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MoS2 hybrid film
Applied Surface Science 493 (2019) 389–395
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Full length article
Sensitive, fast, and stable photodetector based on perovskite/MoS2 hybrid film
T
Bo Suna,c, Shuang Xib, Zhiyong Liua, Xinyue Liua, Ziyi Wanga, Xianhua Tana, Tielin Shia, ⁎ Jianxin Zhouc, Guanglan Liaoa, a
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China School of Mechanical and Electronic Engineering, Nanjing Forestry University, Nanjing 210037, China c State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Photodetector Perovskite MoS2 film Flexible devices Hybrid film
Atomically thin MoS2 film has displayed great potential for future optoelectronics due to its outstanding photonic and electronic properties. However, many important applications, especially for photodetection, are still severely limited by its low light absorption. In this paper, we demonstrate a high-performance photodetector based on perovskite/MoS2 hybrid film, which exhibits sensitive, fast, and stable response under low operation potential. The external photoresponsivity is about 342 A/W at bias potential of 2 V without gate voltage under incident power of 2.2 pW (520 nm), which is superior than most of the photodetectors based on transition metal dichalcogenides and perovskite. The devices show high stability during transient on/off test without any encapsulation, in which the response and recovery time has been recorded as 27 ms and 21 ms, respectively. Besides, the devices can be fabricated on various substrates, including SiO2/Si, transparent glass and flexible PET, etc. The flexible perovskite/MoS2 photodetectors with ultrahigh stability during 20,000 times bending was reported for the first time. We expect the proposed hybrid photodetector would be a competitive candidate in future flexible electronics. Our research also paves the way to integrate various atomically thin films with highly optical absorption materials.
1. Introduction Photodetectors (PDs) play a critical role in various optoelectronic applications, including signal detection, optical communication, and optical imaging, etc. [1–3] High-performance PDs possess of high sensitivity, fast response speed and good endurance are badly needed in practical application [4–7], which further arouse a series challenges to the properties of photoactive materials [8], including high absorptivity, large carrier mobility, suitable band structure, and high stability, etc. Early efforts are mainly dedicated to pursue high-performance PDs based on Si, GaP, and GaAs etc. which always demands vigorous fabrication process. Recent years, PDs composed of nanomaterials and quantum dots, with simple fabrication process and low cost have attracted much attention [9–11]. Although some competitive merits of these PDs have been achieved, the majority of them still limited by small responsivity [12], large dark current [13], and slow response speed [14]. Atomically thin MoS2 film aroused much attention in the past few years regarding its outstanding electrical and optical properties
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[15,16]. Various MoS2-based PDs have been reported with excellent performance [17,18]. However, despite of its superior properties, it is still a huge difficult for MoS2 film to fully absorb the incident light due to its atomically thin feature, which severely hinders the wide application of the MoS2-based optoelectronic devices [19]. Many researches have been devoted to exploit the strategies which can improve the properties of the MoS2-based PDs, including applying surface plasmonic [20,21], exploring van der Waals heterostructures [22–24], and introducing photoactive materials with high absorptivity, such as silicon [25], carbon nanotube [26], GaTe [27], PbS quantum dots [28], etc. Meanwhile, organometal trihalide perovskite CH3NH3PbX3 (X is Cl, Br, or I) is booming as a new generation of optoelectronic material and attracts much attention due to its successful application in photovoltaic devices [29–31]. Recently, we also demonstrated a series of carbon counter electrode based high performance perovskite solar cell [32–35]. The rapid development of photovoltaic devices has stimulated the utilization of perovskite thin film in PDs [36–39]. Although perovskite PDs with architecture similar to solar cell has been demonstrated with fast response, the responsivity is relatively low [40,41].
Corresponding author. E-mail address: [email protected] (G. Liao).
https://doi.org/10.1016/j.apsusc.2019.07.036 Received 15 November 2018; Received in revised form 19 June 2019; Accepted 5 July 2019 Available online 06 July 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
Applied Surface Science 493 (2019) 389–395
B. Sun, et al.
The photoconductive detector composed of hybrid film, such as perovskite/reduced graphene oxide (rGO), perovskite/graphene, demonstrated a good responsivity [42,43]. Unfortunately, the high conductivity of these materials results in a high dark current and low specific detectivity. Recently, the photodetectors constructed by MoS2/CH3NH3PbI3 and WS2/CH3NH3PbI3 hybrid film have been reported with a good performance [44–46]. However, there still have many issues to be resolved urgently. For example, the small size of MoS2 flakes makes them unsuitable for large-area applications [47,48]. The stability of the devices is rarely investigated due to the poor stability of organometal trihalide perovskite film in ambient atmosphere [35,47]. Besides, to the best knowledge of us, there has no relevant reports focused on the flexible MoS2/perovskite photodetectors. In this paper, we proposed a high performance photodetector composed of large-area atomically thin MoS2 film and triple cations lead mixed-halide perovskite layer, which exhibits sensitive, fast, and stable response under low operation potential. Besides, the flexible MoS2/perovskite photodetectors fabricated on the PET substrate with high stability under repeated bending test was demonstrated for the first time. This work paves a new route to exploit the flexible photodetector based on perovskite and various transition metal dichalcogenides (TMDCs) layer.
in a N2 filled glove box: 3 μL of DMF was dropped in an alumina crucible placed aside the samples, then all of them were covered by a Petri dish annealing at 100 °C for 1 h. 2.3. Characterization and measurement Morphology of the atomically thin MoS2 film and perovskite layer was directly observed by optical microscopy (Keyence VHX-1000E) and field emission scanning electron microscopy (FE-SEM, Zeiss Gemini 300), respectively. The thickness of the film was obtained by atomic force microscopy (AFM, Shimadzu SPM9700). Field emission transmission electron microscopy (FE-TEM, FEI Talos F200X) was used to monitor the lattice structure of the MoS2 film. The X-ray diffraction (XRD) analysis of the perovskite layer was conducted by X-ray diffractometer (PANalytical PW3040/60). XPS spectra measurement was performed using X-ray photoelectron spectroscope (VG Multilab 2000 X) to further explore the surface state of the film. Raman shift and steady-state photoluminescence (PL) spectra of the MoS2 film were measured by Raman spectrometer (LabRAM HR800) under the excitation of laser (532 nm). And the time resolved photoluminescence (TRPL) decay curves were collected by PicoQuant FluoTime300. Transmittance spectra of the film were collected by UV–Visible spectrophotometer (Shimadzu UV 2600). The performance of the photodetector was measured by two channel digital source-meter (Keithley 2636B). A fiber laser (Thorlabs LP520-SF15) modulated by function/ arbitrary waveform generator (Keysight 33210A) was used as light source.
2. Experimental section 2.1. Atomically thin MoS2 film growth The MoS2 films were prepared on Si/SiO2 substrate using CVD method in tube furnace. In details, a pre-dissolved MoO3 solution (20 mg/mL in ammonia) was spin-coated on Si/SiO2 substrate to obtain a MoO3 film with about 20 nm thickness. The prepared source substrate was placed in a quartz boat, followed by the loading of growth substrate above the source substrate with the SiO2 side facing down, which then was loaded in the middle of the tube. The distance of the two substrates was maintained at about 2 mm. Another quartz boat containing 0.4 g of sulfur powder was placed outside the main furnace. After that, the oxygen and water vapor in the tube was removed by Ar gas at 1000 sccm and the growth process was conducted at atmospheric pressure under 40 sccm flow of Ar gas. The temperature of the MoO3 substrate in the main furnace was raised gradually and the sulfur powder was heated using heating tape separately. When the temperature of main furnace approach to about 730 °C, the sulfur gas was introduced in reaction region due to the melt and evaporation of sulfur powders. The growth process was continued for 5 min at 820 °C. The furnace then was cooled down naturally and the gas flow was tuned to 200 sccm. The MoS2 film grown on SiO2/Si was transferred on a target substrate via the PMMA-assisted transferring method. The electrode (Ti 5 nm/Au 50 nm) was prepared on the MoS2 film via e-beam and thermal evaporation.
3. Results and discussion Fig. 1a schematically illustrates the structure of the perovskite/ MoS2 hybrid photodetector. The continuous atomically thin MoS2 film was prepared by CVD method. After deposition of the Ti/Au electrode, a triple cations (Cs/MA/FA) mixed perovskite layer was spin-coated. The optical image of MoS2 film was depicted in Fig. 1b. During the growth, some quasi-triangular dots were nucleated randomly and then evolved to triangular grains (Fig. S1). The grains connected with each other as the growth continued and eventually formed the continuous MoS2 film. However, the precursor and reaction time is always controlled to reduce the thickness of the film, resulting in the uncovered area as marked by dashed circle in Fig. 1b. The continuous film then was transferred on target substrate using a PMMA assisted transferring method and the Ti/Au electrode was deposited as shown in the inset of Fig. 1b. The MoS2 film was also transferred on a copper grid for TEM observation (Fig. S2). High resolution TEM image (Fig. 1c) reveals that the film has a high quality single crystal structure with the interplanar spacings of 0.274 and 0.267 nm corresponding to the d-spacings of (100) and (101) planes. To investigate the thickness of the MoS2 film, AFM measurement was conducted at the edge of the film as shown in Fig. 1d. The value is revealed as about 0.8 nm which is agree well with the previous reports on monolayer MoS2 film [49–51]. After spin-coating the perovskite film, the morphology of the devices was observed as shown in Fig. 1e and f. The top view SEM image reveals that the surface layer of the film resembles the morphology of the polycrystalline films without pinholes, in which the grain size is about 200–500 nm. The electrode pattern also can be distinguished from the inset image (low magnification). The sectional view image (Fig. 1f) shows that the thickness of the highly crystalline perovskite layer is about 500 nm. Noteworthy is that the film demonstrates a columnar crystal structure in which the grains can penetrate the whole perovskite layer, substantially reducing carrier recombination at the grain boundaries. Ti/Au electrode is obvious in the sectional view image. However, the MoS2 film is hard to be observed from the image due to its ultrathin nature. XPS spectrum was obtained to further elucidate the surface states of the monolayer MoS2 film as shown in Fig. 2a, in which the
2.2. Perovskite layer deposition The perovskite layer was coated on the MoS2 film by spin-coating of a triple cations lead mixed-halide perovskite solution. The perovskite solution was synthesized using a precursor consisted of 0.2 M methylammonium bromide (MABr,), 1 M formamidinium iodide (FAI), 1.1 M PbI2 and 0.2 M PbBr2 in a mixture (1: 4 volume ratio) of anhydrous Dimethylsulfoxide (DMSO) and N, N-Dimethylformamide (DMF). A predissolved 1.5 M cesium iodide (CsI) solution in DMSO was dropped in the above precursor with the volume ratio of 5:95. The solution then was heated at 60 °C under vigorous stirring for half an hour. After that, 5 μL of triple cations perovskite solution was dropped on the atomically thin MoS2 layer and spin coated using a two-step process (1000 rpm for 10 s and 5000 rpm for 20 s), with dropping of 30 μL of chlorobenzene at 5 s before the end. To improve the quality of the as-prepared perovskite film, a solvent assisted annealing process was performed on a hot plate 390
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Fig. 1. (a) Structural schematic of the photodetector based on perovskite/MoS2 hybrid film. (b) Optical image of MoS2 film, inset: the optical image after deposition of electrode. (c) High resolution TEM image of MoS2 film. (d) AFM image collected from edge of the film. (e) The top view SEM image of the perovskite layer, inset: low resolution image of the device. (f) The sectional view SEM image of the perovskite layer.
characteristic peaks have been marked. The high resolution XPS spectra (Fig. S3) reveals that the peaks located at 230.2 eV and 233.4 eV can be attributed to the 3d5/2 and 3d3/2 states of Mo. The two peaks at about 163.0 eV and 164.2 eV correspond to the 2p3/2 and 2p1/2 states of S. The Raman spectrum of the MoS2 film was displayed in Fig. 3b. As expected, the film demonstrates two sharp peaks centered at about 384.8 cm−1 and 403.8 cm−1, in accordance with the E12g and A1g
modes, respectively. Frequency difference between the peaks is about 19.0 cm−1, which is a clear evidence of a monolayer of MoS2 film [49,50]. Fig. 2c depicted the XRD pattern of the triple cations mixed perovskite film. The sharp peaks located at about 14.06°, 19.98°, 24.57°,28.37°, 31.82°, 34.96°, 40.59° and 43.16° can be attributed to the (110), (112), (202), (220), (310), (312), (224) and (314) lattice planes of a typical tetragonal perovskite structure [34]. Besides, we also
Fig. 2. (a) XPS spectrum of the MoS2 film. (b) Raman spectrum of the MoS2 film (c) XRD spectrum of the perovskite film. (d) XPS spectrum of the perovskite film, (e) Photoluminescence spectra of the perovskite film and perovskite/MoS2 hybrid film. (f) TRPL decay curves of perovskite film and perovskite/MoS2 hybrid film. 391
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Fig. 3. (a) I-V characteristics of the photodetectors. (b) The I-V curves in logarithmic coordinate diagram. (c) Performance of the devices under the illumination of 50 μW/mm2 with different channel length; inset: photoresponsivity varying with the bias potential and channel length. (d) The photocurrent and photoresponsivity of the devices varying with incident power.
at the same condition, a severe PL quenching for the hybrid film can be achieved compared to the pristine perovskite layer, directly proving that a considerable charge carries are extracted via the perovskite/ MoS2 interface. The electric properties of the PDs were then investigated. Fig. 3a displays the I-V characteristics of the photodetector composed of MoS2 film, perovskite film, and perovskite/MoS2 hybrid film. The photocurrent of MoS2 film is about 32 nA at 2 V bias potential with the incident power of 50 nW, while the value increases to about 84 nA after the coating of perovskite layer. The dark current is negligible in Fig. 3a. Thus, the data was transferred in logarithmic coordinate diagram to clearly demonstrate the dark current as shown in Fig. 3b. Obviously, the dark current is increased with bias potential for all of the samples. The value of perovskite/MoS2 hybrid film is about 2.0 pA and 3.8 pA for the bias potential of 1 V and 2 V, respectively. Fig. 3c depicts the performance of the devices with different channel length (from 10 μm to 100 μm) under the illumination of 50 μW/mm2. The devices demonstrate a similar photocurrent. To further evaluate the devices with different channel length, the responsivity was calculated using the following equation: R = (Ilight − Idark)/P, where Ilight and Idark is photocurrent and dark current of the devices, respectively. P is the incident optical power on the photodetector active area. The inset in Fig. 3c displays the responsivity of the photodetector varying with the bias potential and channel length. Obviously, the responsivity decreases as the channel length increases. The smallest channel (10 μm) demonstrates the highest value of 1.7 A/W under the illumination of 50 nW. Considering the varied incident power for the above devices, we further study the relationship between photocurrent, responsivity and incident power as shown in Fig. 3d. Obviously, the photocurrent of the devices is improved as the incident power increases. However, the
observed two diffraction peaks at 12.64° and 47.75° marked by rhombuses, which can be assigned to PbI2 caused by the excess lead during the synthesis of perovskite solution. The XPS spectrum of the perovskite film was shown in Fig. 2d, where the characteristic peaks of C 1s, N 1s, Cs 3d, Pb 4f, I 3d, Br 3d have been marked clearly. The high resolution XPS spectra (Fig. S4) further demonstrates that the peaks at about 285 and 400.5 eV can be attributed to the C 1s state and N 1s state. The peaks at about 724.8/ 738.8 eV, 619.2/630.7 eV, and 68.5/69.3 eV agree well with the 3d5/2 and 3d3/2 states of Cs, I, and Br, respectively. The peaks at 138.4 and 143.3 eV can be assigned to the 4f7/2 and 4f5/2 states. The quantification analysis of XPS data reveals that the atomic ratio of the surface of perovskite film is 0.73% Cs, 22.54% C, 17.13% N, 13.8% Pb, 40.87% I, 4.94% Br, which is in accordance with the predesigned chemical composition Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3. To investigate the light distribution in the hybrid film, we further measured the UV transmittance of the perovskite film (Fig. S5). The UV spectrum reveals that the band edge of the film is located at about 760 nm. The transmittance at 520 nm is about 5.4%, which means most of the incident light was absorbed by perovskite layer before irradiated on MoS2 film. Besides, we obtained the photoluminescence (PL) spectra of the perovskite film and perovskite/MoS2 hybrid film as depicted in Fig. 2e. With the underneath MoS2 layer, the band-to-band transition peak at 1.63 eV displays a significant decrease, indicating that a large number of photo-excited electrons are transferred from the photoactive perovskite layer to MoS2 film. Moreover, the time resolved photoluminescence (TRPL) decay curves also were collected to investigate the charge carrier dynamics at the interfaces as shown in Fig. 2f. The calculated average PL decay time for pristine perovskite film and perovskite/MoS2 hybrid film are 1927 and 284 ns, respectively. Obviously, 392
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Fig. 4. (a) Working mechanism and energy-band diagram of the photodetector based on perovskite/MoS2 hybrid film under illumination. (b) The transient photoresponse of the device under repeated on/off illumination. (c) Response and recovery time of the devices. (d) Long-term stability test of the devices without any encapsulation.
ratio of 2 × 104. To calculate the response and recovery time of the devices, a single on/off cycle is collected as shown in Fig. 4c. Given the 10% and 90% peak value of the photocurrent, the response and recovery time is calculated as 27 ms and 21 ms, which is superior to the latest reported PDs based on MoS2 film [20,21,52]. To further elucidate the stability of the devices, time-dependent photocurrent density at repeated on/off cycles of illumination was collected as shown in Fig. 4d. During the test process (1 h), no obvious degrade is observed. In general, the stability of perovskite is poor under light soaking. However, the triple cations (Cs/MA/FA) mixed perovskite film we proposed here demonstrates a good stability in ambient atmosphere (≈50% RH and 25 °C) and no observed charge accumulation due to the imbalanced charge transport, which can be attributed to the special composition of the film and the perovskite/MoS2 junction formed in the devices. With further PDMS encapsulation, we believe the stability of the device is adequate for the actual application [35]. A noteworthy phenomenon is the devices demonstrate non-negligible response (≈0.3 nA) for light irradiation at zero bias potential as shown in the inset of Fig. 4d, which is rarely found in photoconductive photodetectors. The I-V characteristic under illumination (Fig. S6) reveals that the devices possess a property similar to photovoltaics, which may be a comprehensive effect of the junctions formed at MoS2/Perovskite interface and metal/semiconductor interface. These results further demonstrate the formation of perovskite/MoS2 junction substantially enhance the photoexcited charge carriers separation and transportation.
photoresponsivity is substantially enhanced as the incident power decreases due to the suppressed scattering between the photoexcited charge carriers. The photoresponsivity can be improved to 342 A/W, which is much higher than most of TMDCs film or perovskite-based photodetectors [17,20,39–41]. Another important benefit of the photodetectors is the specific detectivity D*, which is defined as (AΔf)1/2R/ in. Here, A is the effective area, Δf is the electrical bandwidth, in is the noise current which is mainly attributed to the dark current here [22]. The obtained specific detectivity value is about 1.14 × 1012 Jones. Fig. 4a displays the working mechanism and energy-band diagram of the photodetector based on perovskite/MoS2 hybrid film under illumination. As the device is irradiated by the laser, the photo-excited charge carriers are generated immediately in the hybrid film. As illustrated in the schematic, photo-excited charge carrier concentration in the perovskite layer is much higher than that in MoS2 film due to its high photo absorptivity. Then the electrons and holes were separated in the perovskite layer because of its ambipolar charge transport property and the electrons are expected to diffuse into the MoS2 film and collected at the electrode due to the electric field formed at the perovskiteMoS2 junction and Ti-MoS2 junction. The transient photoresponse of the perovskite/MoS2 photodetector was recorded by switching the laser on and off as shown in Fig. 4b. Obviously, the response speed was improved dramatically after the coating of perovskite layer. The measured photocurrent is increase from 2 pA in the dark to about 40 nA under illumination at 1 V bias potential, demonstrating an switching
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Fig. 5. (a) I-V curves of the PDs on transparent glass under front illumination and back illumination. (b) The I-V curves of the PDs on flexible substrate with different channel length. (c) Photocurrent of the flexible devices under transient on/off illumination. (d) Photocurrent ratio of the devices suffered from repeated bending compared with corresponding devices without bending.
including SiO2/Si, transparent glass and flexible PET, etc. The atomically thin MoS2 film synthesized via CVD method shows continuous, homogenous and stable properties. The devices exhibit outstanding performance under low operation potential, with external photoresponsivity ~342 A/W at 2 V without gate voltage under incident power of 2.2 pW, which probably due to the high absorption and long electron/hole diffusion length of the perovskite. Accordingly, the specific detectivity reaches 1.14 × 1012 Jones. Moreover, flexible photodetectors using the perovskite/MoS2 hybrid film on PET substrate were fabricated, demonstrating a quick response and good stability under transient on/off illumination, and also 91% of the photoresponsivity remaining after 20,000 bending cycles. This high-performance photodetector would find diverse applications in the fields of optoelectronic system and flexible electronic system.
Besides, it also indicates that the devices possess a potential self-powered property for future application. To demonstrate the portability of the perovskite/MoS2 hybrid PDs, we also fabricate the devices on transparent glass. Fig. 5a displays the photocurrent of the devices under front illumination and back illumination, which is almost identical to that of the devices on SiO2/Si substrate. The negligible decline of photocurrent under back illumination can be attributed to the slight decrease of incident power caused by the photoabsorption of the glass. Considering the booming demand of flexible optoelectronics, we further fabricate flexible PDs using the perovskite/MoS2 hybrid film on PET substrate as illustrated in Fig. 5b. The performance of the flexible devices with different channel length is similar to the devices on rigid substrate. Besides, the devices demonstrate a quick response and good stability under transient on/off illumination as shown in Fig. 5c. We also investigate the mechanical endurance of the devices by bending repetitiously using the three-point bending setup as displayed in Fig. 5d. The curvature of the devices can be obtained according to the equation: ρ = [h2 + (L/2)2]/2 h, where L is the distance between the two supporting blocks, and h is the depth at the device midpoint. The curvature adopted here is 5 mm. After bending for 20,000 times, the photocurrent value of devices still maintain 91%, compared with the corresponding I-V curves without bending. Noteworthily, there is no obvious decline between 2000 times and 20,000 times, indicating the flexible PDs is able to bear repeated external mechanical force. These results further demonstrate the good portability and stability of the perovskite/MoS2 hybrid PDs.
Acknowledgements The authors acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51675210), the Natural Science Foundation of Jiangsu Province (Grant No. BK20160934), and the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT17R44), the China Postdoctoral Science Foundation (Grant No. 2016M602283). Appendix A. Supplementary data The morphology evolution of MoS2 film, additional TEM image of MoS2 film, high resolution XPS spectra of MoS2 and pervoskite layer, UV transmittance of the perovskite film and the IV characteristic of the PD under illumination. Supplementary data to this article can be found online at https://doi.org/10.1016/j.apsusc.2019.07.036.
4. Conclusions We have demonstrated a high-performance PD based on perovskite/ MoS2 hybrid film, which can be fabricated on various substrates, 394
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References [29]
[1] V. Adinolfi, E.H. Sargent, Photovoltage field-effect transistors, Nature 542 (2017) 324. [2] H. Chen, H. Liu, Z. Zhang, K. Hu, X. Fang, Nanostructured photodetectors: from ultraviolet to terahertz, Adv. Mater. 28 (2016) 403–433. [3] T. Yokota, P. Zalar, M. Kaltenbrunner, H. Jinno, N. Matsuhisa, H. Kitanosako, Y. Tachibana, W. Yukita, M. Koizumi, T. Someya, Ultraflexible organic photonic skin, Sci. Adv. 2 (2016) e1501856. [4] B. Rahmati, I. Hajzadeh, R. Karimzadeh, S.M. Mohseni, Facile, scalable and transfer free vertical-MoS2 nanostructures grown on Au/SiO2 patterned electrode for photodetector application, Appl. Surf. Sci. 455 (2018) 876–882. [5] F. Chen, C. Xu, Q. Xu, Y. Zhu, F. Qin, W. Zhang, Z. Zhu, W. Liu, Z. Shi, Highperformance, self-powered photodetectors based on perovskite and graphene, ACS Appl. Mater. Interfaces 10 (2018) 25763–25769. [6] L. Su, X.N. Yu, K. Li, X.Y. Yao, M. Pecht, Simulation and experimental verification of edge blurring phenomenon in microdefect inspection based on high-frequency ultrasound, IEEE Access 7 (2019) 11515–11525. [7] L. Su, L. Wang, K. Li, J. Wu, G. Liao, T. Shi, T. Lin, Automated X-ray recognition of solder bump defects based on ensemble-ELM, Sci. China Technol. Sci. (2019), https://doi.org/10.1007/s11431-018-9324-3. [8] Muhammad ZahirIqbal, Sana Khan, Salma Siddique, Ultraviolet-light-driven photoresponse of chemical vapor deposition grown molybdenum disulfide/graphene heterostructured FET, Appl. Surf. Sci. 459 (2018) 853–859. [9] O. Ostroverkhova, Organic optoelectronic materials: mechanisms and applications, Chem. Rev. 116 (2016) 13279–13412. [10] Y.K. Kim, S.H. Hwang, S. Kim, H. Park, S.K. Lim, ZnO nanostructure electrodeposited on flexible conductive fabric: a flexible photo-sensor, Sensors Actuators B Chem. 240 (2017) 1106–1113. [11] H. Makhlouf, C. Karam, A. Lamouchi, S. Tingry, P. Miele, R. Habchi, R. Chtourou, M. Bechelany, Analysis of ultraviolet photo-response of ZnO nanostructures prepared by electrodeposition and atomic layer deposition, Appl. Surf. Sci. 444 (2018) 253–259. [12] W. Wei, X.Y. Bao, C. Soci, Y. Ding, Z.L. Wang, D. Wang, Direct heteroepitaxy of vertical inas nanowires on si substrates for broad band photovoltaics and photodetection, Nano Lett. 9 (2009) 2926–2934. [13] D.H. Shin, S. Kim, J.M. Kim, C.W. Jang, J.H. Kim, K.W. Lee, J. Kim, S.D. Oh, D.H. Lee, S.S. Kang, C.O. Kim, S.-H. Choi, K.J. Kim, Graphene/Si-quantum-dot heterojunction diodes showing high photosensitivity compatible with quantum confinement effect, Adv. Mater. 27 (2015) 2614–2620. [14] J.P. Clifford, G. Konstantatos, K.W. Johnston, S. Hoogland, L. Levina, E.H. Sargent, Fast, sensitive and spectrally tuneable colloidal quantum-dot photodetectors, Nat. Nanotechnol. 4 (2009) 40–44. [15] C. Xie, C. Mak, X. Tao, F. Yan, Photodetectors based on two-dimensional layered materials beyond graphene, Adv. Funct. Mater. 27 (2017) 1603886. [16] M.J. Park, K. Park, H. Ko, Near-infrared photodetector achieved by chemicallyexfoliated multilayered MoS2 flakes, Appl. Surf. Sci. 448 (2018) 64–70. [17] Y. Xue, Y. Zhang, Y. Liu, H. Liu, J. Song, J. Sophia, J. Liu, Z. Xu, Q. Xu, Z. Wang, J. Zheng, Y. Liu, S. Li, Q. Bao, Scalable production of a few-layer MoS2/WS2 vertical heterojunction array and its application for photodetectors, ACS Nano 10 (2016) 573–580. [18] B. Sun, T. Shi, Z. Liu, Y. Wu, J. Zhou, G. Liao, Large-area flexible photodetector based on atomically thin MoS2/graphene film, Mater. Des. 154 (2018) 1–7. [19] F. Xia, H. Wang, D. Xiao, M. Dubey, A. Ramasubramaniam, Two-dimensional material nanophotonics, Nat. Photonics 8 (2014) 899–907. [20] S. Bang, D. Ngoc Thanh, J. Lee, Y.H. Cho, H.M. Oh, H. Kim, S.J. Yun, C. Park, M.K. Kwon, J.-Y. Kim, J. Kim, M.S. Jeong, Augmented quantum yield of a 2D monolayer photodetector by surface plasmon coupling, Nano Lett. 18 (2018) 2316–2323. [21] B. Sun, Z. Wang, Z. Liu, X. Tan, X. Liu, T. Shi, J. Zhou, G. Liao, Tailoring of silver nanocubes with optimized localized surface plasmon in a gap mode for a flexible MoS2 photodetector, Adv. Funct. Mater. (2019), https://doi.org/10.1002/adfm. 201900541. [22] M. Long, E. Liu, P. Wang, A. Gao, H. Xia, W. Luo, B. Wang, J. Zeng, Y. Fu, K. Xu, W. Zhou, Y. Lv, S. Yao, M. Lu, Y. Chen, Z. Ni, Y. You, X. Zhang, S. Qin, Y. Shi, W. Hu, D. Xing, F. Miao, Broadband photovoltaic detectors based on an atomically thin heterostructure, Nano Lett. 16 (2016) 2254–2259. [23] L. Ye, H. Li, Z. Chen, J. Xu, Near-infrared photodetector based on MoS2/black phosphorus heterojunction, ACS Photon. 3 (2016) 692–699. [24] Y. Peng, R. Ding, Q. Ren, S. Xu, L. Sun, Y. Wang, F. Lu, High performance photodiode based on MoS2/pentacene heterojunction, Appl. Surf. Sci. 459 (2018) 179–184. [25] A. Henning, V.K. Sangwan, H. Bergeron, I. Balla, Z. Sun, M.C. Hersam, L.J. Lauhon, Charge separation at mixed-dimensional single and multilayer MoS2/silicon nanowire heterojunctions, ACS Appl. Mater. Interfaces 10 (2018) 16760–16767. [26] D. Jariwala, V.K. Sangwan, C.-C. Wu, P.L. Prabhumirashi, M.L. Geier, T.J. Marks, L.J. Lauhon, M.C. Hersam, Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode, Proc. Natl. Acad. Sci. U. S. A. 110 (2013) 18076–18080. [27] F. Wang, Z. Wang, K. Xu, F. Wang, Q. Wang, Y. Huang, L. Yin, J. He, Tunable GaTeMoS2 van der Waals p-n junctions with novel optoelectronic performance, Nano Lett. 15 (2015) 7558–7566. [28] D. Kufer, I. Nikitskiy, T. Lasanta, G. Navickaite, F.H.L. Koppens, G. Konstantatos,
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
395
Hybrid 2D-0D MoS2-PbS quantum dot photodetectors, Adv. Mater. 27 (2015) 176–180. X. Liu, Z. Liu, B. Sun, X. Tan, H. Ye, Y. Tu, T. Shi, Z. Tang, G. Liao, All low-temperature processed carbon-based planar heterojunction perovskite solar cells employing Mg-doped rutile TiO2 as electron transport layer, Electrochim. Acta 283 (2018) 1115–1124. J. Han, Y. Tu, Z. Liu, X. Liu, H. Ye, Z. Tang, T. Shi, G. Liao, Efficient and stable inverted planar perovskite solar cells using dopant-free CuPc as hole transport layer, Electrochim. Acta 273 (2018) 273–281. N. Arora, M.I. Dar, A. Hinderhofer, N. Pellet, F. Schreiber, S.M. Zakeeruddin, M. Graetzel, Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20%, Science 358 (2017) 768–771. Z. Liu, B. Sun, Y. Zhong, X. Liu, J. Han, T. Shi, Z. Tang, G. Liao, Novel integration of carbon counter electrode based perovskite solar cell with thermoelectric generator for efficient solar energy conversion, Nano Energy 38 (2017) 468–476. X. Liu, Z. Liu, H. Ye, Y. Tu, B. Sun, X. Tan, T. Shi, Z. Tang, G. Liao, Novel efficient C60-based inverted perovskite solar cells with negligible hysteresis, Electrochim. Acta 288 (2018) 115–125. Z. Liu, B. Sun, X. Liu, J. Han, H. Ye, Y. Tu, C. Chen, T. Shi, Z. Tang, G. Liao, 15% efficient carbon based planar-heterojunction perovskite solar cells using a TiO2/ SnO2 bilayer as the electron transport layer, J. Mater. Chem. A 6 (2018) 7409–7419. Z. Liu, B. Sun, T. Shi, Z. Tang, G. Liao, Enhanced photovoltaic performance and stability of carbon counter electrode based perovskite solar cells encapsulated by PDMS, J. Mater. Chem. A 4 (2016) 10700–10709. J.H. Cha, J.H. Han, W. Yin, C. Park, Y. Park, T.K. Ahn, J.H. Cho, D.-Y. Jung, Photoresponse of CsPbBr3 and Cs4PbBr6 perovskite single crystals, J. Phys. Chem. Lett. 8 (2017) 565–570. X. Li, F. Cao, D. Yu, J. Chen, Z. Sun, Y. Shen, Y. Zhu, L. Wang, Y. Wei, Y. Wu, H. Zeng, All inorganic halide perovskites nanosystem: synthesis, structural features, optical properties and optoelectronic applications, Small 13 (2017) 1603996. J. Chen, Y. Fu, L. Samad, L. Dang, Y. Zhao, S. Shen, L. Guo, S. Jin, Vapor-phase epitaxial growth of aligned nanowire networks of cesium lead halide perovskites (CsPbX3, X = Cl, Br, I), Nano Lett. 17 (2017) 460–466. L. Li, S. Tong, Y. Zhao, C. Wang, S. Wang, L. Lyu, Y. Huang, H. Huang, J. Yang, D. Niu, X. Liu, Y. Gao, Interfacial electronic structures of photodetectors based on C8BTBT/perovskite, ACS Appl. Mater. Interfaces 10 (2018) 20959–20967. H.L. Zhu, J. Cheng, D. Zhang, C. Liang, C.J. Reckmeier, H. Huang, A.L. Rogach, W.C.H. Choy, Room-temperature solution-processed NiOx:PbI2 nanocomposite structures for realizing high-performance perovskite photodetectors, ACS Nano 10 (2016) 6808–6815. B.R. Sutherland, A.K. Johnston, A.H. Ip, J. Xu, V. Adinolfi, P. Kanjanaboos, E.H. Sargent, Sensitive, fast, and stable perovskite photodetectors exploiting interface engineering, ACS Photon. 2 (2015) 1117–1123. M. He, Y. Chen, H. Liu, J. Wang, X. Fang, Z. Liang, Chemical decoration of CH3NH3PbI3 perovskites with graphene oxides for photodetector applications, Chem. Commun. 51 (2015) 9659–9661. Y. Lee, J. Kwon, E. Hwang, C.-H. Ra, W.J. Yoo, J.-H. Ahn, J.H. Park, J.H. Cho, Highperformance perovskite-graphene hybrid photodetector, Adv. Mater. 27 (2015) 41–46. P.V. Chandrasekar, S. Yang, J. Hu, M. Sulaman, M.I. Saleem, Y. Tang, Y. Jiang, B. Zou, A one-step method to synthesize CH3NH3PbI3:MoS2 nanohybrids for highperformance solution-processed photodetectors in the visible region, Nanotechnol 30 (2019) 085707. C. Ma, Y. Shi, W. Hu, M.H. Chiu, Z. Liu, A. Bera, F. Li, H. Wang, L.J. Li, T. Wu, Heterostructured WS2/CH3NH3PbI3 photoconductors with suppressed dark current and enhanced photodetectivity, Adv. Mater. 28 (2016) 3683–3689. X. Song, X. Liu, D. Yu, C. Huo, J. Ji, X. Li, S. Zhang, Y. Zou, G. Zhu, Y. Wang, M. Wu, A. Xie, H. Zeng, Boosting two-dimensional MoS2/CsPbBr3 photodetectors via enhanced light absorbance and interfacial carrier separation, ACS Appl. Mater. Interfaces 10 (2018) 2801–2809. Y. Wang, R. Fullon, M. Acerce, C.E. Petoukhoff, J. Yang, C. Chen, S. Du, S.K. Lai, S.P. Lau, D. Voiry, D. O’Carroll, G. Gupta, A.D. Mohite, S. Zhang, H. Zhou, M. Chhowalla, Solution-processed MoS2/organolead trihalide perovskite photodetectors, Adv. Mater. 29 (2017) 1603995. F. Liu, J. Wang, L. Wang, X. Cai, C. Jiang, G. Wang, Enhancement of photodetection based on perovskite/MoS2 hybrid thin film transistor, J. Semicond. 38 (2017) 034002. J. Lee, S. Pak, P. Giraud, Y.-W. Lee, Y. Cho, J. Hong, A.R. Jang, H.-S. Chung, W.K. Hong, H.Y. Jeong, H.S. Shin, L.G. Occhipinti, S.M. Morris, S. Cha, J.I. Sohn, J.M. Kim, Thermodynamically stable synthesis of large-scale and highly crystalline transition metal dichalcogenide monolayers and their unipolar n-n heterojunction devices, Adv. Mater. 29 (2017) 1702206. S. Najmaei, Z. Liu, W. Zhou, X. Zou, G. Shi, S. Lei, B.I. Yakobson, J.C. Idrobo, P.M. Ajayan, J. Lou, Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers, Nat. Mater. 12 (2013) 754–759. S. Wu, C. Huang, G. Aivazian, J.S. Ross, D.H. Cobden, X. Xu, Vapor-solid growth of high optical quality MoS2 monolayers with near-unity valley polarization, ACS Nano 7 (2013) 2768–2772. J.Y. Wu, Y.T. Chun, S. Li, T. Zhang, J. Wang, P.K. Shrestha, D. Chu, Broadband MoS2 field-effect phototransistors: ultrasensitive visible-light photoresponse and negative infrared photoresponse, Adv. Mater. 30 (2018) 1705880.
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Full length article
Sensitive, fast, and stable photodetector based on perovskite/MoS2 hybrid film
T
Bo Suna,c, Shuang Xib, Zhiyong Liua, Xinyue Liua, Ziyi Wanga, Xianhua Tana, Tielin Shia, ⁎ Jianxin Zhouc, Guanglan Liaoa, a
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China School of Mechanical and Electronic Engineering, Nanjing Forestry University, Nanjing 210037, China c State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Photodetector Perovskite MoS2 film Flexible devices Hybrid film
Atomically thin MoS2 film has displayed great potential for future optoelectronics due to its outstanding photonic and electronic properties. However, many important applications, especially for photodetection, are still severely limited by its low light absorption. In this paper, we demonstrate a high-performance photodetector based on perovskite/MoS2 hybrid film, which exhibits sensitive, fast, and stable response under low operation potential. The external photoresponsivity is about 342 A/W at bias potential of 2 V without gate voltage under incident power of 2.2 pW (520 nm), which is superior than most of the photodetectors based on transition metal dichalcogenides and perovskite. The devices show high stability during transient on/off test without any encapsulation, in which the response and recovery time has been recorded as 27 ms and 21 ms, respectively. Besides, the devices can be fabricated on various substrates, including SiO2/Si, transparent glass and flexible PET, etc. The flexible perovskite/MoS2 photodetectors with ultrahigh stability during 20,000 times bending was reported for the first time. We expect the proposed hybrid photodetector would be a competitive candidate in future flexible electronics. Our research also paves the way to integrate various atomically thin films with highly optical absorption materials.
1. Introduction Photodetectors (PDs) play a critical role in various optoelectronic applications, including signal detection, optical communication, and optical imaging, etc. [1–3] High-performance PDs possess of high sensitivity, fast response speed and good endurance are badly needed in practical application [4–7], which further arouse a series challenges to the properties of photoactive materials [8], including high absorptivity, large carrier mobility, suitable band structure, and high stability, etc. Early efforts are mainly dedicated to pursue high-performance PDs based on Si, GaP, and GaAs etc. which always demands vigorous fabrication process. Recent years, PDs composed of nanomaterials and quantum dots, with simple fabrication process and low cost have attracted much attention [9–11]. Although some competitive merits of these PDs have been achieved, the majority of them still limited by small responsivity [12], large dark current [13], and slow response speed [14]. Atomically thin MoS2 film aroused much attention in the past few years regarding its outstanding electrical and optical properties
⁎
[15,16]. Various MoS2-based PDs have been reported with excellent performance [17,18]. However, despite of its superior properties, it is still a huge difficult for MoS2 film to fully absorb the incident light due to its atomically thin feature, which severely hinders the wide application of the MoS2-based optoelectronic devices [19]. Many researches have been devoted to exploit the strategies which can improve the properties of the MoS2-based PDs, including applying surface plasmonic [20,21], exploring van der Waals heterostructures [22–24], and introducing photoactive materials with high absorptivity, such as silicon [25], carbon nanotube [26], GaTe [27], PbS quantum dots [28], etc. Meanwhile, organometal trihalide perovskite CH3NH3PbX3 (X is Cl, Br, or I) is booming as a new generation of optoelectronic material and attracts much attention due to its successful application in photovoltaic devices [29–31]. Recently, we also demonstrated a series of carbon counter electrode based high performance perovskite solar cell [32–35]. The rapid development of photovoltaic devices has stimulated the utilization of perovskite thin film in PDs [36–39]. Although perovskite PDs with architecture similar to solar cell has been demonstrated with fast response, the responsivity is relatively low [40,41].
Corresponding author. E-mail address: [email protected] (G. Liao).
https://doi.org/10.1016/j.apsusc.2019.07.036 Received 15 November 2018; Received in revised form 19 June 2019; Accepted 5 July 2019 Available online 06 July 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
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The photoconductive detector composed of hybrid film, such as perovskite/reduced graphene oxide (rGO), perovskite/graphene, demonstrated a good responsivity [42,43]. Unfortunately, the high conductivity of these materials results in a high dark current and low specific detectivity. Recently, the photodetectors constructed by MoS2/CH3NH3PbI3 and WS2/CH3NH3PbI3 hybrid film have been reported with a good performance [44–46]. However, there still have many issues to be resolved urgently. For example, the small size of MoS2 flakes makes them unsuitable for large-area applications [47,48]. The stability of the devices is rarely investigated due to the poor stability of organometal trihalide perovskite film in ambient atmosphere [35,47]. Besides, to the best knowledge of us, there has no relevant reports focused on the flexible MoS2/perovskite photodetectors. In this paper, we proposed a high performance photodetector composed of large-area atomically thin MoS2 film and triple cations lead mixed-halide perovskite layer, which exhibits sensitive, fast, and stable response under low operation potential. Besides, the flexible MoS2/perovskite photodetectors fabricated on the PET substrate with high stability under repeated bending test was demonstrated for the first time. This work paves a new route to exploit the flexible photodetector based on perovskite and various transition metal dichalcogenides (TMDCs) layer.
in a N2 filled glove box: 3 μL of DMF was dropped in an alumina crucible placed aside the samples, then all of them were covered by a Petri dish annealing at 100 °C for 1 h. 2.3. Characterization and measurement Morphology of the atomically thin MoS2 film and perovskite layer was directly observed by optical microscopy (Keyence VHX-1000E) and field emission scanning electron microscopy (FE-SEM, Zeiss Gemini 300), respectively. The thickness of the film was obtained by atomic force microscopy (AFM, Shimadzu SPM9700). Field emission transmission electron microscopy (FE-TEM, FEI Talos F200X) was used to monitor the lattice structure of the MoS2 film. The X-ray diffraction (XRD) analysis of the perovskite layer was conducted by X-ray diffractometer (PANalytical PW3040/60). XPS spectra measurement was performed using X-ray photoelectron spectroscope (VG Multilab 2000 X) to further explore the surface state of the film. Raman shift and steady-state photoluminescence (PL) spectra of the MoS2 film were measured by Raman spectrometer (LabRAM HR800) under the excitation of laser (532 nm). And the time resolved photoluminescence (TRPL) decay curves were collected by PicoQuant FluoTime300. Transmittance spectra of the film were collected by UV–Visible spectrophotometer (Shimadzu UV 2600). The performance of the photodetector was measured by two channel digital source-meter (Keithley 2636B). A fiber laser (Thorlabs LP520-SF15) modulated by function/ arbitrary waveform generator (Keysight 33210A) was used as light source.
2. Experimental section 2.1. Atomically thin MoS2 film growth The MoS2 films were prepared on Si/SiO2 substrate using CVD method in tube furnace. In details, a pre-dissolved MoO3 solution (20 mg/mL in ammonia) was spin-coated on Si/SiO2 substrate to obtain a MoO3 film with about 20 nm thickness. The prepared source substrate was placed in a quartz boat, followed by the loading of growth substrate above the source substrate with the SiO2 side facing down, which then was loaded in the middle of the tube. The distance of the two substrates was maintained at about 2 mm. Another quartz boat containing 0.4 g of sulfur powder was placed outside the main furnace. After that, the oxygen and water vapor in the tube was removed by Ar gas at 1000 sccm and the growth process was conducted at atmospheric pressure under 40 sccm flow of Ar gas. The temperature of the MoO3 substrate in the main furnace was raised gradually and the sulfur powder was heated using heating tape separately. When the temperature of main furnace approach to about 730 °C, the sulfur gas was introduced in reaction region due to the melt and evaporation of sulfur powders. The growth process was continued for 5 min at 820 °C. The furnace then was cooled down naturally and the gas flow was tuned to 200 sccm. The MoS2 film grown on SiO2/Si was transferred on a target substrate via the PMMA-assisted transferring method. The electrode (Ti 5 nm/Au 50 nm) was prepared on the MoS2 film via e-beam and thermal evaporation.
3. Results and discussion Fig. 1a schematically illustrates the structure of the perovskite/ MoS2 hybrid photodetector. The continuous atomically thin MoS2 film was prepared by CVD method. After deposition of the Ti/Au electrode, a triple cations (Cs/MA/FA) mixed perovskite layer was spin-coated. The optical image of MoS2 film was depicted in Fig. 1b. During the growth, some quasi-triangular dots were nucleated randomly and then evolved to triangular grains (Fig. S1). The grains connected with each other as the growth continued and eventually formed the continuous MoS2 film. However, the precursor and reaction time is always controlled to reduce the thickness of the film, resulting in the uncovered area as marked by dashed circle in Fig. 1b. The continuous film then was transferred on target substrate using a PMMA assisted transferring method and the Ti/Au electrode was deposited as shown in the inset of Fig. 1b. The MoS2 film was also transferred on a copper grid for TEM observation (Fig. S2). High resolution TEM image (Fig. 1c) reveals that the film has a high quality single crystal structure with the interplanar spacings of 0.274 and 0.267 nm corresponding to the d-spacings of (100) and (101) planes. To investigate the thickness of the MoS2 film, AFM measurement was conducted at the edge of the film as shown in Fig. 1d. The value is revealed as about 0.8 nm which is agree well with the previous reports on monolayer MoS2 film [49–51]. After spin-coating the perovskite film, the morphology of the devices was observed as shown in Fig. 1e and f. The top view SEM image reveals that the surface layer of the film resembles the morphology of the polycrystalline films without pinholes, in which the grain size is about 200–500 nm. The electrode pattern also can be distinguished from the inset image (low magnification). The sectional view image (Fig. 1f) shows that the thickness of the highly crystalline perovskite layer is about 500 nm. Noteworthy is that the film demonstrates a columnar crystal structure in which the grains can penetrate the whole perovskite layer, substantially reducing carrier recombination at the grain boundaries. Ti/Au electrode is obvious in the sectional view image. However, the MoS2 film is hard to be observed from the image due to its ultrathin nature. XPS spectrum was obtained to further elucidate the surface states of the monolayer MoS2 film as shown in Fig. 2a, in which the
2.2. Perovskite layer deposition The perovskite layer was coated on the MoS2 film by spin-coating of a triple cations lead mixed-halide perovskite solution. The perovskite solution was synthesized using a precursor consisted of 0.2 M methylammonium bromide (MABr,), 1 M formamidinium iodide (FAI), 1.1 M PbI2 and 0.2 M PbBr2 in a mixture (1: 4 volume ratio) of anhydrous Dimethylsulfoxide (DMSO) and N, N-Dimethylformamide (DMF). A predissolved 1.5 M cesium iodide (CsI) solution in DMSO was dropped in the above precursor with the volume ratio of 5:95. The solution then was heated at 60 °C under vigorous stirring for half an hour. After that, 5 μL of triple cations perovskite solution was dropped on the atomically thin MoS2 layer and spin coated using a two-step process (1000 rpm for 10 s and 5000 rpm for 20 s), with dropping of 30 μL of chlorobenzene at 5 s before the end. To improve the quality of the as-prepared perovskite film, a solvent assisted annealing process was performed on a hot plate 390
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Fig. 1. (a) Structural schematic of the photodetector based on perovskite/MoS2 hybrid film. (b) Optical image of MoS2 film, inset: the optical image after deposition of electrode. (c) High resolution TEM image of MoS2 film. (d) AFM image collected from edge of the film. (e) The top view SEM image of the perovskite layer, inset: low resolution image of the device. (f) The sectional view SEM image of the perovskite layer.
characteristic peaks have been marked. The high resolution XPS spectra (Fig. S3) reveals that the peaks located at 230.2 eV and 233.4 eV can be attributed to the 3d5/2 and 3d3/2 states of Mo. The two peaks at about 163.0 eV and 164.2 eV correspond to the 2p3/2 and 2p1/2 states of S. The Raman spectrum of the MoS2 film was displayed in Fig. 3b. As expected, the film demonstrates two sharp peaks centered at about 384.8 cm−1 and 403.8 cm−1, in accordance with the E12g and A1g
modes, respectively. Frequency difference between the peaks is about 19.0 cm−1, which is a clear evidence of a monolayer of MoS2 film [49,50]. Fig. 2c depicted the XRD pattern of the triple cations mixed perovskite film. The sharp peaks located at about 14.06°, 19.98°, 24.57°,28.37°, 31.82°, 34.96°, 40.59° and 43.16° can be attributed to the (110), (112), (202), (220), (310), (312), (224) and (314) lattice planes of a typical tetragonal perovskite structure [34]. Besides, we also
Fig. 2. (a) XPS spectrum of the MoS2 film. (b) Raman spectrum of the MoS2 film (c) XRD spectrum of the perovskite film. (d) XPS spectrum of the perovskite film, (e) Photoluminescence spectra of the perovskite film and perovskite/MoS2 hybrid film. (f) TRPL decay curves of perovskite film and perovskite/MoS2 hybrid film. 391
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Fig. 3. (a) I-V characteristics of the photodetectors. (b) The I-V curves in logarithmic coordinate diagram. (c) Performance of the devices under the illumination of 50 μW/mm2 with different channel length; inset: photoresponsivity varying with the bias potential and channel length. (d) The photocurrent and photoresponsivity of the devices varying with incident power.
at the same condition, a severe PL quenching for the hybrid film can be achieved compared to the pristine perovskite layer, directly proving that a considerable charge carries are extracted via the perovskite/ MoS2 interface. The electric properties of the PDs were then investigated. Fig. 3a displays the I-V characteristics of the photodetector composed of MoS2 film, perovskite film, and perovskite/MoS2 hybrid film. The photocurrent of MoS2 film is about 32 nA at 2 V bias potential with the incident power of 50 nW, while the value increases to about 84 nA after the coating of perovskite layer. The dark current is negligible in Fig. 3a. Thus, the data was transferred in logarithmic coordinate diagram to clearly demonstrate the dark current as shown in Fig. 3b. Obviously, the dark current is increased with bias potential for all of the samples. The value of perovskite/MoS2 hybrid film is about 2.0 pA and 3.8 pA for the bias potential of 1 V and 2 V, respectively. Fig. 3c depicts the performance of the devices with different channel length (from 10 μm to 100 μm) under the illumination of 50 μW/mm2. The devices demonstrate a similar photocurrent. To further evaluate the devices with different channel length, the responsivity was calculated using the following equation: R = (Ilight − Idark)/P, where Ilight and Idark is photocurrent and dark current of the devices, respectively. P is the incident optical power on the photodetector active area. The inset in Fig. 3c displays the responsivity of the photodetector varying with the bias potential and channel length. Obviously, the responsivity decreases as the channel length increases. The smallest channel (10 μm) demonstrates the highest value of 1.7 A/W under the illumination of 50 nW. Considering the varied incident power for the above devices, we further study the relationship between photocurrent, responsivity and incident power as shown in Fig. 3d. Obviously, the photocurrent of the devices is improved as the incident power increases. However, the
observed two diffraction peaks at 12.64° and 47.75° marked by rhombuses, which can be assigned to PbI2 caused by the excess lead during the synthesis of perovskite solution. The XPS spectrum of the perovskite film was shown in Fig. 2d, where the characteristic peaks of C 1s, N 1s, Cs 3d, Pb 4f, I 3d, Br 3d have been marked clearly. The high resolution XPS spectra (Fig. S4) further demonstrates that the peaks at about 285 and 400.5 eV can be attributed to the C 1s state and N 1s state. The peaks at about 724.8/ 738.8 eV, 619.2/630.7 eV, and 68.5/69.3 eV agree well with the 3d5/2 and 3d3/2 states of Cs, I, and Br, respectively. The peaks at 138.4 and 143.3 eV can be assigned to the 4f7/2 and 4f5/2 states. The quantification analysis of XPS data reveals that the atomic ratio of the surface of perovskite film is 0.73% Cs, 22.54% C, 17.13% N, 13.8% Pb, 40.87% I, 4.94% Br, which is in accordance with the predesigned chemical composition Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3. To investigate the light distribution in the hybrid film, we further measured the UV transmittance of the perovskite film (Fig. S5). The UV spectrum reveals that the band edge of the film is located at about 760 nm. The transmittance at 520 nm is about 5.4%, which means most of the incident light was absorbed by perovskite layer before irradiated on MoS2 film. Besides, we obtained the photoluminescence (PL) spectra of the perovskite film and perovskite/MoS2 hybrid film as depicted in Fig. 2e. With the underneath MoS2 layer, the band-to-band transition peak at 1.63 eV displays a significant decrease, indicating that a large number of photo-excited electrons are transferred from the photoactive perovskite layer to MoS2 film. Moreover, the time resolved photoluminescence (TRPL) decay curves also were collected to investigate the charge carrier dynamics at the interfaces as shown in Fig. 2f. The calculated average PL decay time for pristine perovskite film and perovskite/MoS2 hybrid film are 1927 and 284 ns, respectively. Obviously, 392
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Fig. 4. (a) Working mechanism and energy-band diagram of the photodetector based on perovskite/MoS2 hybrid film under illumination. (b) The transient photoresponse of the device under repeated on/off illumination. (c) Response and recovery time of the devices. (d) Long-term stability test of the devices without any encapsulation.
ratio of 2 × 104. To calculate the response and recovery time of the devices, a single on/off cycle is collected as shown in Fig. 4c. Given the 10% and 90% peak value of the photocurrent, the response and recovery time is calculated as 27 ms and 21 ms, which is superior to the latest reported PDs based on MoS2 film [20,21,52]. To further elucidate the stability of the devices, time-dependent photocurrent density at repeated on/off cycles of illumination was collected as shown in Fig. 4d. During the test process (1 h), no obvious degrade is observed. In general, the stability of perovskite is poor under light soaking. However, the triple cations (Cs/MA/FA) mixed perovskite film we proposed here demonstrates a good stability in ambient atmosphere (≈50% RH and 25 °C) and no observed charge accumulation due to the imbalanced charge transport, which can be attributed to the special composition of the film and the perovskite/MoS2 junction formed in the devices. With further PDMS encapsulation, we believe the stability of the device is adequate for the actual application [35]. A noteworthy phenomenon is the devices demonstrate non-negligible response (≈0.3 nA) for light irradiation at zero bias potential as shown in the inset of Fig. 4d, which is rarely found in photoconductive photodetectors. The I-V characteristic under illumination (Fig. S6) reveals that the devices possess a property similar to photovoltaics, which may be a comprehensive effect of the junctions formed at MoS2/Perovskite interface and metal/semiconductor interface. These results further demonstrate the formation of perovskite/MoS2 junction substantially enhance the photoexcited charge carriers separation and transportation.
photoresponsivity is substantially enhanced as the incident power decreases due to the suppressed scattering between the photoexcited charge carriers. The photoresponsivity can be improved to 342 A/W, which is much higher than most of TMDCs film or perovskite-based photodetectors [17,20,39–41]. Another important benefit of the photodetectors is the specific detectivity D*, which is defined as (AΔf)1/2R/ in. Here, A is the effective area, Δf is the electrical bandwidth, in is the noise current which is mainly attributed to the dark current here [22]. The obtained specific detectivity value is about 1.14 × 1012 Jones. Fig. 4a displays the working mechanism and energy-band diagram of the photodetector based on perovskite/MoS2 hybrid film under illumination. As the device is irradiated by the laser, the photo-excited charge carriers are generated immediately in the hybrid film. As illustrated in the schematic, photo-excited charge carrier concentration in the perovskite layer is much higher than that in MoS2 film due to its high photo absorptivity. Then the electrons and holes were separated in the perovskite layer because of its ambipolar charge transport property and the electrons are expected to diffuse into the MoS2 film and collected at the electrode due to the electric field formed at the perovskiteMoS2 junction and Ti-MoS2 junction. The transient photoresponse of the perovskite/MoS2 photodetector was recorded by switching the laser on and off as shown in Fig. 4b. Obviously, the response speed was improved dramatically after the coating of perovskite layer. The measured photocurrent is increase from 2 pA in the dark to about 40 nA under illumination at 1 V bias potential, demonstrating an switching
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Fig. 5. (a) I-V curves of the PDs on transparent glass under front illumination and back illumination. (b) The I-V curves of the PDs on flexible substrate with different channel length. (c) Photocurrent of the flexible devices under transient on/off illumination. (d) Photocurrent ratio of the devices suffered from repeated bending compared with corresponding devices without bending.
including SiO2/Si, transparent glass and flexible PET, etc. The atomically thin MoS2 film synthesized via CVD method shows continuous, homogenous and stable properties. The devices exhibit outstanding performance under low operation potential, with external photoresponsivity ~342 A/W at 2 V without gate voltage under incident power of 2.2 pW, which probably due to the high absorption and long electron/hole diffusion length of the perovskite. Accordingly, the specific detectivity reaches 1.14 × 1012 Jones. Moreover, flexible photodetectors using the perovskite/MoS2 hybrid film on PET substrate were fabricated, demonstrating a quick response and good stability under transient on/off illumination, and also 91% of the photoresponsivity remaining after 20,000 bending cycles. This high-performance photodetector would find diverse applications in the fields of optoelectronic system and flexible electronic system.
Besides, it also indicates that the devices possess a potential self-powered property for future application. To demonstrate the portability of the perovskite/MoS2 hybrid PDs, we also fabricate the devices on transparent glass. Fig. 5a displays the photocurrent of the devices under front illumination and back illumination, which is almost identical to that of the devices on SiO2/Si substrate. The negligible decline of photocurrent under back illumination can be attributed to the slight decrease of incident power caused by the photoabsorption of the glass. Considering the booming demand of flexible optoelectronics, we further fabricate flexible PDs using the perovskite/MoS2 hybrid film on PET substrate as illustrated in Fig. 5b. The performance of the flexible devices with different channel length is similar to the devices on rigid substrate. Besides, the devices demonstrate a quick response and good stability under transient on/off illumination as shown in Fig. 5c. We also investigate the mechanical endurance of the devices by bending repetitiously using the three-point bending setup as displayed in Fig. 5d. The curvature of the devices can be obtained according to the equation: ρ = [h2 + (L/2)2]/2 h, where L is the distance between the two supporting blocks, and h is the depth at the device midpoint. The curvature adopted here is 5 mm. After bending for 20,000 times, the photocurrent value of devices still maintain 91%, compared with the corresponding I-V curves without bending. Noteworthily, there is no obvious decline between 2000 times and 20,000 times, indicating the flexible PDs is able to bear repeated external mechanical force. These results further demonstrate the good portability and stability of the perovskite/MoS2 hybrid PDs.
Acknowledgements The authors acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51675210), the Natural Science Foundation of Jiangsu Province (Grant No. BK20160934), and the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT17R44), the China Postdoctoral Science Foundation (Grant No. 2016M602283). Appendix A. Supplementary data The morphology evolution of MoS2 film, additional TEM image of MoS2 film, high resolution XPS spectra of MoS2 and pervoskite layer, UV transmittance of the perovskite film and the IV characteristic of the PD under illumination. Supplementary data to this article can be found online at https://doi.org/10.1016/j.apsusc.2019.07.036.
4. Conclusions We have demonstrated a high-performance PD based on perovskite/ MoS2 hybrid film, which can be fabricated on various substrates, 394
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References [29]
[1] V. Adinolfi, E.H. Sargent, Photovoltage field-effect transistors, Nature 542 (2017) 324. [2] H. Chen, H. Liu, Z. Zhang, K. Hu, X. Fang, Nanostructured photodetectors: from ultraviolet to terahertz, Adv. Mater. 28 (2016) 403–433. [3] T. Yokota, P. Zalar, M. Kaltenbrunner, H. Jinno, N. Matsuhisa, H. Kitanosako, Y. Tachibana, W. Yukita, M. Koizumi, T. Someya, Ultraflexible organic photonic skin, Sci. Adv. 2 (2016) e1501856. [4] B. Rahmati, I. Hajzadeh, R. Karimzadeh, S.M. Mohseni, Facile, scalable and transfer free vertical-MoS2 nanostructures grown on Au/SiO2 patterned electrode for photodetector application, Appl. Surf. Sci. 455 (2018) 876–882. [5] F. Chen, C. Xu, Q. Xu, Y. Zhu, F. Qin, W. Zhang, Z. Zhu, W. Liu, Z. Shi, Highperformance, self-powered photodetectors based on perovskite and graphene, ACS Appl. Mater. Interfaces 10 (2018) 25763–25769. [6] L. Su, X.N. Yu, K. Li, X.Y. Yao, M. Pecht, Simulation and experimental verification of edge blurring phenomenon in microdefect inspection based on high-frequency ultrasound, IEEE Access 7 (2019) 11515–11525. [7] L. Su, L. Wang, K. Li, J. Wu, G. Liao, T. Shi, T. Lin, Automated X-ray recognition of solder bump defects based on ensemble-ELM, Sci. China Technol. Sci. (2019), https://doi.org/10.1007/s11431-018-9324-3. [8] Muhammad ZahirIqbal, Sana Khan, Salma Siddique, Ultraviolet-light-driven photoresponse of chemical vapor deposition grown molybdenum disulfide/graphene heterostructured FET, Appl. Surf. Sci. 459 (2018) 853–859. [9] O. Ostroverkhova, Organic optoelectronic materials: mechanisms and applications, Chem. Rev. 116 (2016) 13279–13412. [10] Y.K. Kim, S.H. Hwang, S. Kim, H. Park, S.K. Lim, ZnO nanostructure electrodeposited on flexible conductive fabric: a flexible photo-sensor, Sensors Actuators B Chem. 240 (2017) 1106–1113. [11] H. Makhlouf, C. Karam, A. Lamouchi, S. Tingry, P. Miele, R. Habchi, R. Chtourou, M. Bechelany, Analysis of ultraviolet photo-response of ZnO nanostructures prepared by electrodeposition and atomic layer deposition, Appl. Surf. Sci. 444 (2018) 253–259. [12] W. Wei, X.Y. Bao, C. Soci, Y. Ding, Z.L. Wang, D. Wang, Direct heteroepitaxy of vertical inas nanowires on si substrates for broad band photovoltaics and photodetection, Nano Lett. 9 (2009) 2926–2934. [13] D.H. Shin, S. Kim, J.M. Kim, C.W. Jang, J.H. Kim, K.W. Lee, J. Kim, S.D. Oh, D.H. Lee, S.S. Kang, C.O. Kim, S.-H. Choi, K.J. Kim, Graphene/Si-quantum-dot heterojunction diodes showing high photosensitivity compatible with quantum confinement effect, Adv. Mater. 27 (2015) 2614–2620. [14] J.P. Clifford, G. Konstantatos, K.W. Johnston, S. Hoogland, L. Levina, E.H. Sargent, Fast, sensitive and spectrally tuneable colloidal quantum-dot photodetectors, Nat. Nanotechnol. 4 (2009) 40–44. [15] C. Xie, C. Mak, X. Tao, F. Yan, Photodetectors based on two-dimensional layered materials beyond graphene, Adv. Funct. Mater. 27 (2017) 1603886. [16] M.J. Park, K. Park, H. Ko, Near-infrared photodetector achieved by chemicallyexfoliated multilayered MoS2 flakes, Appl. Surf. Sci. 448 (2018) 64–70. [17] Y. Xue, Y. Zhang, Y. Liu, H. Liu, J. Song, J. Sophia, J. Liu, Z. Xu, Q. Xu, Z. Wang, J. Zheng, Y. Liu, S. Li, Q. Bao, Scalable production of a few-layer MoS2/WS2 vertical heterojunction array and its application for photodetectors, ACS Nano 10 (2016) 573–580. [18] B. Sun, T. Shi, Z. Liu, Y. Wu, J. Zhou, G. Liao, Large-area flexible photodetector based on atomically thin MoS2/graphene film, Mater. Des. 154 (2018) 1–7. [19] F. Xia, H. Wang, D. Xiao, M. Dubey, A. Ramasubramaniam, Two-dimensional material nanophotonics, Nat. Photonics 8 (2014) 899–907. [20] S. Bang, D. Ngoc Thanh, J. Lee, Y.H. Cho, H.M. Oh, H. Kim, S.J. Yun, C. Park, M.K. Kwon, J.-Y. Kim, J. Kim, M.S. Jeong, Augmented quantum yield of a 2D monolayer photodetector by surface plasmon coupling, Nano Lett. 18 (2018) 2316–2323. [21] B. Sun, Z. Wang, Z. Liu, X. Tan, X. Liu, T. Shi, J. Zhou, G. Liao, Tailoring of silver nanocubes with optimized localized surface plasmon in a gap mode for a flexible MoS2 photodetector, Adv. Funct. Mater. (2019), https://doi.org/10.1002/adfm. 201900541. [22] M. Long, E. Liu, P. Wang, A. Gao, H. Xia, W. Luo, B. Wang, J. Zeng, Y. Fu, K. Xu, W. Zhou, Y. Lv, S. Yao, M. Lu, Y. Chen, Z. Ni, Y. You, X. Zhang, S. Qin, Y. Shi, W. Hu, D. Xing, F. Miao, Broadband photovoltaic detectors based on an atomically thin heterostructure, Nano Lett. 16 (2016) 2254–2259. [23] L. Ye, H. Li, Z. Chen, J. Xu, Near-infrared photodetector based on MoS2/black phosphorus heterojunction, ACS Photon. 3 (2016) 692–699. [24] Y. Peng, R. Ding, Q. Ren, S. Xu, L. Sun, Y. Wang, F. Lu, High performance photodiode based on MoS2/pentacene heterojunction, Appl. Surf. Sci. 459 (2018) 179–184. [25] A. Henning, V.K. Sangwan, H. Bergeron, I. Balla, Z. Sun, M.C. Hersam, L.J. Lauhon, Charge separation at mixed-dimensional single and multilayer MoS2/silicon nanowire heterojunctions, ACS Appl. Mater. Interfaces 10 (2018) 16760–16767. [26] D. Jariwala, V.K. Sangwan, C.-C. Wu, P.L. Prabhumirashi, M.L. Geier, T.J. Marks, L.J. Lauhon, M.C. Hersam, Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode, Proc. Natl. Acad. Sci. U. S. A. 110 (2013) 18076–18080. [27] F. Wang, Z. Wang, K. Xu, F. Wang, Q. Wang, Y. Huang, L. Yin, J. He, Tunable GaTeMoS2 van der Waals p-n junctions with novel optoelectronic performance, Nano Lett. 15 (2015) 7558–7566. [28] D. Kufer, I. Nikitskiy, T. Lasanta, G. Navickaite, F.H.L. Koppens, G. Konstantatos,
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
395
Hybrid 2D-0D MoS2-PbS quantum dot photodetectors, Adv. Mater. 27 (2015) 176–180. X. Liu, Z. Liu, B. Sun, X. Tan, H. Ye, Y. Tu, T. Shi, Z. Tang, G. Liao, All low-temperature processed carbon-based planar heterojunction perovskite solar cells employing Mg-doped rutile TiO2 as electron transport layer, Electrochim. Acta 283 (2018) 1115–1124. J. Han, Y. Tu, Z. Liu, X. Liu, H. Ye, Z. Tang, T. Shi, G. Liao, Efficient and stable inverted planar perovskite solar cells using dopant-free CuPc as hole transport layer, Electrochim. Acta 273 (2018) 273–281. N. Arora, M.I. Dar, A. Hinderhofer, N. Pellet, F. Schreiber, S.M. Zakeeruddin, M. Graetzel, Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20%, Science 358 (2017) 768–771. Z. Liu, B. Sun, Y. Zhong, X. Liu, J. Han, T. Shi, Z. Tang, G. Liao, Novel integration of carbon counter electrode based perovskite solar cell with thermoelectric generator for efficient solar energy conversion, Nano Energy 38 (2017) 468–476. X. Liu, Z. Liu, H. Ye, Y. Tu, B. Sun, X. Tan, T. Shi, Z. Tang, G. Liao, Novel efficient C60-based inverted perovskite solar cells with negligible hysteresis, Electrochim. Acta 288 (2018) 115–125. Z. Liu, B. Sun, X. Liu, J. Han, H. Ye, Y. Tu, C. Chen, T. Shi, Z. Tang, G. Liao, 15% efficient carbon based planar-heterojunction perovskite solar cells using a TiO2/ SnO2 bilayer as the electron transport layer, J. Mater. Chem. A 6 (2018) 7409–7419. Z. Liu, B. Sun, T. Shi, Z. Tang, G. Liao, Enhanced photovoltaic performance and stability of carbon counter electrode based perovskite solar cells encapsulated by PDMS, J. Mater. Chem. A 4 (2016) 10700–10709. J.H. Cha, J.H. Han, W. Yin, C. Park, Y. Park, T.K. Ahn, J.H. Cho, D.-Y. Jung, Photoresponse of CsPbBr3 and Cs4PbBr6 perovskite single crystals, J. Phys. Chem. Lett. 8 (2017) 565–570. X. Li, F. Cao, D. Yu, J. Chen, Z. Sun, Y. Shen, Y. Zhu, L. Wang, Y. Wei, Y. Wu, H. Zeng, All inorganic halide perovskites nanosystem: synthesis, structural features, optical properties and optoelectronic applications, Small 13 (2017) 1603996. J. Chen, Y. Fu, L. Samad, L. Dang, Y. Zhao, S. Shen, L. Guo, S. Jin, Vapor-phase epitaxial growth of aligned nanowire networks of cesium lead halide perovskites (CsPbX3, X = Cl, Br, I), Nano Lett. 17 (2017) 460–466. L. Li, S. Tong, Y. Zhao, C. Wang, S. Wang, L. Lyu, Y. Huang, H. Huang, J. Yang, D. Niu, X. Liu, Y. Gao, Interfacial electronic structures of photodetectors based on C8BTBT/perovskite, ACS Appl. Mater. Interfaces 10 (2018) 20959–20967. H.L. Zhu, J. Cheng, D. Zhang, C. Liang, C.J. Reckmeier, H. Huang, A.L. Rogach, W.C.H. Choy, Room-temperature solution-processed NiOx:PbI2 nanocomposite structures for realizing high-performance perovskite photodetectors, ACS Nano 10 (2016) 6808–6815. B.R. Sutherland, A.K. Johnston, A.H. Ip, J. Xu, V. Adinolfi, P. Kanjanaboos, E.H. Sargent, Sensitive, fast, and stable perovskite photodetectors exploiting interface engineering, ACS Photon. 2 (2015) 1117–1123. M. He, Y. Chen, H. Liu, J. Wang, X. Fang, Z. Liang, Chemical decoration of CH3NH3PbI3 perovskites with graphene oxides for photodetector applications, Chem. Commun. 51 (2015) 9659–9661. Y. Lee, J. Kwon, E. Hwang, C.-H. Ra, W.J. Yoo, J.-H. Ahn, J.H. Park, J.H. Cho, Highperformance perovskite-graphene hybrid photodetector, Adv. Mater. 27 (2015) 41–46. P.V. Chandrasekar, S. Yang, J. Hu, M. Sulaman, M.I. Saleem, Y. Tang, Y. Jiang, B. Zou, A one-step method to synthesize CH3NH3PbI3:MoS2 nanohybrids for highperformance solution-processed photodetectors in the visible region, Nanotechnol 30 (2019) 085707. C. Ma, Y. Shi, W. Hu, M.H. Chiu, Z. Liu, A. Bera, F. Li, H. Wang, L.J. Li, T. Wu, Heterostructured WS2/CH3NH3PbI3 photoconductors with suppressed dark current and enhanced photodetectivity, Adv. Mater. 28 (2016) 3683–3689. X. Song, X. Liu, D. Yu, C. Huo, J. Ji, X. Li, S. Zhang, Y. Zou, G. Zhu, Y. Wang, M. Wu, A. Xie, H. Zeng, Boosting two-dimensional MoS2/CsPbBr3 photodetectors via enhanced light absorbance and interfacial carrier separation, ACS Appl. Mater. Interfaces 10 (2018) 2801–2809. Y. Wang, R. Fullon, M. Acerce, C.E. Petoukhoff, J. Yang, C. Chen, S. Du, S.K. Lai, S.P. Lau, D. Voiry, D. O’Carroll, G. Gupta, A.D. Mohite, S. Zhang, H. Zhou, M. Chhowalla, Solution-processed MoS2/organolead trihalide perovskite photodetectors, Adv. Mater. 29 (2017) 1603995. F. Liu, J. Wang, L. Wang, X. Cai, C. Jiang, G. Wang, Enhancement of photodetection based on perovskite/MoS2 hybrid thin film transistor, J. Semicond. 38 (2017) 034002. J. Lee, S. Pak, P. Giraud, Y.-W. Lee, Y. Cho, J. Hong, A.R. Jang, H.-S. Chung, W.K. Hong, H.Y. Jeong, H.S. Shin, L.G. Occhipinti, S.M. Morris, S. Cha, J.I. Sohn, J.M. Kim, Thermodynamically stable synthesis of large-scale and highly crystalline transition metal dichalcogenide monolayers and their unipolar n-n heterojunction devices, Adv. Mater. 29 (2017) 1702206. S. Najmaei, Z. Liu, W. Zhou, X. Zou, G. Shi, S. Lei, B.I. Yakobson, J.C. Idrobo, P.M. Ajayan, J. Lou, Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers, Nat. Mater. 12 (2013) 754–759. S. Wu, C. Huang, G. Aivazian, J.S. Ross, D.H. Cobden, X. Xu, Vapor-solid growth of high optical quality MoS2 monolayers with near-unity valley polarization, ACS Nano 7 (2013) 2768–2772. J.Y. Wu, Y.T. Chun, S. Li, T. Zhang, J. Wang, P.K. Shrestha, D. Chu, Broadband MoS2 field-effect phototransistors: ultrasensitive visible-light photoresponse and negative infrared photoresponse, Adv. Mater. 30 (2018) 1705880.