Optical capture capability enhancement by right-angled triangular visible absorber
Introduction
Many absorbers have been reported based on microstructures [1], [2], [3], [4], [5]. From the perspective of absorption bandwidth, absorbers are divided into narrow-band absorbers [6], [7], [8] and wide-band absorbers [9], [10], [11]. According to the absorption spectrum, absorbers can be divided into infrared absorbers [12], microwave absorbers [13], terahertz absorbers [14], and visible light absorbers [15]. Among them, due to the widespread use of visible light in visible absorber and other fields, visible wavelength spectral absorption has become one of the research hotspots [16], [17], [18], [19]. In addition, the addition of metamaterials is the main way to achieve polarization-independent and high-efficiency absorption characteristics of light absorbers at visible wavelengths [20], [21]. In order to realize the function of wide absorption spectrum and high efficiency, some researchers have done a lot of work. Lee et al. proposed a polarization-sensitive tunable visible absorber [22]. The proposed absorber consists of a metal-dielectric multilayer medium and a plasma grating. Nguyen et al. analyzed a perfect visible absorber by plasmonic grating [23]. Broadband absorptivity is above 90% in the wavelength range of 0.4 um to 1.4 um. Wan et al. designed a polarization-insensitive visible absorber by rectangular grating [24]. The polarization-insensitive absorber is designed to achieve a wide band absorption of 300 nm and an incident angle width of 45Ā° for TE and TM modes.
In this paper, in order to improve the absorption of absorbers, a polarization-insensitive thin-film absorber is proposed based on a right-angled triangular grating structure. The presented results show that the average absorption efficiency greater than 90.10% with a spectral range of 300-680 nm and the incident angle can reach 50Ā°. In addition, the changes of groove depth, groove width and coating thickness have a relatively small influence on the absorption rate. Furthermore, compared with the reference planar absorber, the reference triangular absorber, and the reported rectangular visible absorber [24], the designed visible light absorber in this work has better absorption bandwidth and incident angle.
Structure sizes of thin-film absorber are on the order of nanometers, which need to be studied by electromagnetic theory. Theories for studying visible absorbers include modal method [25], rigorous coupled-wave analysis method [26], finite element method [27] and finite time domain difference method [28]. The energy distribution of the electromagnetic field intensity of the absorber is clearly analyzed by finite element method [27]. By determining the boundary conditions, the transmittance and reflectance of the absorber are obtained. The incident energy minus the reflectance and transmittance is the absorbance. The original parameters of the right-angled triangular absorber are optimized by rigorous coupled-wave analysis method [26].
In order to improve the light absorption of the absorber, it is a better method to use a chirped grating [29], [30], [31] combined with a triangular structure. The traditional rectangular grating achieves broadband absorption enhancement by depositing Ni on Si3N4 [24]. However, the production cost of one-dimensional ordered gratings also increases. Wen et al. proposed the concept of adding cascaded rectangular nanometer gratings over the nanometer active layer to achieve broadband absorption enhancement [32]. It is due to the strong coupling between the local surface plasmon resonance and photon mode of the cascaded rectangular grating at the top of the absorption layer. However, there are few studies on chirped period gratings, which need further research. This paper designs a thin-film light absorber in the visible light band. The chirped period absorber absorbing layer composed of right-angled triangles in this paper not only makes up for the loss of metal but also outperforms the reference absorber with planar and triangular structures in the visible wavelength band. In addition, the finite element method [27] is used to analyze and discuss absorber parameters. The presented absorber has a high absorption of visible light in a wide-angle range.
Section snippets
Structure of right-angled triangular grating absorber
The 2D and 3D views of the schematic diagram of the proposed thin-film absorber based on a periodically chirped right-angled triangular grating are shown in Fig. 1. Such a structure is composed of an ITO layer, a right-angle triangular a-Si layer, a planar a-Si absorption layer, and a metal back reflection Ag layer. The structure is composed of ITO material with the refractive index of n. The ITO material in the structure is made up of indium tin oxide. Indium tin oxide (ITO) can control
Characteristics and discussions
The comparison of the power absorptivity of different types is shown in Fig. 7. The reference plane structure is composed of the planar a-Si layer and the Ag back reflection layer, and the reference triangular structure is composed of the triangular a-Si layer and the Ag back reflection layer. Obviously, plane a-Si layer and triangular a-Si layer play an important role in the absorption of incident light. As shown in Fig. 7 (b) and (c), the reference plane structure has the characteristics of
Conclusions
A visible light trapping structure capable of enhancing absorption of the absorber is proposed. The presentation of the absorption layer with the cascade right-angled triangular a-Si layer, the plane a-Si layer and the ITO layer make the absorber visible light absorption. The electric field distribution of the absorber is analyzed to explain the absorption mechanism. The average absorption efficiency more than 90.10% in the incident spectral range of 300-680 nm with wide angle of 50Ā°.
CRediT authorship contribution statement
Jimin Fang: Conceptualization, Data curation, Formal analysis, Writing - Original draft preparation. Bo Wang: Supervision, Project administration, Investigation, Writing- Reviewing and Editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work is supported by the Science and Technology Program of Guangzhou City (202002030284, 202007010001).
References (44)
A polarization insensitive dual-band tunable graphene absorber at the THz frequency
Phys. Lett. A
(2020)- et al.
Polarization and angle insensitive ultra-broadband mid-infrared perfect absorber
Phys. Lett. A
(2020) - et al.
Ultra-broadband metamaterial absorber for infrared transparency window of the atmosphere
Phys. Lett. A
(2019) - et al.
Terahertz metamaterial absorber comprised of H-shaped resonator within split-square ring and its sensory application
Optik
(2019) - et al.
Design of broadband absorber using 2-D materials for thermo-photovoltaic cell application
Opt. Commun.
(2018) - et al.
Ultra-narrow band perfect absorbers based on Fano resonance in MIM metamaterials
Opt. Commun.
(2017) - et al.
Numerical design of a metasurface-based ultra-narrow band terahertz perfect absorber with high Q-factors
Optik
(2019) - et al.
A novel wide-band tunable metamaterial absorber based on varactor diode/graphene
Optik
(2016) - et al.
Numerically investigating a wide-angle polarization-independent ultra-broadband solar selective absorber for high-efficiency solar thermal energy conversion
Sol. Energy
(2019) - et al.
A broadband and polarization-independent metamaterial perfect absorber with monolayer Cr and Ti elliptical disks array
Results Phys.
(2019)