Infrared camouflage is crucial for high-temperature objects to avoid detection, and spontaneous infrared radiation is also an important way for high-temperature objects to dissipate heat. Therefore, selective infrared emission has become significant for the coating design of surfaces such as aircraft, which require low emission in the atmospheric window band (3–5 µm and 8–14 µm) and high emission outside it (5–8 µm). This Letter employs a simple multilayer film structure to achieve selective regulation of the material emission spectrum. Combining the transfer matrix method and genetic algorithm, a multilayer film structure containing 12 layers of three high-temperature-resistant materials (
S
i
O
2
,
T
i
O
2
and Ge) has been designed. It shows fairly low emissivity in two main bands of infrared detection (
ε
3
∼
5
µ
m
=
0.14
,
ε
8
∼
14
µ
m
=
0.21
) and high emissivity outside them (
ε
5
∼
8
µ
m
=
0.86
), and this infrared selectivity can be well maintained with the incident angle rising from 0 to 60 deg. The Poynting vector distribution in the material at different incident wavelengths is analyzed to further explore the interference mechanism to achieve spectral selective emission. The significance of this work lies in the construction of a relatively simple coating design while ensuring efficient infrared camouflage and thermal management performance.
Thin‐film solar cells are favorable because of the reduced material and fabrication cost as well as the advantage of mechanical flexibility. However, due to the reduced thickness of the active layer, the light absorption is also decreased. Herein, a composite light‐trapping structure with a double‐layer antireflection coating on the upper surface and Ag hemispheres on the substrate is proposed to achieve full‐spectrum (350–800 nm) absorption enhancement. The results simulated by the finite‐difference‐time‐domain method show that compared with 100‐nm‐thick bare a‐Si:H solar cell, the short‐circuit current density (Jsc) and photoelectric conversion efficiency are respectively improved by 39% and 38% through adding the optimized composite light‐trapping structure. Excitingly, the light‐trapping effects remain efficient over different thicknesses of the active layer, and the Jsc of a 400‐nm‐thick a‐Si:H thin‐film solar cell can be enhanced to approach the theoretical limit. The light‐trapping method proposed in this study can provide general and valuable guidance for improving the light absorption in various thin‐film solar cells.
In this paper, we have theoretically demonstrated a graphene-mediated near-field radiative thermal modulator based on doped silicon-graphene-doped silicon three-slab configuration. The near-field photon tunneling between the doped silicon emitter and receiver is modulated by changing chemical potential of graphene sheet and the separation distance between the sheet and the emitter. The near-field three-body theory built on fluctuational electrodynamics is used to calculate total radiative heat flux, which could be modulated in a range of 10-70 kW/m 2 with different setup for graphene chemical potential and its position. The underlying mechanism is illustrated as varied coupling behavior of surface plasmon polaritons between doped silicon and graphene sheet. Several dimensionless factors such as normalized heat flux, sensitivity factor and switching factor are also introduced for comprehensive analysis of the performance of modulation effect. The results obtained here will trigger a new way for near-field active thermal management between bulk materials utilizing suspended 2-D materials.
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