High Absorptivity Solar Absorber Based on MIM Resonant Structure
Objective The development and utilization of new energy sources has always been an important human research field.As a green and renewable energy source,solar energy provides an effective way to alleviate the energy crisis.To date,many methods have been proposed for converting solar radiation into other forms of energy and applications,such as photovoltaics and solar cells,light and heat generators,thermoelectric power generation and solar steam power generation,seawater desalination,and photochemical and photocatalytic reactions.Notably,efficient solar energy capture is the key to realizing these applications.Therefore,the ultimate goal of investigating solar absorbers is to completely absorb solar radiation over the entire spectral range and to employ as little photosensitive material as possible.In the past few years,several methods for efficient absorption of solar radiation have been investigated.For example,black paint is widely adopted but exhibits high absorptivity only in ultraviolet and visible wavelengths,which wastes about 28％of solar energy.However,with technological advancement,metamaterials open up many new ways to manipulate electromagnetic waves,and they have many unique optical properties and have been shown to control the polarization state,amplitude,and phase of electromagnetic waves.Changing the light amplitude is a way to control light absorption.Therefore,it is important to study the perfect absorbers for solar energy based on metamaterials.Methods We design a solar absorber with a multi-layer hollow disk stacked structure based on a metal-dielectric-metal(MIM)resonator structure utilizing GaAs and amorphous GST(A-GST).Additionally,the designed solar absorber is simulated and theoretically analyzed using the finite difference method in time domain(FDTD)and data analysis software Matlab.First,the effect of the structural layer number and the difference in dielectric material per layer(using GaAs or A-GST)on the absorption is analyzed,and the structural parameters are optimized for achieving high absorptivity and broad operating bandwidth.Second,the phase parameters,effective impedance,and electromagnetic field strength and vector distributions at the four absorption peaks are analyzed to investigate the physical absorption mechanism.Then,the oblique incidence response from 0° to 50° is also analyzed to further explore the practicality of the absorber.Finally,the structure's ability to absorb and convert solar energy is evaluated by calculating the solar spectrum-weighted absorption efficiency and effective thermal emissivity.Results and Discussions The results of the study show that both GaAs and amorphous state GST materials are extremely helpful in the design of solar absorbers(Fig.6).The structure shows an average absorptivity of 97.48％in the wavelength range of 0.3-2.5 μm and a solar spectrum-weighted absorption efficiency of 98.02％.Meanwhile,the average absorptivity is 96.95％over the entire operating band from 0.3 μm to 4 μm,and the solar spectrum-weighted absorption efficiency is 97.54％(Fig.6).The bandwidth is 2.37 μm for absorptivity greater than 95％and 3.57 μm for absorptivity greater than 90％(Fig.3).The symmetry of the structure itself gives it excellent polarization-independent properties(Fig.1),which is very favorable for solar absorption.Additionally,in the wavelength range of 0.3-2.5 μm,the structure also exhibits a stable response to changes in the incidence angle(Fig.7).The designed solar absorber characterized by ultra-broadband and high absorptivity can provide tremendous advantages in absorption bandwidth and absorption efficiency over previously reported results(Table 2),and also greatly reduce the complexity and cost of fabrication due to the simplicity of the structure.Conclusions We propose a high-absorptivity ultra-broadband solar absorber based on a three-layer MIM strong resonator structure.The dielectric material for each layer of the MIM structure is analyzed with the effect of GaAs or A-GST on the absorptivity discussed.The results of the study show that both materials are highly applicable in the design of solar absorbers.The symmetry of the structure itself gives it excellent polarization-independent properties,which are very favorable for solar absorption.The designed solar absorber is characterized by ultra-broadband and high absorptivity with a simple structure,which greatly reduces the complexity and cost of fabrication.Therefore,it has potential applications in solar energy collection and conversion,photovoltaic devices,and thermal emitter devices.
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