Dear Author, Please correct your galley proofs ...

Postfach 10 11 61 69451 Weinheim Germany Courier services: Boschstraße 12 69469 Weinheim Germany Tel.: (+49) 6201 606 531 Fax: (+49) 6201 606 500 E-mail: [email protected] --------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Dear Author, Please correct your galley proofs carefully and return them no more than four days after the page proofs have been received. Please limit corrections to errors already in the text; cost incurred for any further changes or additions will be charged to the author, unless such changes have been agreed upon by the editor.

To avoid commonly occurring errors, please ensure that the following important items are correct in your proofs (please note that once your article is published online, no further corrections can be made): Names of all authors present and spelled correctly

The editors reserve the right to publish your article without your corrections if the proofs do not arrive in time.

Titles of authors correct (Prof. or Dr. only: please note, Prof. Dr. is not used in the journals)

Note that the author is liable for damages arising from incorrect statements, including misprints.

Addresses and postcodes correct

Please note any queries that require your attention. These are indicated with a Q in the PDF and a question at the end of the document. Reprints may be ordered by filling out the accompanying form. Return the reprint order form by fax or by e-mail with the corrected proofs, to WileyVCH : [email protected]

E-mail address of corresponding author correct (current email address) Funding bodies included and grant numbers accurate Title of article OK All figures included Equations correct (symbols and sub/superscripts)

Corrections should be made directly in the PDF file using the PDF annotation tools. If you have questions about this, please contact the editorial office. The corrected PDF and any accompanying files should be uploaded to the journal’s Editorial Manager site.

www.MaterialsViews.com

FULL PAPERS

Z. Li, H. Qiao, Z. Guo, X. Ren, Z. Huang, X. Qi,* S. C. Dhanabalan, J. S. Ponraj, D. Zhang, J. Li, J. Zhao, J. Zhong, H. Zhang*................. 1705237 High-Performance PhotoElectrochemical Photodetector Based on Liquid-Exfoliated Few-Layered InSe Nanosheets with Enhanced Stability

A photoelectrochemical photodetector fabricated by indium selenide nanosheets with preferable adjustable response performances to sunlight is presented. Specifically, detective ability of such detector can be conveniently regulated by tuning the concentration of electrolyte and the applied potential. The as-fabricated InSe detector shows obvious response to sunlight and its photocurrent density can reach 300 nA cm−2 with no degeneration.

PR OO F

xxxx

UN CO RR EC TE D

1 Q1 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

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

FULL PAPER xxxx

PR OO F

High-Performance Photo-Electrochemical Photodetector Based on Liquid-Exfoliated Few-Layered InSe Nanosheets with Enhanced Stability

Zhongjun Li, Hui Qiao, Zhinan Guo, Xiaohui Ren, Zongyu Huang, Xiang Qi,* Sathish Chander Dhanabalan, Joice Sophia Ponraj, Du Zhang, Jianqing Li, Jinlai Zhao, Jianxin Zhong, and Han Zhang* The band gap of few-layered 2D material is one of the significant issues for the application of practical devices. Due to the outstanding electrical transport property and excellent photoresponse, 2D InSe has recently attracted rising attention. Herein, few-layered InSe nanosheets with direct band gap are delivered by a facile liquid-phase exfoliation approach. We have synthesized a photoelectrochemical (PEC)-type few-layered InSe photodetector that exhibits high photocurrent density, responsivity, and stable cycling ability in KOH solution under the irradiation of sunlight. The detective ability of such PEC InSe photodetector can be conveniently tuned by varying the concentration of KOH and applied potential suggesting that the present device can be a fitting candidate as an excellent photodetector. Moreover, extendable optimization of the photodetection performance on InSe nanosheets would further enhance the potential of the prepared InSe in other PEC-type devices such as dye-sensitized solar cells, water splitting systems, and solar tracking equipment.

1. Introduction

The process of light detection in converting light into electrical signal is an essential phenomenon that plays a pivotal role in sample technological applications such as sensing, communication, and spectroscopy.[1] Recently, 2D materials with single to a few atomic layers have aroused researchers’ great interests and attention. Owing to the absorption spectrum of graphene extending from ultraviolet to far-infrared, it became a promising candidate for broadband photodetection.[2] On the other hand, the weak optical absorption gives rise to low responsivity of graphene-based photodetectors so that the potential applications are greatly limited.[3] Moreover, the reported graphene-based photodetectors have limited responsivity (10−3 to 10−1 A W−1) due to the absence of photoconductive gain.[3e,f,4] The zero band gap of graphene implies no electronic states that allow the generation of photoexcited carriers in developing high-performance optoelectronic devices. Additionally, the absence of band gap in graphene induces high dark current and is unfavorable condition for photodetectors.[3e,5] The introduction of band gap in graphene could be achieved by means of some methods,[6] which is too limited for the application of graphene in wide-range spectral detection. Black phosphorus (BP), an emerging 2D material with intrinsic direct band gap[7] also experiences light-induced fast degradation in ambient condition resulting in rapid loss of its electronic properties.[8] Beyond graphene and BP, transition metal dichalcogenides (TMDs) and several III–VI layered materials set off a new wave of research as they have very high in-plane carrier mobility and low dark currents.[9] The thickness dependence of the band gap creates an opportunity to tailor their electric properties thereby adjusting the cutoff wavelength of the incident light,[10] which offers opportunities for innovative fabrication of optoelectronic and nanoelectronic devices.[11] Most recently, InSe, being a typical III–VI layered material with narrow direct band gap, has attracted great attention of the researchers in the field of 2D materials. 2D InSe with a few layers has been reported to possess high quantum-size confinement effects leading to the abnormal extensively alterable band

UN CO RR EC TE D

Q3 Q4

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

www.afm-journal.de

Z. Li, D. Zhang, J. Li, J. Zhao Faculty of Information Technology Macau University of Science and Technology Macao Z. Li, Z. Guo, X. Qi, S. C. Dhanabalan, J. Zhao, H. Zhang Shenzhen Engineering Laboratory of Phosphorene and Optoelectronics Collaborative Innovation Center for Optoelectronic Science and Technology and Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province Shenzhen University Shenzhen 518060, P. R. China E-mail: [email protected]; [email protected] H. Qiao, X. Ren, Z. Huang, X. Qi, J. Zhong Hunan Key Laboratory of Micro–Nano Energy Materials and Devices and Laboratory for Quantum Engineering and Micro–Nano Energy Technology and School of Physics and Optoelectronic Xiangtan University Hunan 411105, P. R. China J. S. Ponraj Department of Nanoscience and Technology Bharathiar University Coimbatore 641046, India The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201705237.

DOI: 10.1002/adfm.201705237

Adv. Funct. Mater. 2018, 1705237

1705237 (1 of 8)

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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

www.advancedsciencenews.com

in 0.2 m KOH solution under the irradiation of sunlight. Furthermore, the relationship between incident light and concentration of electrolyte was identified and revealed. This research work provides fundamental knowledge regarding the photoresponse performance of InSe-based photodetector. Compared to that of power-supplied devices, the fabrication process of InSe is simple without the use of sophisticated technology.[27]The significant advantage of InSe endows potential applications in sunlight detection, optoelectronics, photovoltaics, and photocatalysis.


2. Results and Discussion

XRD spectrum is used to identify the crystal structure of the as-prepared InSe. All the diffraction peaks given in Figure 1a are in accordance with the Bragg position of InSe (JCPDS34-1431).[28] No interference from the tape base is observed (Figure S1, Supporting Information). The strong intensities of (00l) peaks and disappearance of other diffraction peaks suggest that the samples are in the nanocrystalline form with the exposed large-sized surface being (00l) lattice plane. The absence of impurity peaks in the XRD pattern confirms the high purity of the sample. The resonant (laser excitation 514 nm) Raman spectrum[12c] measurement is carried out to investigate the structure and vibrational modes of the material (Figure 1b). For bulk InSe, four active resonant Raman modes of A ′1 ( Γ 12 ), 3 E′( Γ 13 )-TO&E′′( Γ 33 ), A′′2 ( Γ 11 )-LO, and A ′1 ( Γ 1 ) are observed from 100 to 275 cm−1 and are consistent with the earlier reported study.[20] Apart from them, two new modes A′′2 ( Γ 11 )-TO and E′( Γ 13 )-LO are observed for few-layered sample that indicates the as-synthesized InSe samples are few-layered.[20] Based on the atomic force microscopy (AFM) image (Figure 1c), most of the nanosheets are ≈7–8 atomic layers. More detailed description of the AFM images can be seen in Figure S2 (Supporting Information). According to the previous reports, InSe nanosheets present direct-to-indirect band gap transition with the decrease in the number of layers[12d] and show direct band gap performance when the atomic thickness is more than 6 atomic layers. Therefore, it is reasonable to deduce that most of the as-prepared nanosheets exhibited direct band gap property. The direct band gap performance of InSe makes the large quantity preparation of nanosheets for highly efficient devices possible and is superior to other TMDs where the band gap exists only in the monolayer form. High-resolution transmission electron microscopy (HRTEM) characterization is further carried out to demonstrate the morphologies and microstructures of the exfoliated InSe nanosheets. As depicted in Figure 1d, liquidexfoliated InSe nanosheets are found to have intact lamellar structure after exfoliation processes which indicates the presence of InSe nanosheets with wide lateral dimensions, thereby retaining the inherent merits from bulk InSe. Energy-dispersive X-ray (EDX) analysis mapping of elements from the selected area of Figure 1d confirms the uniform distribution of In and Se elements over the InSe nanosheets (Figure 1e,f) where the molar percent ratio of In and Se is ≈1:1. In addition, HRTEM image and the corresponding selected area electron diffraction (SAED) pattern provide the comprehensive investigation of the microstructure of InSe nanosheets. Figure 1g presents the

1705237 (2 of 8)

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

PR OO F

gap from ≈1.26 eV for the bulk to ≈2.11 eV for the monolayer at room temperature (RT), indicating a large photoresponse spectral range from visible to infrared.[12]The effective electron mass of InSe is as low as 0.14me[13] (me represents free electron mass) which is less than that of MoS2 (0.45me)[14] and Si (0.19me),[15] contributing to the mobility as high as 103 and 104 cm2 V−1 s−1 at RT and liquid-helium temperature, respectively.[12b] Ho et al. reported a dry-oxidation process on InSe nanosheets where mobility reached the values of 423 and 1006 cm2 V−1 s−1 at RT and 78 K, respectively. The aforementioned high mobility is better than the previously reported RT values for phosphorene (275 cm2 V−1 s−1)[16] and other TMD-based FETs (MoS2: ≈200 cm2 V−1 s−1;[17] WSe2: ≈250 cm2 V−1 s−1;[18] WS2: 50±7 cm2 V−1 s−1[19]) In addition to the carrier mobility, response time and responsivity are main factors to be considered in the field of optoelectronics. Lei et al. investigated fewlayered InSe demonstrating a strong photoresponsivity of 34.7 mA W−1 and a fast response time of 488 µs on SiO2/Si substrate during a 532 nm laser irradiation.[20] Interestingly, the report showed that the response time of the fabricated device was as low as 87 µs with a dramatically reduced dark current resulting from the reverse-bias Schottky barrier between InSe and Al electrodes.[21] Tamalampudi et al. have fabricated few-layered InSe photodetectors with a photoresponsivity of 12.3 A W−1 at 450 nm on SiO2/Si and 3.9 A W−1 at 633 nm on flexible polyethylene terephthalate[22] that proved to be superior to the values of graphene[3e] and other reported TMDs (MoS2,[23] GaSe,[24] and GaS[25]). Furthermore, the InSe photodetector illustrated a response time of ≈50 ms and a long-term stability of up to ≈45 min. The fabricated InSe nanosheets by Yang et al. possessed the maximum photoresponsivity of 27 A W−1, and the response time of 0.5 and 1.7 s for the rise and decay, respectively.[12c] Even though great accomplishments have been achieved, the mechanical-exfoliated or deposition-synthesized 2D InSe samples in the formerly reported photodetectors demanded complex and precise processes with low yield, making them inappropriate for specific applications. Meanwhile, most of the investigated InSe photodetectors were devised in thin-film transistor configurations requiring extra power sources that prohibit their usage in realizing devices based on them. The power-supplied devices will stop working in situations such as emergency cutoff or circuit, and therefore, it is significant to design a self-powered device that can function without external energy supply systems.[26] Based on the typical PEC processes, a novel PEC-type photodetector has been constructed to realize the self-powered detection. In addition to this, it’s open and simple fabrication process meets the necessary requirements of active materials. Considering the integrated merits of few-layered InSe, such as higher stability than few-layered black phosphorous, higher carrier mobility than few-layered dichalcogenides,[12b] and direct band gap performance when the thickness is more than 6 atomic layers,[12d] the present paper focuses on the preparation of few-layered InSe nanosheets with the aid of simple liquid-phase exfoliation method. The thicknesses of the nanosheets were found to be a few atomic layers with large lateral size. The as-prepared large-scale InSe nanosheets were utilized in the fabrication of photoelectrochemical (PEC) photodetector with high photocurrent density, sound responsivity, and stable cycling ability

UN CO RR EC TE D

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

www.afm-journal.de


UN CO RR EC TE D

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

www.afm-journal.de

PR OO F


Figure 1. a) XRD pattern of as-prepared InSe nanosheets. b) Raman spectra of bulk InSe and liquid-exfoliated InSe nanosheets. c) AFM image of as-prepared InSe nanosheets. d) TEM image and e,f) relevant EDX analysis mapping of elements from the selected area of (c). The blue spheres refer to indium atoms and the brown spheres refer to selenium atoms. g) HRTEM image of InSe nanosheets and the inset shows SAED pattern.

lattice spacing of 0.347 nm corresponding to the (010) or (100) plane of InSe with the interfacial angle of 60°. Besides that, the SAED pattern given in the inset of Figure 1g depicts the high crystallinity of InSe and the consistency of diffraction spots with the expected crystal structure of InSe. Ultraviolet (UV)– vis–near-infrared (NIR) absorption spectra given in Figure S3 (Supporting Information) cover UV to NIR and the band gap of InSe nanosheets deduced from the absorption spectrum is ≈1.44 eV, which is in coincidence with the previous experimental values.[12b,d] At 808 nm, the extinction coefficient of InSe nanosheets is calculated as 680 L mol−1 cm−1 (Figure S4, Supporting Information), higher than that of BP (≈458 L mol−1 cm−1 deduced from 14.8 L g−1 cm−1).[29] Additionally, the extinction coefficients of InSe nanosheets at other wavelengths are superior to that of graphene, rGO, and h-BN due to the excellent responsivity and absorptivity of InSe nanosheets. The extinction coefficient comparisons at different wavelengths of InSe with the other 2D materials are provided in Table S1 (Supporting Information). Figure 2 demonstrates the optoelectronic performance of PEC type InSe photodetector under simulated sunlight irradiation. It is clear that the as-fabricated photodetector exhibits typical photoresponse behaviors. The InSe working electrode in the linear sweep voltammetry (LSV) curves shows the anode photocurrent at the light and dark current intensity, as depicted in the inset image of Figure 2a. It is noted that the photocurrent density of InSe electrode depends on the bias potential, in which


the maximum value of photocurrent density achieved by InSe electrode is about 15.9 nA cm−2 under the bias potential of 0 V and gradually increases to 315 nA cm−2 when the applied potentials increased from 0 to 1.0 V. The steady growing photocurrent density resulting from the positive effect generated by external potential can efficiently accelerate the electron–hole separation and transportation. Interestingly, the photocurrent density of InSe electrode under 1.0 V is realized to be almost ten times higher than that of 0 V indicating the significant sensitivity of InSe toward the external bias potential. In addition, the obvious photoresponse phenomenon under 0 V also reveals that the as-fabricated device would be used as a self-powered photodetector without any external power sources. It is well known that the rising time is an important index of photodetector. Noticeably, the rising time of the as-fabricated photodetector would be tuned by the bias potential. As depicted in Figure 2b, the rising time would prolong when the bias potential varies from 0 to 0.2 V and further enhanced by elevating the external potential from 0.2 to 0.4 V resulting in a sharp decline of response time but the promotion inverses at much higher potential. The results reveal that the control in the applied bias potential is a feasible method to modulate the photoresponse ability of InSe. Apart from the external applied potential, incident light intensity is discerned to be an interesting key factor that decides the performance of a photodetector. As illustrated in Figure 2c, the photocurrent density of InSe electrode at 1.0 V bias potential shows steady increase by raising the power intensity of the

1705237 (3 of 8)


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

UN CO RR EC TE D

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

www.afm-journal.de

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

PR OO F


Figure 2. a) Photoresponse of InSe nanosheets in 0.2 m KOH electrolyte under external potential of 0–1 V. Inset: LSV measurements of InSe in 0.2 m KOH under dark and light irradiation. b) Calculated rising time of PEC-type InSe photodetector under various external potentials of 0–1.0 V in 0.2 m KOH electrolyte. c) Normalized photocurrent density in InSe photodetector under incident power density of 40, 60, 80, 100, and 120 mW cm−2. d) Fitting curve (circle) and calculated responsivity (triangle) of InSe nanosheets under various power intensities in 0.2 m KOH.

incident sunlight. The photocurrent density at 120 mW cm−2 is 378 nA cm−2 which is two times higher than that at 40 mW cm−2. Apart from this, the photocurrent density can be fitted with P (red dots and line), where P represents the irradiance power intensity and the slope of the fitted curve can be utilized to assess the identical trapping and recombination processes of photocarriers. In order to gain further insight into the photoresponse performance of InSe photodetector, the value of responsivity (R) is obtained from the following equation: R = I/Jlight, where I is the photocurrent density (mA cm−2) and Jlight is the irradiance intensity. The relationship between the photoelectric responsivity and irradiance power intensity (blue dots and line) is illustrated in Figure 2d. It is found that the photoelectric responsivity of InSe electrode varies from 3.3 to 4.9 µA W−1 and is in agreement with the recently reported values of advanced photodetectors (Table S2, Supporting Information). The excellent photocurrent density as well as preferable responsivity of InSe nanosheets guarantees a promising advantage for its application in photodetector. To the best of our knowledge, the stability of photodetector is a critical factor and it should be evaluated before proceeding with practical applications. Herein, both the cycle stability and the time stability of the as-fabricated InSe photodetector have been investigated in 0.2 m KOH electrolyte. Figure 3a presents the LSV curve of InSe electrode after 50 cycles showing undetectable deviation with the initial curve. Meanwhile, the longtime “on–off” switching behavior of InSe is also explored and is given in Figure 3b. It is noted that the photocurrent density can be effectively switched by controlling the on and off process of the light source, and the photocurrent density shows


negligible decay after successive switching operation for 400 s in 0.2 m KOH. In addition, long-time stability measurements of InSe photodetector was carried out in 0.2 m KOH under 1.0 V bias potential (Figure 3c). After 24 h, a slight decrement of photocurrent density from 320.7 to 281.6 nA cm−2 (88% of the initial value) was detected. It confirmed that the as-prepared InSe photodetector has good stability. The obtained superior cycle stability and time stability suggest that the fabricated InSe photodetector is rather stable for optical applications. We have also studied the photoresponse behavior of InSe photodetector with and without bias potential. A typical threeelectrode cell configured of KOH electrolyte with different OH− concentration (C[OH−]) is used to probe the current variations. Figure 4a presents the 2D plot of photocurrent density (Ip) map as a function of applied bias potential and C[OH−]. It is found that Ip of InSe photodetector increases along with both bias potential and C[OH−]. To be more specific, the Ip of InSe photodetector in 0.05 m KOH steadily increases from 0.03 to 0.08 nA cm−2 when improving the bias potential from 0 to 1.0 V. At 0.2 m KOH, Ip shows much stronger dependence on bias potential, which increases from 16.6 nA cm−2 at 0 V to 325.5 nA cm−2 at 1.0 V with a large span value of 308.9 nA cm−2. Thanks to the conception of self-powered photodetector, it can be operated by capturing energy directly from the environment, and InSe preserves potential opportunities as self-powering devices due to its unique optoelectrical performance. Particularly, the value of Ip changes from 0.03 to 15.6 nA cm−2 at a bias potential of 0 V along with the concentration of KOH from 0.05 to 0.2 m, implying that the concentration of electrolyte has a great influence on the performance of InSe photodetector.

1705237 (4 of 8)


UN CO RR EC TE D

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

www.afm-journal.de

PR OO F


Figure 3. a) Cycle stability test of InSe nanosheet based photodetector in 0.2 m KOH. b) Long-time photocurrent response measurements of InSe photodetector under 1.0 V bias potential. c) Long-time stability measurements of InSe photodetector in 0.2 m KOH under 1.0 V bias potential.

Additionally, with the increase of C[OH−] from 0.05 to 0.2 m, Ip of InSe photodetector increases from 0.08 to 315 nA cm−2 at a bias potential of 1.0 V. In our experiments, the photocurrent density of InSe nanosheets can be greatly increased along with external bias. In general, the enhancement of photocurrent occurs because the application of positive potentials across the photoelectrode establishes a potential gradient within InSe nanosheets, promoting the separates holes and electrons and decreases their rate of recombination. As a result, the photocurrent increases with the potential until most photogenerated electrons either react at the surface of the photoelectrode with an electron scavenger or transfer to the cathode under the influence of the electric field,[30] thereby effectively improving the optical current density of the InSe photodetector. It has been reported that Se vacancies form in the crystal during the growth of InSe. Thus, the positive surface of InSe absorbs negative OH− ions, isolating from the electrolyte. In this regard, we take


advantages of KOH as electrolyte for improving the stability of as-prepared InSe nanosheets and modulate the photoresponse performances of InSe photodetector. The accompanying photoresponse performance can be interpreted so that bias potential can promote the separation ratio of photogenerated holes and electrons, and increasing the concentration of electrolyte contributes to more effective PEC reaction and higher photocurrent density. In order to make the above explanations more convincing, we have studied the present experimental results under bias potential at 0.4, 0.5, 0.6, 0.7, and 0.8 V as controlled groups to explore the relationship between Ip and C[OH−] via the fitted exponential asymptotic function

I p = I p0 + A *exp(C [OH− ]/τ )(1) where Ip and C[OH−] are the values of photocurrent density and concentration of OH− at a given condition. As a result, we

1705237 (5 of 8)


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 Q5 55 56 57 58 59

UN CO RR EC TE D

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

www.afm-journal.de

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

PR OO F


Figure 4. a) Photocurrent density map as a function of both applied potential and concentration of KOH. b) Photocurrent density as a function of the concentration of electrolyte (0.05, 0.1, and 0.2 m KOH) under bias potential of 0.4, 0.5, 0.6, 0.7, and 0.8 V. c) Photocurrent tests in neutral Na2SO4 electrolyte (0.5 m) and alkaline KOH electrolyte (0.2, 0.1, and 0.05 m). d) Schematic illustration of the proposed InSe nanosheet-based photodetector.

extract each value of Ip0, A, and τ from the above equation, while the growth factor of Ip can be represented by 1/τ. As shown in Figure 4b, the photocurrent density demonstrates drastic improvement when increasing the KOH concentration from 0.05 to 0.2 m. Meanwhile, the growth factor is 2.3 × 10−2 for 0.4 V and 2 × 10−2 for 0.8 V, which is in accordance with the above result which indicates that adjusting the concentration of electrolyte and external bias potential is an effective way to realize the optimal performance of the as-fabricated InSe photodetector. Furthermore, we have investigated the photoresponse performance of InSe photodetector under 1.0 V potential in various electrolytes (0.5 m Na2SO4, and 0.05, 0.1, and 0.2 m KOH). The current density can be periodically switched “on” and “off” with the time interval of 10 s (Figure 4c). Besides that, the response time (tres.) of InSe photodetector in 0.5 m Na2SO4 and KOH with various concentrations is derived from the time interval of the rise of photocurrent from 10% to 90%, while response constant (τres.) can be calculated with the equation I(t) = I + A*[exp(−t/τ)].[31] The related parameters are summarized in Figure S5 (Supporting Information), in which the fastest response time (tres. = 5 s) is achieved for 0.05 m KOH, while a high responsivity (3.3 µA W−1) is attained for 0.2 m KOH. In order to give a better understanding on the photoresponse mechanism of PEC-type photodetector, a concise schematic illustration is presented in Figure 4d. According to the previous report, few-layer InSe is an n-type semiconductor.[22] With the assistance of KOH electrolyte, the photogenerated electrons could be transported to the electrode more efficiently,[32] thereby prohibiting oxidation procedure at some degree which enables InSe photodetector to sustain both preferable photoresponse activity and environmental robustness. The further


optimization of the photoresponse performances of InSe photodetector can be achieved by altering the concentration of electrolyte to obtain the optimal equilibrium between photocurrent density and charge transfer speed.[33] The results suggest that InSe nanosheets have huge potential toward optoelectronic applications and further adjustment of the external condition might significantly improve the photocurrent density as well as the aggregative photoresponse of PEC-type photodetector.

3. Conclusions

In summary, 2D InSe nanosheets synthesized by an efficient liquid exfoliation method have been successfully utilized in the fabrication of PEC-type photodetector. The as-fabricated photo detector exhibits both satisfactory photocurrent density and responsivity under the irradiation of sunlight. Further experimental results demonstrate that InSe photodetector displays enhanced photoresponse performance and long-term stability under 0.2 m KOH. Meanwhile, we have described the photo response performance relationship between the incident light and concentration of electrolyte. The present work provides fundamental knowledge of the photoresponse performance related to InSe nanosheet based photodetectors. The inherent structure and optoelectronic ability of the InSe ensure its great promise as an emerging building block for optoelectronic devices.

Supporting Information Supporting Information is available from the Wiley Online Library or from the author.

1705237 (6 of 8)



Acknowledgements Z.L., Z.G., and H.Q. contributed equally to this work. The authors acknowledge the financial support from the Science and Technology Development Fund (Grant No. 007/2017/A1), Macao SAR, China, the National Natural Science Foundation of China (Grant Nos. 61435010, 61575089, and 11504312), Science and Technology Innovation Commission of Shenzhen (Grant No. KQTD2015032416270385), Science and Technology Planning Project of Guangdong Province (Grant No. 2016B050501005), the Educational Commission of Guangdong Province (Grant No. 2016KCXTD006), the Provincial Natural Science Foundation of Hunan (Grant No. 2016JJ2132), and the Program for Changjiang Scholars and Innovative Research Team in University (IRT_17R91). J.S. Ponraj kindly acknowledges the support and funding from DST-INSPIRE Faculty Scheme, Government of India.

Conflict of Interest The authors declare no conflict of interest.

Keywords InSe, photodetection, photoelectrochemical detectors, self-powered devices Received: September 12, 2017 Revised: October 21, 2017 Published online:

Z. Hussain, A. Bansil, Z.-X. Shen, Nat. Nanotechnol. 2014, 9, 111; b) R. Lv, J. A. Robinson, R. E. Schaak, D. Sun, Y. Sun, T. E. Mallouk, M. Terrones, Acc. Chem. Res. 2015, 48, 56. [11] a) Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman, M. S. Strano, Nat. Nanotechnol. 2012, 7, 699; b) L. Tao, E. Cinquanta, D. Chiappe, C. Grazianetti, M. Fanciulli, M. Dubey, A. Molle, D. Akinwande, Nat. Nanotechnol. 2015, 10, 227. [12] a) M. Brotons-Gisbert, D. Andres-Penares, J. Suh, F. Hidalgo, R. Abargues, P. J. Rodriguez-Canto, A. Segura, A. Cros, G. Tobias, E. Canadell, P. Ordejon, J. Wu, J. P. Martinez-Pastor, J. F. Sanchez-Royo, Nano Lett. 2016, 16, 3221; b) D. A. Bandurin, A. V. Tyurnina, G. L. Yu, A. Mishchenko, V. Zolyomi, S. V. Morozov, R. K. Kumar, R. V. Gorbachev, Z. R. Kudrynskyi, S. Pezzini, Z. D. Kovalyuk, U. Zeitler, K. S. Novoselov, A. Patane, L. Eaves, I. V. Grigorieva, V. I. Fal’ko, A. K. Geim, Y. Cao, Nat. Nanotechnol. 2017, 12, 223; c) Z. Yang, W. Jie, C. H. Mak, S. Lin, H. Lin, X. Yang, F. Yan, S. P. Lau, J. Hao, ACS Nano 2017, 11, 4225; d) G. W. Mudd, S. A. Svatek, T. Ren, A. Patane, O. Makarovsky, L. Eaves, P. H. Beton, Z. D. Kovalyuk, G. V. Lashkarev, Z. R. Kudrynskyi, A. I. Dmitriev, Adv. Mater. 2013, 25, 5714. [13] N. Kuroda, Y. Nishina, Solid State Commun. 1980, 34, 481. [14] Y. Yoon, K. Ganapathi, S. Salahuddin, Nano Lett. 2011, 11, 3768. [15] A. H. Kahn, Phys. Rev. 1955, 97, 1647. [16] D. J. Perello, S. H. Chae, S. Song, Y. H. Lee, Nat. Commun. 2015, 6, 7809. [17] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, A. Kis, Nat. Nanotechnol. 2011, 6, 147. [18] H. Fang, S. Chuang, T. C. Chang, K. Takei, T. Takahashi, A. Javey, Nano Lett. 2012, 12, 3788. [19] D. Ovchinnikov, A. Allain, Y. S. Huang, D. Dumcenco, A. Kis, ACS Nano 2014, 8, 8174. [20] S. Lei, L. Ge, S. Najmaei, A. George, R. Kappera, J. Lou, M. Chhowalla, H. Yamaguchi, G. Gupta, R. Vajtai, A. D. Mohite, P. M. Ajayan, ACS Nano 2014, 8, 1263. [21] S. Lei, F. Wen, L. Ge, S. Najmaei, A. George, Y. Gong, W. Gao, Z. Jin, B. Li, J. Lou, J. Kono, R. Vajtai, P. Ajayan, N. J. Halas, Nano Lett. 2015, 15, 3048. [22] S. R. Tamalampudi, Y.-Y. Lu, R. U. Kumar, R. Sankar, C.-D. Liao, K. B. Moorthy, C.-H. Cheng, F. C. Chou, Y.-T. Chen, Nano Lett. 2014, 14, 2800. [23] B. Chitara, L. Panchakarla, S. Krupanidhi, C. Rao, Adv. Mater. 2011, 23, 5419. [24] P. Hu, Z. Wen, L. Wang, P. Tan, K. Xiao, ACS Nano 2012, 6, 5988. [25] P. Hu, L. Wang, M. Yoon, J. Zhang, W. Feng, X. Wang, Z. Wen, J. C. Idrobo, Y. Miyamoto, D. B. Geohegan, Nano Lett. 2013, 13, 1649. [26] a) B. Zhang, L. Zhang, W. Deng, L. Jin, F. Chun, H. Pan, B. Gu, H. Zhang, Z. Lv, W. Yang, Z. L. Wang, ACS Nano 2017, 11, 7440; b) S. L. Zhang, Y.-C. Lai, X. He, R. Liu, Y. Zi, Z. L. Wang, Adv. Funct. Mater. 2017, 27, 1606695; c) C. Dagdeviren, Z. Li, Z. L. Wang, Annu. Rev. Biomed. Eng. 2017, 19, 85; d) X. Chen, Y. Wu, A. Yu, L. Xu, L. Zheng, Y. Liu, H. Li, Z. L. Wang, Nano Energy 2017, 38, 91; e) A. Chandrasekhar, N. R. Alluri, M. S. P. Sudhakaran, Y. S. Mok, S.-J. Kim, Nanoscale 2017, 9, 9818. [27] L. Peng, L. Hu, X. Fang, Adv. Funct. Mater. 2014, 24, 2591. [28] J. J. Wang, F. F. Cao, L. Jiang, Y. G. Guo, W. P. Hu, L. J. Wan, J. Am. Chem. Soc. 2009, 131, 15602. [29] Z. Sun, H. Xie, S. Tang, X.-F. Yu, Z. Guo, J. Shao, H. Zhang, H. Huang, H. Wang, P. K. Chu, Angew. Chem., Int. Ed. 2015, 54, 11526. [30] R. J. Candal, W. A. Zeltner, M. A. Anderson, Environ. Sci. Technol. 2000, 34, 3443. [31] B. Chitara, S. Krupanidhi, C. Rao, Appl. Phys. Lett. 2011, 99, 113114. [32] X. Ren, Z. Li, Z. Huang, D. Sang, H. Qiao, X. Qi, J. Li, J. Zhong, H. Zhang, Adv. Funct. Mater. 2017, 27. [33] W. Liu, X. Yan, J. Lang, Q. Xue, J. Mater. Chem. 2012, 22, 8853.

PR OO F

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

UN CO RR EC TE D

Q2

www.afm-journal.de

[1] a) A. Rogalski, Prog. Quantum Electron. 2003, 27, 59; b) J. Clark, G. Lanzani, Nat. Photonics 2010, 4, 438; c) C.-H. Liu, Y.-C. Chang, T. B. Norris, Z. Zhong, Nat. Nanotechnol. 2014, 9, 273. [2] R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Stauber, N. M. R. Peres, A. K. Geim, Science 2008, 320, 1308. [3] a) J. Park, Y. H. Ahn, C. Ruiz-Vargas, Nano Lett. 2009, 9, 1742; b) F. Xia, T. Mueller, R. Golizadeh-Mojarad, M. Freitag, Y.-M. Lin, J. Tsang, V. Perebeinos, P. Avouris, Nano Lett. 2009, 9, 1039; c) X. T. Gan, R. J. Shiue, Y. D. Gao, I. Meric, T. F. Heinz, K. Shepard, J. Hone, S. Assefa, D. Englund, Nat. Photonics 2013, 7, 883; d) A. Pospischil, M. Humer, M. M. Furchi, D. Bachmann, R. Guider, T. Fromherz, T. Mueller, Nat. Photonics 2013, 7, 892; e) F. Xia, T. Mueller, Y.-m. Lin, A. Valdes-Garcia, P. Avouris, Nat. Nanotechnol. 2009, 4, 839; f) T. Mueller, F. Xia, P. Avouris, Nat. Photonics 2010, 4, 297. [4] X. Wang, Z. Cheng, K. Xu, H. K. Tsang, J.-B. Xu, Nat. Photonics 2013, 7, 888. [5] Y. Z. Zhang, T. Liu, B. Meng, X. Li, G. Liang, X. Hu, Q. J. Wang, Nat. Commun. 2013, 4, 1811. [6] B. R. Matis, J. S. Burgess, F. A. Bulat, A. L. Friedman, B. H. Houston, J. W. Baldwin, ACS Nano 2012, 6, 17. [7] L. Li, Y. Yu, G. J. Ye, Q. Ge, X. Ou, H. Wu, D. Feng, X. H. Chen, Y. Zhang, Nat. Nanotechnol. 2014, 9, 372. [8] a) A. Favron, E. Gaufres, F. Fossard, A.-L. Phaneuf-L’Heureux, N. Y. W. Tang, P. L. Levesque, A. Loiseau, R. Leonelli, S. Francoeur, R. Martel, Nat. Mater. 2015, 14, 826; b) Q. Zhou, Q. Chen, Y. Tong, J. Wang, Angew. Chem., Int. Ed. Engl. 2016, 55, 11437; c) J. D. Wood, S. A. Wells, D. Jariwala, K. S. Chen, E. Cho, V. K. Sangwan, X. Liu, L. J. Lauhon, T. J. Marks, M. C. Hersam, Nano Lett. 2014, 14, 6964. [9] D. Kufer, I. Nikitskiy, T. Lasanta, G. Navickaite, F. H. L. Koppens, G. Konstantatos, Adv. Mater. 2015, 27, 176. [10] a) Y. Zhang, T.-R. Chang, B. Zhou, Y.-T. Cui, H. Yan, Z. Liu, F. Schmitt, J. Lee, R. Moore, Y. Chen, H. Lin, H.-T. Jeng, S.-K. Mo,


1705237 (7 of 8)


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 Q6 58 59

Query Q1: Please provide TOC keyword. Q2: As per style, the ‘Authors contribution’ statement has been moved to the Acknowledgment section. Please check. Q3: Please provide the highest academic title (either Dr. or Prof.) for all authors, where applicable. Q4: Please provide the city name and postal code in affiliation 1. Q5: Please check whether all equations have been correctly typeset. Q6: Please provide the page number in ref. (32).

Editorial Office: Wiley-VCH Verlag Boschstraße 12, 69469 Weinheim Germany Tel.: (+49) 6201 606 531 Fax: (+49) 6201 606 500 Email: [email protected] http://www.afm-journal.com

Reprint Order Form 2018 Short DOI: adfm.

Delivery address / Invoice address: Name of recipient, University, Institute, Street name and Street number, Postal Code, Country

Please send me and bill me for Reprints via

_________________________________________________

airmail (+ 25 Euro) surface mail

_________________________________________________

Please send me and bill me for a:

_________________________________________________

Issue copies (25 Euro)

_________________________________________________

high-resolution PDF file (330 Euro).

_________________________________________________

My Email address:

_________________________________________________

__________________________________________________________

__________________________________________________

Please note: It is not permitted to present the PDF file on the internet or on company homepages.

Information regarding VAT Please note that from German sales tax point of view, the charge for Reprints, Issues or Posters is considered as “supply of goods” and therefore, in general, such delivery is a subject to German sales tax. However, this regulation has no impact on customers located outside of the European Union. Deliveries to customers outside the Community are automatically tax-exempt. Deliveries within the Community to institutional customers outside of Germany are exempted from the German tax (VAT) only if the customer provides the supplier with his/her VAT number. The VAT number (value added tax identification number) is a tax registration number used in the countries of the European Union to identify corporate entities doing business there. It starts with a country code (e.g. FR for France, GB for Great Britain) and follows by numbers.

Date and Signature: ___________________________ Credit Card Payment (optional)

-You will receive an invoice.

VISA, MasterCard, AMERICAN EXPRESS Please use the Credit Card Token Generator located at the website below to create a token for secure payment. The token will be used instead of your credit card number. Credit Card Token Generator: https://www.wiley-vch.de/editorial_production/index.php Please transfer your token number to the space below.

VAT no.: ____________________________________________ Credit Card Token Number

(Institutes / companies in EU countries only)

Purchase Order No.: _________________________________ Price list for reprints (The prices include mailing and handling charges. All Wiley-VCH prices are exclusive of VAT) No. of pages

Price (in Euro) for orders of 150 copies 200 copies

50 copies

100 copies

1-4 5-8

345 490

395 573

425 608

445 636

548 784

752 1077

9-12

640

739

786

824

1016

1396

13-16

780

900

958

1004

1237

1701

17-20

930

1070

1138

1196

1489

2022

for every additional 4 pages

147

169

175

188

Wiley-VCH Verlag GmbH & Co. KGaA; Location of the Company: Weinheim, Germany; Trade Register: Mannheim, HRB 432833, Chairman of the Board: Mark Allin General Partner: John Wiley & Sons GmbH, Location: Weinheim, Germany Trade Register Mannheim, HRB 432296, Managing Directors: Sabine Steinbach, Dr. Guido F. Herrmann

300 copies

231

500 copies

315