Two-Dimensional CH3NH3PbI3 Perovskite Nanosheets for Ultrafast

Subscriber access provided by Fudan University

Article

Two-Dimensional CH3NH3PbI3 Perovskite Nanosheets for Ultrafast Pulsed Fiber Lasers Pengfei Li, Yao Chen, Tieshan Yang, Ziyu Wang, Han Lin, Yanhua Xu, Lei Li, Haoran Mu, Bannur Nanjunda Shivananju, Yupeng Zhang, Qinglin Zhang, Anlian Pan, Shaojuan Li, Ding Yuan Tang, Baohua Jia, Han Zhang, and Qiaoliang Bao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b01709 • Publication Date (Web): 20 Mar 2017 Downloaded from http://pubs.acs.org on March 21, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22

ACS Applied Materials & Interfaces

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 ACS Paragon Plus Environment


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

Page 2 of 22

Two-Dimensional CH3NH3PbI3 Perovskite Nanosheets for Ultrafast Pulsed Fiber Lasers Pengfei Li1,§, Yao Chen1,§, Tieshan Yang6, Ziyu Wang3, Han Lin6, Yanhua Xu2, Lei Li4, Haoran Mu1, Bannur Nanjunda Shivananju1, Yupeng Zhang3, Qinglin Zhang5, Anlian Pan5, Shaojuan Li1, Dingyuan Tang4, Baohua Jia6, Han Zhang2, Qiaoliang Bao1,3* 1

Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory

for Carbon-Based Functional Materials and Devices, and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, China. 2

SZU-NUS Collaborative Innovation Centre for Optoelectronic Science &

Technology, and Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518000, China. 3

Department of Materials Science and Engineering, Monash University, Clayton,

Victoria 3800, Australia. 4

Jiangsu Key Laboratory of Advanced Laser Materials and Devices, School of

Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China 5

College of Physics and Microelectronics Science, Key Laboratory for Micro-Nano

Physics and Technology of Hunan Province, Hunan University, Changsha, 410082, China 6

Centre for Micro-Photonics, Faculty of Science Engineering and Technology,

Swinburne University of Technology, Hawthorn, VIC 3122, Australia

KEYWORDS:

2D

perovskite,

Non-linear

property,

Mode-locking, Ultrafast pulse fiber lasers.

1

ACS Paragon Plus Environment

Saturable

absorbers,

Page 3 of 22

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


ABSTRACT: Even though the nonlinear optical effects of solution processed organic-inorganic perovskite films have been studied, the nonlinear optical properties in two-dimensional (2D) perovskites especially their applications for ultrafast photonics are largely unexplored. In comparison to bulk perovskite films, 2D perovskite nanosheets with small thickness of a few unit cells are more suitable for investigating the intrinsic nonlinear optical properties because bulk recombination of photo-carriers and the nonlinear scattering are relatively small. In this research, we systematically investigated the nonlinear optical properties of 2D perovskite nanosheets derived from a combined solution process and vapour phase conversion method. It was found that 2D perovskite nanosheets have stronger saturable absorption properties with large modulation depth and very low saturation intensity compared with bulk perovskite films. Using an all dry transfer method, we constructed a new type of saturable absorber device based on single piece 2D perovskite nanosheet. Stable soliton state mode-locking was achieved and ultrafast picosecond pulses were generated at 1064 nm. This work is likely to pave the way for ultrafast photonic and optoelectronic applications based on 2D perovskites.

2



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

1. INTRODUCTION The hybrid organic–inorganic methyl ammonium lead halide perovskites described by CH3NH3PbX3 (X = I, Br, Cl) have emerged as one of the most intriguing materials for solar energy harvesting due to record high power conversion efficiency which is comparable to that of silicon1, 2, 3. This type of materials have shown excellent optical and electrical properties such as wavelength tunability4, long photocarrier lifetimes5, long carrier diffusion length6, high fluorescence yield7 and ambipolar transport8, many new optoelectronic applications such as light-emitting diodes9, lasers10, waveguide11, field-effect transistors12 and photo-detectors13. In order to fit those applications, the organic-inorganic perovskites in the form from solution processed films to single crystals as well as two-dimensional (2D) nanosheets have been intensively investigated. In particular, while the thickness of bulk perovskites is reduced to a few unit cells, the induced electronic structure change as well as optical tuneability may be observed like other 2D materials, which host the promise for new optoelectronic applications. Many interesting photonic and optoelectronic applications have been demonstrated in low-dimensional perovskites. Owning to size-controlled optical properties as that in conventional quantum dots (QDs), light-emitting prototype devices with a wide range of colours were fabricated using green-emissive colloidal CH3NH3PbBr3 QDs, offering a possible means of improving the colour performance of display technology14, 15. Benefiting from ultra-long carrier diffusion length, one dimensional perovskite wires shown excellent waveguiding properties in terms long prorogation length and small optical loss16. Also because of large exciton binding energy and long diffusion length, perovskite platelets can function as high quality planar whispering gallery mode cavity and provide efficient optical feedback for low threshold optically pumped lasing at room temperature17. Dou and co-workers18 observed color tuning of the photoluminescence (PL) spectrum by changing the sheet thickness as well as chemical composition in 2D perovskites ((C4H9NH3)2PbBr4) with a few unit-cell thickness. Liu et al.19 produced even thinner 2D perovskite (CH3NH3PbX3) 3


Page 4 of 22

Page 5 of 22

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


nanosheets as well as heterostructures with one unit cell thickness of 1.3 nm and found that this material has excellent photoconductive property for light detection. Aside from these optical and photonic applications, the nonlinear optical properties of these exotic materials are largely unexplored though the associated applications in ultrafast photonics are intriguing. Recently, Kalanoor et al.20 reported third-order optical nonlinearities in thin films of methylammonium lead iodide and attribute the highly nonlinear intensity-dependent refractive index to changes in the free-carrier concentration and the Pauli blocking effect. Zhang et al.21 also found organic-inorganic halide perovskites process a large nonlinear refractive index which is several orders of magnitude larger than that of silicon. They further demonstrated a Q-switched nano-second pulsed laser based with a perovskite pulse modulator which is benefit from its saturable absorption effect. These progresses suggest the potential of perovskites to be applied in nonlinear optoelectronic and ultrafast photonic device. Compared with bulk perovskite films, which probably have complex optical processes, 2D perovskite nanosheets with small thickness of a few unit cells are more suitable for investigating the intrinsic nonlinear optical properties because bulk recombination of photo-carriers and the nonlinear scattering are relatively small. In this work, we systematically investigated the nonlinear optical properties of 2D perovskite nanosheets. It was found that 2D perovskite nanosheets have stronger saturable absorption with large modulation depth and very low saturation intensity compared with bulk perovskite films. Using an all dry transfer method, we constructed pulsed fiber laser based on single piece 2D perovskite nanosheet. More importantly, stable mode-locking state was obtained and ultrafast picosecond pulses can be generated. This work is likely to trigger more ultrafast photonic and optoelectronic applications based on 2D perovskites.

2. EXPERIMENTAL 2.1. Material synthesis and characterization. The 2D CH3NH3PbI3 nanosheets were fabricated by a two-step method. Firstly, PbI2 nanosheets as seeds were prepared by dropping its aqueous solution on to the substrate. The aqueous solution was 4



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

prepared by dissolving PbI2 (1 mg, Sigma-Aldrich) powder in distilled water (1 mL) and heated up to 90 °C for 1 hour. The second step was using CVD method to convert PbI2 in to CH3NH3PbI3 nanosheets. The CH3NH3I powders were placed at the center of the CVD furnace while the substrates with PbI2 were placed downstream of the quartz tube. Then the central heating zone was increased up to 130 °C under low-pressure conditions (about 45 Torr) and maintained for 10 min. During the whole vapor conversion process, Argon (Ar) gas was blowed into the chamber as carrier gas with the flow rate of 30 sccm. Then, the furnace was cooled down to room temperature at a rate of 5 °C min-1. The morphology of the perovskite nanosheets was examined by using optical microscopy (Leica, DM2700 M). The crystal structure was investigated by a XRD equipment (PANalytical, Empyrean). The microstructure of perovskite nanosheets were characterized by a TEM microscope (JEOL JEM-2100F, 200 kV). The photoluminescence (PL) measurements were performed on a micro-Raman system (HORIBA JOBIN-YVON, LABRAM HR800) with a 633 nm laser. 2.2. Z-Scan setup. The nonlinear optical properties of the CH3NH3PbI3 nanosheets were performed by a Z-scan setup (as shown in Figure S1) equipped with a femtosecond laser (Coherent, Chameleon) which has a repetition rate of 80 MHz and pulse duration of 140 fs at 800 nm and 1030 nm. The CH3NH3PbI3 perovskite samples was grown on the quartz plate for Z-scan measurements. In our Z-scan setup, an optical attenuator was employed to vary the input laser energy continuously. The laser beam was expanded by a beam expansion system composed of a -25 mm concave lens and a 150 mm convex lens to fill the aperture of the objective lens. The beam, with a beam waist of ∼1.6 μm (Rayleigh range: 20 μm), was focused onto the CH3NH3PbI3 nanosheets, which were mounted on an automated one-dimensional scanning stage. During the measurements, the scanning of the stage enables the movement of the sample in and out of the focal region. In order to accurately focus the beam on the CH3NH3PbI3 nanosheets, an objective lens (10×, NA 0.25) combined with a CCD camera was used to direct the transmitted laser beam. 2.3. Preparation of saturable absorber device. The 2D perovskite nanosheets are 5


Page 6 of 22

Page 7 of 22

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


transferred onto the fiber end-facet by all-dry transfer method (see Figure S2). Firstly, the perovskite nanosheets were synthesized on the PDMS thick film, which is similar to the synthesis on SiO2 wafer19. Following a three-dimensional positioning stage was used to transfer the single perovskite nanosheet onto the fiber end-facet under the optical microscope. The fiber ferrule with single piece of perovskite nanosheet covering on the core area can be directly used as saturable absorber and incorporated into fiber laser cavity for mode-locking experiments. 2.4. Fiber laser cavity. An Ytterbium-doped fiber (THORLABS, Yb1200-4/125, 75 cm) worked as gain medium was reversely pumped by a laser diode (975 LD, 975 nm) through a wavelength division multiplexer (WDM, 980 nm/1060 nm). The direction of light propagation was ensured by a polarization-independent isolator (ISO). The cavity polarization state and intra-cavity birefringence were adjusted by polarization controller (PC). The 10% output was controlled by a10 dB port of a coupler. The total length of cavity is about 50.2 m. The output time-domain profile characteristics and the frequency-domain properties were simultaneously tested by using optical spectrum analyzer (Yokogawa, AQ6370C), the radio frequency (RF) spectrum analysis function (bandwidth: 3 GHz) integrated with oscilloscope (Tektronix, MDO3054, 500 MHz) and the optical power meter (EXFO, PM-1623).

3. RESULTS AND DISCUSSION 3.1. Material Characterizations. A two-step method was developed to prepare 2D hybrid organic-inorganic perovskite nanosheets, as schematically illustrated in Figure S3 and elaborated in our previous work19,22. Specifically, the first step was to nucleate 2D PbI2 nanosheets by casting saturated PbI2 aqueous solution and then heat the substrate at an elevated temperature (~100°C) (Figure S3a). Subsequently, the CH3NH3I molecules were intercalated into the interval sites of PbI2 octahedron layers by using chemical vapor deposition (CVD) method (Figure S3b). The final resulting CH3NH3PbI3 perovskite still maintained the 2D lamellar structure, indicating that the in-plane growth rate is much higher than that of the out-of-plane along the z-axis, due to different surface energies. This means, generally the lower surface energy is 6



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

Figure 1. Material characterizations of 2D CH3NH3PbI3 nanosheets. (a) AFM image of single PbI2 nanosheet on SiO2 substrate. The scale bar is 10 μm. (b) AFM image of single CH3NH3PbI3 perovskite nanosheet on SiO2 substrate. The scale bar is 10 μm. (c) SEM image of the CH3NH3PbI3 perovskite nanosheet. The scale bar is 10 μm. Inset: Optical microscope image of the CH3NH3PbI3 nanosheet. The scale bar is 10 μm. (d) XRD patterns of PbI2 and CH3NH3PbI3 nanosheets. (e) TEM image of a CH3NH3PbI3 perovskite nanosheet. The scale bar is 1 μm. (f) HRTEM image of CH3NH3PbI3 perovskite nanosheet. Inset: SEAD pattern. The scale bar is 4 nm and 4 nm-1 (inset), respectively. expected along the in-plane direction which leads to a faster growth rate23. Figure 1a, b shows the atomic force microscope (AFM) images of the nanosheet before (pure PbI2) and after converting into CH3NH3PbI3. The thickness and root mean square (RMS) roughness of hexagonal PbI2 crystal are about 12 nm and 0.63 nm, while the thickness of the resulted CH3NH3PbI3 crystal is about 25 nm with RMS roughness increased to 3.78 nm, which agrees with the thickness change in previous report (i.e., the thickness of CH3NH3PbI3 is about two times that of PbI2)24. Figure 1c shows the scanning electron microscope (SEM) image of the CH3NH3PbI3 nanosheet, from which we can clearly see the perfect hexagonal shape and clearn surface of 2D 7


Page 8 of 22

Page 9 of 22

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


Figure 2. (a) UV−Visible near-infrared absorption spectrum of the 2D CH3NH3PbI3 perovskite nanosheets. (b) The photoluminescence spectrum of the 2D CH3NH3PbI3 perovskite nanosheets. perovskite. The crystal structures of PbI2 and CH3NH3PbI3 nanosheets were investigated by X-ray diffraction (XRD), as shown in Figure 1d. The main XRD diffraction peaks of PbI2 are observed at 12.8°and 25.6°, which can be indexed to the (001) and (002) facets, respectively. For the converted CH3NH3PbI3 nanosheets, new diffraction peaks at 14.1° and 28.5° are observed, corresponding to the (110) and (220) facets of the organic-inorganic halide perovskite25. It is noteworthy that the diffraction peaks of PbI2 disappeared which indicates a complete conversion of PbI2 into perovskite crystals. Furthermore, the diffraction peaks of high index lattice planes indicates high crystalline quality. Transmission electron microscopy (TEM) was also performed on single CH3NH3PbI3 nanosheets to resolve its microstructure, as shown in Figure 1e, f. The high-resolution TEM image in Figure 1f reveals clear lattice fringes of (200) and (02̅2) facets, revealing a complete conversion of PbI2 into the CH3NH3PbI3 perovskite structure. The inset of Figure 1f shows the corresponding selected-area of electron diffraction. The single set of diffraction pattern suggests single crystal nature of the nanosheet. 3.2. Optical Properties. The optical absorption and luminescence spectra of the CH3NH3PbI3 nanosheets prepared on quartz substrate are shown in Figure 2. The 2D perovskite exhibits strong broadband absorption ranging from 400 to 800 nm (Figure 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 60

Page 10 of 22

2a), which is mainly caused by the interband optical transitions between energy levels in valence band and conduction band. A strong photoluminescence (PL) emission is observed at 760 nm (Figure 2b), which is in good agreement with the energy gap extracted from absorbance as well as previous reports26, 27. In order to investigate the nonlinear optical properties of 2D CH3NH3PbI3 nanosheets, open-aperture Z-scan experiments were performed at 800 nm and 1030 nm28. Figure 3a, b show representative Z-scan results of CH3NH3PbI3 sample measured at 800 nm. The curve in Figure 3a shows a typical saturable absorption response, i.e., with the approaching of the CH3NH3PbI3 sample to the focus point (Z=0), the normalized transmittance increases gradually, which indicates that with the increase of the incident intensity the absorption of CH3NH3PbI3 becomes saturated. Under the excitation of femto-second laser (800 nm), the energy of each photon (1.55 eV) is large enough to excite the electrons from valence band to conductive band in CH3NH3PbI3. When the electrons in valence band have been excited completely or all the available states in conduction band have been occupied, CH3NH3PbI3 nanosheets will not absorb any more photons, that is called saturated absorption. Unlike nonlinear scattering, the saturable absorption indeed is related to the inherent nonlinear optical absorption of CH3NH3PbI3, which can be concluded from the Z-scan results. The Z-scan method is a single beam excitation technique that is able to measure the nonlinear absorption coefficient (β) using the open aperture configuration. Both the signs and the values of the nonlinear coefficients can be determined by this method. In order to quantitatively evaluate the nonlinear optical properties of CH3NH3PbI3 perovskite, we fitted the Z-scan curves in Figure 3a using the following equation, 𝑞0

𝑇(𝑧) = 1 −

𝑧 2 𝑧0

(1)

2√2[1+( ) ]

In formula 1, 𝑞0 = 𝛽𝐼0 𝐿𝑒𝑓𝑓 , which can be obtained by fitting the nonlinear absorption data. 𝑇(𝑧) is the normalized transmittance, β is the nonlinear absorption coefficient, z is the position of sample with respect to the focus point, 𝑧0 is the diffraction length of the beam, 𝐼0 is the peak on-axis intensity at focus, 𝐿𝑒𝑓𝑓 = (1 − 𝑒 −𝛼𝐿 )/𝛼 is the effective length and L is the thickness of the sample. The average 9


Page 11 of 22

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


Figure 3. Nonlinear optical properties of CH3NH3PbI3 perovskite nanosheets. Z-scan profiles measured at (a) 800 nm and (c) 1030 nm. The normalized transmittance versus input peak intensity at (b) 800 nm and (d) 1030 nm. The insets in (b) show the energy diagrams of the linear absorption and saturable absorption. (e) Nonlinear absorption coefficient β as a function of nanosheet thickness. (f) Modulation depths of perovskite nanosheets with different thicknesses. value of 𝛽 is calculated to be about -1.934 × 103 cm GW-1 with the input pumping power of 5.55 GW cm-2. 10



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

Page 12 of 22

Figure 3b shows the normalized transmittance versus input peak intensity at 800 nm. Obviously, the transmittance increases as the incident light intensity getting larger, due to saturation of absorption. Like other 2D saturable absorbers4, 29, the absorption bleaching originates from Pauli blocking principle, that is a large amount of photogenerated carriers causing band filling, as illustrated by the inset of Figure 3b. The saturable absorption in perovskite can be analyzed by the formula:30 𝑇 = 1 − 𝛼𝑠 /(1 + 𝐼/𝐼𝑠𝑎𝑡 ) − 𝛼𝑛𝑠

(2)

where αns is the non-saturable component, αs is the modulation depth, Isat is the saturable intensity, and I is the incident light intensity. By fitting the experimental data in Figure 3b, the αs and the Is are calculated to be about 5.7% and 4.38 GW cm-2, respectively. We further investigated the nonlinear absorption property of CH3NH3PbI3 perovskite at 1030 nm (photon energy slightly smaller than the bandgap) and the experimental results are displayed in Figure 3c, d. Interestingly, saturable absorption is also observed (shown in Figure 3c) This might be associated with the optical transition and band filling of intermediate or defect states. By fitting the experimental data in Figure 3c according to formula 1, one can obtain the nonlinear absorption coefficient -1.894 × 103 cm GW-1 with the input pumping power of 5.55 GW cm-2. Similarly, by fitting the experimental data in Figure 3d according to formula 2, the modulation depth and the saturable intensity are calculated to be around 4.29% and 1.6 GW cm-2, respectively. We further measured the non-linear absorption properties of CH3NH3PbI3 perovskite nanosheets with different thicknesses using a femtosecond laser at 800 nm (Figure S4,5), and the results are summarized in Figure 3e, f. As shown in Figure 3e, the absolute value of absorption coefficient β decreases with the increased nanosheet thickness, which is mainly due to the energy defect state. For the thicker nanosheets, more defects in the crystal would induce more scattering and energy loss, which results in a lower β absolute value. The thin sample with a thickness of 45 nm has

11


Page 13 of 22

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


Table 1. Comparison of nonlinear optical properties. Sample

CH3NH3PbI3

Wavelength

Nonlinear

absorption

(nm)

coefficient: 𝜷 (cm GW ) -1

800

-1.934 × 10

1030

3

Saturable intensity

Reference

Isat (GW cm ) -2

4.38

Present work

-1.894 × 103

1.6

Present work

1060

-2.25 × 103

12.71

Rui Zhang et.al. 21

MoS2

1030

-9.17 ×10-2

114

Kangpeng Wang et.al.29

Graphene

1550

-6 ×10−8

> 0.6

Han Zhang et.al.31

nanosheets CH3NH3PbI3 nanosheets CH3NH3PbI3 bulk films

the largest nonlinear absorption coefficient. Figure 3f shows the dependence of modulation depth on the perovskite nanosheet thickness. It is found that CH3NH3PbI3 nanosheet with the thickness of 105 nm has the highest modulation depth of 22.2 %. For thicker perovskite nanosheet, more light power is required to saturate it due to stronger absorption, thus the saturable absorption intensity is higher and the modulation depth is larger. In Table 1, we have compared the nonlinear absorption coefficient of the CH3NH3PbI3 nanosheets with the one of bulk CH3NH3PbI3 films. Overall, the CH3NH3PbI3 nanosheets exhibit comparable response of the bulk one. The comparison of nonlinear optical parameters of the CH3NH3PbI3 perovskite nanosheets with other two-dimensional materials at different wavelengths are also depicted in Table 1. The absolute value of non-linear absorption coefficient (𝛽) of CH3NH3PbI3 perovskite nanosheets is five orders of magnitude lager than that of MoS2, and 11 orders of magnitude larger than that of graphene. The saturable intensity (Isat) of CH3NH3PbI3 perovskite nanosheets is 1.6 GW cm-2, which is about eight times smaller than that of bulk perovskite and seventy times smaller than that of MoS2. By taking the advantage of the large non-linear absorption coefficient and low saturable intensity, the CH3NH3PbI3 nanosheets may find important applications in passive mode-locking or Q-switching device for ultrafast pulsed lasers 3.3. Ultrafast Pulsed Fiber Lasers. 2D CH3NH3PbI3 perovskite nanosheets were transferred onto the fiber end-facet using an all-dry transfer process (see Figure S1). 12



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

Figure 4. Schematic diagram of the ring cavity of the mode-locked fiber laser. LD, 974 nm laser diode; YDF, ytterbium-doped fiber; WDM, wavelength division multiplexer; ISO, 1064 nm polarization-independent isolator; PC, polarization controller. Inset: optical image of perovskite nanosheet covering on the core area of fiber end-facet. The scale bar is 25 μm. The atomic structure of the 2D perovskite crystal is schematically shown in the right-bottom inset. The fiber with perovskite saturable absorber was incorporated into a ring laser cavity operating at 1064 nm, as schematically shown in Figure 4. Before inserting 2D perovskite sample into laser cavity, we always observed a continuous wave even we adjusted the polarization controllers (PCs) and increased the pump power from 0 to maximum value (591 mW). This can exclude the nonlinear polarization rotation effect in the laser cavity. Once we inserted the 2D perovskite saturable absorber into the laser cavity, we can successfully obtain mode-locked pulse generation at the threshold pump power of 319 mW, which is relatively high due to the large cavity length. Then we kept increasing the pump power up to 486 mW and adjusted the state of the PCs, the performance of stable mode-locked pulse laser can be obtained from 2D perovskite saturable absorber, as shown in Figure 5. The typical mode-locking optical spectrum is shown in Figure 5a. Its bandwidth of 13


Page 14 of 22

Page 15 of 22

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


Figure 5. The laser mode-locking characteristics using the 2D perovskite saturable absorber. (a) Optical spectra. (b) Output pulse train. (c) The individual pulse profile in time domain. (d) The RF spectral profile. Insert: the wideband RF spectrum. The pump power is 485 mW. (e) Output power as a function of pump power at 1064 nm. (f) Long-term stability of the mode-locked dissipative soliton. 3 dB is measured to be about 5.11 nm at the central wavelength of 1064 nm. Figure 5b displays a 4.08 MHz repetition rate of mode-locked pulse train, which matches well with the cavity length (50.2 m). The mode-locked laser pulse has a full width at half maximum (FWHM) of 931 ps (Figure 5c), indicating that the optical pulse is seriously chirped. As a result of normal dispersion, it is dissipative soliton rather than conventional soliton32. This large frequency chirping is also a feature of dissipative soliton, which is a natural result of the balance between the cavity loss, gain, nonlinearity and dispersion. The RF spectrum has been measured, as depicted in Figure 5d, and the signal-to-noise ratio (SNR) is over 53 dB. Moreover, the radio frequency spectrum in

the inset of Figure 5d reveals a wide band from 0 to 300

MHz. This indicates high quality of the output laser pulse that stably operates at a long range up to 50 µs. The relationship of the pump and output power is shown in Figure 5e. It is clearly 14



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

seen that the output power increases linearly from 2.24 mW to 15.71 mW, while the corresponding pump power increased from 93.6 mW to 591 mW, giving an energy efficiency of 2.7 %. The output power under mode-locking state is much smaller than that under continuous-wave state with the absorption property of 2D perovskite. It also be noticed that it remained unchanged mode-locking state even when the pump power achieved the maximum value of 591 mW, which indicates a high stability performance of the perovskite mode-locked laser. The output pulse has a FWHM of 931 ps and large SNR over 53 dB with a peak power of 4.14 W and pulse energy of 3.85 nJ. In order to check the long-term stability of the perovskite based mode-locked lasers, we have continuously monitored the output spectra for seven hours in an ambient environment with humidity under 40%, as shown in Figure 5f. We can clearly see that the mode-locked state is very stable as its 3-dB bandwidth only slightly changed from 5.11 nm to 4.99 nm. It is suggested that the good stability is associated with the high crystallinity of the prepared 2D perovskite nanosheets.

15


Page 16 of 22

Page 17 of 22

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


4. CONCLUSIONS In summary, the nonlinear optical properties of 2D CH3NH3PbI3 perovskite nanosheets were intensively investigated and the passively mode-locked fiber laser using perovskite-based saturable absorber was successfully demonstrated. It was found that 2D perovskite nanosheets have strong saturable absorption with large modulation depth and low saturable intensity as compared to the perovskite bulk film. In particular, the perovskite nanosheet with the thickness of 105 nm has the highest modulation depth of 22.2 % and lowest saturable intensity about 1.8 × 103 GW cm-2. The nonlinear absorption coefficient of perovskite nanosheets is much larger than that of conventional semiconductors. It is also demonstrated that 2D perovskite nanosheets can be used as effective saturable absorber for stable mode-locked pulse generation in ring fiber laser operating at 1064 nm. The output pulse has a FWHM of 931 ps and large SNR over 53 dB with a peak power of 4.14 W and pulse energy of 3.85 nJ. The 2D perovskite shows intriguing potential as a new type of nonlinear optical material and may find important applications in ultrafast photonics.

16



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

ACKNOWLEDGEMENTS We acknowledge the support from the Youth 973 program (2015CB932700), the National Key Research & Development Program (No. 2016YFA0201902), the National Natural Science Foundation of China (No. 51290273 and 91433107), Australian Research Council (DP140101501 and FT150100450), the Department of Science and Technology of Jiangsu Province (No. BK20150053), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and Collaborative Innovation Center of Suzhou Nano Science and Technology. S. Li acknowledges the support from the Natural Science Foundation of Jiangsu Province (No. BK20130328), China Postdoctoral Science Foundation (No.2014M551654) and Jiangsu Province Postdoctoral Science Foundation (No. 1301020A).

17


Page 18 of 22

Page 19 of 22

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


■ ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at… supporting images, Z-scan measurement, the details about all-dry transfer process, material preparation, Z-scan results of different thickness perovskite nanosheets and normalized transmittance (PDF)

■ AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]; [email protected] ORCID Qiaoliang Bao: 0000-0002-6971-789X Author Contributions §

Pengfei Li and Yao Chen: These authors contributed equally.

Notes The authors declare no competing ﬁnancial interest.

18



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

REFERENCES (1) Niu, L.; Zeng, Q. S.; Shi, J.; Cong, C. X.; Wu, C. Y.; Liu, F. C.; Zhou, J. D.; Fu, W.; Fu, Q. D.; Jin, C. H. Controlled Growth and Reliable Thickness-Dependent Properties of Organic-Inorganic Perovskite Platelet Crystal. Adv. Funct. Mater. 2016, 26 (29), 5263–5270. (2) Kitazawa, N.; Watanabe, Y.; Nakamura, Y. Optical Properties of CH 3NH3PbX3 (X= halogen) and Their Mixed-halide Crystals. J. Mater. Sci. 2002, 37 (17), 3585-3587. (3) Ball, J. M.; Lee, M. M.; Hey, A.; Snaith, H. J. Low-temperature Processed Meso-superstructured to Thin-film Perovskite Solar Cells. Energy. Environ. Sci. 2013, 6 (6), 1739-1743. (4) Xing, G.; Mathews, N.; Lim, S. S.; Yantara, N.; Liu, X.; Sabba, D.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C. Low-temperature Solution-processed Wavelength-tunable Perovskites for Lasing. Nat. Mater. 2014, 13 (5), 476-480. (5) de Quilettes, D. W.; Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S. Impact of Microstructure on Local Carrier Lifetime in Perovskite Solar Cells. Science 2015, 348 (6235), 683-686. (6) Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O. F.; Sargent, E. H.; Bakr, O. M. Low Trap-state Density and Long Carrier Diffusion in Organolead Trihalide Perovskite Single Crystals. Science 2015, 347 (6221), 519-522. (7) Tian, Y.; Peter, M.; Unger, E.; Abdellah, M.; Zheng, K.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Mechanistic Insights into Perovskite Photoluminescence Enhancement: Light Curing with Oxygen can Boost Yield Thousandfold. Phys. Chem. Chem. Phys. 2015, 17 (38), 24978-24987. (8) Giorgi, G.; Fujisawa, J.; Segawa, H.; Yamashita, K. Small Photocarrier Effective Masses Featuring Ambipolar Transport in Methylammonium Lead Iodide Perovskite: A Density Functional Analysis. J. Phys. Chem. Lett. 2013, 4 (24), 4213-4216. (9) Li, J.; Bade, S. G. R.; Shan, X.; Yu, Z. Single-Layer Light-Emitting Diodes Using Organometal Halide Perovskite/Poly(ethylene oxide) Composite Thin Films. Adv. Mater. 2015, 27 (35), 5196-5202. (10) Deschler, F.; Price, M.; Pathak, S.; Klintberg, L. E.; Jarausch, D. D.; Higler, R.; Hüttner, S.; Leijtens, T.; Stranks, S. D.; Snaith, H. J. High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 2014, 5 (8), 1421-1426. (11) Suárez, I.; Bisquert, J.; Mora-Seró, I.; Martínez-Pastor, J. P. Polymer/Perovskite Amplifying Waveguides for Active Hybrid Silicon Photonics. Adv. Mater. 2015, 27 (40), 6157–6162. (12) Chin, X. Y.; Cortecchia, D.; Yin, J.; Bruno, A.; Soci, C. Lead Iodide Perovskite Light-emitting Field-effect Transistor. Nat. Commun. 2015, 6, 7383. (13) Domanski, K.; Tress, W.; Moehl, T.; Saliba, M.; Nazeeruddin, M. K.; Grätzel, M. Working Principles of Perovskite Photodetectors: Analyzing the Interplay Between Photoconductivity and Voltage-Driven Energy-Level Alignment. Adv. Funct. Mater. 2015, 25 (44), 6936–6947. (14) Gonzalez-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Maximizing the Emissive Pproperties of CH3NH3PbBr3 Perovskite Nanoparticles. J. Mater. Chem. A. 2014, 3 (17), 9187-9193. (15) Zhang, F.; Zhong, H.; Chen, C.; Wu, X. G.; Hu, X.; Huang, H.; Han, J.; Zou, B.; Dong, Y. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS nano 2015, 9 (4), 4533–4542.

19


Page 20 of 22

Page 21 of 22

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


(16) Wang, Z.; Liu, J.; Xu, Z. Q.; Xue, Y.; Jiang, L.; Song, J.; Huang, F.; Wang, Y.; Zhong, Y. L.; Zhang, Y. Wavelength-tunable Waveguides Based on Polycrystalline Organic-inorganic Perovskite Microwires. Nanoscale 2015, 8 (12), 6258-6264. (17) Zhang, Q.; Ha, S. T.; Liu, X.; Sum, T. C.; Xiong, Q. Room-temperature Near-infrared High-Q Perovskite Whispering-gallery Planar Nanolasers. Nano Lett. 2014, 14 (10), 5995-6001. (18) Dou, L.; Wong, A. B.; Yu, Y.; Lai, M.; Kornienko, N.; Eaton, S. W.; Fu, A.; Bischak, C. G.; Ma, J.; Ding, T. Atomically Thin Two-dimensional Organic-inorganic Hybrid Perovskites. Science 2015, 349 (6255), 1518-1521. (19) Liu, J.; Xue, Y.; Wang, Z.; Xu, Z.-Q.; Zheng, C.; Weber, B.; Song, J.; Wang, Y.; Lu, Y.; Zhang, Y.; Bao, Q. Two-Dimensional CH3NH3PbI3 Perovskite: Synthesis and Optoelectronic Application. ACS Nano 2016, 10 (3), 3536-3542. (20) Kalanoor, B. S.; Gouda, L.; Gottesman, R.; Tirosh, S.; Haltzi, E.; Zaban, A.; Tischler, Y. R. Third-Order Optical Nonlinearities in Organometallic Methylammonium Lead Iodide Perovskite Thin Films. ACS Photonics 2016, 3 (3), 361-370. (21) Zhang, R.; Fan, J.; Zhang, X.; Yu, H.; Zhang, H.; Mai, Y.; Xu, T.; Wang, J.; Snaith, H. J. Nonlinear Optical Response of Organic-Inorganic Halide Perovskites. ACS Photonics 2016, 3 (3), 371-377. (22) Zhang, Y.; Wang, Y.; Xu, Z. Q.; Liu, J.; Song, J.; Xue, Y.; Wang, Z.; Zheng, J.; Jiang, L.; Zheng, C.; Huang, F.; Sun, B.; Cheng, Y. B.; Bao, Q. Reversible Structural Swell-Shrink and Recoverable Optical Properties in Hybrid Inorganic-Organic Perovskite. ACS Nano 2016, 10 (7), 7031-7038. (23) Zhang, Z. Y.; Lagally, M. G. Atomistic Processes in the Early Stages of Thin-film Growth. Science 1997, 276 (5311), 377-383. (24) Yin, W. J.; Chen, H.; Shi, T.; Wei, S. H.; Yan, Y. Origin of High Eelectronic Quality in Structurally Disordered CH3NH3PbI3 and the Passivation Effect of Cl and O at Grain Boundaries. Adv. Electron. Mater. 2015, 1 (6) 1500044. (25) Wakamiya, A.; Endo, M.; Sasamori, T.; Tokitoh, N.; Ogomi, Y.; Hayase, S.; Murata, Y. Reproducible Fabrication of Efficient Perovskite-based Solar Cells: X-ray Crystallographic Studies on the Formation of CH3NH3PbI3 Layers. Chem. Lett. 2014, 43 (5), 711-713. (26) Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-infrared Photoluminescent Properties. Inorg. Chem. 2013, 52 (15), 9019-9038. (27) Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith, H. J. Enhanced Photoluminescence and Solar Cell Performance Via Lewis Base Passivation of Organic– inorganic Lead Halide Perovskites. ACS Nano 2014, 8 (10), 9815-9821. (28) Sheik-Bahae, M.; Said, A. A.; Wei, T. H.; Hagan, D. J.; Van Stryland, E. W. Sensitive Measurement of Optical Nonlinearities Using a Single Beam. IEEE J. Quantum Electron. 1990, 26 (4), 760-769. (29) Wang, K. P.; Feng, Y. Y.; Chang, C. X.; Zhan, J. X.; Wang, C. W.; Zhao, Q. Z.; Coleman, J. N.; Zhang, L.; Blau, W. J.; Wang, J. Broadband Ultrafast Nonlinear Absorption and Nnonlinear Refraction of Layered Molybdenum Dichalcogenide Semiconductors. Nanoscale 2014, 6 (18), 10530-10535. (30) Garmire, E. Resonant Optical Nonlinearities in Semiconductors. IEEE J. Sel. Top. Quantum Electron. 2000, 6 (6), 1094-1110. (31) Zhang, H.; Virally, S.; Bao, Q. L.; Ping, L. K.; Massar, S.; Godbout, N.; Kockaert, P. Z-scan Measurement of the Nonlinear Refractive Index of Graphene. Opt. Lett. 2012, 37 (11), 1856-1858. 20



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

(32) Grelu, P.; Akhmediev N. Dissipative Solitons for Mode-locked Lasers. Nat. Photonics 2012, 6 (2), 84-92.

21


Page 22 of 22

Page 23 of 22

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


TOC Figure

22


Two-Dimensional CH3NH3PbI3 Perovskite Nanosheets for Ultrafast

Recommend Documents