High Performance Flexible Perovskite Solar Cells with a Metal Sulfide

Subscriber access provided by University of Winnipeg Library

Article

High Performance Flexible Perovskite Solar Cells with a Metal Sulfide Electron Transport Layer of SnS2 by Room Temperature Vacuum Deposition Weijing Chu, Xin Li, Shuiping Li, Jingdi Hou, Qinghui Jiang, and Junyou Yang ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b01405 • Publication Date (Web): 19 Dec 2018 Downloaded from http://pubs.acs.org on December 20, 2018

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 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 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.

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 27 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 Applied Energy Materials

High Performance Flexible Perovskite Solar Cells with a Metal Sulfide Electron Transport Layer of SnS2 by Room Temperature Vacuum Deposition Weijing Chu, Xin Li, Shuiping Li, Jingdi Hou, Qinghui Jiang, Junyou Yang* State Key Laboratory of Material Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, P.R. China.

1

ACS Paragon Plus Environment

ACS Applied Energy Materials 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 In this work, high mobility n-type SnS2 semiconductor films have been fabricated by vacuum deposition at room temperature and employed as the electron transport layer of flexible perovskite solar cells for the first time. The deposited SnS2 film exhibits homogeneous microstructure and good energy-level matching and presents a fast charge mobility and collection rate. By introducing SnS2 layer as an electron transport layer in fabricating flexible PKSC devices, a high cell performance with negligible hysteresis and an improved stability have been achieved. Since ZnO can be damaged by MAPbI3, the introduction of SnS2 buffer layer seems to be useful for improving the stability. By optimizing the SnS2 film thickness, a maximum power conversion efficiency of 13.2% with negligible hysteresis effect has been achieved in the device with a 60 nm SnS2 electron transport layer, due to the optimal coverage, electron extraction and large charge recombination resistance. This work demonstrates an encouraging prospect of SnS2 for high performance flexible perovskite solar cells, and also provides a new vision to the research and development of flexible perovskite photovoltaic devices for future applications. KEYWORDS: SnS2 film, vacuum deposition method, high mobility, electron transport layer, flexible perovskite solar cell

2


Page 2 of 27

Page 3 of 27 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


INTRODUCTION With the boom of portable and wearable electronic devices, increasing attention has been focused on flexible solar cells because they can meet the needs for solar power generation where sunlight is available.1-4

Among

them,

the

low-temperature

process

of

organic–inorganic hybrid perovskite solar cells (PKSCs) is more compatible and suitable for flexible substrate thus more promising for portable power source.5-9 In the past few years, encouraging progress has been made continuously in bending durability, fabrication and efficiency of flexible perovskite solar cells.10-14. However, compared with rigid PKSCs and traditional amorphous silicon15 and CIGS (CuInxGa(1-x)Se2) flexible thin film solar cells, there is still a long way to go for flexible PKSCs. As well known to all, the electron transport layer (ETL) plays an important role in collecting photogenerated electrons to photoanode of PKSCs,16 is one of key factors for the photovoltaic performance of a flexible PKSCs. By now, high efficient flexible PKSCs are usually based on the organic ETL, like PCBM with expensive cost. Metallic oxide thin film is the most frequently adopted material for the ETL in the state-of-the-art rigid planar PKSCs.17 However, it is not applicable to thermolabile plastic substrate of flexible PKSCs due to the high temperature fabrication process. Low temperature

3



preparation have been employed to serve as the electron selective layer in flexible PKSCs, for example: ZnO,18 Zn2SnO4,19,20 SnO2.21,22 Their compatibility with the perovskite absorption layer and photovoltaic performance are still concerns to be reckoned. More recently, metal sulfides have received much attention as candidates for ETL in rigid PKSCs because of their availability, proper energy-level and no high-temperature process as high as conventional metallic oxides. Liu et al.23 proposed ZnS/CdS double-layer ETL by low-temperature solution process and achieved a power conversion efficiency (PCE) of 11.2% in a rigid PKSC; Zhao et al.24 demonstrated that In2S3 nanoflake array was an efficient ETL for perovskite solar cells, due to enhanced light trapping, optimized band structure and low recombination leading to a high-efficiency. Logically, those metal sulfides compatible in chemical stability, fabrication process and band structure with the perovskite and flexible substrate should be applicable and favorable in flexible PKSCs. However, no related work has been reported on the trial of metal sulfide as ETL in flexible pervskite solar cells yet.25 As a cost-effective and eco-friendly n-type direct band-gap semiconductor SnS2, which has an adjustable band gap (2.1-3.38 eV), exhibits excellent photoelectric properties and promising application in many fields such as field effect transistor,26 solar cell,27 and

4


Page 4 of 27

Page 5 of 27 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


photocatalyst.28 Recently, Ma et al.25 reported a low temperature processed 2D SnS2 nanosheets as a new electron transport layer in PKSC for the first time and achieved a PCE of 13.63% in the rigid device. In this paper, SnS2 thin films were fabricated by vacuum deposition and employed as the ETL of flexible PKSCs for the first time. By introducing SnS2 layer as an electron transport layer in fabricating flexible PKSC devices, a high cell performance with negligible hysteresis and an improved stability have been achieved. Since ZnO can be damaged by MAPbI3, the introduction of SnS2 buffer layer seems to be useful for improving the stability. By optimizing the SnS2 film thickness, the maximum PCE of the SnS2 based devices have been promoted to 13.2% with negligible hysteresis effect. As a first attempt, this work demonstrates an encouraging prospect of SnS2 for high performance flexible PKSCs, and also provides a new insight to the flexible perovskite photovoltaic devices for future applications.

5



RESULTS AND DISCUSSION

Figure 1. (a) The XRD pattern of SnS2 film; (b) XPS patterns of the SnS2 samples. The enlarged XPS spectrum of S 2p (c) and Sn 3d (d). To obtain well crystallized stannic disulfide film, a room temperature vacuum deposition method was applied. SnS2 film with different thickness was deposited on cleaned PEN/ITO substrate by vacuum deposition without further annealing. X-ray diffraction (XRD) patterns of deposited samples with different thickness are presented in Figure 1a to determine the crystal structure of the films. The thickness of the deposited film can be easily controlled by

6


Page 6 of 27

Page 7 of 27 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


varying the vacuum deposition time, obviously, the films of different thickness exhibit similar XRD patterns. As is clearly shown in Figure S1, Due to the deposited films are only dozens of nanometer in thickness, only one peak at 14.6° corresponding to the (001) plane of hexagonal phase SnS2 (JCPDS card no. 00-023-0677) was detected and the other peaks belong to the ITO substrate. It is confirmed that the vacuum deposited SnS2 film can easily crystallize without further annealing process. To further verify the composition of vacuum deposited films, XPS measurement was performed and the results were shown in Figure 1b, 1c and 1d respectively. Compared with the bare ITO substrate, the substrate covered with vacuum deposited film presents a Sn 3d5/2 peak at 487.1 eV and a S 2p3/2 peak at 162.35 eV corresponding to Sn4+and S2-, respectively. These results are in good agreement with the literature reported results,29 indicating the SnS2 nature of the deposited film. The magnified XPS spectrum in Figure 1c further presents a peak at 164eV of the 2p of elemental S, which should be attributed to higher partial pressure of volatile S component during the process of vacuum evaporation. EPMA mapping analysis confirms the homogeneous distribution of S and Sn in the film (Figure S2), while the atomic ratio of Sn and S by EPMA is 1:2.11. Considering the contribution of elemental S to the

7



atomic ratio, as demonstrated by XPS in Figure 1c, the vacuum deposited film samples are SnS2 with good crystallinity. SEM morphologies of the vacuum deposited films were further observed and presented in Figure S3, it demonstrates that the SnS2 films are uniform and compact in microstructure. That is to say, the room temperature vacuum deposition can fabricate homogeneous and compact crystalline SnS2 films, which will benefit to improve the performance of flexible PKSCs on thermal unstable plastic substrate.

Figure 2.(a) Diagram of PEN/ITO/ETL/MAPbI3/Spiro/Au device structure. (b) Schematic of the band alignment of flexible solar device based on SnS2 ETL. Figure 2a manifests the schematic configuration of a flexible PKSC device based on the PEN/ITO/ETL/MAPbI3/Spiro/Au structure and a real flexible PKSC device is shown in Figure S4, in which the vacuum deposited SnS2 films with different thickness were employed as ETLs to fabricate flexible PKSCs as detailed in the

8


Page 8 of 27

Page 9 of 27 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


experimental section. For the ETL of a specific PKSC, it is necessary for its conduction band minimum to match with those of the perovskite and photoanode to ensure a smooth carrier transfer. In this case, the conduction band minimum (CBM) position of the SnS2 film was measured by ultraviolet photoelectron spectroscopy (UPS) method and the UV-vis absorption spectra were collected and illustrated in Figure S5, and the optical band gap of SnS2 of 2.78 eV, in accordance with the literature,30 is obtained from the UV-vis absorption spectra by Tauc formula.31 Correspondingly, the energy level alignment diagram of the flexible PKSCs based on SnS2 ETL is shown in Figure 2b. As the most widely used electron transport layer (ETL) materials in flexible PKSCs, ZnO cause the thermal decomposition of MAPbI3 film and affects the performance of devices. Obviously, the conduction band minimum of SnS2 film is closer to that of MAPbI3 than ZnO, effectively improving the energy alignment between MAPbI3 and ITO electrode by decreasing their energy offset and facilitating the charge transport from active layer to photoanode. The band analysis demonstrates SnS2 film is an appropriate electron transport layer. The surface morphology of MAPbI3 deposited on different SnS2 films were presented in Figure S6a-c. It can be seen that the morphology of perovskite layer shows indifference with the

9



thickness variation of SnS2 film and presents a homogeneous and compact microstructure. Therefore, the influence of SnS2 substrate is small on the one-step deposition MAPbI3 films. As shown in the Figure S7, atomic Force Microscope (AFM) analysis characterized the surface quality of SnS2 substrates with different thickness and perovskite films on them. Different SnS2 films and perovskite films grown on the SnS2 substrates both exhibit the homogeneous crystal morphology. The results of AFM verify the analysis of SEM.

Figure 3. Cross-sectional SEM image of the 30nm (a, d), 60nm (b, e), 80nm (c, f) SnS2 ETL and PKSC devices. The cross section SEM micrographs of different SnS2 films and corresponding PKSCs were displayed in the Figure 3. As derived from Figure 3a-c, the thickness parameters are about 30nm, 60nm and 80nm respectively, the vacuum deposited SnS2 films are

10


Page 10 of 27

Page 11 of 27 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


homogeneous in thickness direction. Figure 3d-f present the corresponding section morphology of the flexible devices with the PEN/ITO/different SnS2/MAPbI3/Spiro/Au structure. It can be seen that all the devices present uniform and tight-bound interfaces, and the MAPbI3 layers manifest large grain size with good crystallinity, where the size of a MAPbI3 grains agreement with the thickness of the MAPbI3 active layer. The reduced grain boundary is beneficial to lowering recombination behavior of photoinduced electron and hole and faciliate the carrier transmission.

Figure 4. UV-visible absorption spectra of the MAPbI3 films deposited on SnS2 substrate with different thickness. Figure S8 illustrates the influence of the different thickness SnS2 film on the transmittance of the PEN/ITO substrates. Compared with the bare substrate, the transmittance of the SnS2 covered substrate reduces slightly in the range of 450~500 nm, which corresponds with the absorption peak of the optical band gap of SnS2. In order to 11



Page 12 of 27

investigate the effect of light capturing, UV-visible absorption spectra analysis was performed and the results were shown in the Figure 4. As can be seen, all the MAPbI3 films based on different SnS2 substrate present similar absorption trend, all generating absorption in 760nm corresponding to the absorption limit of MAPbI3. Compared with the MAPbI3 films on the 30nm SnS2 substrate, the MAPbI3 films on 60nm and 80nm have stronger light absorption, which will be beneficial to increasing current density.

Table 1. The photovoltaic parameters of flexible perovskite devices based on different SnS2 ETLs.

SnS2 Thickness

Jsc (mA/cm2)

Voc

FF

PCE (%)

30

20.07

1.012

0.55

10.60

60

21.70

1.011

0.60

13.20

80

21.15

1.010

0.57

12.18

12


Page 13 of 27 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 J-V plots of (a) flexible PKSCs based on different SnS2 ETLs (a) and (b) the flexible PKSCs with an ETL of 60nm SnS2 under reverse and forward bias scans. (c) IPCE spectra of the optimized flexible device based 60 nm SnS2 ETL. (d) Steady-state PCE and photo-current density at maximum power point as a function of time for 60 nm SnS2 based PKSC. Afterwards, a number of flexible devices with the structure PEN/ITO/different SnS2/MAPbI3/Spiro/Au were assembled. Figure 5a demonstrates the J-V curves of flexible devices obtained under a solar irradiation 100 mW cm-2, AM 1.5. The mean photovoltaic parameters, such as open circuit voltage (Voc), short-circuit current density (Jsc), factor (FF) and power conversion efficiency (PCE), were listed and compared in Table 1. The statistical distributions of

13



the parameters, including Voc, Jsc, FF and PCE , were shown in Figure S9, where the performances of the flexible devices based on different SnS2 ETLs were compared. It can be seen that the Jsc and FF increase firstly and then decrease with the increase of SnS2 thickness, and an optimal PCE of 13.2% has been achieved in the flexible device with a SnS2 ETL of 60 nm. Moreover, as shown by the J-V measure with different scan directions in Figure 5b, the hysteresis effect is almost negligible for the flexible device based on the 60nm SnS2 ETL. It is indicated that the integrated current calculated in IPCE shown in Figure 5c is 20.78 mA cm-2, which is consistent with the Jsc value obtained from J-V curves within the margin of error. Moreover, the steady-state current density is 19.4 mA cm-2 with a PCE of 12.97%, which is clearly shown in Figure 5d. SnS2 is an n type semiconductor with high carrier mobility and the intrinsic carrier mobility of SnS2 single crystal can even be up to 1 cm2v-1s-1.22 To measure the electron transport capability of the vacuum deposited SnS2 film, here the carrier mobility was characterized by the SCLC (Space charge limited current) method based on the only electron transport layer devices (ITO/ SnS2/Ag),32 and the results are shown in Figure S10. The obtained carrier mobility is 0.17 cm-2v-1s-1 and it is higher than those of some

14


Page 14 of 27

Page 15 of 27 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


conventional oxide ETLs such as ZnO and TiO2.33, 34 This indicates that SnS2 will display a high efficient electron transmission as an electron transport layer. To further understand the carrier transport behavior of the SnS2 ETL, the steady-state photoluminescence spectra (PL) were collected and exhibited in the Figure S11. All semi-devices show an obvious luminescence peak around 760 nm for MAPbI3. Compared to the flexible semi-device without the SnS2 ETL, the luminescence peak intensity of MAPbI3 reduces obviously with the introduction of SnS2 ETL, and the quenching degree of the peak varies with the change of SnS2 thickness, further confirming that the SnS2 can effectively collect electrons to the ITO electrode. As the quenching degree of the peak corresponds to the charge collection rate in the electron transport layer, rapid electronic collection rate contributes to the increase of JSC. It can be seen that the quenching degree of the fluorescence peak first increases with the thickness of the SnS2 ETL, and receives the maximum at the 60 nm SnS2 ETL and decreases slightly when further increasing the thickness of SnS2 ETL to 80 nm. That is why the short-circuit current density Jsc of the flexible perovskite solar cells first increases with the SnS2 thickness until 60nm and then drops slightly, as listed in Table 1. Electrical impedance spectroscopy (EIS) of the flexible PKSCs 15



based on different SnS2 ETLs were collected to study the carrier transport and recombination behavior and shown in Figure S12. Under a 900 mV forward bias, the Nyquist plots of different flexible devices were presented, and equivalent circuit model was inserted in the top left of the Figure S12. The semicircle of the plot indicates the Rrec of the interface between the SnS2 ETL and the perovskite layer. Similarly with the tendency of fluorescence quenching degree, the Rrec increases firstly with the thickness of SnS2 and achieve the maximum at 60 nm and then decreases when further increases the SnS2 thickness to 80 nm. If the SnS2 film is too thin to cover the whole substrate, the recombination rate of photo-generated carriers will increase, thus leading to a low Rrec. On the other hand, if the thickness of SnS2 film is enough to ensure a good coverage to the whole substrate, further increase of the thickness means the increase of carrier transport distance, therefore, the recombination rate also increases and the Rrec decreases. The variation of Rrec with bias voltage was shown in Figure S13. It manifests change trend of Rrec for different devices under different bias conditions. For the same device, Rrec drops with the increasing forward bias voltage; for the different devices, the Rrec display a similar trend as the 900 mV, which explain the reason of the variation of FF. As is shown in FigureS14a, the device based SnS2 manifests the higher PCE of

16


Page 16 of 27

Page 17 of 27 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


13.20% with a Jsc of 21.70 mA cm-2, a Voc of 1.011 V, a FF of 0.60. Comparatively, the device based ZnO shows the PCE of 11.12% with a Jsc of 21.40 mA cm-2, a Voc of 0.945 V, a FF of 0.55. Moreover,

in Figure S14b, it demonstrates a shorter carrier lifetime

in the SnS2-based perovskite layer than that of ZnO ETL. Apparently, the perovskite/SnS2 system can provide a faster electron transfer process and lower interface recombination in comparison with the perovskite/ZnO system.

Figure 6. The stability of the flexible PKSCs with and without SnS2 as ETL, respectively. The stability of the PKSCs has also been observed and presented in Figure 6. Obviously, the device with ZnO ETL degrades very severely under the 40-50% humidity, resulting in about 30% loss of the initial PCE after 30 days. Comparatively, the device based on

17



SnS2 exhibits an excellent long-term stability, its PCE remains almost constant, and it loses only 7% PCE after stored for 30 days. This research work paves a way that SnS2 is a promising alternative ETL material for large area roll-to-roll flexible perovskite solar cells.

EXPERIMENTAL SECTION Materials and chemicals. SnS2 powder (99.5%) was purchased from Changsha Huajing powder Co. Ltd. The MAI (CH3NH3I) was obtained according the literature report35 of other chemicals and reagents were supplied by Alfa Aesar without further purification. Fabrication of SnS2 film as ETL by vacuum deposition. SnS2 crystal powder as evaporation source, SnS2 film was deposited on the clean PEN/ITO substrate by vacuum evaporation(without substrate heating), without further annealing, the vacuum degree is 10-4 Pa and the deposition rate is about 0.2 A°/s. Fabrication of ZnO film as ETL by solution method. ZnO nanoparticles were prepared according to our previous work.32 The thickness of ZnO is hard to distinguish by SEM due to the formation ultra-thin film. A compact ZnO film was deposited on the ITO surface by spin coating (3000 r, 30 s) and the procedure was repeated three times. Device fabrication. The as-patterned PEN/ITO substrates were

18


Page 18 of 27

Page 19 of 27 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


cleaned with acetone, ethanol and deionized water in turn and blow-dried by clean nitrogen. Then the dried PEN/ITO substrates were treated ultraviolet O3 plasma for 10 min. The SnS2 electron transport layers were prepared by vacuum deposition under room temperature without post annealing. Next the uniform and compact MAPbI3 film were grow up on the top of SnS2 substrate by anti-solvent, one-step method: here, 0.462 g PbI2 and 0.159g MAI powder were dissolved in DMF solution (with the mole ratio of 1:1) as precursor solution, 30 μL solutions above mentioned were spin coated on the top of SnS2 film (3000 r, 40 s), in the latter spin-coating step, 80 μL chlorobenzene solution was dropped onto the wet substrates at the first 10 s (3000 r). After that, the MAPbI3 film were annealed at 100 °C or 45 min. Then, the Spiro-MeOTAD layer was spin-coated on the top of annealed MAPbI3 film from a stock

solution

(4000

r,

30

s),which

contained

72.3

mg

spiro-OMeTAD in 1 mL chlorobenzene with the addition of 28.8 mL 4-tert-butylpyridine and 35 mL Li-TFSI/acetonitrile solution. Finally, 80nm Au electrodes were deposited on the above substrates. Characterization. The constitution of the film prepared by vacuum deposition was confirmed X-ray photoelectron spectroscope (XPS, AXIS-ULTRA DLD-600W, Kratos). Crystal structure of SnS2 films were determined with X-ray diffractometer (XRD, X’Pert Pro Philip,

19



PANalytical B.V.). X-Ray Electron Probe Microanalyzer (EPMA, EPMA-8050G, SHIMADZU) was employed to investigate the mapping analysis. The chemical composition and distribution of constituents were observed by electron probe micro analyzer (EPMA, EPMA-8050G, Shimadzu). Atomic force spectroscopy (AFM, SPM9700, Shimadzu) was used to study surface roughness of the films with tapping mode. The top and cross-section morphology of the SnS2 and perovskite films were observed with a scanning electron microscope (SEM, GeminiSEM300, Carl Zeiss). The transmittance of the prepared SnS2 substrates and absorption spectrum of the MAPbI3 films were studied with a Lambda 950 UV-vis spectrophotometer. The current density-voltage (J-V) characteristics curves were obtained using a Keithley 2400 source meter under one-sun AM 1.5G (100 mW cm-2) illumination with a solar light simulator. Steady-state photoluminescence (PL, LabRAM HR800, Horiba JobinYvon) spectrums were recorded.The internal impedance of flexible solar cells were measured with a electrochemical workstation (CHI660E, Chenhua, Shanghai), with the frequency ranging from 0.1 Hz to 100 MHz in the dark.

CONCLUSION Here, SnS2 thin films have been deposited by vacuum evaporation at

20


Page 20 of 27

Page 21 of 27 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


room temperature and employed as the ETL of flexible perovskite solar cells for the first time. The deposited SnS2 film exhibits homogeneous morphology and matching energy alignment and presents a fast charge mobility and collection rate. The flexible PKSCs based on the 60nm SnS2 ETL has achieved a highest photovoltaic performance of 13.2% with negligible hysteresis, due to the optimal coverage, electron extraction and large charge recombination resistance. As a first attempt, this research work paves a way that SnS2 is a promising alternative ETL material for large area roll-to-roll flexible perovskite solar cells.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org. EPMA spectra, SEM images, AFM images, UPS spectra, Box chart of photovoltaic parameters, Steady-state current and PCE, Transmission spectra, J1/2-Vapp-Vbi characteristic curves, Rec plots of various flexible perovskite solar cells, TR-PL spectra.

AUTHOR INFORMATION Corresponding Author

21



*Email: [email protected]. ORCID Junyou Yang: 0000-0003-0849-1492 Author Contributions W. Chu, X. Li, and S. Li contributed equally to this work. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work is co-financed by National Natural Science Foundation of China (Grant No. 51572098, 51632006, 51772109 and 51872102), the Fundamental Research Funds for the Central Universities (No. 2018KFYXKJC002), Open Fund of State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology (Grant No. 2016-KF-5), Graduates' Innovation Fund, Huazhong University of Science and Technology (No. 5003110025). The technical assistance from the Analytical and Testing Center of HUST is likewise gratefully acknowledged.

REFERENCES (1) Hu, X.; Huang, Z.; Zhou, X.; Li, P.; Wang, Y.; Huang, Z.; Su, M.; Ren, W.; Li, F.; Li, M.; Chen, Y.; Song, Y. Wearable Large-Scale Perovskite Solar-Power Source via

22


Page 22 of 27

Page 23 of 27 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


Nanocellular Scaffold. Adv. Mater. 2017, 29, 1703236. (2) Wu, Z.; Li, P.; Zhang, Y.; Zheng, Z. Flexible and Stretchable Perovskite Solar Cells: Device Design and Development Methods. Small Methods 2018, 2, 1800031. (3) Ishizuka, S.; Yamada, A.; Matsubara, K.; Fons, P.; Sakurai, K.; Niki, S. Development of High-Efficiency Flexible Cu(In,Ga)Se2 Solar Cells: A Study of Alkali Doping Effects on CIS, CIGS, and CGS Using Alkali-Silicate Glass Thin Layers. Curr. Appl. Phys. 2010, 10, S154-S156. (4) Cui, Y.; Yao, H.; Gao, B.; Qin, Y.; Zhang, S.; Yang, B.; He, C.; Xu, B.; Hou, J. Fine-Tuned Photoactive and Interconnection Layers for Achieving over 13% Efficiency in a Fullerene-Free Tandem Organic Solar Cell. J. Am. Chem. Soc. 2017, 139, 7302-7309. (5) Bi, C.; Chen, B.; Wei, H.; DeLuca, S.; Huang, J. Efficient Flexible Solar Cell based on Composition-Tailored Hybrid Perovskite. Adv. Mater. 2017, 29, 1605900. (6) Wang, Y.; Duan, C.; Li, J.; Han, W.; Zhao, M.; Yao, L.; Wang, Y.; Yan, C.; Jiu, T. Performance Enhancement of Inverted Perovskite Solar Cells Based on Smooth and Compact PC61BM:SnO2 Electron Transport Layers. ACS Appl. Mater. Interfaces 2018, 10, 20128-20135. (7) Khadka, D. B.; Shirai, Y.; Yanagida, M.; Noda, T.; Miyano, K. Tailoring the Open-Circuit Voltage Deficit of Wide-Band-Gap Perovskite Solar Cells Using Alkyl Chain-Substituted Fullerene Derivatives. ACS. Appl. Mater. Interfaces 2018, 10, 22074-22082. (8) Yang,W. Iodide Management in Formamidinium-Lead-Halide-based Perovskite Layers for Efficient Solar Cells. Science 2017, 356, 1376–1379. (9) Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T. B.; Duan, H. S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Photovoltaics. Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345, 542-546. (10) Kaltenbrunner, M.; Adam, G.; Glowacki, E. D.; Drack, M.; Schwodiauer, R.; Leonat, L.; Apaydin, D. H.; Groiss, H.; Scharber, M. C.; White, M. S.; Sariciftci, N. S.; Bauer, S. Flexible High Power-Per-Weight Perovskite Solar Cells with Chromium Oxide-Metal Contacts for Improved Stability in Air. Nat. Mater. 2015, 14, 23



1032-1039. (11) Chu, K.; Song, B. G.; Yang, H.-I.; Kim, D.-M.; Lee, C. S.; Park, M.; Chung, C.-M. Smart Passivation Materials with a Liquid Metal Microcapsule as Self-Healing Conductors for Sustainable and Flexible Perovskite Solar Cells. Adv. Funct. Mater. 2018, 28, 1800110. (12) Wang, S.; Hou, K.; Xing, Y.; Dong, Q.; Wang, K.; Lv, Y.; Shi, Y. Flexibly Assembled and Readily Detachable Photovoltaics. Energy Environ. Sci. 2017, 10, 2117-2123. (13) Ryu, U.; Jee, S.; Park, J. S.; Han, I. K.; Lee, J. H.; Park, M.; Choi, K. M. Nanocrystalline Titanium Metal-Organic Frameworks for Highly Efficient and Flexible Perovskite Solar Cells. ACS Nano 2018, 12, 4968-4975. (14) Kim, H. I.; Kim, M.-J.; Choi, K.; Lim, C.; Kim, Y.-H.; Kwon, S.-K.; Park, T. Improving the Performance and Stability of Inverted Planar Flexible Perovskite Solar Cells Employing a Novel NDI-Based Polymer as the Electron Transport Layer. Adv. Energy Mater. 2018, 8, 1702872. (15) Ramakrishna, M.; Kumari, J.; Venkanna, K.; Agarwal, P. Hydrogenated Amorphous Silicon Solar Cells Fabricated at Low Substrate Temperature 110°C on Flexible PET Substrate. AIP Conference Proceedings, 2018, 1953, 100040. (16) Wang, C.; Zhao, D.; Yu, Y.; Shrestha, N.; Grice, C. R.; Liao, W.; Cimaroli, A. J.; Chen, J.; Ellingson, R. J.; Zhao, X.; Yan, Y. Compositional and Morphological Engineering of Mixed Cation Perovskite Films for Highly Efficient Planar and Flexible Solar Cells with Reduced Hysteresis. Nano Energy 2017, 35, 223-232. (17) Wang, C.; Xiao, C.; Yu, Y.; Zhao, D.; Awni, R. A.; Grice, C. R.; Ghimire, K.; Constantinou, I.; Liao, W.; Cimaroli, A. J.; Liu, P.; Chen, J.; Podraza, N. J.; Jiang, C.-S.; Al-Jassim, M. M.; Zhao, X.; Yan, Y. Understanding and Eliminating Hysteresis for Highly Efficient Planar Perovskite Solar Cells. Adv. Energy Mater. 2017, 7, 1700414. (18) Heo, J. H.; Lee, M. H.; Han, H. J.; Patil, B. R.; Yu, J. S.; Im, S. H. Highly Efficient Low Temperature Solution Processable Planar Type CH3NH3PbI3 perovskite Flexible Solar Cells. J. Mater. Chem.A 2016, 4, 1572-1578. 24


Page 24 of 27

Page 25 of 27 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


(19) Liu, M.; Yang, J.; Feng, S.; Zhu, H.; Zhang, J.; Li, G.; Peng, J. Composite Photoanodes of Zn2SnO4 Nanoparticles Modified SnO2 Hierarchical Microspheres for Dye-Sensitized Solar Cells. Mater. Lett. 2012, 76, 215-218. (20) Shin, S. S.; Yang, W. S.; Yeom, E. J.; Lee, S. J.; Jeon, N. J.; Joo, Y. C.; Park, I. J.; Noh, J. H.; Seok, S. I. Tailoring of Electron-Collecting Oxide Nanoparticulate Layer for Flexible Perovskite Solar Cells. J. Phys. Chem.Lett. 2016, 7, 1845-1851. (21) Wang, C.; Guan, L.; Zhao, D.; Yu, Y.; Grice, C. R.; Song, Z.; Awni, R. A.; Chen, J.; Wang, J.; Zhao, X.; Yan, Y. Water Vapor Treatment of Low-Temperature Deposited SnO2 Electron Selective Layers for Efficient Flexible Perovskite Solar Cells. ACS Energy Lett. 2017, 2, 2118-2124. (22) Wang, C.; Zhao, D.; Grice, C. R.; Liao, W.; Yu, Y.; Cimaroli, A.; Shrestha, N.; Roland, P. J.; Chen, J.; Yu, Z.; Liu, P.; Cheng, N.; Ellingson, R. J.; Zhao, X.; Yan, Y. Low-Temperature Plasma-Enhanced Atomic Layer Deposition of Tin Oxide Electron Selective Layers for Highly Efficient Planar Perovskite Solar Cells. J. Mater. Chem. A 2016, 4, 12080-12087. (23) Liu, J.; Gao, C.; Luo, L.; Ye, Q.; He, X.; Ouyang, L.; Guo, X.; Zhuang, D.; Liao, C.; Mei, J.; Lau, W. Low-Temperature, Solution Processed Metal Sulfide as An Electron Transport Layer for Efficient Planar Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 11750-11755. (24) Hou, Y.; Chen, X.; Yang, S.; Zhong, Y. L.; Li, C.; Zhao, H.; Yang, H. G. Low-Temperature Processed In2S3 Electron Transport Layer for Efficient Hybrid Perovskite Solar Cells. Nano Energy 2017, 36, 102-109. (25) Zhao, E.; Gao, L.; Yang, S.; Wang, L.; Cao, J.; Ma, T. In Situ Fabrication of 2D SnS2 Nanosheets as a New Electron Transport Layer for Perovskite Solar Cells. Nano Research 2018, 5974, 1-11. (26) De, D.; Manongdo, J.; See, S.; Zhang, V.; Guloy, A.; Peng, H. High on/off Ratio Field Effect Transistors based on Exfoliated Crystalline SnS2 Nano-Membranes. Nanotechnology 2012, 24, 025202. (27) Bai, Y.; Zong, X.; Yu, H.; Chen, Z. G.; Wang, L. Scalable Low-Cost SnS2 Nanosheets as Counter Electrode Building Blocks for Dye-Sensitized Solar Cells. 25



Chemistry 2014, 20, 8670-8676. (28) Zhang, Y. C.; Du, Z. N.; Li, K. W.; Zhang, M.; Dionysiou, D. D. High-Performance Visible-Light-Driven SnS2/SnO2 Nanocomposite Photocatalyst Prepared via In situ Hydrothermal Oxidation of SnS2 Nanoparticles. ACS. Appl. Mater. Interfaces 2011, 3, 1528-1537. (29) Chen, D.; Shen, G.; Tang, K.; Lei, S.; Zheng, H.; Qian, Y. Microwave-Assisted Polyol Synthesis of Nanoscale SnSx (x=1, 2) Flakes. J. Cryst. Growth 2004, 260, 469-474. (30) Sekhar, C.; Malay, K.; Dhruba, D. Structure and Photoconductive Properties of Dip-Deposited SnS and SnS2 Thin Films and Their Conversion to Tin Dioxide by Annealing in Air. Thin Solid Films 1999, 35,72-78. (31) Morales, I.; Mendoza Temis, J.; Lopez-Vieyra, J. C.; Barea, J.; Hirsch, J. G.; Frank, A.; Velazquez, V. Exploring the Nuclear Landscape by Image Reconstruction Techniques. Revista Mexicana De Fisica 2007, 53, 28-34. (32) Chu, W.; Yang, J.; Jiang, Q.; Li, X.; Xin, J. Enhancement of Photovoltaic Performance of Flexible Perovskite Solar Cells by Means of Ionic Liquid Interface Modification in a Low Temperature All Solution Process. Appl. Surf. Sci. 2018, 440, 1116-1122. (33) Yu, W.; Huang, L.; Yang, D.; Fu, P.; Zhou, L.; Zhang, J.; Li, C. Efficiency Exceeding 10% for Inverted Polymer Solar Cells with a ZnO/Ionic Liquid Combined Cathode Interfacial Layer. J. Mater. Chem. A 2015, 3, 10660-10665. (34) Li, X.; Yang, J.; Jiang, Q.; Lai, H.; Li, S.; Xin, J.; Chu, W.; Hou, J. Low-Temperature Solution-Processed ZnSe Electron Transport Layer for Efficient Planar Perovskite Solar Cells with Negligible Hysteresis and Improved Photostability. ACS Nano 2018, 9, 41354-41362. (35) Hou, Y.; Yang, J.; Jiang, Q.; Li, W.; Zhou, Z.; Li, X.; Zhou, S. Enhancement of photovoltaic performance of perovskite solar cells by modification of the interface between the perovskite and mesoporous TiO2 film. Sol. Energ. Mat. Sol. C. 2016, 155, 101-107.

26


Page 26 of 27

Page 27 of 27 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


GRAPHICAL ABSTRACT

27


High Performance Flexible Perovskite Solar Cells with a Metal Sulfide

Recommend Documents