Nanoflake Single Crystals - American Chemical Society

Dec 21, 2017 - Wei Zheng, Xufan Xiong, Richeng Lin, Zhaojun Zhang, Cunhua Xu, and Feng Huang*. State Key Laboratory of Optoelectronic Materials and ...
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Balanced photodetection in one-step liquid-phase synthesis CsPbBr micro/nanoflake single crystal 3

Wei Zheng, Xufan Xiong, Richeng Lin, Zhaojun Zhang, Cunhua Xu, and Feng Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b18093 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 22, 2017

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Balanced photodetection in one-step liquid-phase synthesis CsPbBr3 micro/nanoflake single crystal Wei Zheng,† Xufan Xiong,† Richeng Lin,† Zhaojun Zhang,† Cunhua Xu† and Feng Huang†,* †

State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials, Sun

Yat-sen University, Guangzhou 510275, China ABSTRACT: Here, we reported a low-cost and high-compatibility one-step liquid-phase synthesis method for synthesizing high purity CsPbBr3 micro/nanoflake single crystal. Based on the high purity CsPbBr3, we further prepared a low-dimensional photodetector capable of balanced photodetection, involving both high external-quantum-efficiency and rapid temporal-response, which is barely realized in previously reported low-dimensional photodetectors.

KEYWORDS: CsPbBr3, Luminescence, Balanced photodetection, Perovskite, Liquid-phase synthesis

TOC:

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1. INTRODUCTION With excellent physical characteristics, such as high mobility and appropriate flexibility,1,2 twodimensional (2D) materials are potential candidates for new generation optoelectronic devices, In the past few years, various 2D materials were used to fabricate low-dimensional photoconductive detector via mechanical exfoliation and CVD methods.3 In spite of high photoresponsivity and external quantum efficiency (EQE),4,5 those devices are also bound to slow temporal-response (several seconds to hundreds of seconds). The reasons are explained as follows. Generally, in a photoconductive detector, after generating electron-hole pairs, one type of the carriers (such as holes, captured by surface and inner defects) is trapped and the other (such as electrons) is flowing.6 If the flowing ones recirculated multiple times during the lifetime of the trapped ones, then ultra-high EQE and photoconductive is achieved for the reason that many charge carriers are collected for every exciton generated. However, this mechanism inevitably causes an increasing response time. An optical-sensor suited for communication and imaging must simultaneously provide high photoresponsivity and rapid temporal-response. However, as mentioned above, those two parameters are negatively correlated. To balance fast response-speed and high photoresponsivity (balanced photodetection), the most effective way is to synthesize high crystal quality 2D materials without inner defect so as to artificially modulate the number of surface trap centers by surface treatment.7 In this experiment, a low-temperature liquid-phase synthesis (LPS) method was proposed to synthesize inner-defect-free, smooth-surface and single-crystallinity inorganic perovskite CsPbBr3 micro/nanoflake single crystal. As expected, the as-grown CsPbBr3 single crystal was

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confirmed to be capable of maintaining balanced photodetection, behaving relatively high photoresponsivity and fast temporal-response simultaneously. Typically, under illumination of 275 nm LED light, the CsPbBr3 micro/nanoflake based device reaches a responsivity of 2.776 A/W (corresponding EQE of 1254 %), and an imaging-compatible response time of 20 ms. As a potential alternative to CVD method, the LPS method provides a new way to synthesize highquality perovskite single crystals on any substrate, contributing to the development of balanced low-dimensional photodetector with rapid temporal-response and high photoresponsivity. 2. EXPERIMENTAL METHODS 2.1. Material Synthesis. CsPbBr3 micro/nanoflakes were synthesized by LPS method. First, the prepared solution of DMF (3 mL) with CsBr (1 mmol) and PbBr2 (2 mmol) was placed under a heater (90 oC) for heating. After that, 20 µL of the solution was dropped on an SiO2 or PET substrate by pipette. With decreasing temperature, the DMF was continuously evaporated. Meanwhile, some of the solution was absorbed by the capillary to accelerate the formation of 2D CsPbBr3. Finally, when the DMF was completely evaporated, high quality CsPbBr3 micro/nanoflakes were obtained on the substrates. 2.2. Materials characterization. A X-ray diffractometer of Panalytical X’Pert Pro with CuKα radiation (λ = 1.5406 Å), a transmission electron microscope (FEI; Tecnai G2 F30 and 300 kV) equipped with HR-TEM and an atomic force microscope AFM (Bruker, Dimension Fastscan) were used to characterize the crystal structure of CsPbBr3 micro/nanoflake synthesized on PET and SiO2 substrates. A Raman spectrometer of Jobin Yvon LabRAM HR with 325 nm laser as excitation was used to collect room temperature photoluminescence spectrum. SEM and

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EDS were measured using scanning electron microscopy instrument of ZEISS AURIGA with Oxford INCAPent aFET-x3 and Hitachi S-4800. 2.3. Device measurement. The dark current, photocurrent and time-dependent photoresponse were all measured in atmospheric environment, by a normal prober and SourceMeter of Keithley 2636B, a 275 nm LED, and an optical power meter of Ophir (NOVA II header and PD300-UV probe). 3. RESULTS AND DISCUSSION A convenient, low-cost and high-compatibility one-step LPS method was adopted to prepare high quality CsPbBr3 micro/nanoflakes, as shown in Figure 1a. Firstly, high-purity CsBr and PbBr2 powders were directly resolved into N,N-dimethylformamide (DMF), which was then kept under a 90 ff heater in atmospheric environment until it accomplished its full dissolve and formed CsPbBr3-DMF solution. Subsequently, some of the solution were dropped to the substrate (PET or SiO2), which produces high-crystallinity tetragonal CsPbBr3 micro/nanoflakes until a complete evaporation. The typical products grown on SiO2 and PET substrates are shown in Figure 1b. It is clearly observed that the morphology and surface smoothness of the synthesized samples are irrelevant to the substrate type. Compared with CVD method, our designed LPS method can grow samples at a lower temperature (90 ff) on flexible substrate in atmospheric environment.8 In comparison with the recently reported multi-step solution method in nitrogen environment (see ref.9), our method of synthesizing precursors first and then growing CsPbBr3 is more convenient for operation and can also achieve large-scale CsPbBr3 micro/nanoflakes production.

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The synthesized sample is proved to be CsPbBr3 by X-ray diffraction (XRD) characterization, as shown in Figure 1c. It can be calculated from the data that d002 = 5.78 and d004 = 2.90 Å, which are indexed to orthorhombic (Pnma, 3D perovskite structure) with lattice parameters a = 8.21, b = 8.26, and c = 11.76 Å, which are consistent with those of reported XRD data of CsPbBr3.10 It is to be noted that the d002 value is very close to the d001 value of the cubic phase CsPbBr3 (a = 5.87, b = 5.87, and c = 5.87 Å) which cannot be excluded by XRD data alone,11 therefore, further confirmation of the orthorhombic phase of the sample will be conducted by subsequent HRTEM and SAED data. For an in-depth study of the synthesized samples, comprehensive measurements on their morphology, structure and optical properties were carried out. Smooth surfaces and edges are observed from the scanning electron microscopy (SEM) image of the CsPbBr3 micro/nanoflakes on SiO2 substrate (Figure 2a). Figures 2b, 2c, and 2d are the element maps of Cs, Pb and Br, respectively, indicating uniform elements distribution. The atomic force microscopies (AFM, see more information in Figure 2S) scanning result of a selected product, as shown in Figure 2e, once again confirm its ultra-smooth surface. In order to have a thorough analysis of its microstructure, we characterized the CsPbBr3 micro/nanoflakes (on Cu grid covered by carbon thin film) by high resolution transmission electron microscopy (HRTEM), as shown in Figure 2f. Bright diffraction spots indicate a tetragonal structure, whose interplanar spacing is 0.83 nm for (100) plane and 0.82 nm for (010) plane. These values deviate sharply from that of the cubic phase CsPbBr3. Thus, based on our previous analysis of XRD, we can clearly confirm that the synthesized CsPbBr3 material is orthorhombic phase. Moreover, the bright spots and regular tetragonal structure of the selected

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area electron diffraction (SAED) in Figure 2g further support the high crystal quality of the sample. Figure 2h shows the photoluminescence spectrum of the CsPbBr3 micro/nanoflakes measured at room temperature. The emission centers at about 546 nm, and the calculated band gap is 2.28 eV, which are consistent with the results of the previously reported pure CsPbBr3 by Kovalenko et al. (550 nm). and Kanatzidis et al. (551 nm), see Table 1.12-13 Through characterizations, it is proved that the LPS method is unconstrained by the substrate type, and can be used to synthesize abundant high-crystallinity CsPbBr3 micro/nanoflakes at a relatively low temperature (90 oC) in atmospheric environment. We depicted the synthesis mechanism of CsPbBr3 micro/nanoflakes via LPS method in Figure 3a. Firstly, when relatively high-temperature CsBr-PbBr2-DMF solution is dropped to the surface of SiO2 (or PET), a large temperature gradient between the droplet surface and the external environment along the normal direction of substrate appears. Crystal nucleus first forms on the surface of the droplet, and then grows along surface in-plane direction to produce extremely thin crystals. With evaporation of the solution, the thin crystals near the droplet edge separate from the solution, no longer grow thicker, and adsorb on the substrate. To show the process more intuitively, the real optical photographs are inserted into the temperature dependent plot of the solution, as shown in Figure 3b. The original crystals attached to the substrate are the thinnest, with blue to transparent color; the later deposited ones are thicker and larger in yellow color. Since the droplets are extremely small and the evaporation are so rapid, most of the crystals are difficult to grow into thicker bulk crystals. Finally, after a complete evaporation, all the crystals adsorb on the substrate surface with tetragonal morphology. Due to different completion time of

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crystal formation and liquid evaporation, the obtained crystals exhibit diverse thickness and colors, as shown in Figure 3c. Furthermore, the high-quality CsPbBr3 micro/nanoflake was fabricated into a planar photoconductive device with 100 nm Au as electrodes. Its schematic representation (on PET substrate) is shown in Figure 4a, and macro and micro photo images are displayed in Figure 4b and inset. Here, a 275 nm LED was used as light source for all measurements. Figure 4c shows IV characteristic curves of the photodetector under dark environment and illumination of 275 nm light with varying power density. They show obvious linear relationship, indicating the device’s good physical contact with electrodes. The dark current is 286 pA at 5 V bias, while under illumination (light power density of 5.2 mW/cm2), the photocurrent is 14700 pA. Obviously, the photo/dark current ratio is two orders of magnitude, indicating a large signal of noise ratio. Photoresponsivity (R), one of the most important parameters for photodetector, represents the detector’s sensitivity to optical signal. It can be calculated by R = ( I light − I dark ) / ( Plight S ) , where Ilight is photocurrent,

Idark dark current, Plight power density of illumination, and S area of

the channel.14 Figure 4d shows the relationship between R and voltage under illumination with increasing power density. External quantum efficiency (EQE), referring to the internal gain of a device, is obtained by η=Rhc / ( eλ ) , where h denotes Planck constant, c velocity of light, e element charge, and λ wavelength of incident light. Figure 4e shows the relationships among EQE, R and illumination density. Under 5 V bias and 5.2 mW/cm2 illumination density, EQE and R of the 2D CsPbBr3 photodetector are up to 1254% and 2.776 A/W, respectively.

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Response speed is also an important parameter for photodetector. Figure 4f gives the temporal response of the CsPbBr3 device illuminated under 275 nm light with increasing power density. Figure 4g is an enlarged view of Figure 4f under 4.5 mW/cm2, with a rise time of 40 ms and a decay time of 20 ms (imaging compatible). Besides, the CsPbBr3 photodetector also behaves good repeatability (Figure 4h) and flexibility (Figure 4i, as the incident light is perpendicular to the device plane, the light receiving area reduces with increasing bending degree, finally resulting in a decreasing photocurrent). Table 2 summarizes the figures of merits for typical reported 2D photodetectors. It can be found that unbalanced photodetection prevails among current 2D photodetectors, i.e., high EQE and rapid temporal-response cannot be obtained at the same time. For example, Ref

15

reported

MoS2 based 2D photodetector achieved a high EQE of 19,466%, but a long response time up to several seconds, which can be hardly applied to dynamic optical signal capture; Ref. 7 reported 2D PbI2 photodetector achieved ultra-fast temporal-response of 55 µs, but low EQE of only 0.0028%, which is incapable of weak-light detection. This predicament is attributed to the persistence-photoconductive-effect (PP-effect) in photoconductive detectors:16-17 One-type photogenerated carriers are trapped by the material surface or inner defects while the others recirculate multiple times during the lifetime of the trapped ones.6 More surface and inner defects cause longer PP-effect, resulting in high EQE but slow temporal-response. On the contrary, less defects contribute to shorter PP-effect, leading to fast temporal-response but low EQE. For a photodetector meeting the needs of real-applications, it is necessary to balance the photodetection: and meanwhile possess a relatively high EQE (> 90%) and a relatively fast temporal-response (< 50 ms), instead of ultra-high EQE with slow temporal-response or ultra-

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fast temporal-response with low EQE. Through horizontal comparison of the 2D photodetectors in Table 2, we can see that our reported one perfectly achieves a balanced photodetection. Moreover, compared to the reported CsPbBr3-based photodetectors (see Table 3), our device has a EQE with as high as two orders of magnitude, showing an advantage for weak-light detection. 5. CONCLUSIONS To sum up, the LPS method was designed to synthesize high purity CsPbBr3 micro/nanoflakes. Based on the synthesized sample, we fabricated a tow-dimensional photodetector with high photoresponsivity (2.776 A/W), high EQE (1254 %), and fast temporalresponse (rise time of 40 ms and decay time of 20 ms), which has satisfied the practical demand of balanced photodetection. This work provides a low-cost and fast synthesis method for highcrystallinity 2D perovskites, which are promising candidates for the fabrication of CsPbBr3 micro/nanoflake based flexible photoelectronic devices.

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Figure 1. Preparation of CsPbBr3 micro/nanoflakes. a) Illustration of the synthesis of CsPbBr3 MSCs by LPS method. First, CsBr and PbBr2 powders and DMF are added to the reagent bottle in turn, and heated to 90 °C. Then a small amount of DMF-CsPbBr3 solution is dropped on SiO2/PET substrate at room temperature. After cooling and evaporating the solution, CsPbBr3 micro/nanoflake was obtained on the substrate surface. b) Optical images of CsPbBr3 grown on SiO2 and PET substrates, respectively. c) XRD patterns of the CsPbBr3 micro/nanoflakes (on PET substrate) and theoretical result. d) Crystal structure of the CsPbBr3, which is a typical perovskite structure.

Figure 2. Characterization of CsPbBr3 micro/nanoflakes. a) SEM image of a typical CsPbBr3 micro/nanoflake, symmetrical tetragonal structure and smooth surface are clearly observed,

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indicating its high crystal quality. b), c) and d) are the element maps of Cs, Pb and Br, respectively, revealing a high uniformity of the synthesized CsPbBr3 micro/nanoflake. e) AFM image of the CsPbBr3 micro/nanoflake, showing smooth surface. f) HRTEM image of the CsPbBr3 micro/nanoflake viewed along the [001] zone, exhibiting bright diffraction spots and distinct tetragonal structure with interplanar spacing of 0.83 and 0.82 nm for (100) and (010) planes, respectively. g) Selected-area electron diffraction of the CsPbBr3 micro/nanoflake, indicating a tetragonal structure. h) Photoluminescence spectrum at room temperature excited by 325 nm laser, with center wavelength of about 546 nm.

Figure 3. Mechanism description of LPS method. a) Schematic representation of CsPbBr3 micro/nanoflake growth mechanism. b) The real growth process of CsPbBr3 micro/nanoflake

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from nucleation to adsorption on SiO2 substrate with decreasing solution temperature, observed by optical microscope. c) The left column displays CsPbBr3 micro/nanoflake grown on a SiO2 substrate, and the right is on a PET substrate. Different colors indicate different thicknesses.

Figure 4. CsPbBr3 micro/nanoflake based flexible device and its photoresponse measurements. (a) Schematic view of a CsPbBr3 micro/nanoflake optoelectronic device (thickness: 100 nm) on PET substrate, which is deposited with Au electrodes by thermal evaporation. (b) A photograph of the device; the inset is its micrograph. (c) I-V characteristic curves of the device under dark condition and illumination of 275 nm light with varying power density. The dark current is 50 pA at 0 V and 286 pA at 5 V. (d) Responsivity of the device illuminated under 275 nm light with

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varying power density. (e) Plots of light power density versus responsivity and EQE. (f) Temporal response of the detector illuminated under 275 nm pulse with increasing power density. (g) An enlarged view of the time-dependent photocurrent, where the rise time is 40 ms and the decay time is 20 ms. (h) Time-dependent response of the device illuminated under 275nm pulse light with quick switching of 8 cycles, confirming a good stability and repeatability. (i) Different temporal responses of the device under three-degree (Level 1, Level 2, Level 3) bendings.

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Table 1. Luminescence center of CsPbBr3 perovskites Materials

Luminescence center

Reference

CsPbBr3 single crystal CsPbBr3 bulk CsPbBr3 micro/nanoflakes

550 nm 551 nm 546 nm

Kovalenko et al. 12 Kanatzidis et al. 13 This work

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Table 2. Figures of merits for 2D photodetectors 2D Materials

Light

Bias voltage

Responsivity

EQE

Rise time

Decay Time

Reference

MoS2

561 nm

8V

880 A/W

19466%

4s

9s

15

SnSe

White Light

0.5 V

330 A/W

-

>10 s

>15 s

18

MoS2

633 nm

1V

300 A/W

58880 %

>1 s

>1 s

19

InSe

Visible Light

1V

0.1~27 A/W

12.65~5700%

0.5 s

1.7 s

20

GaSe

Visible Light

10 V

0.03 A/W

-

>1 s

>3 s

21

NiSe

White Light

1V

0.009 A/W

-

8s

15 s

22

SnS2

390 nm

15 V

0.470 A/W

150 %

0.15 s

0.15 s

23

CH3NH3PbI3

365 nm

1V

0.036 A/W

12.254 %

0.23 s

0.19 s

24

Visible Light

0.6 V

0.0000019 A/W

-

0.5 s

1.1 s

25

WSe2

532 nm

1V

0.007 A/W

0.1 %

0.001 s

0.001 s

26

PbI2

450 nm

1.9 V

0.0001 A/W

0.000055 s

0.000110 s

7

CsPbBr3

275 nm

5V

2.776 A/W

0.04 s

0.02 s

This work

Black Phosphorus

1254 %

Table 3. Figures of merits for CsPbBr3-based photodetectors Decay

Materials

Light

Responsivity

EQE

Rise time

CsPbBr3 microparticles

422 nm

0.l8 A/W

42 %

1.8 ms

1.0 ms

27

CsPbBr3 microparticles

422 nm

0.01 A/W

40 %

0.2 ms

1.2 ms

28

CsPbBr3 2D nanosheet

422 nm

0.25 A/W

53 %

0.019 ms

0.025 ms

9

CsPbBr3 micro/nanoflakes

275 nm

2.776 A/W

1254 %

40 ms

20 ms

This work

time

Reference

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ASSOCIATED CONTENT Corresponding Author *[email protected] ACKNOWLEDGMENT This work was supported by National Natural Science Foundation of China (No. 61604178, 91333207, U1505252 and 61427901), Guangdong Natural Science Foundation (No. 2014A030310014), China Postdoctoral Science Foundation (No. 2015M580752), and Guangzhou Science and Technology Program (No. 201607020036).

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(12) Dirin, D. N.; Cherniukh, I.; Yakunin, S.; Shynkarenko, Y.; Kovalenko, M. V. SolutionGrown CsPbBr3 Perovskite Single Crystals for Photon Detection. Chemistry of Materials 2016, 28, 8470-8474. (13) Stoumpos, C. C.; Malliakas, C. D.; Peters, J. A.; Liu, Z.; Sebastian, M.; Im, J.; Chasapis, T. C.; Wibowo, A. C.; Chung, D. Y.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G. Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection. Crystal Growth & Design 2013, 13, 2722-2727. (14) Zheng, W.; Huang, F.; Zheng, R.; Wu, H. Low-Dimensional Structure Vacuum-UltravioletSensitive (λ < 200 nm) Photodetector with Fast-Response Speed Based on High-Quality AlN Micro/Nanowire. Adv. Mater. 2015, 27, 3921-3927. (15) Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A. Ultrasensitive photodetectors based on monolayer MoS2. Nat. Nanotechnol. 2013, 8, 497-501. (16) Jeon, S.; Ahn, S.-E.; Song, I.; Kim, C. J.; Chung, U. I.; Lee, E.; Yoo, I.; Nathan, A.; Lee, S.; Robertson, J.; Kim, K. Gated three-terminal device architecture to eliminate persistent photoconductivity in oxide semiconductor photosensor arrays. Nature Materials 2012, 11, 301305. (17) Lany, S.; Zunger, A. Anion vacancies as a source of persistent photoconductivity in II-VI and chalcopyrite semiconductors. Physical Review B 2005, 72, 035215. (18) Zhao, S.; Wang, H.; Zhou, Y.; Liao, L.; Jiang, Y.; Yang, X.; Chen, G.; Lin, M.; Wang, Y.; Peng, H.; Liu, Z. Controlled synthesis of single-crystal SnSe nanoplates. Nano Research 2015, 8, 288-295. (19) Choi, W.; Cho, M. Y.; Konar, A.; Lee, J. H.; Cha, G.-B.; Hong, S. C.; Kim, S.; Kim, J.; Jena, D.; Joo, J.; Kim, S. High-Detectivity Multilayer MoS2 Phototransistors with Spectral Response from Ultraviolet to Infrared. Adv. Mater. 2012, 24, 5832-5836. (20) Yang, Z.; Jie, W.; Mak, C.-H.; Lin, S.; Lin, H.; Yang, X.; Yan, F.; Lau, S. P.; Hao, J. WaferScale Synthesis of High-Quality Semiconducting Two-Dimensional Layered InSe with Broadband Photoresponse. Acs Nano 2017, 11, 4225-4236. (21) Zhou, Y.; Nie, Y.; Liu, Y.; Yan, K.; Hong, J.; Jin, C.; Zhou, Y.; Yin, J.; Liu, Z.; Peng, H. Epitaxy and Photoresponse of Two-Dimensional GaSe Crystals on Flexible Transparent Mica Sheets. Acs Nano 2014, 8, 1485-1490. (22) Applied Physics LettersCai, C.; Ma, Y.; Jeon, J.; Huang, F.; Jia, F.; Lai, S.; Xu, Z.; Wu, C.; Zhao, R.; Hao, Y.; Chen, Y.; Lee, S.; Wang, M. Epitaxial Growth of Large-Grain NiSe Films by Solid-State Reaction for High-Responsivity Photodetector Arrays. Adv. Mater. 2017, 29, 1606180. (23) Ye, G.; Gong, Y.; Lei, S.; He, Y.; Li, B.; Zhang, X.; Jin, Z.; Dong, L.; Lou, J.; Vajtai, R.; Zhou, W.; Ajayan, P. M. Synthesis of large-scale atomic-layer SnS2 through chemical vapor deposition. Nano Research 2017, 10, 2386-2394. (24) Pengfei, L.; Shivananju, B. N.; Yupeng, Z.; Shaojuan, L.; Qiaoliang, B. High performance photodetector based on 2D CH3NH3PbI3 perovskite nanosheets. Journal of Physics D: Applied Physics 2017, 50, 094002. (25) Ren, X.; Li, Z.; Huang, Z.; Sang, D.; Qiao, H.; Qi, X.; Li, J.; Zhong, J.; Zhang, H. Environmentally Robust Black Phosphorus Nanosheets in Solution: Application for SelfPowered Photodetector. Advanced Functional Materials 2017, 27, 1606834. (26) Groenendijk, D. J.; Buscema, M.; Steele, G. A.; de Vasconcellos, S. M.; Bratschitsch, R.; van der Zant, H. S. J.; Castellanos-Gomez, A. Photovoltaic and Photothermoelectric Effect in a Double-Gated WSe2 Device. Nano Letters 2014, 14, 5846-5852.

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(27) Li, X.; Yu, D.; Cao, F.; Gu, Y.; Wei, Y.; Wu, Y.; Song, J.; Zeng, H. Healing All-Inorganic Perovskite Films via Recyclable Dissolution-Recyrstallization for Compact and Smooth Carrier Channels of Optoelectronic Devices with High Stability. Advanced Functional Materials 2016, 26, 5903-5912. (28) Dong, Y.; Gu, Y.; Zou, Y.; Song, J.; Xu, L.; Li, J.; Xue, F.; Li, X.; Zeng, H. Improving AllInorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect. Small 2016, 12, 5622-5632.

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