Highly Sensitive Flexible Photodetectors Based on Self-Assembled

Research Article www.acsami.org

Highly Sensitive Flexible Photodetectors Based on Self-Assembled Tin Monosulfide Nanoflakes with Graphene Electrodes Ganesan Mohan Kumar,† Xiao Fu,† Pugazhendi Ilanchezhiyan,*,† Shavkat U. Yuldashev,† Dong Jin Lee,‡ Hak Dong Cho,‡ and Tae Won Kang† †

Nano-Information Technology Academy (NITA) and ‡Quantum-Functional Semiconductor Research Center, Dongguk University, Seoul 04620, Republic of Korea S Supporting Information *

ABSTRACT: Tin monosulfide (SnS) nanostructures have attracted huge attention recently because of their high absorption coefficient, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Here, in this paper, we report on the low-cost hydrothermal synthesis of the self-assembled SnS nanoflake-like structures in terms of performance for the photodetectors. High-performance photodetectors were fabricated using SnS nanoflakes as active layers and graphene as the lateral electrodes. The SnS photodetectors exhibited excellent photoresponse properties with a high responsivity of 1.7 × 104 A/W and have fast response and recovery times. In addition, the photodetectors exhibited long-term stability and strong dependence of photocurrent on light intensity. These excellent characteristics were attributed to the larger surface-to-volume ratio of the self-assembled SnS nanoflakes and the effective separation of the photogenerated carriers at graphene/SnS interfaces. Additionally, a flexible photodetector based on SnS nanoflakes was also fabricated on a flexible substrate that demonstrated similar photosensitive properties. Furthermore, this study also demonstrates the potential of hydrothermal-processed SnS nanoflakes for highperformance photodetectors and their application in flexible low-cost optoelectronic devices. KEYWORDS: tin monosulfide, nanoflakes, graphene, flexible, photodetectors

1. INTRODUCTION

compound, Sn and S, are cheap, non-toxic, and abundant in nature. Different morphologies of SnS, such as nanoparticles,20−22 nanoplatelets,23,24 nanorods,25,26 nanoflowers,27,28 and nanosheets,29−31 have been reported by chemical vapor deposition,32 electrochemical deposition,33 solution-phase synthesis,34 hydrothermal methods,35 and so forth. Recently, Deng et al.36 synthesized the crystalline SnS nanoribbons using solutionphase synthesis to demonstrate the field-effect transistor and photodetectors with excellent performance. Similarly, Mahdi et al. and Zhou et al. have also reported on photodetectors based on the SnS nanobelts and the flexible SnS thin films active along the NIR region.37,38 All of these reports augment that the SnS nanostructures are remarkable candidates for highperformance photodetector functions. In this work, we demonstrate a low-cost simple hydrothermal route for the synthesis of the self-assembled SnS nanoflakes. In addition, to showcase their potential for electronic applications, we have investigated their photoelectronic properties by fabricating a photodetector using the SnS nanoflakes as the active layer and graphene as the lateral electrodes on Si/SiO2

Recently two-dimensional (2D) nanostructures have attracted huge attention for their unique electronic, physical, and chemical properties.1−3 Among various 2D-layered materials, the narrow band gap IV−VI series of the semiconducting materials has attracted significant attention owing to their optical, electronic, and optoelectronic applications such as photovoltaics and near-infrared (NIR) detectors.4−11 Tin monosulfide (SnS) belonging to the IV−VI group is an optically active material in the NIR and visible regions of the electromagnetic spectrum and is of great interest for their applications in photovoltaics, field-effect transistors, and NIR detectors.12,13 SnS has an orthorhombic crystal structure that can be considered as a distorted NaCl structure, where each tin atom is coordinated by six sulfur atoms with three short Sn−S bonds within the layer and three long bonds in the next layer without any dangling bonds on the surface.14 Moreover, owing to its favorable physical and chemical properties, SnS has also received more attention for its application in photodetectors, photocatalysts, and lithium-ion batteries.15−18 It has both direct and indirect band gap around 1.3 and 1.09 eV, high conductivity, and large absorption coefficient (>104 cm−1) that makes it a promising light-absorbing material for photovoltaics.19 Furthermore, the constituent elements of this © 2017 American Chemical Society

Received: July 10, 2017 Accepted: August 30, 2017 Published: August 30, 2017 32142

DOI: 10.1021/acsami.7b09959 ACS Appl. Mater. Interfaces 2017, 9, 32142−32150

Research Article

ACS Applied Materials & Interfaces

Figure 1. (a) Low-magnification SEM image of the as-prepared SnS nanoflakes and (b) high-magnification SEM image of the as-prepared SnS nanoflakes. The image reveals that the samples are composed of self-assembled nanoflake-like structures. (c) TEM image and (d) HRTEM image of the self-assembled nanoflakes. Inset in (d) shows the SAED pattern of SnS. lithography and oxygen plasma (etching) processing. Then, a suitable amount of the as-synthesized SnS nanoflake powders was dispersed in ethanol/water (80:20) solution and tip-sonicated for 30 min to form a homogeneous dispersion. The resultant dispersion was centrifuged at 2000 rpm for 20 min. After centrifugation, the supernatant was collected by a pipette [scanning electron microscopy (SEM) image of the supernatant is shown in Figure S1]. Then, the SnS supernatants were deposited on a predefined channel established between the graphene electrodes via dropcasting. Finally, an Ag paste was applied onto the graphene electrodes and heat-treated at 80 °C for 10 min to improve the electrical contact. 2.4. Characterization. The morphological evolution of SnS was examined using SEM (XL30 SFEG, FEI) and high-resolution transmission electron microscopy (HRTEM-JEM 3010). The crystal structure of the SnS nanoflakes was inferred through X-ray diffraction (XRD). The Raman measurements were performed in a micro-Raman spectrometer using an excitation wavelength of 532 nm. The optical properties of the SnS nanoflakes were recorded by employing a Varian Cary ultraviolet−visible (UV−vis) spectrometer. The current−voltage (I−V) characteristics were studied using a Keithley 617 semiconductor parameter analyzer.

substrate. In our experiments, graphene grown via chemical vapor deposition (CVD) was used as transparent electrodes, owing to their excellent electrical and thermal conductivity, transparency, and flexibility. The internal electric field established between graphene and SnS could benefit the separation of photogenerated electrons and holes without the need for any bias voltage. This is why, the fabricated photodetector exhibits a high photoresponsivity and high stability under light illumination. A physical mechanism has also been discussed for the observed enhancement in photocurrent values (explained using a band diagram).

2. EXPERIMENTAL SECTION 2.1. Materials. All chemicals used in the experiments were of analytical grade and used without further purification. Tin(II) chloride (SnCl2·2H2O), thiourea (CH4N2S), citric acid, and ethylene glycol (EG) were purchased from Sigma-Aldrich. 2.2. Materials Synthesis. In a typical synthesis, 0.5 mmol of SnCl2·2H2O, thiourea, and citric acid (1.5 mmol) were dissolved into 30 mL of EG under magnetic stirring to form an even solution. Ammonium solution (2 mL) was then added dropwise into this solution. The solution was then transferred into a Teflon-lined stainless autoclave (60 mL capacity) and subjected to hydrothermal treatment at 190 °C for 18 h. After the hydrothermal treatment, black products were collected by centrifugation, followed by washing several times with deionized water and ethanol. The final product was dried at 60 °C for 24 h. 2.3. Device Fabrication. The graphene layers were grown on a Cu foil by the CVD method at 1020 °C under a methane/hydrogen flow at 600 mTorr. Before transferring the graphene layers, the Si/ SiO2 (300 nm) substrates were precleaned by ultrasonication in alcohol and deionized water for 10 min to obtain an intact surface. For the fabrication of the photodetector device, graphene grown from CVD was initially transferred onto the Si/SiO2 (300 nm) and polyethylene terephthalate (PET) substrates. The graphene electrodes with a channel length of 15 μm were then made using photo-

3. RESULTS AND DISCUSSION Figure 1a displays the typical SEM image of the as-synthesized products. From the images, it is observed that the morphology of the synthesized samples reveals a self-assembled flakelike nanostructure with an average diameter of 1 μm. The highmagnification image of the self-assembled flakelike structures is shown in Figure 1b, which depicts the structure to be composed of aggregated nanoflakes with crumpled morphologies. The aggregated nanoflakes with few nanometer thickness appear to be connected with each other to form the selfassembled SnS nanostructures. The morphology of the SnS nanoflakes was further investigated by transmission electron microscopy (TEM). Figure 1c displays the TEM image of the self-assembled SnS nanoflakes. As can be seen in the image, the 32143


Research Article


laterally to result the observed SnS nanostructures via Ostwald ripening.39−41 Next, to elucidate the phase structure of the chemically synthesized SnS nanoflakes, the XRD measurement was carried out, and the result is shown in Figure 3a. As can be seen in the figure, all of the characteristic peaks in the pattern could be indexed to the orthorhombic phase of SnS (JCPDS no. 39-0354 with cell constant a = 4.1300 Å, b = 11.260 Å, and c = 3.960 Å). Raman spectroscopy was also carried out to study the phase structure of the SnS nanoflakes. Figure 3b shows the Raman spectrum of the SnS nanoflakes fitted by Gaussian functions. As can be seen in Figure 3b, the Raman spectrum shows four distinct peaks at 152, 186, 219, and 301 cm−1. According to the previous literature, these peaks could be attributed to orthorhombic SnS. The observed vibration modes at 186, 219, and 301 cm−1 correspond to the Ag modes.41−44 The peak observed at 152 cm−1 is assigned to the B3g mode of SnS.38,45 In addition, no other additional peaks were observed in the Raman data. The result of the Raman modes is also consistent with the previous reports on the SnS crystals46,47 and is in agreement with the XRD measurements of the synthesized sample. The optical properties of SnS nanoflakes were investigated by performing UV−vis absorption measurements on the SnS dispersions. The inset shows the dispersion of the SnS nanoflakes in ethanol. The UV spectrum shown in Figure 4a exhibits a strong absorption over the entire visible region and extended absorption along the lower infrared region of the spectrum. The optical energy gap of the SnS nanoflakes was then evaluated by using the relation, (αhν)n = A(hν − Eg), where A is the constant, α is the absorption coefficient, hν is the photon energy, and n is either 2 for a direct semiconductor or 1/2 for an indirect semiconductor. The band gap of SnS nanoflakes was estimated using Tauc’s plot by extrapolating the linear portion of the (αhν)2 versus hν and (αhν)0.5 versus hν, shown in Figure 4b,c. The band gap value was estimated to be around 1.41 and 1.45 eV for direct and indirect transition, respectively, which is similar to the values quoted in previous works.48−50 This band gap could allow a high absorption coefficient and an efficient electron−hole pair generation under illumination. Encouraged by the self-assembled morphology and good crystallinity, we constructed a photodetector device based on the SnS nanoflakes to explore its potential for photonics applications. The SnS photodetectors were fabricated on the Si/SiO2 substrates with lateral graphene electrodes (refer Experimental Section for a detailed procedure). Figure 5

edge portion of the nanoflakes is lighter than that of the center and consists of flakelike nanostructures, which is in accordance with the SEM images. Figure 1d shows the HRTEM image of the self-assembled nanoflakes. Inset in Figure 1d shows the selected area electron diffraction (SAED) pattern which corresponds to (080) and (111) planes of the orthorhombic SnS. These structures possess a high surface-to-volume ratio that could increase the active area for absorbing the incident photons, thereby increasing the overall photocurrent and photodetector performance. The mechanism involved in the formation of the selfassembled nanoflake-like structures could be explained using a multistep growth process that involves decomposition, agglomeration, and coalescence of SnS.39 As illustrated in Figure 2, during the initial stage, the SnS nanoparticles were

Figure 2. Schematic illustration of the formation mechanism of the self-assembled SnS nanoflake-like structures.

formed because of the decomposition of the as-obtained precursor consisting of Sn, followed by the formation of nucleation clusters. Then, these nucleation clusters lead an oriented coalescence of the SnS nanoparticles, resulting in irregular SnS nanoflakes. The nanoflakes in turn act as nucleation sites, which will agglomerate to form large nanoflakes. The newly formed SnS nanoflakes self-assemble to minimize the surface energy and could grow vertically and

Figure 3. (a) XRD pattern and (b) Raman spectra (fitted using Gaussian functions) of the SnS nanoflakes. 32144


Research Article


shows the schematic representation of the procedure to fabricate the SnS nanoflake photodetector with the graphene electrode on the Si/SiO2 substrate. Prior to the device fabrication, the quality of the synthesized graphene was initially analyzed using the Raman spectrum shown in Figure 6. The

Figure 6. Raman spectra of graphene transferred onto a SiO2/Si substrate (point B) and etched into a gap (point A). Inset: Optical image of the patterned graphene electrodes with a gap of 15 μm.

Raman spectrum of the transferred graphene layer on SiO2 shows two strong peaks, that is, the G peak at 1595 cm−1 and the 2D peak at 2698 cm−1. A relatively small Raman peak at 1356 cm−1 is identified with a disorder-induced band or D band. The strong G peak and the weak D peak indicate the high quality of CVD-grown graphene.51,52 The inset in Figure 6 shows the optical image of the device structure, showing a channel length of 15 μm. The current−voltage (I−V) curve of the graphene/SnS/ graphene device under dark condition is shown in Figure 7a (inset shows the digital image of the fabricated device). Here, the curve shows a nonlinear behavior, indicating the formation of a Schottky-like junction at the graphene and SnS interfaces. Here, we believe the nanoflakes to provide two uneven Schottky barriers at the two contacts with the graphene electrodes, thereby resulting in the observed nonlinear I−V characteristics. Figure 7b illustrates the I−V curves of the SnS photodetector under illumination by light. In contrast to the dark condition, the current increases significantly under light illumination, indicating the contribution from photogenerated carriers. The dark current of the device was 5 × 10−7 A at a bias voltage of 3 V. However, under light illumination, the current

Figure 4. (a) UV−vis absorption spectrum of the SnS nanoflakes (Inset: Photograph of the SnS nanoflakes suspension). (b,c) Tauc’s plot extracted from the absorption spectrum revealing their optical band gap.

Figure 5. Schematic representation of the procedure to fabricate the SnS nanoflake photodetector with graphene electrodes on the SiO2/Si substrate and the overall device structure. 32145


Research Article


Figure 7. (a) I−V curves of the graphene/SnS/graphene structure under dark conditions. Inset: A digital image of the fabricated device. (b) I−V curves of the graphene/SnS/graphene structure under different light intensities (0.7−1.2 mW/m2). (c) Time-dependent photocurrent response of the graphene/SnS/graphene photodetector device under light illumination. (d) Enlarged version of a single photocurrent response showing rise and decay times.

Figure 8. (a) Voltage-dependent photoresponse characteristics of the graphene/SnS/graphene structure under light illumination. (b) Enlarged version of the photoresponse characteristics at 1 V.

increases to 3.8 × 10−6 A at the same bias voltage, indicating excellent ultrahigh sensitivity of the SnS nanoflakes. Furthermore, the photocurrent of the device was also noted to be dependent on the incident power intensities of the illumination light. Upon increasing the light intensities, larger photocurrents are generated. This suggests that the photocurrents are determined by the amount of photogenerated carriers under light illumination. In our device, under light illumination both forward- and reverse-biased currents increase, implying that the photoexcited electron−hole pairs increase the concentration of

the majority carriers, as the Schottky barrier heights modulate with light illumination.53 To study the stability and response speed, a time-dependent photoresponse of the photodetector device was measured. Figure 7c shows the photocurrent of the SnS devices with repetitive switching of light on/off condition under zero bias. The photocurrent of the device could be noted to rapidly switch between on and off modes after the light is turned on and off. When the light is turned on, the photocurrent of the device increases from 6.7 × 10−9 to 2.5 × 10−8 A. The light 32146


Research Article


response of the device appears promising for large-area photodetector applications. To further characterize the photodetector performance, photoresponsivity (R) of the SnS photodetector was calculated based on the equation, R = Ip/PS, where Ip is the photocurrent, S is the active area (1.95 × 10−7 m2) under illumination, and P is the incident light intensity. The responsitivity was found to be 1.7 × 104 A/W under light intensity (1.2 mW/m2). It is worth mentioning that the responsivity of the fabricated SnS photodetector is higher than those of the reported SnS thinfilm-based photodetectors.37,54 Such high responsivity may come from a higher surface-to-volume ratio and higher density of this self-assembled SnS nanoflake structure (that results in the efficient light absorption as discussed in SEM and UV). This increased light absorption enhances electron−hole pair generation, leading to an enhancement in photocurrent and high photoresponsivity of the proposed device. To demonstrate the photoresponse behavior of our fabricated graphene/SnS/graphene structure, we propose the following photoresponse mechanism to elucidate charge transfer in the SnS/graphene lateral structure. Figure 10a

response of the device remains identical with no obvious degradation, indicating excellent photocurrent stability of the SnS photodetector. Figure 7d shows the magnified view of one of the switching cycle. The rising time presented here is defined as the time of beginning from turning on the light (t = 0 s) to reach the 90% values of the maximum current. The rise time and the decay time were calculated to be 0.3 and 0.4 s, respectively, which reveal fast and excellent photoelectric performances. Furthermore, the voltage-dependent switching characteristics of the photodetector were also investigated by varying the different bias voltages from 1 to 3 V (as shown in Figure 8). The photocurrent rise and decay upon turning on/off the light under varying bias voltage infers good stability and repeatability of the photodetector. A linear increase in the photocurrent was observed with a minimum current value of 1.65 × 10−7 A at a bias voltage of 1 V to a maximum value of ≈1.9 × 10−6 A at a bias voltage of 3 V. This result shows that the photoresponse of the device can also be tuned by applying an appropriate bias voltage. Additionally, the photoresponse of the device was explored under different light intensities at 1 and 3 V bias voltages as shown in Figure 9. Here, the value of the

Figure 10. Schematic band diagram of the graphene/SnS/graphene photodetector under (a) dark condition and (b) illumination. The built-in electric field assists in separating the electron/hole pairs under illumination without any applied bias.

shows the energy band diagram of the graphene SnS photodetector device under dark condition. Owing to the difference in work function between graphene and SnS, a Schottky-like junction is formed at the SnS/graphene interface. As a result of this, a built-in electric field would be developed at the graphene/SnS interface. This field leads to the separation of the photogenerated electrons and holes without any applied bias. Under light illumination (with photon energies larger than SnS), the photogenerated electron−hole pairs in SnS are separated at the graphene/SnS interface. This charge separation induced by the built-in electric field results in band bending at the graphene/SnS interface (because of the difference in work function). The photogenerated carriers are then swept into the graphene electrodes, resulting in the observed photocurrent (Figure 10b). A significant increase in photocurrent is also observed when the structure is positive or negative biased. This also demonstrates that the current is dominated in this regime by the photoexcited carriers. To demonstrate the flexible applications, the flexible photodetectors were also fabricated by using the SnS nanoflakes with the graphene electrodes on PET substrates (refer Device Fabrication section for detailed procedure). The flexibility of graphene and the mild solution-based fabrication method could additionally offer the possibility to fabricate the SnS photodetectors on flexible substrates for flexible applications. Figure 11a displays the I−V curve of the flexible

Figure 9. (a,b) Variation of the photoresponse characteristics of the graphene/SnS/graphene photodetector under different intensities of light illumination (0.9−1.2 mW/m2) at 1 and 3 V bias voltages.

photocurrent increases to 5 × 10−7, 6.3 × 10−7, and 8 × 10−7 A with different light intensities (0.9, 1.0, and 1.2 mW/ m2) for 1 V and the photocurrent increases to 2.1 × 10−6, 2.9 × 10−6, and 4 × 10−6 A (0.9, 1.0, and 1.2 mW/m2) for 3 V (the photoresponse of the device under different light intensities at 2 V is shown in Figure S2), demonstrating SnS to have excellent reproducibility of the photodetectors. The highly stable and fast 32147


Research Article


were also prepared on flexible substrate using graphene. The flexible photodetectors revealed excellent bending durability and similar photosensitive properties. The current investigation results personify the nanostructured SnS nanoflakes to be a promising building block for high-performance optoelectronic devices.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b09959. SEM image of the self-assembled SnS nanoflakes, timedependent photoresponse characteristics, and I−V characteristics under dark condition of the flexible graphene/SnS/graphene device (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Pugazhendi Ilanchezhiyan: 0000-0001-5816-8496 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (no. 2014R1A2A1A12066298) and by the Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (no. 2017R1D1A1B03032759) and (2016R1A6A1A03012877).

Figure 11. I−V curves of the flexible graphene/SnS/graphene photodetector before and after bending conditions (inset: a digital photograph of the flexible device). (b) Time-dependent photoresponse curve of the device after 25 bending cycles.

■

SnS photodetector before and after the bending conditions under illumination. Inset in the Figure 11a shows the digital image of the device. In the case of a bending process, 25 bending cycles were studied. At a bias voltage of 3 V, the photocurrents of the flexible device remained unchanged, revealing that the photocurrents of the flexible device have no effect on the conductance of the flexible detector under bending condition. I−V curve of the SnS flexible photodetector under dark conditions is illustrated in Figure S3 (Supporting Information). From the results, it can be seen that the conductance remains unchanged for the SnS nanoflake film even after 25 bending cycles. The time-dependent responses of the photodetector measured over 25 bending cycles is displayed in Figure 11b, demonstrating the superior stability and flexibility of the fabricated photodetector. These results indicate that the photodetector based on the SnS nanoflakes offers excellent stability and may endow it with promising applications in flexible devices.

REFERENCES

(1) Geim, A. K.; Novoselov, K. S. The Rise of Graphene. Nat. Mater. 2007, 6, 183−191. (2) Huang, X.; Yin, Z.; Wu, S.; Qi, X.; He, Q.; Zhang, Q.; Yan, Q.; Boey, F.; Zhang, H. Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications. Small 2011, 7, 1876−1902. (3) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5, 263−275. (4) Hickey, S. G.; Waurisch, C.; Rellinghaus, B.; Eychmüller, A. Size and Shape Control of Colloidally Synthesized IV−VI Nanoparticulate Tin(II) Sulfide. J. Am. Chem. Soc. 2008, 130, 14978−14980. (5) Fu, X.; Ilanchezhiyan, P.; Kumar, G. M.; Cho, H. D.; Zhang, L.; Chan, A. S.; Lee, D. J.; Panin, G. N.; Kang, T. W. Tunable UV-Visible Absorption of SnS2 Layered Quantum Dots Produced by Liquid Phase Exfoliation. Nanoscale 2017, 9, 1820−1826. (6) Kumar, G. M.; Xiao, F.; Ilanchezhiyan, P.; Yuldashev, S.; Kang, T. W. Enhanced Photoelectrical Performance of Chemically Processed SnS2 Nanoplates. RSC Adv. 2016, 6, 99631−99637. (7) Zhou, X.; Zhang, Q.; Gan, L.; Li, H.; Xiong, J.; Zhai, T. Booming Development of Group IV-VI Semiconductors: Fresh Blood of 2D Family. Adv. Sci. 2016, 3, 1600177. (8) Zhou, X.; Zhou, N.; Li, C.; Song, H.; Zhang, Q.; Hu, X.; Gan, L.; Li, H.; Lü, J.; Luo, J.; Xiong, J.; Zhai, T. Vertical Heterostructures Based on SnSe2/MoS2 for High Performance Photodetectors. 2D Mater. 2017, 4, 025048. (9) Zhou, X.; Zhang, Q.; Gan, L.; Li, H.; Zhai, T. Large-Size Growth of Ultrathin SnS2 Nanosheets and High Performance for Phototransistors. Adv. Funct. Mater. 2016, 26, 4405−4413. (10) Li, B.; Huang, L.; Zhong, M.; Li, Y.; Wang, Y.; Li, J.; Wei, Z. Direct Vapor Phase Growth and Optoelectronic Application of Large

4. CONCLUSIONS In summary, the self-assembled 2D flakelike SnS nanostructures were synthesized by a simple and low-cost hydrothermal technique. The photoelectric properties of the synthesized nanostructures were investigated by fabricating the photodetectors using SnS nanoflakes as the active material and graphene as the transparent electrodes. The device reached a high photoresponsivity of 1.7 × 104 A/W and a high stability under light illumination. Furthermore, the SnS photodetectors 32148


Research Article

ACS Applied Materials & Interfaces Band Offset SnS2/MoS2 Vertical Bilayer Heterostructures with High Lattice Mismatch. Adv. Electron. Mater. 2016, 2, 1600298. (11) 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 Res. 2017, 10, 2386−2394. (12) Reddy, K. T. R.; Reddy, N. K.; Miles, R. W. Photovoltaic Properties of SnS Based Solar Cells. Sol. Energy Mater. Sol. Cells 2006, 90, 3041−3046. (13) Vidal, J.; Lany, S.; d’Avezac, M.; Zunger, A.; Zakutayev, A.; Francis, J.; Tate, J. Band-Structure, Optical Properties, and Defect Physics of the Photovoltaic Semiconductor SnS. Appl. Phys. Lett. 2012, 100, 032104. (14) Xu, Y.; Al-Salim, N.; Bumby, C. W.; Tilley, R. D. Synthesis of SnS Quantum Dots. J. Am. Chem. Soc. 2009, 131, 15990−15991. (15) Zhang, H.; Hu, C.; Wang, X.; Xi, Y.; Li, X. Synthesis and Photosensitivity of SnS Nanobelts. J. Alloys Compd. 2012, 513, 1−5. (16) Chao, J.; Wang, Z.; Xu, X.; Xiang, Q.; Song, W.; Chen, G.; Hu, J.; Chen, D. Tin Sulfide Nanoribbons as High Performance Photoelectrochemical Cells, Flexible Photodetectors and VisibleLight-Driven Photocatalysts. RSC Adv. 2013, 3, 2746−2753. (17) Vaughn, D. D.; Hentz, O. D.; Chen, S.; Wang, D.; Schaak, R. E. Formation of SnS Nanoflowers for Lithium ion Batteries. Chem. Commun. 2012, 48, 5608−5610. (18) Lu, J.; Nan, C.; Li, L.; Peng, Q.; Li, Y. Flexible SnS nanobelts: Facile Synthesis, Formation Mechanism and Application in Li-ion batteries. Nano Res. 2013, 6, 55−64. (19) Avellaneda, D.; Nair, M. T. S.; Nair, P. K. Photovoltaic Structures using Chemically Deposited Tin Sulfide Thin Films. Thin Solid Films 2009, 517, 2500−2502. (20) Ning, J.; Men, K.; Xiao, G.; Wang, L.; Dai, Q.; Zou, B.; Liu, B.; Zou, G. Facile Synthesis of IV−VI SnS Nanocrystals with Shape and Size Control: Nanoparticles, Nanoflowers and Amorphous Nanosheets. Nanoscale 2010, 2, 1699−1703. (21) Ham, G.; Shin, S.; Park, J.; Choi, H.; Kim, J.; Lee, Y.-A.; Seo, H.; Jeon, H. Tuning the Electronic Structure of Tin Sulfides Grown by Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2013, 5, 8889− 8896. (22) Lu, F.; Yang, J.; Li, R.; Huo, N.; Li, Y.; Wei, Z.; Li, J. GasDependent Photoresponse of SnS Nanoparticles-Based Photodetectors. J. Mater. Chem. C 2015, 3, 1397−1402. (23) de Kergommeaux, A.; Lopez-Haro, M.; Pouget, S.; Zuo, J.-M.; Lebrun, C.; Chandezon, F.; Aldakov, D.; Reiss, P. Synthesis, Internal Structure, and Formation Mechanism of Monodisperse Tin Sulfide Nanoplatelets. J. Am. Chem. Soc. 2015, 137, 9943−9952. (24) Rath, T.; Gury, L.; Sánchez-Molina, I.; Martínez, L.; Haque, S. A. Formation of Porous SnS Nanoplate Networks from Solution and Their Application in Hybrid Solar Cells. Chem. Commun. 2015, 51, 10198−10201. (25) Suryawanshi, S. R.; Warule, S. S.; Patil, S. S.; Patil, K. R.; More, M. A. Vapor−Liquid−Solid Growth of One-Dimensional Tin Sulfide (SnS) Nanostructures with Promising Field Emission Behavior. ACS Appl. Mater. Interfaces 2014, 6, 2018−2025. (26) Tripathi, A. M.; Mitra, S. Tin Sulfide (SnS) Nanorods: Structural, Optical and Lithium Storage Property Study. RSC Adv. 2014, 4, 10358−10366. (27) Li, S.; Zuo, S.; Wu, Z.; Liu, Y.; Zhuo, R.; Feng, J.; Yan, D.; Wang, J.; Yan, P. Stannous Sulfide/Multi-walled Carbon Nanotube Hybrids as High-Performance Anode Materials of Lithium-ion Batteries. Electrochim. Acta 2014, 136, 355−362. (28) Li, S.; Zheng, J.; Hu, Z.; Zuo, S.; Wu, Z.; Yan, P.; Pan, F. 3DHierarchical SnS Nanostructures: Controlled Synthesis, Formation Mechanism and Lithium-ion Storage Performance. RSC Adv. 2015, 5, 72857−72862. (29) Liu, X.; Li, Y.; Zhou, B.; Wang, X.; Cartwright, A. N.; Swihart, M. T. Shape-Controlled Synthesis of SnE (E = S, Se) Semiconductor Nanocrystals for Optoelectronics. Chem. Mater. 2014, 26, 3515−3521.

(30) Zhang, Y.; Lu, J.; Shen, S.; Xu, H.; Wang, Q. Ultralarge Single Crystal SnS Rectangular Nanosheets. Chem. Commun. 2011, 47, 5226−5228. (31) Brent, J. R.; Lewis, D. J.; Lorenz, T.; Lewis, E. A.; Savjani, N.; Haigh, S. J.; Seifert, G.; Derby, B.; O’Brien, P. Tin(II) Sulfide (SnS) Nanosheets by Liquid-Phase Exfoliation of Herzenbergite: IV−VI Main Group Two-Dimensional Atomic Crystals. J. Am. Chem. Soc. 2015, 137, 12689−12696. (32) Bade, B. P.; Garje, S. S.; Niwate, Y. S.; Afzaal, M.; O’Brien, P. Tribenzyltin(IV)chloride Thiosemicarbazones: Novel Single Source Precursors for Growth of SnS Thin Films. Chem. Vap. Deposition 2008, 14, 292−295. (33) Kang, F.; Ichimura, M. Pulsed Electrodeposition of Oxygen-Free Tin Monosulfide Thin Films using Lactic acid/Sodium lactate Buffered Electrolytes. Thin Solid Films 2010, 519, 725−728. (34) Liu, Y.; Hou, D.; Wang, G. Synthesis and Characterization of SnS Nanowires in Cetyltrimethylammoniumbromide (CTAB) Aqueous Solution. Chem. Phys. Lett. 2003, 379, 67−73. (35) Salavati-Niasari, M.; Ghanbari, D.; Davar, F. Shape Selective Hydrothermal Synthesis of Tin Sulfide Nanoflowers Based on Nanosheets in the Presence of Thioglycolic Acid. J. Alloys Compd. 2010, 492, 570−575. (36) Deng, Z.; Cao, D.; He, J.; Lin, S.; Lindsay, S. M.; Liu, Y. Solution Synthesis of Ultrathin Single-Crystalline SnS Nanoribbons for Photodetectors via Phase Transition and Surface Processing. ACS Nano 2012, 6, 6197−6207. (37) Mahdi, M. S.; Ibrahim, K.; Hmood, A.; Ahmed, N. M.; Azzez, S. A.; Mustafa, F. I. A Highly Sensitive Flexible SnS Thin Film Photodetector in the Ultraviolet to Near Infrared Prepared by Chemical Bath Deposition. RSC Adv. 2016, 6, 114980−114988. (38) Zhou, X.; Gan, L.; Zhang, Q.; Xiong, X.; Li, H.; Zhong, Z.; Han, J.; Zhai, T. High Performance Near-Infrared Photodetectors Based on Ultrathin SnS nanobelts Grown via Physical Vapor Deposition. J. Mater. Chem. C 2016, 4, 2111−2116. (39) Yu, J.; Tang, H. Solvothermal Synthesis of Novel Flower-like Manganese Sulfide Particles. J. Phys. Chem. Solids 2008, 69, 1342− 1345. (40) Khan, M. D.; Akhtar, J.; Malik, M. A.; Akhtar, M.; Revaprasadu, N. Phase-Pure Fabrication and Shape Evolution Studies of SnS Nanosheets. New J. Chem. 2015, 39, 9569−9574. (41) Ilanchezhiyan, P.; Kumar, G. M.; Kang, T. W. Electrochemical Studies of Spherically Clustered MoS2 Nanostructures for Electrode Applications. J. Alloys Compd. 2015, 634, 104−108. (42) Raadik, T.; Grossberg, M.; Raudoja, J.; Traksmaa, R.; Krustok, J. Temperature-Dependent Photoreflectance of SnS Crystals. J. Phys. Chem. Solids 2013, 74, 1683−1685. (43) Sinsermsuksakul, P.; Heo, J.; Noh, W.; Hock, A. S.; Gordon, R. G. Atomic Layer Deposition of Tin Monosulfide Thin Films. Adv. Energy Mater. 2011, 1, 1116−1125. (44) Radovsky, G.; Popovitz-Biro, R.; Staiger, M.; Gartsman, K.; Thomsen, C.; Lorenz, T.; Seifert, G.; Tenne, R. Synthesis of Copious Amounts of SnS2 and SnS2/SnS Nanotubes with Ordered Superstructures. Angew. Chem., Int. Ed. 2011, 51, 12316−12320. (45) Sohila, S.; Rajalakshmi, M.; Ghosh, C.; Arora, A. K.; Muthamizhchelvan, C. Optical and Raman scattering studies on SnS nanoparticles. J. Alloys Compd. 2011, 509, 5843−5847. (46) Chandrasekhar, H. R.; Humphreys, R. G.; Zwick, U.; Cardona, M. Infrared and Raman Spectra of the IV-VI Compounds SnS and SnSe. Phys. Rev. B: Solid State 1977, 15, 2177−2183. (47) Cheng, S.; Conibeer, G. Physical Properties of Very Thin SnS Films Deposited by Thermal Evaporation. Thin Solid Films 2011, 520, 837−841. (48) Patel, M.; Chavda, A.; Mukhopadhyay, I.; Kim, J.; Ray, A. Nanostructured SnS with Inherent Anisotropic Optical Properties for High Photoactivity. Nanoscale 2016, 8, 2293−2303. (49) Xin, C.; Zheng, J.; Su, Y.; Li, S.; Zhang, B.; Feng, Y.; Pan, F. Few-Layer Tin Sulfide: A New Black-Phosphorus-Analogue 2D Material with a Sizeable Band Gap, Odd−Even Quantum Confine32149


Research Article

ACS Applied Materials & Interfaces ment Effect, and High Carrier Mobility. J. Phys. Chem. C 2016, 120, 22663−22669. (50) Yang, Y.-B.; Dash, J. K.; Xiang, Y.; Wang, Y.; Shi, J.; Dinolfo, P. H.; Lu, T.-M.; Wang, G.-C. Tuning the Phase and Optical Properties of Ultrathin SnSx Films. J. Phys. Chem. C 2016, 120, 13199−13214. (51) Zhang, B. Y.; Liu, T.; Meng, B.; Li, X.; Liang, G.; Hu, X.; Wang, Q. J. Broadband High Photoresponse from Pure Monolayer Graphene Photodetector. Nat. Commun. 2013, 4, 1811. (52) Roy, K.; Padmanabhan, M.; Goswami, S.; Sai, T. P.; Ramalingam, G.; Raghavan, S.; Ghosh, A. Graphene−MoS2 Hybrid Structures for Multifunctional Photoresponsive Memory Devices. Nat. Nanotechnol. 2013, 8, 826−830. (53) Mukherjee, B.; Cai, Y.; Tan, H. R.; Feng, Y. P.; Tok, E. S.; Sow, C. H. NIR Schottky Photodetectors Based on Individual SingleCrystalline GeSe Nanosheet. ACS Appl. Mater. Interfaces 2013, 5, 9594−9604. (54) Wang, J.; Lian, G.; Xu, Z.; Fu, C.; Lin, Z.; Li, L.; Wang, Q.; Cui, D.; Wong, C.-P. Growth of Large-Size SnS Thin Crystals Driven by Oriented Attachment and Applications to Gas Sensors and Photodetectors. ACS Appl. Mater. Interfaces 2016, 8, 9545−9551.

32150


Highly Sensitive Flexible Photodetectors Based on Self-Assembled

Recommend Documents