center and edge of the solar cell. The maximum output power decreases exponentially with the temperature difference. The output power under an external load resistance of 1 Ω is almost inversely proportional to the temperature difference. According to the experimental results, when the temperature difference between the center and edge of the solar cell changes from 0 K to 60 K, the open-circuit voltage, maximum output power, output current, and power under external load resistance of 1 Ω would decrease by 4.8%, 4.8%, 5.1%, and 9.8%, respectively. The photovoltaic efficiency decreases when the temperature distribution is nonuniform.

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