Controllable Vapor-Phase Growth of Inorganic Perovskite Microwire

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Controllable Vapor-Phase Growth of Inorganic Perovskite Microwire Networks for High-Efficiency and Temperature-Stable Photodetectors Ying Li, Zhifeng Shi, Lingzhi Lei, Zhuangzhuang Ma, Fei Zhang, Sen Li, Di Wu, Tingting Xu, Xinjian Li, Chongxin Shan, and Guotong Du ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.8b00348 • Publication Date (Web): 04 May 2018 Downloaded from http://pubs.acs.org on May 5, 2018

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Controllable Vapor-Phase Growth of Inorganic Perovskite Microwire Networks for High-Efficiency and Temperature-Stable Photodetectors Ying Li,1 Zhifeng Shi,*1 Lingzhi Lei,1 Zhuangzhuang Ma,1 Fei Zhang,1 Sen Li,1 Di Wu,1 Tingting Xu,1 Xinjian Li,*1 Chongxin Shan,1 and Guotong Du2 1

Key Laboratory of Materials Physics of Ministry of Education, Department of Physics and

Engineering, Zhengzhou University, Daxue Road 75, Zhengzhou 450052, China 2

State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and

Engineering, Jilin University, Qianjin Street 2699, Changchun 130012, China

ABSTRACT: Recently, metal halide perovskites have attracted tremendous research interests due to their exceptional optoelectronic properties, showing great application potentials in the fields of solar cells, light-emitting diodes, and photodetectors. However, most of the previously reported perovskite photodetectors are based on the polycrystalline perovskite films, and the amounts of defects and large grain boundaries in the films are unfavorable for further improvement the performance of the device. In this study, high-quality CsPbCl3 microwire networks (MWNs) were successfully prepared by a vapor-phase method. By changing the evaporation temperature of source powders, a series of MWs with different width and coverage can be obtained. Ag electrodes were thermally deposited onto the surface of the mica substrate

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through a shadow mask, and symmetrically structured photoconductive detectors were fabricated. The performance of the studied photodetector is remarkable in terms of its high on/off photocurrent ratio of 2.0×103, a photoresponsivity of 14.3 mA/W, and a fast response speed of 3.212/2.511 ms. It is worth noting that the fast varying optical signal can be detected even at a high frequency of 3500 Hz. More importantly, the proposed CsPbCl3 MWNs photodetectors without encapsulation demonstrate a remarkable operation stability over the test in air ambient, can withstand a high working temperature of 373 K for 9 h continuous operation, and nearly 70% of the original photocurrent of the photodetectors has been retained, further confirming the ultrastable device operation. Note that this is the first report on high-temperature operation behaviors of perovskite photodetectors. The results in this study may promote the development of stable and high-efficiency perovskites photodetectors compatibility for practical applications under harsh conditions.

KEYWORDS: perovskite, photodetector, CsPbCl3 microwire, response speed, stability


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Photodetectors, which convert incident optical signals to electrical signals, are of great importance in optical communication, astronomy, photography, environment sensing, medical analysis, and safety equipment.1,2 Recently, metal halide perovskite materials have received intensive attention due to their superior capabilities in large-scale manufacturing and costeffective in photodetection applications.3−13 The attractive properties of such materials are their tunable bandgap, strong optical absorption, large carrier diffusion length, high and well-balanced carrier mobility, and simple material processing method. Besides, such newly-emerging metal halide perovskites have regained attentions for their big success in solar cells,14 light-emitting diodes,15 lasers,16 and memristors.17 By contrast, the study on perovskite photodetectors is relatively rare compared to the large efforts on luminescent and solar cells fields, and the previous studies are more inclined to organic-inorganic hybrid perovskites. However, the poor stability of the materials is a major obstacle to their potential applications and reliable device operation. This is because that such hybrid perovskites are easily decomposed into lead-halide and organic-halide in air ambient, and also the ion migration of CH3NH3+ generated by the electric field will lead to short lifetime and efficiency recession of the perovskite-based optoelectronic devices.18−21 Due to the limitation of organic-inorganic hybrid perovskite, inorganic cesium lead halide perovskites (CsPbX3, X=I, Br, and Cl) without any organic cations began to draw a great attention of the scientific community and were considered to be a possible way to solve the above problems because the limitations of being vulnerable to the oxygen, moisture, electrical field, light, and heat can be effectively overcome.22−24 Currently, some studies have proved the photoelectric properties of the inorganic lead halide perovskites, focusing mainly on the CsPbX3 thin films.3−5,7 Compared to the large efforts on CsPbBr3 and CsPbI3 perovskites, the study on CsPbCl3 perovskites is relatively less intensive.


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Among them, Zhang and co-workers reported a transparent ultraviolet photodetector based on inorganic CsPbCl3 nanocrystals thin films. The fabricated device exhibits a high sensitivity to ultraviolet light with high photocurrent on/off ratio and responsivity.25 Although CsPbX3 thin films photodetectors have achieved high photoresponsivity and fast response speed, there still lacks important breakthroughs that could promote perovskite photodetectors into the commercialization stage.26−28 This is probably due to that in the thin films system, the further improvement in the performance of photodetectors is limited, such as a low external quantum efficiency due to the short lifetime of photogenerated carriers and a large number of grain boundaries in polycrystalline structures. Besides, another important issue in thin films-based photodetectors is their device stability. Therefore, a few recent studies start concentrating on the perovskite nanometer and micron structures, which are characterized by less grain boundaries, longer lifetime of the photogenerated carriers, lower defect/trap density, and smaller recombination rate.29−31 For example, Liu et al. reported photodetectors based on solutionprocessed scattered CsPbBr3 nanoplatelets with lateral size as large as 10 µm, in which the photoresponsivity of the single CsPbBr3 nanoplatelet photodetectors is as high as 34 A/W with a bias of only 1.5 V.29 Also, it should be mentioned herein that the ternary compounds of CsPbX3 are not easily dissolving in common solvents, restricting the potential application in solutionprocessed devices. Compared with the solution-processed way, vapor-phase deposition has been widely used in the synthesis of high-quality optoelectronic materials, providing another flexible and convenient method for semiconductor nanostructures growth.32 Besides, the size of vapordeposited CsPbX3 could be accurately controlled compared with the solution-processed one. In this work, high-quality horizontal CsPbCl3 MWNs with controlled morphology were successfully prepared through a simple vapor-phase epitaxial growth on mica substrates. This


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method overcomes the problem of CsCl being poorly soluble in common solvents. As the evaporation temperature of source powders increases, the MWs become thick and gradually form a network structure, until the formation of a full film coverage. Further, metal-semiconductormetal perovskite photodetectors were fabricated and studied by using well-connected CsPbCl3 MWNs as the light absorber. The photodetectors exhibit a high on/off photocurrent ratio of 2.0×103, a responsivity of 14.3 mA/W, and a fast response speed of 3.212/2.511 ms. More importantly, the studied photodetectors, even without encapsulation, demonstrate significant operation stability against oxygen and water degradation in a continuous current mode, and can efficiently sustain the photodetection ability at a high temperature of 373 K for 9 h continuous operation, indicating a high temperature tolerance and ideal compatibility for practical applications. It is reasonably believed that the inorganic CsPbCl3 MWNs can serve as good building blocks for fabricating high-performance photodetectors that can operate well at high temperature. In this experiment, horizontal CsPbCl3 MWNs have been synthesized via a facile one-step chemical vapor deposition method by using a double temperature zone tube furnace, equipped with mass flow controllers and pressure control. The synthesis procedure starts with a freshly cleaved mica substrate (Figure 1a). The precursor used a mixture of CsCl and PbCl2 powders in a molar ratio of 3:1 and was heated in the high temperature zone of the tubular furnace at the temperature range of 520‒600 °C. The mica was used as substrate to collect the products and placed in low temperature zone of the tubular furnace, and the temperature was set to 360 °C. Ultrahigh-purity argon was employed as the carrier gas, and the reaction pressure was maintained at 180 Torr. For each experiment, the evaporation temperature of source powders was varied at five temperature points (520, 540, 560, 580, and 600 °C) to evaluate its effect on


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the morphology properties of CsPbCl3 products. Consequently, five samples were prepared, which were named as A, B, C, D, and E, respectively (Figure 1b). The corresponding preparation parameters were summarized in Table 1. The right-bottom pane of Figure 1 displays the corresponding photographs of the prepared CsPbCl3 product (sample C) and the bare mica substrate. Further, a photodetector was fabricated based on as-synthesized CsPbCl3 MWNs. By depositing Ag onto the CsPbCl3 MWNs using a mask, patterned Ag electrodes bridge was fabricated with a width of 135 µm (Figure 1c).

Figure 1. (a−c) Preparation process of the CsPbCl3 MWNs photodetectors. The left-bottom pane shows the schematic diagram of the synthesis setup. The right-bottom pane presents the typical morphology of the produced CsPbCl3 MWNs. Table 1. Summary of the corresponding preparation parameters Sample No. A B C D E

Molar ratio CsCl:PbCl2 3:1 3:1 3:1 3:1 3:1

Pressure (Torr) 180 180 180 180 180

Temperature Zone I (°C) 520 540 560 580 600


Temperature Zone II (°C) 360 360 360 360 360

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The microstructures of the produced CsPbCl3 MWNs were characterized with Jeol-7500F field emission scanning electron microscopy (SEM). X-ray diffraction (XRD) patterns were recorded by Panalytical X’Pert Pro. The element composition in the products was studied using energydispersive X-ray spectroscopy (EDS), which attached to the SEM. X-ray photoelectron spectroscopy (XPS) was performed using a SPECS XR50 system. The absorption of the CsPbCl3 MWNs was recorded with a Shimadzu UV-3150 spectrophotometer. The photoluminescence (PL) spectra of the CsPbCl3 MWNs were measured with a double grating spectrofluorometer (Horiba; Fluorolog-3). The PL lifetime was measured using a fluorescence lifetime measurement system with a pulsed LED (Horiba; NanoLED, 330 nm). The electrical and optoelectrical measurements were performed in air and at room temperature (RT), using a semiconductor characterization system (Keithley 2400-SCS), an optical chopper (SRS, SR540), a monochromator, a light source, and an oscilloscope (Tektronix, DPO2012B). Figure 2a‒e show the SEM images of the as-synthesized CsPbCl3 MWNs, and some distinct trends are revealed. At a low evaporation temperature of source powders (520 °C, sample A), some CsPbCl3 MWs, horizontally oriented on the mica (001) surface, formed a network through single wires linked to each other. Typically, the width of these wires is ~1.5 µm and their length is several tens of micrometers. It should be mentioned herein that there is no intentionally deposition of a wetting layer prior to perovskite growth, therefore the growth of CsPbCl3 MWs should begin with the heterogeneous nucleation of CsPbCl3 nanocrystals on the mica surface. An additional observation is that many CsPbCl3 MWs are parallel to each other, forming angles at the junctions of MWs, and most interconnected wires is 60° or 120° angle. While, there are many misaligned MWs, which is likely because of the stress and/or nucleation at the cleavage edge of mica substrate. As the evaporation temperature was increased to 540 °C (sample B, Figure 2b),


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the distribution density of CsPbCl3 MWs increases obviously and simultaneously, an increasing trend of width of CsPbCl3 MWs can be observed. The inset in Figure 2b is a magnified SEM image, from which one can see that the MWs are triangular pyramidal with smooth and welldefined surfaces, and these triangular MWs are strongly connected to the underlying mica. Further increasing the evaporation temperature to 560 °C and above (Figure 2c‒e), the distribution density of CsPbCl3 MWs was dramatically increased, and the surface coverage of products increased gradually because more new MWs emerge and they substantially fill up the empty area between the networks. The inset in Figure 2c also confirms the right triangular crosssection by measuring SEM image (45° tilted). We can see from the cross-section view of this line that the apex angle of the triangle is 90o. Consequently, the CsPbCl3 MWs accumulate to form a dense film with only a few holes on the surface when the evaporation temperature was intentionally raised to 600 °C (sample E, Figure 2e). By contrast, the morphology of CsPbCl3 MWNs obtained at high temperatures (sample D, E) deteriorated obviously compared with the counterparts at low temperatures (sample A‒C). We consider that the deteriorated morphology may be due to the fast evaporation rate of source powders, inducing an imperfect crystallization of CsPbCl3 MWNs on the substrate. The crystallographic properties of the as-synthesized CsPbCl3 MWNs were studied by XRD, and sample C was taken as the representative considering that five samples share the similar spectra features and they all possess the same diffraction peaks. Note that the XRD patterns of bare mica were also put together for a better comparison (green curve in Figure 2f). As shown in Figure 2f, the sample C presents only one diffraction peak at 22.59°, which could be assigned to the (110) plane of crystalline CsPbCl3, without other diffractions except for the phases from the underlying mica substrate, indicating the formation of a cubic perovskite structure (space group: Pm 3 m, a=5.561 Å). The above


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observations suggests the epitaxial growth of CsPbCl3 MWNs and the (110) lattice plane is parallel to the substrate surface.33

Figure 2. (a‒e) SEM images of CsPbCl3 MWNs grown on mica with different evaporation temperature of source powders from 520 to 600 °C. The insets in (b‒e) are the locally magnified SEM images of the CsPbCl3 MWNs. (f) XRD patterns of the CsPbCl3 MWNs (sample C), the bare mica substrate and the standard XRD of CsPbCl3 (PDF card: JCPDS No. 01-075-0408). To study the chemical composition of the CsPbCl3 products (sample C), EDS measurements were performed. As shown in Figure 3a, except for the elements of Cs, Pb, and Cl (the detection signals of K, Al, and Si come from the underlying mica substrate), no other element was detected, and the molar ratio of the elements Cs, Pb, and Cl is approximately 1:1:3 as expected from the sample’s stoichiometry. Further, EDS mapping measurements were carried out to investigate the element distribution of the as-synthesized CsPbCl3 MWNs. As shown in Figure 3b, the elements are evenly distributed throughout the networks and perfectly match well with the corresponding SEM image. We further carried out the XPS measurements to study the chemical composition


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and bond states of the produced CsPbCl3 MWNs. Figure 3c shows the wide XPS spectrum of the CsPbCl3 MWNs (sample C), where the signal peaks of Cl (196 eV), Pb (136.5 and 141.4 eV), Cs (722.1 and 736.1 eV), C (282 eV), and N (411 eV) elements were obtained within a specific detection range, which also indicates that the crystalline CsPbCl3 MWNs were well-fabricated. And the molar ratio of incorporated Cs, Pb, and Cl elements is similar to the ideal stoichiometric molar ratio of CsPbCl3. Figure 3d shows the XPS spectra of Cl 2p and Pb 4f of CsPbCl3 MWNs to further analyze the chemical bond configuration of the elements. The two peaks of Cl 2p can be fitted with the binding energies of 197.5 and 195.8 eV, which correspond to the Cl 2p1/2 and Cl 2p3/2 levels, respectively. The doublet states with binding energies of 141.4 and 136.5 eV indicated the existence of Pb 4f5/2 and Pb 4f7/2, respectively. Since the energy levels of the Pb 4f5/2 and Pb 4f7/2 are obviously different from the energy levels in PbCl2 and metallic lead,34,35 the contributions of two Pb 4f peaks are therefore assigned to the stoichiometric CsPbCl3. The optical properties of the CsPbCl3 MWNs were studied by measuring the steady-state PL spectra and ultraviolet-visible absorption at RT. A pronounced absorption peak at 415 nm was observed from Figure 3e. The PL spectrum of the CsPbCl3 MWNs has a highly symmetric emission peak at 420 nm, and the corresponding full width half maximum (FWHM) is about 15.2 nm. It is worth noting that no sub-bandgap emission was observed in the PL spectrum, which is usually related to the defects in perovskites, thereby demonstrating that high-quality perovskite product was obtained. We further performed the time-resolved PL measurements to investigate the optical recombination dynamics of the CsPbCl3 MWNs. As shown in Figure 2f, the PL decay from the CsPbCl3 MWNs can be fitted by three-exponential fitting, and average PL decay lifetime is 30.5 ns, different from the recent reports for perovskite thin films or nanocrystals where the carrier radiative lifetimes are normally a few nanoseconds.36,37 Such a relatively large


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radiative lifetime along with the remarkable PL performance implies an reduced nonradiative recombination centers at the inside and/or surface of CsPbCl3 MWs, allowing longer time for collection and transport photogenerated carriers in the photodetectors.

Figure 3. (a) EDS spectra of the as-synthesized CsPbCl3 MWNs. (b) SEM image of the CsPbCl3 MWNs and the corresponding EDS mapping results (Cs, Cl, and Pb elements). (c) Wide XPS spectrum of the CsPbCl3 MWNs. (d) The XPS spectra corresponding to Pb 4f (bottom pane) and Cl 3d (upper pane) of CsPbCl3 MWNs. (c) Normalized PL spectra and optical absorption spectra of the CsPbCl3 MWNs obtained at RT condition. (d) PL decay spectrum and the fitting curve of CsPbCl3 MWNs. To assess the photoresponse capability of the perovskite MWNs, sample C was chosen as the detection target. Patterned Ag electrodes were thermally deposited onto the surface of the CsPbCl3 MWNs by using a home-made shadow mask. As illustrated in the energy band diagram shown in Figure 4a, the Ag/CsPbCl3 interface is expected to generate a rectifying junction due to the relatively small work function. Two Schottky barriers exist at the Ag/CsPbCl3 interface,


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forming a metal-semiconductor-metal photodetector. Such detectors with a classic structure were extensively employed in optoelectronics, because it combines ease fabrication with facile integration and high performance. Upon illumination, if the photon energy is larger than that of the semiconductor bandgap, the CsPbCl3 MWNs will absorb photons to produce a lot of electron-hole pairs. These electron-hole pairs were quickly separated and collected by opposite electrodes under the external electrical field, resulting in a drastic increase in the photocurrent. Thus, the CsPbCl3 MWNs photodiode can work effectively. Although there is a low Schottky contact barrier at the Ag/CsPbCl3 interface, the energy barrier can be effectively compensated by a low external bias, and therefore the conduction or carrier transport from CsPbCl3 to the contact electrodes occurs. Under the external electric field, a substantial increase in free carrier density can be expected owing to the photoelectric effect, and thus the increased carrier density in CsPbCl3 MWNs upon illumination reduces the effective barrier height, resulting in the easier carriers tunneling and carrier transport, and also contributing to a substantial increase in conductivity. Figure 4b shows the spectral photoresponse of the studied CsPbCl3 MWNs photodetector in the 325‒650 nm wavelength range. Obviously, it is easy to see that the photodetector is sensitive to the light wavelength less than 425 nm, and nearly blind to the light wavelength longer than 430 nm. The obtained spectral selectivity is well in consistent with the absorption curve shown in Figure 3e.


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Figure 4. (a) Energy band diagrams of the Ag/CsPbCl3/Ag structure. (b) Spectral response of the studied photodetectors. (c) I‒V characteristics of the CsPbCl3 MWNs photodetector measured under dark and under different illumination powers. (d) Photocurrent and photoresponsivity obtained at different light illumination powers. (e) Time response of the studied photodetectors with different light illumination intensity. (f) I‒T curves of the photodetectors under different bias voltages.


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Figure 4c shows the current-voltage (I‒V) characteristic curves of the CsPbCl3 MWNs photodetectors under dark and upon light illumination at a wavelength of 405 nm and light intensity from 0.7 mW to 15 mW. With the increase of the illumination power, the photocurrent increased gradually. This result suggests that at a higher optical power, a larger number of charge carriers were generated, resulting in an enhanced photocurrent. In addition, the formula of R = (Ip‒Id)/Popt·S was employed to calculate the photoresponsivity (R) of the CsPbCl3 MWNs photodetectors, where Ip is the photocurrent, Id is the dark current, Popt is the illumination intensity of incident light, and S is the effective lighting area. The red line in Figure 4d is the changing trend of photoresponsivity as a function of incident light power, and it was found to be 14.3 mA/W at 0.7 mW. It is noteworthy that when we reduce the light power or have a smaller device area, the photodetector will have a higher photoresponsivity. Figure 4e shows the timedependent photocurrent curves (I‒T) at 10 V bias with 405 nm light illumination at successive on/off cycles, in which both turn-on time and turn-off time of incident light are 20 s. The on/off ratio of a photodetector is defined as the photocurrent to dark, and a remarkable switching ratio higher than 2×103 was achieved. Eight cycles of photocurrent switching demonstrate a response reproducibility and stability of the CsPbCl3 MWNs photodetector. In addition, we also measured the I‒T curves of the CsPbCl3 MWNs detector under a series of applied bias, with the incident light on and off. As shown in Figure 4f, with the increase of the applied bias voltage, the photocurrent sharply increases by several orders of magnitude in a very short time, which is presumably due to the increase in carrier drift velocity at higher bias. These curves demonstrate the reproducible and stable photoresponse with adjustable on/off photocurrent ratios. When the light was turned on and off, the current reversibly switched between high and low conductance with high repeatability and stability, and such characteristics guarantee the accuracy of the


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photodetector to detect a relatively weak light signal. As well known, the inorganic CsPbCl3 perovskite is a wide bandgap semiconductor, making it a potential candidate for fabricating the ultraviolet photodetectors. Figure S1 (Supporting Information) shows the I‒V curves of the device in dark and under 265 nm illumination with different light intensities, and a remarkable switching ratio higher than 6×103 was achieved. Further, we compared the characteristic parameters of such devices with other ultraviolet photodetectors and the corresponding data were summarized in Table S1 (Supporting Information).

Figure 5. (a) Schematic diagram of the CsPbCl3 MWNs photodetector for measuring the photoresponse speed. (b‒d) Photoresponse of the CsPbCl3 MWNs photodetector irradiated by a pulsed light with different frequencies at 5 V. A single normalized period of the photoresponse was used for calculating the tr and tf of the photodetectors at (e) 100 Hz and (f) 3500 Hz, respectively.


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In order to get the response speeds of the CsPbCl3 MWs photodetector, the incident light (405 nm, 13 mW) with different frequencies was illuminated on the photodetector switched by a mechanical chopper, and we used an oscilloscope to record the photocurrent signals in real time. Figure 5a is the corresponding schematic diagram of the test circuit. Figure 5b‒d describe the photoresponse curves of the CsPbCl3 MWNs photodetector to pulsed light at different frequencies, with a voltage bias of 5 V. It can be observed that the photodetector can detect the changing light signal quickly and accurately. Note that the photocurrent signal can still be measured as increasing the frequency to 3500 Hz, suggesting that the proposed photodetectors have the ability to detect the rapidly changing optical signals. As shown in Figure 5e, the rise time (tr) and the fall time (tf) of the device at 100 Hz were calculated to be 3.212 ms and 2.511 ms, respectively. And the response speed of 127.9/122 µs was obtained at 3500 Hz, as seen in Figure 5f. We all know that the long-term operation stability is a challenge for perovskite-based optoelectronic devices, especially for hybrid halide perovskites, which are vulnerable to environmental heat and oxygen/moisture. By contrast, all-inorganic is more stable by replacing methylammonium with inorganic cesium.18−21 Theoretically, after working continuously for a long time for the photodetectors, increased heating effect would generate, and the device temperature will increase, which would inevitably lead to the rapid diffusion of structural defects generally. As a result, the photogenerated carriers would be quickly trapped by these trap states. Therefore the long-term stability and thermal stability of the perovskite photodetectors are also very important parameters.38,39 To further demonstrate the long-term stability, the photocurrent of the CsPbCl3 MWNs photodetectors without unencapsulation versus running time was monitored in air condition (RT, 35‒50% humidity). During the measurement, an applied bias of


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5 V and a light irradiation power of 3 mW were maintained. As shown in Figure 6a, the photocurrent of the studied photodetectors exhibited a stable behavior after operation continuously for 9 h, and nearly 85% of the original photocurrent was retained. The results indicate that the proposed CsPbCl3 MWNs photodetectors possess a remarkable working stability, and also suggest that the high-crystalline and well-aligned CsPbCl3 MWNs can be employed as an effective light absorber for stable photodetector applications. In real life, the photodetectors must work outdoors with inconsistent conditions, such as a harsh environment with a high temperature. Therefore, temperature-dependent photocurrent measurements were performed to assess the temperature tolerance of the proposed CsPbCl3 MWNs photodetectors. For measurements, the photodetector device was mounted on a heating plate and the working temperature was heated externally to 333 and 373 K, and other conditions remain unchanged for comparison. As shown in Figure 6b, the photocurrent decreases to 66% of the initial value after a long testing period of 9 h at 333 K. As the working temperature was elevated to 373 K, the photocurrent curve drops rapidly and finally maintains at a steady level of ~60%. We attribute this reduction of photocurrent to the increased structural defects induced by the heating effect, by which the photogenerated carriers were trapped quickly. Note that the photocurrent is recoverable if the heating effect is eliminated by cooling process. As shown in Figure S2 (Supporting Information), we tested the I‒T curves for the unencapsulated device at RT (black line), 373 K (red line), and after naturally cooled down to RT (blue line), respectively. It can be seen that the photocurrent is reduced and the dark current increases at 373 K. When the heated device was cooled to RT naturally, the photocurrent increased and the dark current decreased accordingly, demonstrating the nearly identical values as compared with the measured data at RT. The above experiments indicate that the proposed perovskite photodetectors have a good


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temperature tolerance and also suggest that the CsPbCl3 MWNs is suitably compatible for practical applications under harsh conditions. Up to now, there have been no reports on the hightemperature operation action for perovskite photodetectors, thus our results are useful and original for progressing towards practical photodetectors with a high temperature tolerance. Note that the special morphology and structure of the MWNs benefit the device stability. For comparison, a counterpart photodetector based on CsPbCl3 thin film was fabricated. Figure S3 (Supporting Information) summarizes the normalized photocurrent of the unencapsulated CsPbCl3 thin film and CsPbCl3 MWNs photodetectors as a function of running time at RT, and only ~43% of the original photocurrent of the CsPbCl3 thin film photodetector was retained.

Figure 6. Normalized photocurrent of the CsPbCl3 MWNs photodetectors without encapsulation over time at (a) RT, (b) 333 K, and (c) 373 K, respectively. In conclusion, a vapor-phase epitaxial growth approach was developed to synthesize the highquality CsPbCl3 MWNs. As the evaporation temperature of the source powders increases, the MWs become thick and gradually form a network structure, until the formation of full film coverage. By using the well-connected CsPbCl3 MWNs as the light absorber, metalsemiconductor-metal photodetectors were further fabricated. The device exhibit a high on/off photocurrent ratio of 2.0×103, a photoresponsivity of 14.3 mA/W, and a fast response speed of 3.212/2.511 ms, confirming that the photodetector can follow the rapidly changing optical


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signals. More importantly, the proposed CsPbCl3 MWNs photodetectors without encapsulation demonstrate a remarkable operation stability in the long time test in air ambient, and can sustain a high working temperature of 373 K for 9 h continuous operation, suggesting a high temperature tolerance and good compatibility for practical applications even in harsh conditions. This work opens the door for the fabrication of stable and high-performance perovskite photodetectors under ambient and harsh conditions, making practical applications of such photodetectors a real possibility. ASSOCIATED CONTENT Supporting Information Available: The Supporting Information is available free of charge on the ACS Publications website at DOI: I‒V characteristics and I‒T curves of the CsPbCl3 MWNs photodetector; I‒T curves of the unencapsulated device at RT, 373 K, and after naturally cooled down to RT, respectively; normalized photocurrent of the unencapsulated CsPbCl3 thin film and CsPbCl3 MWNs photodetectors as a function of running time at RT; table S1 comparison of the characteristics parameters of photodetectors. AUTHOR INFORMATION Corresponding Authors *E-mail: (Z.S.) [email protected]. *E-mail: (X.L.) [email protected]. Notes The authors declare no competing financial interests.


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ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Nos. 11774318, 11604302,

61176044

and

11504331),

the

China

Postdoctoral

Science

Foundation

(2015M582193 and 2017T100535), the Science and Technology Research Project of Henan Province (162300410229), the Postdoctoral Research Sponsorship in Henan Province (2015008), the Outstanding Young Talent Research Fund of Zhengzhou University (1521317001), and the Startup Research Fund of Zhengzhou University (1512317003). REFERENCES (1) Wang, W. H.; Ma, Y. R.; Qi, L. M. High-Performance Photodetectors Based on Organometal Halide Perovskite Nanonets. Adv. Funct. Mater., 2017, 27, 1603653. (2) Wang, X.; Tian, W.; Liao, M.; Bando, Y.; Golberg, D. Recent Advances in Solution-Processed Inorganic Nanofilm Photodetectors. Chem. Soc. Rev., 2014, 43, 1400‒1422. (3) Tong, G. Q.; Geng, X. S.; Yu, Y. Q.; Yu, L. W.; Xu, J.; Jiang, Y.; Sheng, Y.; Shi, Y.; Chen, K. J. Rapid, Stable and Self-Powered Perovskite Detectors via a Fast Chemical Vapor Deposition Process. RSC Adv., 2017, 7, 18224‒18230. (4) Pandey, K.; Chauhan, M.; Bhatt, V.; Tripathi, B.; Yadav, P.; Kumar, M. High-Performance Self-Powered Perovskite Photodetector with a Rapid Photoconductive Response. RSC Adv., 2016, 6, 105076‒105080. (5) Dou, L.; Yang, Y.; You, J. B.; Hong, Z.; Chang, W. H.; Li, G.; Yang, Y. Solution-Processed Hybrid Perovskite Photodetectors with High Detectivity. Nat. Commun., 2014, 5, 5404. (6) Tang, X. S.; Zu, Z. Q.; Shao, H. B.; Hu, W.; Zhou, M.; Deng, M.; Chen, W. W.; Zang, Z. G.; Zhu, T.; Xue, J. M. All-Inorganic Perovskite CsPb(Br/I)3 Nanorods for Optoelectronic Application. Nanoscale, 2016, 8, 15158‒15161. (7) Chen, H. W.; Sakai, N.; Jena, A. K.; Sanehira, Y.; Ikegami, M.; Ho, K. C.; Miyasaka, T. A Switchable High-Sensitivity Photodetecting and Photovoltaic Device with Perovskite Absorber. J. Phys. Chem. Lett., 2015, 6, 1773‒1779.


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For Table of Contents Use Only

Controllable Vapor-Phase Growth of Inorganic Perovskite Microwire Networks for High-Efficiency and Temperature-Stable Photodetectors Ying Li,1 Zhifeng Shi,*1 Lingzhi Lei,1 Zhuangzhuang Ma,1 Fei Zhang,1 Sen Li,1 Di Wu,1 Tingting Xu,1 Xinjian Li,*1 Chongxin Shan,1 and Guotong Du2 Perovskite photodetectors were fabricated by using well-connected CsPbCl3 microwire networks as the light absorber, and a high-performance photodetection ability was achieved with a high temperature tolerance.

TOC GRAPHICS


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Controllable Vapor-Phase Growth of Inorganic Perovskite Microwire

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