Synthesis and high ammonia gas sensitivity of (CH3NH3)PbBr3-xIx perovskite thin film at room temperature

Journal Pre-proof Synthesis and high ammonia gas sensitivity of (CH3 NH3 )PbBr3−x Ix perovskite thin film at room temperature Wanli Jiao, Jing He, Lei Zhang

PII:

S0925-4005(20)30133-7

DOI:

https://doi.org/10.1016/j.snb.2020.127786

Reference:

SNB 127786

To appear in:

Sensors and Actuators: B. Chemical

Received Date:

5 November 2019

Revised Date:

19 January 2020

Accepted Date:

28 January 2020

Please cite this article as: Jiao W, He J, Zhang L, Synthesis and high ammonia gas sensitivity of (CH3 NH3 )PbBr3−x Ix perovskite thin film at room temperature, Sensors and Actuators: B. Chemical (2020), doi: https://doi.org/10.1016/j.snb.2020.127786

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Synthesis and high ammonia gas sensitivity of (CH3NH3)PbBr3-xIx perovskite thin film at room temperature

Wanli Jiao， Jing He， Lei Zhang＊

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(School of Material Science and Engineering, Shandong University of Technology, Zibo 255049, PR China)

Highlights

A new organic inorganic hybrid perovskite material of MAPbBr3-xIx has been synthesized.

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The results of gas sensing tests show favourable sensing performance to ammonia, acetone and ethanol

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including good selectivity, rapid response-recovery and acceptable stability.

To ammonia, the sensing mechanism is actions reversible exchange of MA+ and NH4+; to acetone and ethanol,

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the whole gas sensing process

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physical reversible charges transfer to intrinsic bromide vacancies and uncoordinated Pb2+ cations dominates

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Abstract: A new organic inorganic hybrid perovskite material of MAPbBr3-xIx has been synthesized via a simple one step spinning method. The crystal structure, microstructure and surface morphologies, surface physic-chemical

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state were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy dispersion spectrum (EDS), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). Meanwhile, ammonia, ethanol and acetone sensing tests were evaluated at room temperature of 15◦C and the results show favourable response and selectivity towards ammonia. The gas sensing mechanism of MAPbBr3-xIx perovskite based sensor is also discussed. In ammonia gas sensing process, the adsorption, cation exchange and the reversible

weak bonding between MA+ and NH4+ dominate the response and recovery processes. Furthermore, long time and high concentration ammonia gas exposure might accelerate the irreversible decomposition of MAPbBr3-xIx perovskite, which results in a decline in response value. To acetone and ethanol gases, the physical reversible tranfer of electrons from gas molecules to intrinsic bromide vacancies and uncoordinated Pb2+ cations in MAPbBr3-xIx perovskite might be the core of the gas sensing process, which results in short response-recovery time

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(less than 20 s), good repeatability, stability in wider range of gas concentration.

Keywords: (CH3NH3)PbBr3-xIx perovskite; thin film; gas sensor; room temperature gas sensing

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1. Introduction

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With the development of industry technique, the threat from some man-made poisonous, flammable gases, the

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byproduct of industrial civilization, to public health becomes more and more serious, such as eye, skin and nervous system of human. As a important tool to detect various types of the dangerous gases, metal oxide semiconductor

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(MOS) gas sensors have been widely investigated and applied, in spite of their deficiency of high working temperature [1,2], unsatisfied selectivity [3,4] and powerless in the detection of trace gas [5,6]. Researchers have

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paid enough effort to unleash the potential of MOS based gas sensor. For the components of sensing material, some new candidates, such as Ce-doped In2O3 [7], SnS2 [8], Dy2O3 [9], V2O5/ZnV2O6 [10], Ni-doped CaCu3Ti4O12 [11],

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reduced graphene oxide compound [12,13], conducting polymers [14-17], et al., have been synthesized and tested. Besides, highly porous sensing materials, such as nanowire bundle-like WO3-W18O49 [18], 3D porous ZnO microspheres [19], branch-like NiO/ZnO [20], CeO2-SnO2 nanosheets [21], et al., fabricated by hydrothermal or electrospinning method have shown improved gas sensing performance due to their higher effective reaction area. Miniaturization, integration and multifunction are the future of gas sensor, which requires the sensing material to be

easily forming into film. But it is difficult for normal MOS to match substrate, resulting in falling off from substrate. This might be the cause thin film type gas sensor receives less attention. Inorganic halides and methylammoniam lead perovskite materials (MAPbX3), as a new excellent light harvester with the structure of ABX3, have attracted great interests of researchers due to their incident photo-to-electron conversion efficiency (IPCE) over 20%. At present, some researchers discover that perovskite materials can interact with some gas atmosphere. It has been reported that the color of MAPbI3 [22,23] and MAPbBr3 [24] changed when

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they were exposed to ammonia gas, which leaded to resistance change of perovskite materials. Exhilaratingly, all the changes occurred at room temperature meaning less energy consumption, simpler sensor design and safer working conditions. While, for MOS sensors, gas detection (take NH3 for example [25-29]) at room temperature

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needs the sensing materials owing some special character such as nanosized particles, porous microstructure and

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special composition which need more complex preparation process compared with that of perovskite materials (only dissolving, spinning and drying). Antonio Tricoli et al. reported the detection of Oxygen with various

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concentration by CsPbBr3 [30]. Organ-inorganic layered (C4H9NH3)2PbI4 was reported in B. D. Fahlman’ works in

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which it exhibited favourable selectivity and response to p-xylene at the working temperature of 140℃ [31]. In addition, some researches have reported about the X-site substitution in perovskite structure by Cl- and SCN-

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[32,34]. In spite of the promising prospect, a obvious defect of perovskite materials, the unsatisfied stability, were mentioned almost in all research reports [35-38]. If the I- on X-site is replaced by other halide ions with smaller size

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(Br- or Cl-), the crystallization structure of perovskite will transform from tetragonal into cubic phase which might make the perovskite more stable. In this study, a new perovskite MAPbBr3-xIx thin film, in which I- ions at X-sites is replaced partly by Br- ions, has been successfully synthesized by a simple spin coating method and characterized. The gas sensing properties at the working temperature of 15℃, the lowest working temperature as we know, have been investigated. We reveal

that the gas sensing mechanism of MAPbBr3-xIx in ammonia is deffer from that in ethanol and acetone. 2. Experimental 2.1 Synthesis of MAPbBr3-xIx perovskite thin film In our study, methylammonium iodide (MAI, not less than 99 wt%) was purchased from Hangzhou Zhongneng Optoelectr-onic Co., Ltd, China. Other chemical reagents, lead bromide (PbBr2) and N,N-dimethylformamide (DMF) were all AR grade and purchased from China National Pharmaceutical Group Corporation, without any

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further treatment. A one step spinning method was used to fabricate the perovskite thin film and the procedure was as follows: PbBr2 of 1.1 g and MAI of 0.48 g were dissolved in 6 ml DMF with stirring at 70℃ for 30 min to form a uniform precursor solution in light yellow color. After ultrasonic cleaning, interdigital electrode substrate (4 mm ×

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6 mm) was immersed in 1 M NaOH solution and 1 M HCl solution for 20 min in sequence, then washed by

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deionized water for three times, finally dried by nitrogen. The as-prepared precursor solution was dropped on the

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treated interdigital electrode substrate and then spin-coated at 3000 rpm for 30 s. Subsequently, the coated substrate was heated at 100℃ for 20 min to eliminate residual DMF and promote the crystallization process of perovskite.

2.2 Characterization

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Finally, the MAPbBr3-xIx perovskite thin film formed.

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The crystal structure of perovskite thin film was characterized by an X-ray diffractometer, XRD (model: D/max-RB with an accelerating voltage of 40 kV) with an Cu Kα1 radiation (λ = 1.54059 Ǻ). The XRD patterns

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were recorded using a scan rate of 8 °/min, step size of 0.02 ° at room temperature. The microstructure morphology and element distribution of perovskite thin film were recorded by a field-emission scanning electron microscope (FE-SEM, FEI Quanta 250 with an accelerating voltage of 30 kV) and Energy Dispersion Spectrum (EDS), respectively. Furthermore, to analyze the surface morphology of perovskite thin film, an atomic froce microscpoe (AFM, model: Dimension Edge, Bruker Nano Inc.) analysis was carried out. A X-ray photoelectron spectroscopy

(XPS) was used to characterize the surface physic-chemical state of perovskite thin film by using a multi-technical surface analysis system (model: ESCALAB250, Thermo VG, America) with an Al Kα radiation(1486.6 eV), and the energy calibration was set to the binding energy of C 1s core level electron of 284.6 eV. 2.3 Sensor preparation and gas sensing test The as-prepared substrate coated by MAPbBr3-xIx perovskite thin film was welded on a special pedestal shown as Fig. 1. The golden electrode on each end of the substrate connected to one metal terminal which supplied the test

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voltage of 5.0 V. Because the gas sensing tests were performed at room temperature, the other four metal terminals were empty. A gas sensing system from ZhenZhou Winsen Technology Co., LTD. (model: WS-30A) was used to recorded the voltage (or resistance) patterns. Environmental conditions in our experiments were as followed: the

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pressure was of 100-103 kPa, the working temperature (room temperature) was 15℃ and the relative humidity was

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about 42%. In the testing system, the gas response and recovery processes occurred in a sealed chamber (about 18.0

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L in volume) including a gas inlet and outlet. Dry ammonia (NH3, 99.99%) was supplied by a sealed gas bag. Acetone and ethanol gases were obtained via the evaporation of the corresponding injected pure liquids whose volume had

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be converted into required gas concentration. Gas response (S) is defined as S=Ra/Rg, where Ra and Rg are the resistances of the tested sensor in air and in target gas, respectively. Response and recovery time is defined as the

respectively.

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time taken by the sensor to achieve 90% of the total resistance change in the case of adsorption and desorption,

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Fig. 1 The schematic diagram of MAPbBr3-xIx perovskite thin film based gas sensor.

3. Results and discussion 3.1 Materials characterization To confirm the crystal structure of the synthesized thin film, a XRD analysis was performed and the resulted pattern is show as Fig. 1. From Fig. 1, the diffraction peaks at 14.9 °, 21.3 °, 26.2 °, 30.4 °, 34.1 ° and 43.4 ° can be

assigned to the crystal planes of (100), (110), (008), (200), (201) and (202), respectively, which can be indexed as the inorganic perovskite structure of CsPbBr3 [31] more perfectly than any other in our database. In addition, the diffraction peak at 26.2 ° does not belong to the character diffraction peaks of CsPbBr3, but it fits well the diffraction peak of hybridization perovskite of (C4H9NH3)2PbI4 [31]. So the synthesized thin film owes definite perovskite structure and is signed by MAPbBr3-xIx. Fig. 2 XRD pattern of MAPbBr3-xIx perovskite thin film.

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The SEM images of MAPbBr3-xIx perovskite thin film are shown in Fig. 3. From Fig. 3 a, it can been seen that the thin film is not compact and smooth, showing the character of irregular polygon or star shapes. Besides, these polygons and stars are not absolute isolation but interconnected, which makes the thin film a conductive whole, not

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fragments. And no any trace of residual DFM can be found. From the image of cross section of our perovskite layer,

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Fig.3 b, the thickness of the film is about 1 μm. The EDS area element mapping record is shown as Fig.3 c-h which

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indicate that the elements of C, N, Br, Pb and I present with uniform diffusion. The AFM results are shown in Fig. 4, from which it is obvious that the perovskite particles connected to each

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other are of polygon shapes and about 1 μm in size. And the perovskite thin film is not compact due to some obvious cracks, which is consistent with the result from the SEM image.

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Fig. 3 (a) SEM images of MAPbBr3-xIx perovskite layer, (b) crossing section of perovskite layer, (c-h) EDS area element mapping.

Fig. 4 AFM images of MAPbBr3-xIx layer surface morphologies. (a) plan image, (b) 3-D profile

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The elemental composition and chemical states of the MAPbBr3-xIx perovskite thin film surface measured by XPS are shown as Fig. 5. Fig. 5 a shows the XPS survey spectrum. It is evident that the main constituent elements are I, Br, Pb, N and C. From Fig. 5 b, the signal peak of I 3d is split into two peaks at 627.8 eV and 616.3 eV, which are assigned to I-. The evident peaks of Pb 4f3/2 and Pb 4f5/2 is located at 140.1 eV and 135.3 eV, respectively, shown in Fig. 5 c, which are assigned to Pb2+. In Fig. 5 e, a single peak of N 1s at 399.3 eV can be ascribed to

benzenoid amino group (-NH-). Furthermore, signal peak of the spectrum in Fig. 5 d located at 65.5 eV can be assigned to Br-. Fig. 5 XPS spectra of MAPbBr3-xIx perovskite thin film (a) survey spectra, (b) I 3d, (c) Pb 4f, (d) Br 3d and (e) N 1s.

3.2 Gas sensing performance of MAPbBr3-xIx perovskite thin film based sensor In practice, the gas sensing performance of traditional gas sensor has instantiated by means of recording the change of sensor’s resistance. For MOS gas sensors, the working temperature is a major factor which infects the

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response and recovery processes. However, perovskite based gas sensor can work at room temperature [30-32]. In our tests, at the working temperature of 15℃, the real-time resistances of the as-prepared gas sensor were recorded before and after exposing in 100 ppm of ammonia, acetone and ethanol gases, respectively, and the results are

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shown in Fig. 6. The resistance of MAPbBr3-xIx sensor is about 25000 kΩ in air, which decreases to 2200 kΩ in

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ammonia (Fig. 6 a), 8000 kΩ in acetone (Fig. 6 b) and 17500 kΩ in ethanol (Fig. 6 c), respectively. It is evident that

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the sensor’s resistance decreases in all tested gases and recovers after the tested gases being pumped out, which indicates that the gas sensing performance is similar to that of n-type semiconductor sensor. Furthermore, the

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response-recovery curves show short response and recovery times of 10 to 20 s. Fig. 6 Real-time resistance curves of MAPbBr3-xIx perovskite thin film to 100 ppm tested gas of (a) ammonia gas, (b) acetone and (c)

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ethanol.

In order to estimate the effect of gas concentration on gas sensing performance of the as-prepared MAPbBr3-xIx

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sensor, the response-recovery curves to ammonia, acetone and ethanol gases were measured and the results are shown in Fig. 7. From Fig. 7 a, it is evident that the response value increases with increasing gas concentration from 50 to 500 ppm in all tested gases. To ammonia, the response value is 7.5 to 50 ppm and increases to the top value of 29.7 to 500 ppm. To acetone and ethanol, the response values in low concentration of 50 ppm are 1.7 and 1.5, respectively. With increasing gas concentration, the gas response value to acetone shows obvious increase to

the max value of 13.4; while the increasing ethanol concentration does not cause the obvious increase of response of the sensor and the top value is 7.0 to 500 ppm. As a summary of above, the as-prepared sensor shows good response and selectivity towards ammonia, especially in low gas concentration (Fig. 7 b). Fig. 7 (a) Responses of MAPbBr3-xIx perovskite thin film sensor to ammonia, acetone and ethanol with different gas concentrations, (b)

partial enlarged detail of figure (a).

Fig. 8 Repeatability stability of MAPbBr3-xIx perovskite thin film sensor in 500 ppm gas. (a) ammonia, (b) acetone, (c) ethanol.

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Stability is also important performance for gas sensor including long-term and short-term stability. Unsatisfied long-term stability is universal for inorganic-organic hybrid perovsk ite material which should decompose in the natural environment slowly, due to the presence of H2O and O2. So Fig. 8 shows only the short-term stability curves

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of the as-prepared MAPbBr3-xIx sensor to 500 ppm ammonia, acetone and ethanol gases. From Fig. 8 a, it is shown

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that the responses in the first two response-recovery cycles are similar and favourable (response values of 25.6 and

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26.3), but a slightly decrease of response value presents in third (23.9) and forth (22.9) cycles, which indicates something special might occurs in gas sensing process. However, in Fig. 8 b or c, all the response and recovery

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curves are similar including response value, response and recovery time, which suggests a favourable short-term stability in acetone and ethanol gases.

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3.3 Gas sensing mechanism

For MOS gas sensor, the gas sensing mechanism has been agreed on a worldwide consensus to be a surface

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controlling process described by three steps: adsorption, redox and desorption, in which obvious change of sensor’s resistance takes place. The core of the theoretical model is the change of the depletion layer thickness caused by redox between absorbed oxygen and reducing gas. In contrast, the gas sensing mechanism of perovskite material is now on the elementary stage without any mature mechanism support. B. D. Fahlman suggested that the physical adsorption of p-xylene on (C4H9NH3)2PbI4 was the key to p-xylene gas sensing mechanism [31]. G. Kahavelakis et

al. reported that the electrons transfered from O3 to Pb2+ neutralized the excess positive charges, resulting in modulating the surface recombination rate of the perovskite sensing material, which was similar to the model of the (MOS) sensor to O3 [32]. Ruimin Zhu et al. explained the gas sensing mechanism of MAPbBr3 to NO2 by electrons transfer between NO2 and MAPbBr3 molecules [33]. In ammonia gas sensing process, the red MAPbBr3-xIx thin film turned into gray and recovered when ammonia gas was evacuated, which indicates the presence of chemical reaction. In our opinion, MA+ ions on A sites are

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replaced by NH4+ when exposure to ammonia gas and return to A-sites again when ammonia is eliminated. Besides, a simple redox model is proposed to explain the process including a reduction reaction of MA+ to MA and a

MAPbBr3-xIx (s) + NH3 (g)

MAPbBr3-xIx·MA (s)

(1)

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oxidation reaction of NH3 to NH4+. And the process can be expressed by the following reversible reaction:

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The replacement of MA+ cations by NH4+ should not destroy the perovskite structure. Furthermore, it is suggested that the dissociated MA molecular still bonds to [PbX6]4- through some weak physical way and the bonding might

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be broken when ammonia gas is expelled. In the process of recovery, NH4+ ions are replaced by MA+ ions which

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return to A-sites, reduced NH3 molecules are expelled. This replacement leads to decrease and increase of gas sensor’s resistance, showing the response and recovery of the MAPbBr3-xIx sensor to ammonia. Our experimental

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results in low ammonia concentration are shown as Fig. 6 a and agreed with the conclusions from the works of C. R. McNeill [24] and S. Ptasinska [39].

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However, the longer time exposure and higher concentration ammonia (500 ppm) lead to some decline in response value shown as Fig. 8 a, which is not in accordance with the above mechanism completely. To obtain deeper insight, extreme experiments were performed. The MAPbBr3-xIx sensor was set in 1×105 ppm ammonia gas for 20 min. After treatment, the color of the sensor changed from red to gray and did not recover. The crystal structure of the gray sample was characterized by XRD and the result is shown in Fig. 9 a, in which the characteristic diffraction

peaks of original perovskite shown in Fig. 2 disappear completely. And three new characteristic peaks signed by ‘▼’ and ‘◇’can be indexed by PbBr1.2I0.8 and PbBr2 according to JCPDS No. 43-0948 and 46-0992, respectively. We suppose that some other reactions performed in our ammonia sensing process, which can be summarized by the following equations: MAPbBr3-xIx (s)

MABr1-xIx (s) + PbBr2 (s)

MABr1-xIx (s) + NH3 (g)

MA (s) + NH4Br1-xIx (s)

(2) (3)

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Due to the presence of H2O and O2, the MAPbBr3-xIx thin film should decompose slowly described by the irreversible reaction equation 2. Ammonia molecule owns stronger polarity than that of MA which makes MA+ being replaced by NH4+ easily. With increasing ammonia concentration, the cations replacement process shown as

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equation 3 is accelerated, which in turn improves the decomposition in equation 2, resulting in absolute phase

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transformation of the MAPbBr3-xIx thin film and irreversible gray color. The two processes are simultaneous and

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independent of each other. The decomposition of MAPbBr3-xIx keeps proceeding but negligible when it is exposed to low concentration ammonia (less than 200 ppm) because of the slow reaction velocity. Meanwhile, the exchange

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between NH4+ and MA+ and the bonding of MA to NH4PbBr3-xIx are rapid. So the satisfied response-recovery processes present. When exposed to higher ammonia concentration of 500 ppm, increasing the exposure time, the

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response value decreases gradually and the recovery time increases shown as Fig. 8 a. This means that the cumulative effect of decomposition can not be negligible. The deteriorated ammonia atmosphere (ultra high

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concentration or longer exposure time) should make the decomposition of MAPbBr3-xIx perovskite thin films worse.

Fig. 9 XRD patterns of MAPbBr3-xIx perovskite thin film after treatment (a) by ammonia, (b) by acetone, and (c) by ethanol.

Unlike the color change in ammonia sensing process, there were little detectable color change about the MAPbBr3-xIx thin film in acetone and ethanol sensing processes. To further investigation, the as-prepared sensors

were washed by acetone or ethanol liquid for 10 s and characterized by XRD subsequently. The XRD results are shown in Fig. 9 b and c. It is evident that all the characteristic peaks, signed by ‘*’ , are similar to those in Fig. 2, indicating that the MAPbBr3-xIx sensors show satisfied stability in acetone and ethanol sensing processes. It is accepted that lead halide perovskite owns ambipolar charger transporters including hole active group and electron active group, but the electrons will not transfer from cations to final electronic structure of lead halide perovskite, which results in high resistance of perovskite material. In addition, shortage of bromide and uncoordinated Pb2+

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ions lead to the formation of positive charge net structure in lead halide perovskite, which causes perovskite material response to environmental gases [30,32]. When exposed to acetone (ethanol) gas, a rapid adsorption process of acetone (ethanol) molecules forms on the surface of MAPbBr3-xIx sensor. Subsequently, electrons should

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transfer from acetone (ethanol) molecules to the intrinsic bromide vacancies and uncoordinated Pb2+ ions, which

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neutralizes the excess positive charges in MAPbBr3-xIx sensor, thus the resistance decreases. When acetone (ethanol)

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is pumped out, the electrons transfer process interrupts and the resistance of sensor recovers. So the whole response and recovery processes are physical reversible adsorption and desorption without any damage to MAPbBr3-xIx

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sensor, which is confirmed by Fig. 9 b and c.

In summary, the as-prepared MAPbBr3-xIx sensor shows a favourable potential application in low concentration

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ammonia detection owning to the rapid response and recovery, satisfied selectivity. For deeper insight of the sensing mechanism, satisfied long term stability and repeatability, further exploration should be performed.

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4 Conclusion

Overall, organic-inorganic hybrid perovskite material of MAPbBr3-xIx, a new candidate of gas sensing materials, has been synthesized by a one step spinning method. The results of gas sensing tests show favourable sensing performance at the working temperature of 15℃. To ammonia, the MAPbBr3-xIx sensor has the highest response value of 29.7 (500 ppm), good selectivity, rapid response-recovery and acceptable stability in low concentration

(less than 200 ppm). Adsorption, cation exchange and reversible weak bonding of MA+ and NH4+ are the key roles to gas sensing process. Meanwhile, long time exposure to high concentration ammonia will accelerate the irreversible decomposition of MAPbBr3-xIx, which causes the unsatisfied long-time stability. To acetone and ethanol gases, physical reversible electrons transfer to intrinsic bromide vacancies and uncoordinated Pb2+ cations dominates the whole gas sensing process, which leads to considerable sensing performance including short response-recovery time (less than 20 s), good repeatability and evident response value of 13.4 and 7.1 to 500 ppm

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acetone and ethanol, respectively.

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References

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[1] B. Zhang, G. N. Liu, M.Cheng, Y. Gao, L. J. Zhao, S. Li, F. M. Liu, X. Yan, T. Zhang, P. Sun, G. Y. Lu, The

lP

preparation of reduced graphene oxide-encapsulated α-Fe2O3 hybrid and its outstanding NO2 gas sensing properties at room temperature. Sens. Actuators B: Chem., 261 (2018) 252-263.

na

[2] H.M. Jeong, J.H. Kim, S.Y. Jeong, C.H. Kwak, J.H. Lee, Co3O4-SnO2 hollow heteronanostructures: facile control of gas selectivity by compositional tuning of sensing materials via galvanic replacement, ACS Appl. Mater.

ur

Interfaces, 8 (2016) 7877-7883.

[3] S.J. Hwang, K.I. Choi, J.W. Yoon, Y.C. Kang, J.H. Lee, Pure and palladium-loaded Co3O4 hollow hierarchical

Jo

nanostructures with giant and ultraselective chemiresistivity to xylene and toluene, Chem. Eur. J., 21 (2015) 5872-5878.

[4] H.S. Woo, C.H. Kwak, J.H. Chung, J.H. Lee, Co-doped branched ZnO nanowires for ultraselective and sensitive detection of xylene, ACS Appl. Mater. Interfaces, 6 (2014) 22553-22560. [5] H.Y. Xu, D.X. Ju, W.R. Li, J. Zhang, J.Q. Wang, B.Q. Cao, Superior triethylaminesensing properties based on

TiO2/SnO2 n-n heterojunction nanosheets directly grown on ceramic tubes, Sens. Actuators B: Chem., 228 (2016) 634-642. [6] M.H. Li, H.C. Zhu, B. Wang, J. Cheng, W.P. Yan, S.F. Xia, Z.N. Tang, Ultrasensitive and highly selective detection of methoxy propanol based on Ag-decorated SnO2 hollow nanospheres, Sens. Actuators B: Chem., 232 (2016) 545-556. [7] X. J. Liu, L. Jiang, X. M. Jiang, X. Y. Tian, X. Sun, Y. L. Wang, W. D. He, P. Y. Hou, X. L. Deng, X. J. Xu,

ro of

Synthesis of Ce-doped In2O3 nanostructure for gas sensor applications. Applied Surface Science, 428 (2018) 478-484.

[8] Y. H. Kima, D. T. Phana, S. Ahna, K. H. Namb, C. M. Park, K. J. Jeon, Two-dimensional SnS2 materials as

-p

high-performance NO2 sensors with fast response and high sensitivity. Sens. Actuators B: Chem., 255 (2018)

re

616-621.

lP

[9] X. Dong, X. L. Cheng, X. F. Zhang, L. L. Sui, Y. M. Xu, S. Gao, H. Zhao, H. Huo, A novel coral-shaped Dy2O3 gas sensor for high sensitivity NH3 detection at room temperature. Sens. Actuators B: Chem., 255 (2018)

na

1308-1315.

[10] B. X. Xiao, H. Huang, X. T. Y. J Song, J. L. Qu, Facile synthesis of layered V 2O5/ZnV2O6 heterostructures

ur

with enhanced sensing performance. App. Sur. Sci., 447 (2018) 569-575. [11] A. Boontum, D. Phokharatkul, J. H. Hodaka, A. Wisitsoraat, S. K. Hodak, H 2S sensing characteristics of

Jo

Ni-dope01d CaCu3Ti4O12 films synthesized by a sol-gel method. Sens. Actuators B: Chem., 260 (2018) 877-887. [12] B. Zhang,

M. Cheng, G. N. Liu, Y. Gao, L. J. Zhao, S. Li, Y. P. Wang, F. M. Liu, X. S. Liang, T. Zhang, G. Y. Lu, Room

temperature NO2 gas sensor based on porous Co3O4 slices/reduced graphene oxide hybrid. Sens. Actuators B: Chem., 263 (2018) 387-399. [13] M. Shafiei, J. Bradford, H. Khan, C. Piloto, W. Wlodarski, Y. X. Li, N. Motta, Low-operating temperature NO2

gas sensor based on hybrid two-dimensional SnS2-reduced graphene oxide. Sens. Actuators B: Chem., 462 (2018) 330-336. [14] C. H. Liu, H. L. Tai, P. Zhang, Z. Yuan, X. S. Du, G. Z. Xie, Y. D. Jiang, A high-performance flexible gas sensor based on self-assembled PANI-CeO2 nanocomposite thin film for trace-level NH3 detection at room temperature. Sens. Actuators B: Chem., 261 (2018) 587-597. [15] S. Abdulla, T. L. Mathew, B. Pullithadathil, Highly sensitive, room temperature gas sensor based on polyaniline-

ro of

multiwalled carbon nanotubes (PANI/MWCNTs) nanocomposite for trace-level ammonia detection. Sens. Actuators B: Chem., 221 (2015) 1523-1534.

[16] P.G. Su,C. T. Lee, C. Y. Chou, Flexible NH3 sensors fabricated by in situ self-assembly of polypyrrole,

-p

Talanta, 80 (2009) 763-769.

[17] O. S. Kwon, E. Park, O. Y. Kweon, S. J. Park, J. Jiang, Novel flexible chemical gas sensor based on poly(3,4-

re

ethylenedioxythiophene) nanotube membrane, Talanta, 82 (2010) 1338-1343.

[18] Y. Xiong, Z. Y. Zhu, T. C. Guo, H. Li, Q. Z. Xue, Synthesis of nanowire bundle-like WO3-W18O49

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heterostructures for highly sensitive NH3 sensor application. Journal of Hazardous Materials, 353 (2018) 290-299. [19] Z. Shen, X. D. Zhang, X. H. Ma, Y. Chen, M. Liu, C. Chen, S. P. Ruan, Synthesis of hierarchical 3D porous

na

ZnO microspheres decorated by ultra-small Au nanoparticles and its highly enhanced acetylene gas sensing ability. J. Alloys Compd., 731 (2018) 1029-1036.

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[20] N. Kaur, D. Zappaa, M. Ferroni, N. Poli, M. Campanini,R. Negrea, E. Comini, Branch-like NiO/ZnO heterostructures for VOC sensing. Sens. Actuators B Chem. 262 (2018) 477-485.

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[21] S. H. Yan, X. Y. Liang, H. S. Song, S. Y. Ma, Y. Lu, Synthesis of porous CeO2-SnO2 nanosheets gas sensors with enhanced Sensitivity. Ceram. Int., 44 (2018) 358-363. [22] Y. X. Zhao, K. Zhu, Optical bleaching of perovskite (CH3NH3)PbI3 through room-temperature phase transformation induced by ammonia. Chem. Commun.,50 (2014) 1605-1607. [23] C. X. Bao, J. Yang, W. D. Zhu, X. X. Zhou, H. Gao, F. M. Li, G. Fu, T. Yu, Z. G. Zou, A resistance change effect in perovskite CH3NH3PbI3 films induced by ammonia. Chem. Commun., 51 (2015) 15426-15429.

[24] S. Ruan, J. F. Lu, N. Pai, H. Ebendorff-Heidepriem, Y. B. Cheng, Y. Ruan, C. R. McNeill, An optical fibre-based sensor for the detection of gaseous ammonia with methylammonium lead halide perovskite. J. Mater. Chem. C, 6 (2018) 6988-6995. [25] H. X. Tang, M. Yan, H. Zhang, S. Z. Li, X. F. Ma, M Wang, D. R. Yang, A selective NH3 gas sensor based on Fe2O3-ZnO nanocomposites at room temperature. Sens. Actuators B Chem. 114 (2006) 910–915. [26] N. V. Hieu, L. T. B. Thuy, N. D. Chien, Highly sensitive thin film NH3 gas sensor operating at room temperature

ro of

based on SnO2/MWCNTs composite. Sens. Actuators B Chem. 129 (2008) 888-895.

[27] Q. Q. Lin, Y. Li, M. J. Yang, Tin oxide/graphene composite fabricated via a hydrothermal method for gas sensors working at room temperature. Sens. Actuators B Chem. 173 (2012) 139-147.

-p

[28] R. Ghosh, A. Singh, S. Santra, S. K. Ray, A. Chandra, P. K. Guha, Highly sensitive large-area multi-layered

re

graphene-based flflexible ammonia sensor, Sens. Actuators B Chem. 205 (2014) 67-73.

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[29] H. Li, W. Y. Xie, B. Liu, C. X. Wang, Y. R. Wang, X. C. Duan, Q. H. Li, T. H. Wang, Gas modulating effect in room temperature ammonia sensing, Sens. Actuators B Chem. 242 (2017) 404-411.

na

[30] H. J. Chen, M. Zhang, R. H. Bo, C. Barugkin, J. H. Zheng, Q. S. Ma, S. J. Huang, W. Y. Ho-Baillie, K. R. catchpole, A. Tricoli, Superior self-powered room-temperature chemical sensing with light-activated inorganic

ur

halides perovskite. Chem. Sen., 10 (2017) 1702571-1702577. [31] M. Y. Zhu, L. X. Zhang, J. Yin, J. J. Chen, L. J. Bie, B. D. Fahkman, Physisorption induced p-xylene

Jo

gas-sensing performance of (C4H9NH3)2PbI4 layered perovskite. Sens. Actuators B: Chem., 282 (2019) 659-664. [32] G. Kakavelakis, E. Gagaoudakis, K. Petridis, V. Ptromichelaki, V Binas, G. Kiriakidis, E. Kymakis, Solution processed CH3NH3PbI3-xClx perovskite based self-powered ozone sensing element operated at room temperature. ACS. Sens., 3 (2018) 135-142.

[33] R. M. Zhu, Y. Z. Zhang, H. Zhong, X. L. Wang, H. Xiao, Y. L. Chen, X. Y. Li. High-performance room-temperature NO2 sensors based on CH3NH3PbBr3 semiconducting films: Effect of surface capping by alkyl chain on sensor performance. J. Phys. Chem. Solids, 129 (2019) 270-276. [34] Y. Zhuang, W. J. Yuan, L. Qian, S. Chen, G. Q. Shi, High-performance gas sensors based on a thiocyanate ion-doped organometal halide perovskite. Phys. Chem. Chem. Phys., 19 (2017) 12876-12881. [35] J. H. Kim, S. H. Kim, Sub-second pyridine gas detection using a organometal halide perovskite functional dye.

ro of

Dyes Pigments, 134 (2016) 198-202.

[36] H. H. Fang, S. Adjokatse, H. T. Wei,J. Yang, G. R. Blake, J. S. Huang, J. Even, M. A. Loi, Ultrahigh sensitivity of methylammonium lead tribromide perovskite single crystal to environmental gases. Sci. Adv., 2 (2016) 1600534-

-p

1600542.

re

[37] S.H. Kim, A. Kirakosyan, J. Choi, J. H. Kim, Detection of volatile organic compounds (VOCs), aliphatic

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amines, using highly fluorescent organic-inorganic hybrid perovskite nanoparticles. Dyes Pigments, 147 (2017) 1-5.

na

[38] M. A. Stoeckel, M. Gobbi, S. Bonacchi, F. Liscio, L. Ferlauto, E. Orgiu, P. Samorì, Reversible, Fast, and Wide-Range Oxygen Sensor Based on Nanostructured Organometal Halide Perovskite. Adv. Mater., (2017)

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1702469-1702475.

[39] W. X. Huang, J. S. Manser, S. Sadhu, P. V. Kamat and S. Ptasinska, Direct Observation of Reversible

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Transformation of CH3NH3PbI3 and NH4PbI3 Induced by Polar Gaseous Molecules. J. Phys. Chem. Lett., 7 (2017) 5068-5073.

Author Biographies

Wanli JIAO, female, (1977 - ), associate professor, works in Shandong University of Technology. Focus on synthesis and characterization of semiconductor sensing materials and preparation of porous nano microstructure materials. Jing HE, female, (1979 - ), lecturer, works in Shandong University of Technology. Focus on synthesis and characterization nano semiconductor light sensitive materials.

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Lei ZHANG, male, (1977 - ), associate professor, works in Shandong University of Technology. Focus on synthesis and characterization of semiconductor gas sensing materials.

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Fig. 1 The schematic diagram of MAPbBr3-xIx perovskite thin film based gas sensor.

Intensity (a.u.)

(008)

(200) (202) (110)

(201)

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(100)

2 Theta (degree)

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Fig. 2 XRD pattern of MAPbBr3-xIx perovskite thin film.

a

b

2μm

20 µm

µm 11 µm

1 µm µm

f

g

ee

1 µm µm

Pb

N

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I

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Br

C

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cc

11 µm µm

µm 11 µm

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11 µm µm

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element mapping.

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Fig. 3 (a) SEM images of MAPbBr3-xIx perovskite layer, (b) crossing section of perovskite layer, (c-h) EDS area

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a

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Fig. 4 AFM images of MAPbBr3-xIx layer surface morphologies. (a) , (b) 3D

I3d

b

Binding Energy (eV)

Binding Energy (eV)

Pb4f

e

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Intensity (a. u.)

N1s

Binding Energy (eV)

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Binding Energy (eV)

Br 3d

d

Intensity (a. u.)

Intensity (a. u.)

c

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Br3d

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Intensity (a. u.)

Pb4f C1s N1s

I 3d

Intensity (a. u.)

a

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Binding Energy (eV)

Fig. 5 XPS spectra of MAPbBr3-xIx perovskite thin film (a) survey spectra, (b) I 3d, (c) Pb 4f, (d) Br 3d and (e) N 1s.

Resistance (kΩ)

Resistance (kΩ)

b

a

Time (s)

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Resistance (kΩ)

Time (s)

Time (s)

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Fig. 6 Real-time resistance curves of MAPbBr3-xIx perovskite thin film in 100 ppm tested gas of (a) ammonia gas,

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(b) acetone and (c) ethanol.

500 ppm

Ammonia

× Acetone Ethanol

200 ppm 100 ppm 50 ppm

Time (s)

50 ppm

Gas out

Ammonia

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× Acetone Ethanol

Gas in

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Response (Ra/Rg)

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Response (Ra/Rg)

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Time (s)

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Fig. 7 (a) Responses of MAPbBr3-xIx perovskite thin film sensor in ammonia, acetone and ethanol with different gas

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concentrations, (b) partial enlarged detail of figure (a).

Response (Ra/Rg)

a

Time (s)

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Response (Ra/Rg)

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Response (Ra/Rg)

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(c) ethanol.

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Fig. 8 Repeatability stability of MAPbBr3-xIx perovskite thin film sensor in 500 ppm gas. (a) ammonia, (b) acetone,

▼PbBr1.2I0.8 ◇ ▼

▼

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b

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c

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Intensity (a.u.)

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a

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Fig. 9 XRD patterns of MAPbBr3-xIx perovskite thin film after treatment (a) by ammonia, (b) by acetone, and (c) by

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ethanol.