CsPbBr3 Photodetectors via

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Boosting Two-dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation Xiufeng Song, Xuhai Liu, Dejian Yu, Chengxue Huo, Jianping Ji, Xiaoming Li, Shengli Zhang, Yousheng Zou, Gangyi Zhu, Yongjin Wang, Mingzai Wu, An Xie, and Haibo Zeng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14745 • Publication Date (Web): 27 Dec 2017 Downloaded from http://pubs.acs.org on December 27, 2017

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ACS Applied Materials & Interfaces

Boosting Two-dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation Xiufeng Song†#, Xuhai Liu†#, Dejian Yu†, Chengxue Huo†, Jianping Ji†, Xiaoming Li†, Shengli Zhang†*, Yousheng Zou†, Gangyi Zhu‡, Yongjin Wang‡, Mingzai Wu§, An Xie∥, Haibo Zeng†* †

Institute of Optoelectronics & Nanomaterials, MIIT Key Laboratory of Advanced

Display Materials and Devices, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.

E-mail: [email protected], [email protected] ‡

Grünberg Research Centre, Nanjing University of Posts and Telecommunications,

Nanjing 210003, China. §

School of Physics and Materials Science, Anhui University, Hefei 230601,

P.R.China. ∥

Key Laboratory of Functional Materials and Applications of Fujian Province,

College of Materials Science and Engineering, Xiamen University of Technology, Xiamen 361024, P.R.China.

KEYWORDS: CsPbBr3; MoS2; charge transfer; carrier separation; photodetector 1 ACS Paragon Plus Environment

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ABSTRACT Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices due to their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate the all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers, and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMDs based photodetector. Significantly, the interfacial charge transfer from the CsPbBr3 to MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5×1010 Jones due to the high efficient photoexcited carrier separation at the interface of MoS2 and CsPbBr3. The photoresponsivity of this hybrid device presents an improvement of three orders of magnitude compared with a MoS2 device without CsPbBr3. The response time of the device is also shortened from 65.2 ms to 0.72 ms after coupling with MoS2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high performance optoelectronic devices.

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Introduction Two-dimensional (2D) materials have received enormous attention due to its unique structures, excellent physical properties and wide application prospects.1-3 For example, graphene exhibits exceptionally high carrier mobility, unique optical characteristics, and superb mechanical flexibility, which make it a promising candidate material for next-generation flexible electronics and optoelectronics. In addition, single-layer transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2), are also rising because of the excellent quantum efficiency and semiconducting property with tunable bandgap in the range of 1-2 eV, which drives them to be important supplements and alternatives to graphene in novel optoelectronic devices.4-8

TMDs have been widely applied in photodetectors with excellent photodetecting properties, such as a high photoresponsivity of 2200 A/W,9 1010-1011 Jones10, and a fast response time of 40 µs.11

a photodetectivity of

However, such superior

performance are usually obtained at special conditions, such as being measured in vacuum12 or with picowatt intensity of the incident light,13 which is mainly resulted from the low light absorption limiting the generation of the carriers in the atomically thin layer,7-8 preventing the practical application of these TMDs based photodetectors. Various investigations have been carried out to improve the light harvesting capacity for enhancing the characteristics of the 2D materials based photodetectors.5,

14-17



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Introducing a strong light absorption layer to cooperate with 2D materials is expected to be an efficient approach to improve the photocurrent and the quantum efficiency of the detectors.7-8

Konstantatos et.al have achieved a hybrid PbS/Garphene

phototransistors with ultrahigh responsivity of ∼107 A/W.18

Since then, a series of

nanomaterials, such as PbS19-20, graphene quantum dots21, rhodamine 6G (R6G)22 and organolead perovskites,23-28 have been

manipulated on TMDs to modify the

photoreponse of the TMDs based photodetectors.

Moreover, all-inorganic cesium lead halides (CsPbX3, X = Cl, Br, I) represent an emerging class of materials owing to their high carrier mobility, long carrier diffusion length, excellent visible light absorption.29-30

Also, the high quantum efficiency

(over 90%), narrow line width and high stability make these all-inorganic perovskites suitable for the application in novel optoelectronics.31-35 Song et al. synthesized high-quality CsPbBr3 nanosheets and assembled flexible photodetectors, which exhibited a high sensitivity of 0.64 A/W and a light on/off ratio of >103.36

Lee et.al

have reported a hybrid graphene–CsPbBr3-xIx NCs photodetector with high photosensitivity

of

8.2×108

A/W.37

graphene-organolead perovskite,37-42

However,

similar

to

the

hybrid

these hybrid photodetectors suffer from the

large dark current, low light on/off ratio and long response time owing to the semimetal channel. Here, we report a superior performance hybrid CsPbBr3 perovskite/MoS2 photodetector with high photoresponsivity of 4.4 A/W and external quantum efficiency (EQE) of 302%. The light absorbance of the heterostructure is enhanced when the MoS2 monolayer is combined with CsPbBr3 nanosheets. The 4 ACS Paragon Plus Environment

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photo-induced electron-hole pairs in the perovskite are separated by electrons injecting to MoS2, which reduce the probability of charge recombination. The dark current is suppressed and the photoresponsivity is significantly improved. We systematically

investigate

the

photodetector

performance

(photoresponsivity,

detectivity and photoswitching), and the results demonstrate that the hybrid CsPbBr3 perovskite/MoS2 photodetector has great potential to be applied in high performance optoelectronic devices.

Results and discussion Figure 1a presents the schematic diagram of the hybrid MoS2/inorganic perovskite (CsPbBr3) device. A continuous MoS2 monolayer was grown on c-plane sapphire substrate with chemical vapor deposition (CVD) (Figure S1). After transferring the MoS2 films on the heavily p-doped Si wafer with 300 nm thick SiO2 substrate, Cr/Au electrodes with a thickness of 5 nm/75 nm was fabricated onto Si/SiO2 via standard photolithography and electron beam evaporation. The CsPbBr3 nanosheets (Figure S2) were then drop-casted, which was followed by annealing the device at 60 °C for one minute on a hotplate.

The channel region of the obtained hybrid MoS2/CsPbBr3

photodetector is shown in Figure S3.

The charge transfer process is illustrated in Figure 1b. When a laser irradiates on the CsPbBr3, the electron-hole pairs are generated and then transferred to the MoS2 film. We have employed density-functional theory (DFT) calculations to probe the electronic structure in the hybrid MoS2/CsPbBr3 heterostructure. As shown in Figure 5 ACS Paragon Plus Environment


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1c and Figure S4, the valence band (conduction band) of the MoS2 monolayer and CsPbBr3 nanosheets is -6.0 eV (-4.2 eV) and -5.7 eV (-3.3 eV), respectively, hence the hybrid junction is expected to be type-II with a band offset of 0.9 eV. This large band offset provides a strong force to separate the photogenerated electron-hole pairs in the CsPbBr3 layer. Therefore, the electrons transfer to the MoS2 layer and the holes are localized in the CsPbBr3 layer (Figure 1d). The more superior light absorption is an excellent advantage of this hybrid MoS2/CsPbBr3 configuration. UV-visible spectra are obtained to investigate the optical characteristics of the hybrid MoS2/CsPbBr3 perovskite structure. Figure 2 presents the UV-visible absorption spectra of the pure MoS2, CsPbBr3 and the hybrid MoS2/CsPbBr3 film. The pristine MoS2 film shows three absorption peaks. Two absorption peaks at 615 nm and 658 nm are resulted from the direct excitonic transitions at the Brillouin zone K point in MoS2. The peak at about 350-500 nm is related to optical transitions between the valence and conduction bands. For CsPbBr3 nanosheets, the absorption peak is at about 515 nm. In comparison, the absorption spectrum of the hybrid MoS2/CsPbBr3 perovskite is enhanced both at 350-500 nm and 615-658 nm, which can be regarded as the co-absorption of MoS2 and CsPbBr3 films. The enhanced optical absorption facilitates the application exploration of the hybrid MoS2/CsPbBr3 films. The photoluminescence (PL) spectra are also measured to evaluate the transfer and recombination of the charge carriers between MoS2 and CsPbBr3 perovskite. As


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shown in Figure 3a, both the CsPbBr3 and the hybrid MoS2/CsPbBr3 exhibit a PL peak at 525 nm, which corresponds to the band gap of CsPbBr3. However, at the same experimental condition, a dramatically severer PL quenching for the hybrid MoS2/CsPbBr3 perovskite can be obtained compared with the pristine CsPbBr3, which indicates much lower PL quantum yield of the hybrid MoS2/CsPbBr3 perovskite film. The time-resolved PL decay transient measurements are carried out to study the charge carrier dynamics at the interfaces as shown in Figure 3b and Table S1. The obtained average lifetimes for pristine CsPbBr3 and hybrid MoS2/CsPbBr3 are 7.46 ns and 1.67 ns, respectively. When coupled with MoS2, the PL lifetime of CsPbBr3 is shortened compared with the pristine CsPbBr3, which indicates that a considerable charge transfer can occur at the MoS2/CsPbBr3 interface. The exciton binding energy shows the interaction strength of the electrons and holes. Low exciton binding energy can facilitate the separation of the electrons and holes in the solar cells and photodetectors.43 The temperature dependent PL spectra of the CsPbBr3 with or without MoS2 films are presented in Figure S5. The calculated exciton binding energy of CsPbBr3 and MoS2/CsPbBr3 are 72.4 meV and 40.5 meV, respectively. The lower exciton binding energy in MoS2/CsPbBr3 indicates that the generated excitons in the hybrid structure tend to separate more easily during the device operation process, which is beneficial to increase the photocurrent of the photodetector based on MoS2/CsPbBr3. The decrease of the PL quantum yield, lifetime and exciton binding energy is ascribed to effective charge carrier transfer from CsPbBr3 to MoS2. When a laser is illuminated onto the CsPbBr3 perovskite film, the photo-induced electron-hole 7 ACS Paragon Plus Environment


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pairs are produced and recombined within the lifetime of photoexcited electrons. The photons are subsequently released and the PL is obtained corresponding to the bandgap of the CsPbBr3 nanosheets. As shown in Figure 1d, when coupled with MoS2, the chemical potential of the conduction band of MoS2 is lower than that of CsPbBr3 nanosheets, which provides a high potential difference to separate the photo-induced electron-hole pairs. Moreover, the exciton binding energy of CsPbBr3 perovskite is only about 72.4 meV, which cannot overcome the effect of the built-in electric field across the interface to split electron-hole pairs44. Therefore, the electrons can be easily transferred to the MoS2 monolayer to fill the empty states. The probability of recombination of photo-induced electron-hole pairs in CsPbBr3 nanosheets is limited due to the confinement of the electrons in MoS2. As a result, the intensity of the PL decreases and the quenching behavior occurs in a hybrid MoS2/CsPbBr3 perovskite structure. It can be an efficient strategy to apply an electron collection layer for tailoring charge transfer process to tune and design the light-matter interaction in the heterojunction devices.

Due to the efficient electron transfer from CsPbBr3 to MoS2, a MoS2 monolayer can be used as an electron collecting layer for perovskite photodetectors to improve the photoelectrical response characteristics. We have prepared photodetectors based on hybrid MoS2/CsPbBr3 and investigated the output properties of photoelectric response by measuring the current-voltage characteristics under dark and illuminated conditions. The I-V curves are linear, indicating a good ohmic contact between the Au electrodes and MoS2/CsPbBr3 channel (Figure S6). The excitation wavelength is a 8 ACS Paragon Plus Environment

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crucial parameter for a photodetector. The MoS2/CsPbBr3 detector displays a high photocurrent when the excitation wavelength is shorter than 525 nm (Figure 4a). However, when the excitation wavelength is above 525 nm, the generated photocurrent decreases dramatically. Especially, with the excitation wavelength is above 550 nm, no observable photocurrent can be obtained. When an illumination is shed on a photodetector, photons are absorbed and electron-hole pairs are generated through band-to-band transition. Therefore, it requires that the incident photons with a certain wavelength must be absorbed by the perovskite/MoS2 to generate the photocurrent. The curve of photocurrent (in Figure 4a) depending on the excitation wavelength is essentially in agreement with that of the absorption of MoS2/CsPbBr3 (Figure 2). The wavelength rejection ratio (I500 nm/I600nm, the ratio of the current under irradiation at the wavelength of 500 nm and 600 nm) of the photodetector is larger than 102, as shown in Figure 4a, which indicates that the photodetector exhibits relatively high signal-to-noise ratio.

When the incident photon energy is larger than the energy band gap, it can enhance the number of the photoexcited electrons and increase the photocurrent if the incident optical power density is increased. To analyze the quantitative dependence of the photocurrent on the optical intensity, we measured the current vs. bias voltage (I−V) characteristics of the hybrid MoS2/CsPbBr3 device as a function of the optical power intensity. Figure 4b shows the illumination intensity dependence of the I-V curves excited at 442 nm with a semiconductor laser under different illumination intensities ranging from 0 to 61.8 mW/cm2. The current is about 30 nA at 10 V in 9 ACS Paragon Plus Environment


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darkness. With illumination, the current increases dramatically with the incident optical intensity from 0.02 mW/cm2 to 61.8 mW/cm2. The maximum value of current on/off ratio is estimated to be more than 104, which indicates that the hybrid MoS2/CsPbBr3 device exhibits a good light-switching behavior. The photocurrent (Iph = Ilight − Idark) measured at Vds = 10 V as a function of the laser power density (P) is shown in Figure 4c. The generated photocurrent increases sublinearly with the light power density, due to the increase of the photogenerated carriers. The increase of the generated photocurrent can be fitted by a power law equation of Iph ≈ Pα, where P is the light power density and α represents the index of the power law. For our hybrid MoS2/CsPbBr3 device, the fitted value of α is 0.81, which is deviated from the ideal index of α = 1. It is because that the trap states at the interface of perovskite and MoS2 can lead to a recombination of photoexcited carriers.23-24 It should be noted that some ligands can be obtained on the surface of the CsPbBr3 perovskite nanosheets, which can trap electrons and holes leading to a final saturation of the generated photocurrent. This phenomenon was also reported previously in TMD photodetectors,9 organic perovskite/TMD,23-24 organic perovskite/graphene.38-39

The figures-of-merit, such as photoresponsivity (R), detectivity (D*), external quantum efficiency (EQE), response speed are usually employed to compare different photodetectors to evaluate the performance of a photodetector. R is the ratio between the photocurrent and the total incident optical power intensity on the photodetector, which can be defined as: R = Iph/P.S (S is effective area of photosensitive region, with a channel length of 20 µm and a channel width of 1 mm in this case. As shown in 10 ACS Paragon Plus Environment

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Figure 4d, under 442 nm light illumination at Vds = 10 V, a remarkable R decrease is observable with the increase of the light intensity. This is because that the trap states are present either on the surface of perovskite nanosheets or at the MoS2/CsPbBr3 interface. The density of electron trapping states is reduced under a high illumination intensity, resulting in saturation of the photoresponse.9, 45 In particular, it exhibits a generated photocurrent with a very low power density of 0.02 mW/cm2, which corresponds to a high responsivity of 4.4 A/W. This result is superior to most of other perovskite photodetectors.36,

46-49

We believe that a higher responsivity can be

achieved if a lower incident light intensity is applied.

The spectral responsivity is another important parameter for a photodetector, which refers to the photoresponse ability of the device upon an incident monochromatic light. It is related to the ability of the material to absorb photons with energy above the band gap of the material. We determined the spectral responsivity of our MoS2/CsPbBr3 heterojunction detector under illuminating monochromatic light of 350–650 nm, measured at 2 V, 5 V and 10 V, as shown in Figure 4e. The hydride detector presents a very high responsivity at the wavelength of 350-550 nm, and then exhibits a dramatic decrease at a longer wavelength. This variation tendency of responsivity with the wavelength is consistent with the absorption spectrum of the MoS2/CsPbBr3. The responsivity can increase up to 1.27 A/W when the incident photon energy reaches 2.36 eV (525 nm), which is in line with the highest absorption of the MoS2/CsPbBr3. This value of the responsivity is comparable to the other 2D



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crystals-based photodetectors, such as MoS2 (0.12 A/W),10 WSe2 (0.15 A/W)11 and InSe (12.3 A/W).50

The specific detectivity (D*) is a figure of merit to show the sensitivity of a photodetector. The specific detectivity is related to noise-equivalent power (NEP), the sensor area (S) and frequency bandwidth (B), which is given as following: ∗ =

() ⁄

NEP =

(1)

⁄

(2)

where in is the measured noise current, R is the responsivity. The shot noise current is the main contribution for the noise current in this case,25, 47, 51

the detectivity can also be written as:

∗ = (

/)

(3)

⁄

where e and Idark are the elementary charge and the dark current, respectively. Figure 4d also displays the detectivity of our MoS2/CsPbBr3 photodetector with different incident light power intensity. Under illumination of 442 nm with 61.8 mW/cm2 at 10 V, the obtained D* is 2.0×108 Jones. When decreasing the incident light power to 0.02 mW/cm2, the calculated D* can be as high as 2.5×1010 Jones, which is comparable to WSe2/CH3NH3PbI3 (2.2×1010 Jones),24 perovskite/MoS2/APTES (1.38×1010 Jones),23 1T-MoS2/CH3NH3PbI3 (1011 Jones),26 CsPbBr3(4.56×108 Jones)47 and Au/CsPbBr3 (1.684×109 Jones)47(Table S2).


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EQE is another important factor to evaluate a detector performance, which is the ratio of the number of the electron–hole pairs in the photocurrent to the total number of incident photons. We have measured the EQE of MoS2/CsPbBr3 heterojunction detector, as presented in Figure 4f. The EQE is high at the wavelength between 350-525 nm. In comparison, a dramatic decrease of the EQE can be obtained above 525 nm, which is corresponding to the photocurrent and photoresponsivity dependence on the incident light wavelength. The highest EQE is 302% under illumination of 442 nm at 10 V.

The

excellent

photoresponse

characteristics

indicate

that

the

hybrid

MoS2/CsPbBr3 possesses a great potential in the application of photodetectors. In order to investigate the effects of the MoS2 and CsPbBr3 on the photodetecting performance of the hybrid MoS2/CsPbBr3 photodetectors, the MoS2 and CsPbBr3 photodetectors were also prepared and the optical-electrical performance are shown in figure S7 and S8. We compare the photoresponse characteristics of perovskite photodetectors hybridized with or without MoS2. As shown in Figure 5a, the value of dark current for the CsPbBr3/MoS2, CsPbBr3 and MoS2 devices is approx. In the range of 0.1-1 nA. The photocurrent of the three devices are 5030 nA, 1230 nA and 54 nA, respectively. The calculated On/Off light ratio of the CsPbBr3/MoS2, CsPbBr3 and MoS2 devices are 16700, 14300 and 150, respectively. The current-voltage curves in Figure 5a demonstrate that the dark current of the device increases almost three times by adding the layer of MoS2, which is consistent



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with that previous reported in WSe2-CH3NH3PbI2.24 Similar results can be also obtained in the condition of a light irradiation. The photocurrent of the hybrid MoS2/CsPbBr3 photodetector is also several times higher compared with pristine CsPbBr3 under a light irradiation. This phenomenon reveals that the main effect of MoS2 is to improve the transport of the charge carriers. The current increase (in darkness or under light irradiation) is attributed to the improvement of the equivalent mobility or the concentration of carriers by the evolution of the band structure of perovskite by adding MoS2 layers. In contrary, the dark current of MoS2 device is closed to 0.3 nA no matter hybrided with CsPbBr3 or not. However, when irradiated with a laser, the photocurrent of MoS2/CsPbBr3 increases from 54 nA to 5030 nA with an improvement of 100 times compared with pristine MoS2. This is due to the high light absorption and high efficient photoelectric transformation efficiency of the perovskite, the photo-induced carriers in CsPbBr3 transfer to MoS2, and enhanced the photocurrent.

The

calculated

photoresponsivity

is

presented

in

Figure

5b.

The

photoresponsivity of the MoS2/CsPbBr3 device is improved nearly 20 or 1000 times at different incident optical power compared with that of the CsPbBr3 or MoS2 device. For the wavelength dependence, the responsivity and EQE of CsPbBr3 are improved about 20 times after combined with MoS2 (Figure S9). The high improvement of photoresponsivity is consistent with the previous work of organolead perovskite with


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TMDs,23-26 which is due to the special band gap of the hybrid perovskite/MoS2, facilitating the electron transfer to MoS2. To further understand the mechanism of the performance enhancement of the hybrid MoS2/CsPbBr3 photodetector, we have also analyzed the band alignment of MoS2 and CsPbBr3in darkness and under laser illumination. In darkness, the interface junction of the hybrid system shows a type II band alignment with a band offset at the valence band and conduction band (Figure 6a). The difference of the Fermi level of the MoS2 and CsPbBr3 leads to the formation of the depletion regions, which provides a built-in electric field to drive the electrons across the interface and separate the electron-hole pairs in perovskite. While under the light illumination, electron-hole pairs are generated in the perovskite nanosheets (Figure 6b). Due to the strong driving force of the built-in electric field, electrons are transferred to the MoS2 layer, whereas the holes are confined in the perovskite nanosheets. The accumulated electrons in the MoS2 layer raise (lower) the Fermi level of MoS2 layer (perovskite nanosheets) and reduce the Schottky barrier at the contact, which can prompt the carrier transport, leading to the higher photocurrent. Moreover, the confined holes are located in the perovskite nanosheets and the photo-excited electrons in MoS2 layers are recirculated, resulting in the photoresponse gain and an enhancement of the responsivity in the hybrid MoS2/CsPbBr3 photodetector. In should be noted that we have mainly focused on the charge transfer process at the MoS2/CsPbBr3 interface in the above discussion.



Furthermore,

the response time

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is also crucial to high-performance

photodetectors, which indicate the detection speed of the photodetectors in the practical

application.

The

time-resolved

photoresponse

of

the

perovskite

photodetector with or without MoS2 was investigated by an oscilloscope as shown in Figure 7a and Figure S10. The photocurrent of the two type perovskite based photodetector is consistent and repeatable with different incident light intensity and bias voltage. In Figure 7b the experimental curves of the rising and decay process could be fitted by a stretched exponential function: = + ! "(#/$)

(4)

Where I0 is the dark current, A is the amplitude of current, t is the response time, τ is the time constant which is considered as the lifetime of the carriers. The rising and decay time of the hybrid perovskite/MoS2 photodetector are calculated to be 0.72 ms and 1.01 ms, respectively. The rising and decay time is faster than that of perovskites based devices.48-49, 52 In comparison, the temporal photoresponse of the perovskite photodetector is also measured, as shown in Figure S10. The calculated rising and decay time is 62.5 ms and 18.2 ms. The response time of the hybrid MoS2/CsPbBr3 photodetector is approximately two orders of magnitude faster than that of the perovskite photodetector. The difference in the rising and decay time between the perovskite photodetector with or without MoS2 is resulted from the carrier transfer from perovskite to MoS2. A great amount of charge carrier traps could exist at the interface between CsPbBr3 and the SiO2 substrate, which can hinder the charge carrier


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transport and lower the response time of the photodetector. When the MoS2 layer was introduced to the device, the MoS2 layer can induce the trap passivation on the substrate, which can facilitate the charge carrier transport. Moreover, the efficient charge separation at the CsPbBr3/MoS2 interface can further ensure the very fast response time of the photodetector based on the hybrid structure.

Transistor characteristics of the hybrid perovskite/MoS2 photodetector are also explored at room temperature. However, no transistor characteristics can be observed in these CsPbBr3 photodetectors with and without MoS2 at room temperature. Most of the organic-inorganic perovskite transistor could not be operated at room temperature due to phonon scattering, ion drift, and molecular polarization.53-54 Further work should be explored in terms of the transistor characteristics of the hybrid perovskite/TMDs photodetectors to regulate the performance of the photodetector.

Conclusion In summary, we have demonstrated high-performance photodetectors with 2D MoS2 layer and all inorganic CsPbBr3 perovskite nanosheets. The devices present a broad absorption spectrum between 350-800 nm due to the large absorption of the CsPbBr3. The quenching and shortened lifetime of PL indicate an efficient charge transfer from CsPbBr3 to MoS2. We have obtained a responsivity of 4.4 A/W and a high external quantum efficiency of 302% in the CsPbBr3/MoS2 photodetector due to the large light absorbance and the efficient interfacial charge separation. The hybrid photodetector 17 ACS Paragon Plus Environment


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exhibits a high response speed with the rising and decay time of 0.72 ms and 1.01 ms, respectively. The results indicate that 2D nanomaterials coupled with perovskite layers can be an excellent candidate to achieve the next-generation high-performance photodetectors. Experiment Section Materials: All the reagents were purchased from Aladdin without further purification.

Synthesis of MoS2: To synthesize MoS2, CVD method was performed in a tube furnace with a 1-inch quartz tube. 4mg MoCl5 powder was placed in a ceramic boat located in the center of the furnace. 1g sulfur powder was placed in another ceramic boat at the upper stream side maintained at 120°C. Sapphire substrates ( oriented single crystals) were put in the furnace at the downstream side of the MoCl5 powder. The furnace temperature was raised up to 850°C at a ramping rate of 25°C/min. The system was kept at a pressure around 50 Pa with a 50 sccm Ar flow. After the temperature was held for 10 min, the furnace was then naturally cooled to room temperature.

Synthesis of CsPbBr3: All the procedures were conducted under ambient condition at room temperature. Firstly, 1 mmol CsBr and 0.5 mmol PbBr2 were dissolved into 15 ml DMSO to synthesize the precursor solutions. Then, 0.2 ml precursor was injected into 1 ml octadecylamine/acetic acid solution (0.05 g/ml) under magnetic stirring. 15 ml toluene was also added into this solution. After stirring for 5 min, the solution was centrifugated at 5000 rpm for 1 min. The precipitation was redispersed in toluene and 18 ACS Paragon Plus Environment

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centrifugated again to rule out the residual ligands, which was finally dispersed in 4 ml of toluene.34

Characterization: The morphology and crystal structure of the products were analyzed by X-ray diffractometer (Bruker Advanced D8), optical microscope (Olympus BX51), scanning electron microscope (FEI Quanta 250F), transmission electron microscopy (FEI Tecnai G20), atomic force microscopy (Bruker Multimode 8). The optical spectra were characterized by PL spectroscopy (Horiba, HRi 320, 442nm laser wavelength), UV-vis-IR (Shimadzu, UV3600), time-resolved PL decay Transients (Horiba FL-TCSPC) and X-ray photoemission spectroscopy (PHI QUANTERA II).

Device fabrication and measurement: The obtained MoS2 films were transferred onto Si/SiO2 substrates with polystyrene (PS) thin films. The Au electrodes were fabricated on MoS2 films by photolithography and electron-beam evaporation, leading to a channel length of 20 µm and a channel width of 1 mm. To fabricate the hybrid MoS2/CsPbBr3 device, two identical drops of the as-prepared CsPbBr3 solution were coated onto the previously prepared substrates with the MoS2 layer. The devices were

then heated on a hot plate at 60 °C for 10 min to remove the toluene residual. The electrical properties of the samples were measured by Keysight B1500A Semiconductor Device Analyzer at room temperature under ambient conditions. A 442 nm wavelength laser with a facula diameter 8 mm was used as the light source (MDL-III-442/100mW). The light intensity was measured using an optical power



meter (Newport PMKIT-21-01). The transient responses were analyzed by modulating output frequency of the laser using a digital oscilloscopy (Tektronix TDS2024c). The wavelength dependent responsivity measurement was obtained with Zolix DSR101UV-B UV detector spectral responsivity measurement system.

Calculation method: The structural optimizations and electronic structure calculations are performed in the context of density functional theory as implemented in VASP code.55 Exchange correlation energies are considered by the generalized gradient approximation (GGA) using the screened hybrid functional, HSE06.56 The wave functions are constructed using a projected augmented wave approach with plane wave cutoff energy of 520 eV. The convergence threshold was set as 10-4 eV in energy and 10-3 eV/Å in force. For monolayer MoS2, we set the x and y directions parallel and the z direction perpendicular to the layer plane, and a large vacuum space of 20 Å is set along the c-axis, the direction perpendicular to the surface, to avoid any interaction between the layer and its periodic images. The Brillouin zone integration is sampled using a set of 13 × 13 × 1 Monkhorst−Pack k-points.

ASSOCIATED CONTENT

Supporting Information. Optical and AFM image of MoS2 (S1); SEM, XRD and AFM of CsPbBr3 nanosheets (S2); Optical image and cross-section SEM of device (S3); Calculated band structure of MoS2 and CsPbBr3 (S4); Temperature dependent PL spectra of CsPbBr3 and MoS2/CsPbBr3 (S5); Drain-source characteristic of MoS2/CsPbBr3 device (S6); Electrical properties of MoS2 transistor (S7); Drain-source characteristic 20 ACS Paragon Plus Environment

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of CsPbBr3 photodetector (S8); Photoresponsivity and EQE of CsPbBr3 photodetectors with or without MoS2 (S9); Time-resolved photoresponse of the CsPbBr3 photodetector (S10); PL lifetimes of CsPbBr3 and MoS2/CsPbBr3 (Table S1); Comparison of 2D/Perovskite photodetectors performance (Table S2).

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], [email protected]

Author Contributions # X.Song and X.Liu contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by NSFC (51502139, 51572128, 21403109, 51672132), NSFC-RGC (5151101197), the National Key Basic Research Program of China (2014CB931702), the Fundamental Research Funds for the Central Universities (No. 30915012205, 30916015106, 30917014107), Natural Science Foundation of Jiangsu Province (BK20140769), Jiangsu Planned Projects for Postdoctoral Research Funds (1701168C), China Postdoctoral Science Foundation funded project (2014M560425) and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education. This work was also supported by open 21 ACS Paragon Plus Environment


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fund of Fujian Provincial Key Laboratory of Functional Materials and Applications (Xiamen University of Technology) (fma2017207).

REFERENCES 1. Song, X.; Hu, J.; Zeng, H., Two-Dimensional Semiconductors: Recent Progress and Future Perspectives. J. Mater. Chem. C 2013, 1 (17), 2952-2969. 2. Huo, C.; Yan, Z.; Song, X.; Zeng, H., 2D Materials via Liquid Exfoliation: a Review on Fabrication and Applications. Sci. Bull. 2015, 60 (23), 1994-2008. 3. Song, X.; Li, Q.; Ji, J.; Yan, Z.; Gu, Y.; Huo, C.; Zou, Y.; Zhi, C.; Zeng, H., A Comprehensive Investigation on CVD Growth Thermokinetics of h-BN White Graphene. 2D Mater. 2016, 3 (3), 035007. 4. Salehzadeh, O.; Tran, N. H.; Liu, X.; Shih, I.; Mi, Z., Exciton Kinetics, Quantum Efficiency, and Efficiency Droop of Monolayer MoS2 Light-Emitting Devices. Nano Lett. 2014, 14 (7), 4125-4130. 5. Eda, G.; Maier, S. A., Two-Dimensional Crystals: Managing Light for Optoelectronics. ACS Nano 2013, 7 (7), 5660-5665. 6. Buscema, M.; Island, J. O.; Groenendijk, D. J.; Blanter, S. I.; Steele, G. A.; van der Zant, H. S. J.; Castellanos-Gomez, A., Photocurrent Generation with Two-Dimensional van der Waals Semiconductors. Chem. Soc. Rev. 2015, 44 (11), 3691-3718. 7. Kufer, D.; Konstantatos, G., Photo-FETs: Phototransistors Enabled by 2D and 0D Nanomaterials. ACS Photon. 2016, 3 (12), 2197-2210. 8. Xie, C.; Mak, C.; Tao, X.; Yan, F., Photodetectors Based on Two-Dimensional Layered Materials Beyond Graphene. Adv. Funct. Mater. 2016, 27 (19), 1603886. 9. Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A., Ultrasensitive Photodetectors Based on Monolayer MoS2. Nat. Nanotechnol. 2013, 8 (7), 497-501. 10. Choi, W.; Cho, M. Y.; Konar, A.; Lee, J. H.; Cha, G.-B.; Hong, S. C.; Kim, S.; Kim, J.; Jena, D.; Joo, J.; Kim, S., High-Detectivity Multilayer MoS2 Phototransistors with Spectral Response from Ultraviolet to Infrared. Adv. Mater. 2012, 24 (43), 5832-5836. 11. Pradhan, N. R.; Ludwig, J.; Lu, Z.; Rhodes, D.; Bishop, M. M.; Thirunavukkuarasu, K.; McGill, S. A.; Smirnov, D.; Balicas, L., High Photoresponsivity and Short Photoresponse Times in Few-Layered WSe2 Transistors. ACS Appl. Mat. Interfaces 2015, 7 (22), 12080-12088. 12. Zhang, W.; Huang, J.-K.; Chen, C.-H.; Chang, Y.-H.; Cheng, Y.-J.; Li, L.-J., High-Gain Phototransistors Based on a CVD MoS2 Monolayer. Adv. Mater. 2013, 25 (25), 3456-3461. 13. Kang, D.-H.; Kim, M.-S.; Shim, J.; Jeon, J.; Park, H.-Y.; Jung, W.-S.; Yu, H.-Y.; Pang, C.-H.; Lee, S.; Park, J.-H., High-Performance Transition Metal Dichalcogenide


Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Photodetectors Enhanced by Self-Assembled Monolayer Doping. Adv. Funct. Mater. 2015, 25 (27), 4219-4227. 14. Gao, L.; Chen, C.; Zeng, K.; Ge, C.; Yang, D.; Song, H.; Tang, J., Broadband, Sensitive and Spectrally Distinctive SnS2 Nanosheet/PbS Colloidal Quantum Dot Hybrid Photodetector. Light Sci. Appl. 2016, 5, e16126. 15. Peng, B.; Ang, P. K.; Loh, K. P., Two-Dimensional Dichalcogenides for Light-Harvesting Applications. Nano Today 2015, 10 (2), 128-137. 16. Cho, E. H.; Song, W. G.; Park, C. J.; Kim, J.; Kim, S.; Joo, J., Enhancement of Photoresponsive Electrical Characteristics of Multilayer MoS2 Transistors using Rubrene Patches. Nano Research 2015, 8 (3), 790-800. 17. Li, X.; Zhu, J.; Wei, B., Hybrid Nanostructures of Metal/Two-Dimensional Nanomaterials for Plasmon-Enhanced Applications. Chem. Soc. Rev. 2016, 45 (11), 3145-3187. 18. Konstantatos, G.; Badioli, M.; Gaudreau, L.; Osmond, J.; Bernechea, M.; de Arquer, F. P. G.; Gatti, F.; Koppens, F. H. L., Hybrid Graphene-Quantum Dot Phototransistors with Ultrahigh Gain. Nat. Nanotechnol. 2012, 7 (6), 363-368. 19. Kufer, D.; Nikitskiy, I.; Lasanta, T.; Navickaite, G.; Koppens, F. H. L.; Konstantatos, G., Hybrid 2D–0D MoS2–PbS Quantum Dot Photodetectors. Adv. Mater. 2015, 27 (1), 176-180. 20. Hu, C.; Dong, D.; Yang, X.; Qiao, K.; Yang, D.; Deng, H.; Yuan, S.; Khan, J.; Lan, Y.; Song, H.; Tang, J., Synergistic Effect of Hybrid PbS Quantum Dots/2D-WSe2 Toward High Performance and Broadband Phototransistors. Adv. Funct. Mater. 2016, 27 (2), 1603605. 21. Chen, C.; Qiao, H.; Lin, S.; Man Luk, C.; Liu, Y.; Xu, Z.; Song, J.; Xue, Y.; Li, D.; Yuan, J.; Yu, W.; Pan, C.; Ping Lau, S.; Bao, Q., Highly Responsive MoS2 Photodetectors Enhanced by Graphene Guantum Dots. Sci. Rep. 2015, 5, 11830. 22. Yu, S. H.; Lee, Y.; Jang, S. K.; Kang, J.; Jeon, J.; Lee, C.; Lee, J. Y.; Kim, H.; Hwang, E.; Lee, S.; Cho, J. H., Dye-Sensitized MoS2 Photodetector with Enhanced Spectral Photoresponse. ACS Nano 2014, 8 (8), 8285-8291. 23. Kang, D.-H.; Pae, S. R.; Shim, J.; Yoo, G.; Jeon, J.; Leem, J. W.; Yu, J. S.; Lee, S.; Shin, B.; Park, J.-H., An Ultrahigh-Performance Photodetector based on a Perovskite–Transition-Metal-Dichalcogenide Hybrid Structure. Adv. Mater. 2016, 28 (35), 7799-7806. 24. Lu, J.; Carvalho, A.; Liu, H.; Lim, S. X.; Castro Neto, A. H.; Sow, C. H., Hybrid Bilayer WSe2–CH3NH3PbI3 Organolead Halide Perovskite as a High-Performance Photodetector. Angew. Chem. Int. Ed. 2016, 55 (39), 11945-11949. 25. Ma, C.; Shi, Y.; Hu, W.; Chiu, M.-H.; Liu, Z.; Bera, A.; Li, F.; Wang, H.; Li, L.-J.; Wu, T., Heterostructured WS2/CH3NH3PbI3 Photoconductors with Suppressed Dark Current and Enhanced Photodetectivity. Adv. Mater. 2016, 28 (19), 3683-3689. 26. Wang, Y.; Fullon, R.; Acerce, M.; Petoukhoff, C. E.; Yang, J.; Chen, C.; Du, S.; Lai, S. K.; Lau, S. P.; Voiry, D.; O'Carroll, D.; Gupta, G.; Mohite, A. D.; Zhang, S.; Zhou, H.; Chhowalla, M., Solution-Processed MoS2/Organolead Trihalide Perovskite Photodetectors. Adv. Mater. 2016, 29 (4), 1603995. 23 ACS Paragon Plus Environment


Page 24 of 34

27. Peng, B.; Yu, G.; Zhao, Y.; Xu, Q.; Xing, G.; Liu, X.; Fu, D.; Liu, B.; Tan, J. R. S.; Tang, W.; Lu, H.; Xie, J.; Deng, L.; Sum, T. C.; Loh, K. P., Achieving Ultrafast Hole Transfer at the Monolayer MoS2 and CH3NH3PbI3 Perovskite Interface by Defect Engineering. ACS Nano 2016, 10 (6), 6383-6391. 28. Fengjing, L.; Jiawei, W.; Liang, W.; Xiaoyong, C.; Chao, J.; Gongtang, W., Enhancement of Photodetection Based on Perovskite/MoS2 Hybrid Thin Film Transistor. J. Semicond. 2017, 38 (3), 034002. 29. Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V., Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 2015, 15 (6), 3692-3696. 30. Yettapu, G. R.; Talukdar, D.; Sarkar, S.; Swarnkar, A.; Nag, A.; Ghosh, P.; Mandal, P., Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths. Nano Lett. 2016, 16 (8), 4838-4848. 31. Huang, H.; Polavarapu, L.; Sichert, J. A.; Susha, A. S.; Urban, A. S.; Rogach, A. L., Colloidal Lead Halide Perovskite Nanocrystals: Synthesis, Optical Properties and Applications. NPG Asia Mater. 2016, 8, e328. 32. Cao, F.; Yu, D.; Li, X.; Zhu, Y.; Sun, Z.; Shen, Y.; Wei, Y.; Wu, Y.; Zeng, H., Highly Stable and Flexible Photodetector Arrays Based on Low Dimensional CsPbBr3 Microcrystals and On-paper Pencil-drawn Electrodes. J. Mater. Chem. C 2017, 5, 7441-7445. 33. Yu, D.; Cao, F.; Shen, Y.; Liu, X.; Zhu, Y.; Zeng, H., Dimensionality and Interface Engineering of 2D Homologous Perovskites for Boosted Charge Carrier Transport and Photodetection Performances. J. Phys. Chem. Lett. 2017, 8, 2565−2572. 34. Yu, D.; Cai, B.; Cao, F.; Li, X.; Liu, X.; Zhu, Y.; Ji, J.; Gu, Y.; Zeng, H., Cation Exchange-Induced Dimensionality Construction: From Monolayered to Multilayered 2D Single Crystal Halide Perovskites. Adv. Mater. Interfaces 2017, 4 (19), 1700441. 35. Liu, X.; Yu, D.; Cao, F.; Li, X.; Ji, J.; Chen, J.; Song, X.; Zeng, H., Low-Voltage Photodetectors with High Responsivity Based on Solution-Processed Micrometer-Scale All-Inorganic Perovskite Nanoplatelets. Small 2017, 13 (25), 1700364. 36. Song, J.; Xu, L.; Li, J.; Xue, J.; Dong, Y.; Li, X.; Zeng, H., Monolayer and Few-Layer All-Inorganic Perovskites as a New Family of Two-Dimensional Semiconductors for Printable Optoelectronic Devices. Adv. Mater. 2016, 28 (24), 4861-4869. 37. Kwak, D.-H.; Lim, D.-H.; Ra, H.-S.; Ramasamy, P.; Lee, J.-S., High Performance Hybrid Graphene-CsPbBr3-xIx Perovskite Nanocrystal Photodetector. RSC Adv. 2016, 6 (69), 65252-65256. 38. Lee, Y.; Kwon, J.; Hwang, E.; Ra, C.-H.; Yoo, W. J.; Ahn, J.-H.; Park, J. H.; Cho, J. H., High-Performance Perovskite–Graphene Hybrid Photodetector. Adv. Mater. 2015, 27 (1), 41-46. 24 ACS Paragon Plus Environment

Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


39. Wang, Y.; Zhang, Y.; Lu, Y.; Xu, W.; Mu, H.; Chen, C.; Qiao, H.; Song, J.; Li, S.; Sun, B.; Cheng, Y.-B.; Bao, Q., Hybrid Graphene–Perovskite Phototransistors with Ultrahigh Responsivity and Gain. Adv. Optical Mater. 2015, 3 (10), 1389-1396. 40. Spina, M.; Lehmann, M.; Náfrádi, B.; Bernard, L.; Bonvin, E.; Gaál, R.; Magrez, A.; Forró, L.; Horváth, E., Microengineered CH3NH3PbI3 Nanowire/Graphene Phototransistor for Low-Intensity Light Detection at Room Temperature. Small 2015, 11 (37), 4824-4828. 41. Dang, V. Q.; Han, G.-S.; Trung, T. Q.; Duy, L. T.; Jin, Y.-U.; Hwang, B.-U.; Jung, H.-S.; Lee, N.-E., Methylammonium Lead Iodide Perovskite-Graphene Hybrid Channels in Flexible Broadband Phototransistors. Carbon 2016, 105, 353-361. 42. Qian, L.; Sun, Y.; Wu, M.; Xie, D.; Ding, L.; Shi, G., A Solution-Processed High-Performance Phototransistor based on a Perovskite Composite with Chemically Modified Graphenes. Adv. Mater. 2017, 29 (22), 1606175. 43. Voznyy, O.; Sutherland, B. R.; Ip, A. H.; Zhitomirsky, D.; Sargent, E. H., Engineering Charge Transport by Heterostructuring Solution-Processed Semiconductors. Nat. Rev. Mater. 2017, 2, 17026. 44. Li, X.; Wu, Y.; Zhang, S.; Cai, B.; Gu, Y.; Song, J.; Zeng, H., CsPbX3 Quantum Dots for Lighting and Displays: Room-Temperature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes. Adv. Funct. Mater. 2016, 26 (15), 2435-2445. 45. Zheng, Z.; Yao, J.; Xiao, J.; Yang, G., Synergistic Effect of Hybrid Multilayer In2Se3 and Nanodiamonds for Highly Sensitive Photodetectors. ACS Appl. Mat. Interfaces 2016, 8 (31), 20200-20211. 46. Li, X.; Yu, D.; Cao, F.; Gu, Y.; Wei, Y.; Wu, Y.; Song, J.; Zeng, H., Healing All-Inorganic Perovskite Films via Recyclable Dissolution–Recyrstallization for Compact and Smooth Carrier Channels of Optoelectronic Devices with High Stability. Adv. Funct. Mater. 2016, 26 (32), 5903-5912. 47. Dong, Y.; Gu, Y.; Zou, Y.; Song, J.; Xu, L.; Li, J.; Xue, J.; Li, X.; Zeng, H., Improving All-Inorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect. Small 2016, 12 (40), 5622-5632. 48. Zhou, J.; Chu, Y.; Huang, J., Photodetectors Based on Two-Dimensional Layer-Structured Hybrid Lead Iodide Perovskite Semiconductors. ACS Appl. Mat. Interfaces 2016, 8 (39), 25660-25666. 49. Tang, X.; Zu, Z.; Shao, H.; Hu, W.; Zhou, M.; Deng, M.; Chen, W.; Zang, Z.; Zhu, T.; Xue, J., All-Inorganic Perovskite CsPb(Br/I)3 Nanorods for Optoelectronic Application. Nanoscale 2016, 8 (33), 15158-15161. 50. Tamalampudi, S. R.; Lu, Y.-Y.; Kumar U, R.; Sankar, R.; Liao, C.-D.; Moorthy B, K.; Cheng, C.-H.; Chou, F. C.; Chen, Y.-T., High Performance and Bendable Few-Layered InSe Photodetectors with Broad Spectral Response. Nano Lett. 2014, 14 (5), 2800-2806. 51. Saidaminov, M. I.; Adinolfi, V.; Comin, R.; Abdelhady, A. L.; Peng, W.; Dursun, I.; Yuan, M.; Hoogland, S.; Sargent, E. H.; Bakr, O. M., Planar-Integrated Single-Crystalline Perovskite Photodetectors. Nat. Commun. 2015, 6, 8724. 25 ACS Paragon Plus Environment


Page 26 of 34

52. Hu, X.; Zhang, X.; Liang, L.; Bao, J.; Li, S.; Yang, W.; Xie, Y., High-Performance Flexible Broadband Photodetector Based on Organolead Halide Perovskite. Adv. Funct. Mater. 2014, 24 (46), 7373-7380. 53. Matsushima, T.; Hwang, S.; Sandanayaka, A. S. D.; Qin, C.; Terakawa, S.; Fujihara, T.; Yahiro, M.; Adachi, C., Solution-Processed Organic–Inorganic Perovskite Field-Effect Transistors with High Hole Mobilities. Adv. Mater. 2016, 28 (46), 10275-10281. 54. Chin, X. Y.; Cortecchia, D.; Yin, J.; Bruno, A.; Soci, C., Lead Iodide Perovskite Light-Emitting Field-Effect Transistor. Nat. Commun. 2015, 6, 7383. 55. Kresse, G.; Hafner, J., Ab initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47 (1), 558-561. 56. Heyd, J.; Scuseria, G. E.; Ernzerhof, M., Erratum: “Hybrid Functionals Based on a Screened Coulomb Potential” [J. Chem. Phys. 118, 8207 (2003)]. J. Chem. Phys. 2006, 124 (21), 219906.


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Figure caption Figure 1. Hybrid MoS2/CsPbBr3 perovskite heterostructure. a) Schematic illustration of the hybrid MoS2/CsPbBr3 photodetector. b) Schematic illustration of the charge transfer from CsPbBr3 to MoS2 with laser illumination. c) Alignment of the densities of states of MoS2 and CsPbBr3. d) Energy-band structure of MoS2 and CsPbBr3. Figure 2. UV-Vis absorption spectra of the MoS2, perovskite and MoS2/CsPbBr3 hybrid film. Figure 3. a) Photoluminescence spectra of the pure perovskite and MoS2/CsPbBr3 hybrid film. b) Time-resolved PL decay transients measured at 515 nm for pure CsPbBr3 and MoS2/CsPbBr3 structure. Figure 4. Photoinduced response of the hybrid MoS2/CsPbBr3 photodetector. a) Photocurrent of the hybrid device as a function of the illumination wavelength. b) Drain-source characteristic in darkness and under different illumination intensities. c) Photocurrent and on/off ratio of the photodetector as a function of illumination intensity. d) Power intensity dependent photoresponsivity and detectivity under 442 nm laser illumination at 10 V. e) Photoresponsivity and f) EQE as a function of illumination wavelength at the voltage of 2 V, 5 V and 10 V. Figure 5. Optoelectronic performance comparison of the perovskite photodetector with or without MoS2. a) I–V characteristics of the two devices in darkness and under 442 nm laser illumination. b) Photoresponsivity of the two devices as the function of the power intensity. Figure 6. Schematic diagram of the charge generation and transport process at MoS2/CsPbBr3 heterojunction. a) in darkness. b) under light irradiation. Figure 7. Time-resolved photoresponse of the hybrid MoS2/CsPbBr3 photodetector under 442 nm laser illumination. a) Photoswitching behavior of the hybrid device at different voltages and incident optical power intensity.

b) Temporal photocurrent

response of the hybrid device with rising time (0.72 ms) and decay time (1.01 ms).



Figure 1 227x172mm (300 x 300 DPI)

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CsPbBr3 Photodetectors via

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