Inorganic Halide Perovskite Electromagnetic Wave Absorption System with Ultra‐Wide Absorption Bandwidth and High Thermal‐Stability

Halogen perovskite, a novel semiconductor material that has gained momentum in the energy sector, has also emerged in the field of electromagnetic wave (EMW) protection. Inorganic halogen perovskites are expected to perform well owing to their excellent stability and dielectric properties. In this study, a CsPbBr3/Carbon nanotubes (CNTs) composite is designed using a convenient antisolvent method. In addition to an ultrawide absorption bandwidth (5.56 GHz) and ultrahigh absorption strength (|Reflection loss| = 51.74 dB), the composite shows excellent thermal stability and environmental tolerance. In an air environment, its EMW‐absorbing performance can be maintained at a high level at a temperature below 400 °C. CNTs build an efficient conductive network between CsPbBr3 to enhance the conduction loss of the composite, while it brings more defects and vacancies to the surface of CsPbBr3 to form electrical polarization centers which improving the polarization loss of the composite. This is the first study of the application of inorganic halogen perovskites in the field of EMW absorption. The excellent EMW‐absorbing performance and stability of CsPbBr3/CNTs demonstrate the great potential of inorganic halogen perovskites in the field of EMW absorption and provide a valuable reference and feasible strategy for regulating and controlling the EMW‐absorbing performance of perovskite materials.


Inorganic Halide Perovskite Electromagnetic Wave Absorption System with Ultra-Wide Absorption Bandwidth and High Thermal-Stability
Zhi Zhang, Ziming Xiong, Yao Yao, Xiaomin Shi, Pin Zhang, Zhiqian Yang, Qing Zhao,* and Wenke Zhou* DOI: 10.1002/aelm.202201179 of organisms. [1] To cope with the everincreasing electromagnetic radiation, new types of high-performance electromagnetic wave (EMW) absorbing materials have become a research hotspot in the field of electromagnetic protection. [2] Characterized by their high light absorption coefficient, long carrier diffusion length, strong photoluminescence properties, low cost, and simple preparation process, halogen perovskites (ABX 3 , A = CH 3 NH 3 + , Rb + , Cs + ; B = Ge 2+ , Sn 2+ , Pb 2+ ; X = Cl − , Br − , I − ) have been widely studied and used in the fields of solar batteries, LEDs, laser devices, and photoelectric detectors in recent years. [3] Meanwhile, because it has a highly balanced electron/hole mobility, it is a typical semiconductor material with great potential for application in the field of EMW absorption. [4] According to recent research on the application of organic-inorganic hybrid perovskite MaPbX 3 (Ma = CH 3 NH 3

Introduction
Despite the great convenience they bring to our lives, electronic devices can generate large amounts of electromagnetic radiation, which poses a potential threat to the health Moreover, as the most promising new-generation photovoltaic material, MaPbX 3 easily decomposes in high-temperature and humid environments because of its volatile organic components, which significantly hinders its commercial application in new energy fields. [6] The use of inorganic cations, such as Cs + , as a substitute for the organic version for the preparation of caesium-lead halide perovskites (CsPbX 3 ) has become a new solution to address the thermal instability of organicinorganic hybrid perovskites. [7] CsPbX 3 is characterized by a high quantum efficiency (>90%), narrow emissivity (<30 nm), and high carrier mobility. Under conditions of high relative humidity (90-95%, 25 °C), extreme temperature (100 °C or −22 °C), and no encapsulation, its photoelectric energy conversion efficiency can reach 12%. [8] This also provides a reference for solving the problem of EMW absorption performance limitations caused by the low stability of MaPbX 3 . [9] To date, there have been no studies on the application of CsPbX 3 in EMW absorption. However, given its similar physicochemical properties to MaPbX 3 , CsPbX 3 is expected to become a new type of EMW-absorbing material with excellent absorbing performance and high stability. [10] In this study, we prepared CsPbBr 3 (CPB) according to the principle of supersaturated recrystallization by rapidly mixing polar and nonpolar solvents and then separating and crystallizing Cs + , Pb 2+ , and Brions quickly. [11] According to a study on the EMW-absorbing performance of CPB, CPB shows a moderate absorption strength for incident EMW within the range of 2-18 GHz, the EAB is too narrow, and the additive amount of absorbent is excessive. To improve the EMWabsorbing performance of Cs-based perovskites, Carbon nanotube (CNTs) were used in the preparation of CPB, and a CPB/ CNTs (CC) composite was successfully prepared. Studies have shown that by controlling the additive amount of CNTs, CC exhibits an extremely high EMW absorption strength and a wide EAB, and the absorber thickness and the additive amount of absorbent are significantly decreased. This is because, after the use of CNTs, the three-dimensional orthorhombic phase structure of CPB is partially damaged, a large number of defects and vacancies appear, and the charge polarization intensity of CPB significantly increases. Meanwhile, CNTs form an efficient electronic transmission network between CPB grains, which accelerates the charge transfer rate inside the composite and improves the conduction loss performance of the CC. Finally, the EMW-absorbing performance of the CC at high temperatures was studied. Compared with the MaPbBr 3 /CNTs (MC) composite, CC was confirmed to have excellent EMW-absorbing performance while maintaining good thermal stability. This research provides a reliable reference for the application of caesium-lead halide perovskites in the field of EMW absorption and offers a new option for the production of highperformance and long-acting EMW-absorbing devices.

Synthesis of CC Composites
The CC was obtained by adding CNTs during CPB preparation and thorough mixing. The synthesis process of CC composites was shown in Scheme 1. The CC preparation process was as follows: a 10-mg mL −1 CNTs/DMSO solution was prepared. The CNTs solution was added to the 0.4-mol mL −1 CPB solution pro-rata. The solution was then stirred at 25 °C for 60 min. The CPB/CNTs solution was quickly pipetted into an excessive amount of anisole. The solution was allowed to stand, washed, and dried to obtain the CC composite. CCs were prepared according to mass ratios of 20:1, 16:1, 12:1, 8:1, and 3:1 (CPB:CNTs), and they were named as CC-0, CC-1, CC-2, CC-3, and CC-4, respectively. The synthesis process of CPB, MPB and MC composites could be found in Scheme S1 (Supporting Information). The detailed materials, preparation, and characterization are presented in the Supporting Information.

Evaluation of EMW Absorption Performance
Based on transmission line theory, the electromagnetic parameters of the samples, including the real (ε′ and µ′) and imaginary (ε″ and µ″) parts of the dielectric constant and permeability, were determined using an Agilent PNA N5244A vector network analyzer in the range of 2-18 GHz. [12] The attenuation constant (α) is a parameter used to reflect the loss ability of the absorbing material to the incident EMW and is related to the frequency of the incident EMW. The relationship between the attenuation constant and frequency of the incident EMW (f) can be established using the following formula: [13] where c is the speed of light in vacuum. At the same time, the intrinsic impedance ratio (Z) of the absorbing material is an Scheme 1. Schematic illustration of synthesizing CC composite.

www.advelectronicmat.de
important factor affecting the performance of the absorbing material, which reflects the level of EMW entering the absorbing material. When Z > 0.3, the EMW fully enters the absorbing material, and Z can be calculated using Equations (2) and (3): [14] / r 0 Here, Z r is the material's intrinsic impedance, Z 0 is the free space impedance, and , , Reflection loss (RL) is a key parameter that reflects the intensity of reflected waves after EMW is dissipated by absorbing materials and is the most important index for evaluating the performance of EMWabsorbing materials. When RL < −10 dB, more than 90% of the incident EMW is considered to be dissipated, and the frequency range of the incident EMW with RL < −10 dB is called EAB. RL can be obtained using the following formula: [14] tanh 2 c d 0 where Z d is the normalized input impedance at the corresponding thickness, d is the thickness of the wave-absorbing material, and h is Planck's constant. Additionally, the matching thickness (t m ) at peak frequency (f m ) can be calculated as follows: [14] 4 4 , 1,3,5,… where λ is the wavelength of the incident EMW. The detailed materials, preparation, and characterization are presented in the Supporting Information.

Results and Discussion
To study the lattice morphology, microstructure, and EMWabsorbing performance of CPB prepared using the anti-solvent method, the CPB XRD spectrum, Raman spectrum, PL spectrum, SEM image, and images of the changes in the real and imaginary parts of the dielectric constant along with the change in incident EMW frequency are shown in Figure 1a-c.
The CPB images for the changes in the real and imaginary parts of the magnetic permeability, the change in the incident EMW frequency, and the CPB's 3D RL diagrams under two different additive amounts (35 and 70 wt%) are shown in Figure S1a-c (Supporting Information). The XRD spectrum shows that the crystal structure of CPB is a three-dimensional orthogonal perovskite structure. [ 6 ] 4− octahedron. [16] The PL spectrum of CPB was centered at ≈533 nm, which is similar to previously reported results.
[15a] Analysis of the XRD, Raman, and PL spectra revealed that CPB with an orthorhombic phase structure and high crystallinity was successfully prepared. Complete cubic CPB single crystals were also observed in the SEM image ( Figure 1b). The prepared CPB single crystals had smooth surfaces and uniform sizes (≈2 µm). There is a large spacing between crystalline grains, which may pose a challenge to the transfer of free electrons among CPB microcrystals, thus chipping away at the electric conductivity and reducing CPB's EMW-absorbing performance. Previous studies have proven that CPB is a dielectric material with no magnetic performance. Therefore, this study mainly probed the dielectric constant of CPB ( Figure 1c). The magnetic permeability of CPB is shown in Figure S1a (Supporting Information). Figure 1c shows the changes in the real and imaginary parts of CPB's dielectric constant and the frequency of EMW under both high and low additive amounts. The fluctuation form of ε′ under both additive amounts conforms to the general law of resonant dispersion curves. [17] Meanwhile, ε″ exhibits a large peak value, which corresponds to the resonance absorption caused by the electron transition inside the CPB. Moreover, the linewidth of the ε″ absorption curve approximately reflects the intensity of the relaxation process. The line widths of both CPB 35 wt% and CPB 70 wt% were low, indicating that the intensity of the polarization relaxation inside the CPB caused by the incident EMW was low. The anomalous dispersion regimes of CPB 35 wt% and CPB 70 wt% appear at 14.7 and 17.0 GHz, respectively. The anomalous dispersion regime is usually a region with a high absorption strength. As a result, CPB 35 wt% and CPB 70 wt% are likely to exhibit EMW absorption property at 14.7 and 17.0 GHz, respectively. This conclusion can be verified by the RL diagrams in Figure S1b,c (Supporting Information). The crystal structure, micromorphology, and electromagnetic parameters of the MPB microcrystals prepared using a similar method were also studied. The XRD spectrum (Figure 1d) shows that the characteristic diffraction peak of the prepared MPB crystals is similar to that of the reported MPB microcrystals prepared using the single-crystal growth method. [4a,18] The main characteristic diffraction peaks of MPB and their corresponding crystal planes are shown in the Figure 1d [19] respectively. The PL spectrum of MPB appears at 549.1 nm, and the corresponding bandgap is 2.27 eV. This result is consistent with the known intrinsic band structure of MPB. [20] Figure 1f Figure 1g,h, respectively, from which it can be seen that both CPB and MPB have a certain RL intensity, and the RL intensity under a high additive amount is higher than that under a low additive amount. More importantly, except for the 70-wt% MPB sample with observable EAB, the other three samples showed no significant EAB. This indicates that EAB, which is narrow compared to CPB materials, restricts further application of CPB in the field of EMW absorption. Broadening the EAB of CPB while ensuring their stability has become the key to the preparation of CPB-based high-efficiency EMW-absorbing materials. Therefore, the preparation of the CC composite is expected to improve the relaxation polarization characteristics of CPB by constructing a highly efficient conductive network through CNTs. In addition, it is necessary to investigate the variations in the electromagnetic parameters and impedance-matching properties of CC with different composition ratios, as shown in Figure 1i.
The relevant parameters of the CC composite prepared by regulating the component ratio, such as the phase composition, lattice morphology, micromorphology, and EMW absorbing properties, are shown in Figure 2. The XRD spectra of CC-1, CC-2, and CC-3 (Figure 2a) reveal that the use of CNTs in the process of CPB preparation mitigates the generation of cubicphase CPB. The main characteristic diffraction peaks of CPB exist when the proportion of CNTs is low. With an increase in the CNTs content, the CPB in the CC was gradually replaced by Cs 4 PbBr 6 . Of note, the half-peak width of the diffraction peak of CC-1 increased compared to the characteristic www.advelectronicmat.de diffraction peaks of CPB, indicating that CNTs can also lead to a decrease in the crystallinity of CPB. Both the production of 0-dimensional perovskite Cs 4 PbBr 6 and the reduced crystallinity of CPB lead to more ionic vacancies and defects inside the composite, which can help enhance the relaxation polarization in the dielectric loss mechanism. [15a] Raman spectroscopy is mainly used to determine the physicochemical state of CNTs in CC. Peak D of the CC sample at 1337.6 cm −1 is attributed to the vibration mode of the crystal at the symmetry point A 1g of CNTs, while peak G at 1577.4 cm −1 is present due to the first-order scattering of E 2g phonons by the carbon atoms on the track sp 2 . [21] In addition, the intensity ratio between peak D and peak G, that is, I D /I G , can be considered a key indicator for crystallinity evaluation. The I D /I G values of samples CC-1, CC-2, and CC-3 were 1.13, 1.11, and 1.07, respectively, and they were not affected by the change in the content of the components in CC. This indicates that the physicochemical state of the CNTs in CC is stable, and the change in the component ratio of the composite does not lead to a change in the lattice morphology of the CNTs. The PL spectrum of CC is shown in Figure 2c. Compared with the PL peak of CPB, the PL peak of CC moved leftward to ≈520 nm. This is because it was influenced by Cs 4 PbBr 6 (517 nm). Because the intensity of the PL peak of Cs 4 PbBr 6 is nearly 20 times higher than that of CPB, a small amount of Cs 4 PbBr 6 in CC causes its PL peak to move significantly leftward. [15] With an increase in the CNTs content in CC, the microtopography of CC also changed significantly, as shown in Figure 2c-e. When the CNTs content was low, cubicphase CPB was still observed (Figure 2d). When the CNTs content was increased, CPB's cubic-phase structure was damaged, and Cs 4 PbBr 6 played a dominant role. The CPB/Cs 4 PbBr 6 composite exhibited a random distribution of irregularly shaped crystals. This result was consistent with the results of the XRD analysis. Meanwhile, in the SEM image, CNTs are mainly distributed on the CPB surface and in the grain gaps. Owing to the excellent conductivity of CNTs, a channel for electrons to freely transfer among CPB grains was successfully established.
To study the effect of the establishment of a conductive network among grains on the EMW absorbing performance of CPB, the changing relationship between the real and imaginary parts of the dielectric constant and the magnetic permeability of CC and the frequency of the incident EMW are shown in  Figure S2 (Supporting Information), respectively. The real part of the dielectric constant of CC shows an obvious downward trend with an increase in the EMW frequency because dielectric polarization cannot catch up with the change rate of the alternating electric field in the high-frequency range. Generally, the real and imaginary parts of the dielectric constant of CC show an upward trend with increasing CNTs content. According to the free electron theory, there is a negative correlation between the resistivity ρ and ε″ (ε′′ ≈ 1/πε 0 ρf), where ε 0 is the free space impedance and f is the incident EMW frequency. [22] The increase in the imaginary part of CC indicates that the use of CNTs decreases the resistivity of CC but improves its conductivity, which is conducive to an increase in the conduction loss intensity in the process of EMW absorption. At the same time, the dielectric loss tangent is an important basis for analyzing the dielectric loss performance of absorber, which can be obtained from Supporting Information . In addition, as an electromagnetic wave absorbing material dominated by the dielectric loss mechanism, the slight magnetic loss property of the permeability of CC sample may originate from natural resonance and exchange resonance ( Figure S2b The attenuation constant (α) and intrinsic impedance ratio (Z) of a material are important for studying its EMW-absorbing performance. The attenuation constant and intrinsic impedance ratio of CC are shown in Figure 2h,i, respectively. According to Figure 2h, CC's attenuation capacity to incident EMW gradually improves with the increase in the CNTs content, and the attenuation constants of CCs with all component ratios exceed 100 in the high-frequency band which could be considered to have an effective loss capacity for incident EMW. [23] This indicates that CC can achieve an effective attenuation loss for high-frequency EMW entering the interior. However, the high attenuation loss capacity alone does not guarantee excellent EMW-absorbing performance. Whether the EMW can enter the absorbing material or be reflected on the surface of the material is also a key factor affecting the absorbing performance of the material. The intrinsic impedance ratio (Z) of a material is an indicator used to evaluate the difficulty of the EMW entering the absorbing material. Usually, when Z > 0.3, it is considered that the electromagnetic wave can enter into the absorbing material smoothly. [23] The higher ratio ensures that more EMW can propagate into the absorber. The Z value of the CC is shown in Figure 2i. Only the Z values of CC-0 and CC-1 are greater than 0.3 within the range of 2-18 GHz, indicating that EMW can effectively enter these two samples for attenuation. The Z value of CC-2 is greater than 0.3 within the range of 12-18 GHz, indicating that the sample has good transmittance for high-frequency EMW while a large number of lowfrequency EMWs are reflected on the surface. Generally, either prominent attenuation and dissipation or intrinsic impedance ratio is not conducive to high-efficiency electromagnetic wave absorption. The only way to achieve high-efficiency electromagnetic wave absorption is to find a balance between them. In the range of 2-18 GHz, Z CC − 0 ≥ Z CC − 1 ≥ 0.3. In the range of 6-18 GHz, α CC − 0 ≥ α CC − 1 ≥ 100. Therefore, through the analysis of attenuation constant and intrinsic impedance ratio, CC-0 and CC-1 is more likely to obtain excellent electromagnetic wave absorption performance than other samples.
The RL directly reflects the EMW-absorbing performance of a material. RL diagrams of the CC samples with different component ratios are shown in Figure 3a-e. The corresponding absorber thicknesses were 1-5 mm. The region confined

www.advelectronicmat.de
by the red lines corresponds to RL < −10 dB, and the region confined by the yellow lines corresponds to RL < −20 dB. The maximum EAB values of the samples and their corresponding EMWs are shown in Figure 3f. The EAB values of the samples (CC-0 and CC-1) exceeded 5 GHz when the CNT content in CC was low. The EAB value of CC-0 at 2.56 mm ranges from 8.84 to 14.24 GHz, basically covering the X-band EMW, so it is an ideal choice for X-band EMW-shielding materials. The maximum EAB value was observed for CC-1. It reaches 5.56 GHz (11.96-17.52 GHz) when the content of CC-1 is 35 wt% and the absorber thickness is 1.91 mm. This is the first report on cesium lead halide perovskite-based-absorbing materials so far, and has also achieved excellent EAB performance. With a further increase in the CNTs content (CC-2, CC-3), the EAB value of the samples decreased but could still exceed 4.5 GHz, and the corresponding absorber thickness decreased accordingly (below 1.6 mm). This provides an ideal choice for thin light-absorbing materials. When the CNTs content is close to that of a Cs-based perovskite (CPB/Cs 4 PbBr 6 :CNTs ≈ 3:1), the EAB value of CC-4 is equal to 0. This is because the Z value of the samples is much lower than 0.3 under a high content of CNTs and most of the EMWs are reflected on the surface of the absorber. CC-4 mainly exhibited electromagnetic shielding properties. The EAB and EMW absorption strengths are two key indicators used to evaluate the performance of absorbing materials. The peak frequencies (f m , > ) corresponding to the maximum absorption strengths of the CC samples are shown in Figure 3. Because samples CC-0, CC-1, and CC-2 had a wider EAB, the absorption strengths of these three samples were further studied, as shown in Figure 4. Figure 4 shows the maximum absorption strength and absorber thickness of samples CC-0, CC-1, and CC-2, respectively, as well as the correlation between Z d and t m . First, CC-1 has the widest EAB, and its maximum absorption strength is also higher than that of other samples. When the CNTs content is 35 wt% and the absorber thickness is 2.2 mm, sample CC-1 reaches its maximum absorption strength, that is, RL = −51.74 dB at 12.12 GHz. Figure 4b,e,h shows the normalized input impedances of CC-0, CC-1, and CC-2, respectively. The Z d value of each sample at the maximum peak frequency ( m1 f ) is close to 1.0, and the absorption strength of the samples decreases when Z d ≠ 1.0. This indicates that a good impedance matching performance can help enhance the EMW-absorbing performance of a material. In addition, for all three samples, with an increase in absorber thickness, the absorption peak gradually moved toward lower frequencies. This phenomenon can be explained using quarter-wavelength theory. The matching thickness of the absorption peak was calculated using Equation (6). The red blocks are near the λ/4 curve, indicating that the absorption mechanism of the CC samples is based on quarter-wavelength theory. In addition, Debye relaxation is an important EMW loss mechanism in the dielectric loss mechanism. The Cole-Cole curves of CC samples are provided in Figure S3 (Supporting Information), which plays an important role in explaining the polarization loss mechanism of samples. The main EMW absorption strengths of CC samples with different component ratios and their corresponding frequencies are listed in Table 1. From the maximum absorption strength and EAB of the samples used, CC-1 showed the highest EMW-absorbing performance compared with other samples ( Figure S2c, Supporting Information).
The excellent EMW-absorbing performance of these CC materials depends on the combined action of the CPB and CNTs. Good impedance matching of the CC materials was achieved by adjusting the ratio of the two components. The schematic plot of the EMW absorbing mechanism is shown in Scheme 2. As a typical dielectric loss-type-absorbing material, CNTs can form a high-quality conductive network, which lays www.advelectronicmat.de the foundation for free electrons to move freely among the CPB crystals. A large amount of field-induced micro current entered the CC in an alternating electric field. The resulting conduction loss effectively converts the electromagnetic energy into thermal energy. [24] In addition, as another important mechanism for dielectric loss, the polarization loss effect was also used to significantly improve the EMW-absorbing performance of the CCs. First, owing to the use of CNTs, the crystal structure of CPB was damaged, thus generating surface defects and vacancies, which could serve as the polarization centers to enhances the EMW attenuation capacity. In an external electric field, the space charge polarization effect of CC is significantly enhanced. Secondly, since CPB and CNTs have different dielectric constants and conductivities, charge accumulation would occur on the interface of these two media, which could be considered as the capacitor-like structure to result in an interfacial polarization effect. Finally, multiple scattering between the 3D network structures composed of CPB and CNTs prolongs the internal travel path of the EMW and promotes EMW attenuation. [25] Because it has been proven that CPB exhibits higher thermal stability than MPB, the lattice morphology and absorbing performance of heated CC-2 were studied to investigate the thermal stability of CNTs-containing CC and the change in its EMWabsorbing performance. MC samples with the same component ratio and heat-treatment conditions were used as controls. As shown in Figure 5a, the main XRD spectra of the CC samples treated at 200 and 400 °C were highly consistent with those of the unheated CC-2 samples, and their main diffraction peaks corresponded well to the characteristic diffraction peaks of CPB/ Cs 4 PbBr 6 . Meanwhile, according to the PL spectra of CC-2, CC 200, and CC 400 in Figure S4a (Supporting Information), the PL peaks of all three samples are located near 520 nm, and their half-peak widths are close to each other, indicating that the lattice morphology of the CC samples did not change significantly after heat treatment. As shown in Figures 3c and 5b,c, the EAB of the CC samples did not change significantly after heat treatment, except that the maximum value of the EMW absorption strength decreased after treatment at 400 °C. This indicates that CNTs-doped CC maintains good thermal stability, and its EMW-absorbing performance remains high after heat treatment. Therefore, CC is a potential high-temperature resistant absorbent material. The electromagnetic parameters, attenuation loss performances, and intrinsic impedance ratios of CC-2, CC 200, and CC 400 are essentially the same in Figures S4d-f (Supporting Information), indicating the excellent thermal stability of CC.
To probe the principle and influencing factors of the hightemperature resistance and high EMW-absorbing performance of CC, the XRD spectrum (Figure 5d), PL spectrum ( Figure S4b, Supporting Information), and RL performance diagrams (Figures 5e,f and Figure S4c, Supporting Information) of the MC samples are presented. Figure 5d shows that the main diffraction peaks of the unheated sample MC 25 are highly consistent with those of MPB at room temperature, and no other impurity peaks appear. In the XRD spectrum of MC 200 heated to 200 °C, the intensity of the diffraction peaks corresponding to MPB decreased and impure peaks appeared. The main diffraction peaks in the XRD spectrum of MC 400 heated to 400 °C corresponded to PbBr 3 crystals, and the diffraction peaks corresponding to MPB disappeared. The PL spectrum also confirms that the lattice morphology of MC changed significantly owing to heat treatment. This indicates that heat treatment led to the decomposition of a large amount of MPB in the MC sample and damage to the three-dimensional conductive network structure, which is composed of MPB crystals and CNTs and contains a multi-polarization center. Heat treatment also had a significant negative impact on the EMW-absorbing performance. According to Figure 5e,f and Figure S4c (Supporting Information), the EMW absorbing performance of the MC sample (EAB and absorption strength) decreased significantly with an increase in the heat treatment temperature. The electromagnetic parameters, attenuation loss and intrinsic impedance ratio of MPB and MC could be found in Figures S4 (Supporting  Information). A study on the EMW-absorbing performance of CC and MC at high temperatures indicates that, on the one hand, the good thermal stability of CPB plays a decisive role in maintaining the excellent EMW-absorbing performance at high temperatures; on the other hand, the excellent EMW-absorbing performance of CC is based on the combined action of CPB and CNTs, and there would be no EMW-absorbing property if there was only a conductive network but no multi-polarization center.

Conclusion
In this study, a CC composite consisting mainly of inorganic halogen perovskite CPB was successfully prepared. CC exhibited excellent EMW-absorbing performance and good thermal stability. The EAB value and maximum absorption intensity of CC reached 5.56 GHz and |RL| = 51.74 dB, respectively, in an air environment at 25 °C. Its EMW-absorbing performance remained unchanged in an air environment at 400 °C. The excellent absorption performance of CC is based on the combined action of CPB and CNTs, with the former serving as a polarization center and the latter constituting a good conductive network. The conduction loss mechanism and polarization loss mechanism have been brought into full play, which is the key to excellent EMW-absorbing performance. This is the first study on the application of CPB and their composites in the field of EMW absorption. This confirms that inorganic halogen perovskites have a good future in the field of EMW absorption and have great potential as high-temperatureresistant EMW-absorbing materials.

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.