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Molten Salt Assisted Growth of Perovskite Films with Submillimeter-Sized Grains Yu Hou, Hongwei Qiao, Shuang Yang, Chunzhong Li, Huijun Zhao, and Hua Gui Yang Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 22 Dec 2016 Downloaded from http://pubs.acs.org on December 23, 2016

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Industrial & Engineering Chemistry Research

Molten Salt Assisted Growth of Perovskite Films with Submillimeter-Sized Grains Yu Hou,†,§,‡ Hongwei Qiao,†,‡ Shuang Yang,† Chunzhong Li,† Huijun Zhao, § and Hua Gui Yang*,†

†

Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science

and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China §

Centre for Clean Environment and Energy, Gold Coast Campus, Griffith University,

Queensland 4222, Australia

KEYWORDS: single crystal; submillimeter size; perovskite film; molten salt; solar cell

ABSTRACT: Single crystalline structures with less grain boundaries and longer carrier diffusion length are essential for high performance perovskite solar cells. In this paper, we report a molten salt assisted method to gain a perovskite film with submillimeter-sized single crystal domains by using excess ammonium salt for the first time. The resulted crystal size can reach 0.5 mm, and an aspect ratio over 1000. Photovoltaic device based on this film exhibits a champion power conversion efficiency (PCE) of 10.12%. This synthetic strategy enables the formation of

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submillimeter sized perovskite films firstly, which holds promise for the understanding of crystallization in organic-inorganic perovskite and paves the way to enhance the efficiency of perovskite solar cells.

1. INTRODUTION

As we all know, the band-gap, light absorption coefficient and charge carrier diffusion length are the key parameters to evaluate light-absorbing materials. For a certain kind of photoactive material, band-gap and light absorption coefficient are generally fixed values. Therefore, a critical issue in achieving higher efficiency is to reduce the energy loss in charge transport and collection. Semiconductor with single crystalline structure is an ideal material used in solar cell devices because of its less surface crystal defects, high carrier mobility, longer charge carrier diffusion length and carrier lifetime.1-6 These will directly affect the efficiency of the conductive electrode to collect photo-generated carriers at both ends of the p-n junction, which determine the power conversion efficiency (PCE) of photovoltaic devices.7 Over the past few years, organic-inorganic hybrid perovskite solar cells (PSCs) have drawn intensive research interests owing to the advantages of low-cost, high power conversion efficiency and flexibility.8-13 Most recently, the PCE of PSCs has attained a certified value of 22.1%, reaching the standard of commercial photovoltaic devices.14


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In order to meet the charge carrier diffusion length of perovskite materials, light-absorbing layer of perovskite solar cells is generally composed of polycrystalline film with a mean crystal size below 1 micrometer. The charge carrier diffusion length of perovskite materials in present reports is typically between 100 nm to 1000 nm.1 Moreover, numerous studies have confirmed the charge carrier diffusion length of perovskites is directly related to its crystal size.15-21 The presence of large amounts of surface defect states will lead to the trapping of carriers and further recombination easily, resulting in transmission loss.22,23 In addition, it has been demonstrated that when the single crystal size reaches centimeter domain, the carrier diffusion length can increase to 175 µm, much higher than that of perovskite polycrystalline films.24 Therefore, by enhancing the size of the perovskite crystals, the carrier diffusion length can increase over 100 times, and thus can significantly improve the efficiency of the resulted devices.25-29 Numerous researches have been done to get large sized crystals, but it is still a great challenge to be applied in solar cells.3-6, 30, 31

Herein, we develop a molten salt assisted method to efficiently control the growth of perovskite films by using excess ammonium salt. The resulted crystal size can reach 0.5 mm, and an aspect ratio over 1000. The perovskite films have less obvious grain boundaries with large single crystals. With the introduction of ammonium salt, a molten phase is initially formed. Then it evolves into ordered porous structure and becomes large single crystals during the annealing process finally. Photovoltaic device based on this film exhibits a power conversion efficiency of


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10.12%. This synthetic strategy enables the formation of submillimeter sized perovskite films for the first time and would also provide effective means in boosting the efficiency of perovskite solar cells.

2. EXPERIMENTAL SECTION

2.1. Synthesis of methylammonium iodide (CH3NH3I).30 According to the reported literature, CH3NH3I was synthesized by reacting 24 mL of methylamine solution (CH3NH2, 33 wt% in ethanol, Aldrich), 10 mL of hydroiodic acid (HI, 57 wt% in water, Aldrich), and 100 mL of ethanol (99.7%, Shanghai Lingfeng Chemical reagent) in a 250 mL round-bottom flask under nitrogen atmosphere at 0 °C for 2 h with stirring. Then the white precipitates were dried at 60 °C in a vacuum oven night. Finally, the white coloured powder was collected and stored under argon atmosphere before use.

2.2. Preparation mesoporous TiO2 layer on FTO substrates. The fluorine-doped tin oxide (FTO) conducting glass substrate (NSG, 8 Ω/square) was patterned by etching with Zn powder and 2 M HCl diluted in DI water. The etched FTO substrate was then cleaned in an ultrasonic bath containing acetone for 20 min, ethanol for 20 min, rinsed with DI water and dried with clean dry air. For the preparation of mesoporous TiO2 electron transport layers (ETLs), a compact TiO2 blocking layer was first made by spin-coating 0.15 M titanium diisopropoxide bis(acetylacetonate) (75 wt% in isopropanol, Aldrich) in 1-butanol (99.8 %, Aldrich) solution on the FTO substrate at 2000 r.p.m. for 20 s, followed by heated at 125 °C for 5 min. After cooling


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to room temperature, the diluted P25 paste was spin-coated on the compact TiO2 blocking layer at 4000 r.p.m. for 30 s, where the pristine P25 paste was prepared by previous report and diluted in ethanol (0.13 g mL-1).32 After annealed at 500 °C for 30 min, the mesoporous TiO2 film was immersed in 0.02 M aqueous TiCl4 (Sinopharm, AR) solution at 70 °C for 40 min. After rinsing with DI water and drying, the film was heated at 500 °C for 30 min.

2.3. Fabrication of hybrid perovskite solar cells. The CH3NH3PbI3 absorber layer was deposited on the TiO2 ETL by a two-step deposition method. The 1 M PbI2 solution was prepared by dissolving 462 mg PbI2 (99.9985%, Alfa Aesar) in 1 mL of N,N-dimethylformamide (DMF, 99.9%, Alfa Aesar), stirring at 343 K for 12 h. The solution was spin-coated on the ETL films at 3000 r.p.m. for 15 s. The PbI2 layer coated ETLs were dried at room temperature for 10 min and then heated at 373 K for 5 min to remove the DMF solvent. Then 60 mg mL-1 CH3NH3I solution was coated in above-mentioned substrate by spin coating at 3000 r.p.m. for 30 s. The film was heated at 373K for 20 min to eliminate the 2-propanol (99.5 %, Sigma-Aldrich) solvent. Next we put 3 to 5 grams CH3NH3Cl power on basal plates, heating the substrate at 373 K for 60 minutes with perovskite film having 2 cm distance above the heating plate to deposite CH3NH3Cl. To complete the devices, the perovskite films were spin-coated with hole transport layers using a solution of 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) at 3000 r.p.m. for 30 s and then evaporated with 110 nm Ag electrodes. The spiro-MeOTAD solution was prepared by dissolving 72.3 mg of spiro-MeOTAD in 1 mL of


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chlorobenzene, to which 28.8 µL of 4-tert-butyl pyridine and 17.5 µL of lithium Bis(trifluoromethanesulfonyl)imide (Li-TFSI) solution (520 mg Li-TSFI in 1 mL acetonitrile, Sigma-Aldrich, 99.8%) were added. The obtained solar cells were left in a desiccator for 72 h before tested. All the device fabrication processes were carried out under controlled atmospheric conditions and a humidity of < 1%.

2.4. Characterization. The morphology and structure of the perovskite films were characterized by field emission scanning electron microscopy (FESEM, HITACHI S4800), atomic force microscopy

(AFM,

Veeco/DI)

and

high-resolution

transmission

electron

microscopy (HRTEM, JEOL JEM-2010F, F20, 200 kV). Micro-grid copper network was used for the TEM tests. The XRD spectra of the prepared perovskite films were measured using powder X-ray diffraction (XRD, Bruker D8 Advanced Diffractometer, Cu Kαradiation, 40 kV). Ion chromatography (Dionex DX-600) was used to detect halogen content of anions in solution. Samples were dipped in isopropyl alcohol solution, then measured until dissolved. The absorption spectra of the perovskite films were measured by using a Cary 500 UV-Vis-NIR Spectrophotometer. The photoluminescence measurement was acquired at room temperature using a UV-Vis-NIR fluorescence spectrophotometer (Fluorolog-3-P). The solar cells were illuminated using a solar light simulator (Oriel, 91160, AM 1.5 globe) and the power of the simulated light was calibrated to 100 mW cm-2 using a Newport Oriel PV reference cell system


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(model 91150 V). The J-V curves of solar cells were measured using a Keithley 2400 digital sourcemeter.

3. RESULTS AND DISCUSSION

3.1. Preparation and Characterization of the Perovskite Films. The perovskite film was synthesized by a two-step method. The first step was preparation of perovskite film by reported solution-based sequential deposition method. The second step was forming submillimeter-sized crystals through the introduction of ammonium salt. CH3NH3Cl was deposited on the surface of fabricated perovskite film. Then black colour of the film gradually faded away and became transparent following the sediment of ammonium salt. Meanwhile the molten salt between solid and liquid was formed under the observation with naked eyes. To understand the change, we quantitatively analyzed the amount of CH3NH3Cl existed on the film surface by using ion chromatography, and found that molar ratio of Cl and I in the film was about 8.25: 1. Therefore we speculate that introduction of chloride ion will most likely induce lead ion coordinated, so that the original perovskite materials dissolved to form a molten salt.

To investigate the crystal structure of perovskite film, Field Emission Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were measured. As presented in Figure 1a, the size of perovskite crystals can achieve 0.5 mm, showing a branch-like structure, which was attributable to the oriented growth. Meanwhile, glass substrate with a few bare perovskite thin films would result in a certain decline in the coverage. Under high magnification


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SEM, perovskite crystals with a very smooth surface can be observed, also have no significant grain boundary even under the higher multiples (Figure 1b). In order to further study on crystal structures of perovskite thin films, we deposited it on a substrate of micro - grid copper network for TEM observation. The dimension of perovskite thin slice is approximately 7 µm × 9 µm (Figure 1c). The materials except for the black sheet-shaped film represent the substrate of TEM measurement. Then we made the selected area electron diffraction (Figure 1d) and found the sheet shaped material displays a clear single crystal diffraction spots, which proves its single crystal characteristics.

Subsequently, we analyzed the surface characteristics of perovskite thin films using atomic force microscopy (AFM). We observed that the size of crystals is extremely beyond 20 µm × 20 µm (Figure 2a). Its geometry is consistent with above results. We further studied longitudinal section of thin film, found the thickness of about 500 nm was as the same as the thickness of perovskite thin film before molten salts reaction (Figure 2b). After depositing a certain amount of CH3NH3Cl, we get transparent molten salt films, which would convert into CH3NH3PbI3 after removed excess CH3NH3Cl by heat treatment. For catching on the subsequent step of crystallization and crystal formation, we showed XRD patterns of the films annealed with different times. As shown in Figure 2c, the film deposited for the first time is fully compatible with CH3NH3PbI3. Then the original CH3NH3PbI3 diffraction peaks are almost disappeared with the CH3NH3Cl deposition completed, becoming transparent amorphous molten salt. After heated


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5 min, the CH3NH3PbI3 (110) and (220) peaks appear all over again.11, 33 Meanwhile, CH3NH3Cl diffraction peaks (asterisk-marked) can be observed. This is likely because the elevated temperature promotes the crystallization of excessive CH3NH3Cl. With the heating time increasing to 60 min, highly (110) oriented square perovskite crystals can be observed at 60 min without else peaks. After heated for 120 min, little change happens, showing that 60 min is the best reaction time. We propose that a new precursor phase must formed in this reaction. Then the CH3NH3PbI3 perovskite crystal domains grow during the decomposition of the intermediate phase, which are caused by the release of gaseous CH3NH3Cl, following the reaction equation:

PbI2 + xCH3NH3I + yCH3NH3Cl → (CH3NH3)x+yPbI2+xCly → CH3NH3PbI3 + CH3NH3Cl (g)↑34

3.2. Morphology of the Perovskite Films during Heat Treatment. At the same time, we also characterized the morphology of the products during heat treatment (Figure 3). When the deposition of CH3NH3Cl is completed, regular pattern of several tens of microns forms. Central cross-like skeletal structure is probably the production of incomplete reaction of CH3NH3PbI3, while the surrounding area may be excess CH3NH3Cl. When the heating time is 5 min, large amounts of CH3NH3Cl are decomposed and volatile, followed by the formation of a mesoporous structure. When heating time is increased to 25 min, these mesoporous structures along with the loss of salts, fused together to form a structure having a small number of large chunks of the space micron level. Under the reaction time of 60 min, CH3NH3Cl almost completely volatilized to obtain a large perovskite crystal with branch-like texture.


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Moreover, we further explored the amount of deposited chloride salt. As shown in Figure 4, before the reaction, dimensions of perovskite crystals are small, in size between 200 nm ~ 400 nm. When introducing a small amount of salt, perovskite crystals obtain a substantial increase, which have reached micron grade in the average size and large particle sizes even have reached 3000 nm. Continuing to increase the proportion to the amount of salt deposited elemental chlorine and iodine content of 1.37: 1, crystal sizes further enhance, more than 2000 nm in average, with decrease in coverage. When the content ratio is 4.12: 1, the perovskite crystal particle size reached 5000 nm. Finally, when the deposition ratio is 8.25: 1, the maximum crystal size was obtained, reaching a sub-millimeter level. From high-powered SEM images (Figure 4f), it is seem that the perovskite film has dense smooth surface, no obvious crystal boundary.

3.3. Optical Properties and Photovoltaic Data. It is well known that the optical properties generally change with the increase in the size of the perovskite crystals. Therefore, photoluminescence and UV-vis absorption spectra were tested and the results are shown in Figure 5. The comparative sample (Control) is perovskite sample before molten salt reaction process. With the increase of the perovskite crystal size, the fluorescence spectrum peak moves from 795 nm to 775 nm, showing apparent blue shift. It indicates that a defect density of large perovskite crystal is lower.22, 23 Meanwhile, the visible light absorption band edge has a red shift, with a better spectral absorption property compared to the original perovskite thin film.26, 35 The photocurrent density-photovoltage (J-V) curves of typical solar cells were measured under


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irradiation with air mass (AM)-1.5 global simulated sunlight at an intensity of 100 mW cm-2. All scans were taken from forward bias to short circuit with a scan rate of 0.15 V s-1.36 As shown in Figure 5c, the perovskite based device yields the PCE of 10.12% with the open circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF) are 900 mV, 17.80 mA cm-2 and 63%, respectively. The hysteresis behavior of this device was measured and it delivered slightly lower PCE value (9.22%) with forward scan than that of reverse scan (10.12%) under the scan rate of 0.15 V s−1 (Figure S1). The external quantum efficiency (EQE) was also measured and the integrated current density for of as-prepared perovskite solar cell was 17.40 mA cm-2, in good agreement with the similar measured Jsc (Figure S2). To investigate the reproducible property of the perovskite solar cells, PCE of 30 individual cells composed of the perovskite films was statistically measured. As shown in Figure 5d, devices based on perovskite films with submillimeter crystals are highly reproducible.

4. CONCLUSIONS

In conclusion, we have demonstrated a new method to obtain thin films with large single crystals by introducing excess ammonium salt to control crystal growth process. The resulted crystal size can reach up to 0.5 mm, and an aspect ratio over 1000. At the same time, photovoltaic devices based on this film exhibit the champion power conversion efficiency of 10.12%. More importantly, we further found that a molten phase is initially formed and, it evolves into ordered porous structure and finally becomes large single crystals during the annealing process. This


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approach to fabricating large crystal films will provide new effective avenues to further improve device performance.


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FIGURES

Figure 1. (a, b) SEM images, (c) TEM image and (d) Selected area election diffraction pattern of the as-prepared perovskite films.


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a

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b

c

Figure 2. (a) AFM image of the as-prepared perovskite film. (b) Height profiles of the white line. (c) XRD patterns of the films annealed with different times. Asterisks denote the major reflections from CH3NH3Cl.


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a

b

c

d

Figure 3. SEM images of the films synthesized with different annealing times of 0 (a), 5 (b), 25 (c) and 60 (d) min, respectively.


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a

b

c

d

e

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Figure 4. SEM images of perovskite films synthesized with different amounts of CH3NH3Cl. The content ratios of salt deposited elemental chlorine and iodine are 0:1, 0.68:1, 1.37:1, 4.12:1, 8.25:1.


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aa

bb

cc

dd

Figure 5. (a) Photoluminescence spectra on as-prepared perovskite film. (b) UV-vis absorbance spectra on as-prepared perovskite film. (c) J-V curves under AM 1.5 simulated illumination of a typical device based on as-prepared perovskite film. (d) Histograms showing the variation in PCE for 30 individual perovskite solar cells based on single-crystal perovskite films.


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ASSOCIATED CONTENT

Supporting Information

The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. FB-SC and SC-FB J-V curves, external quantum efficiency spectra of as-prepared perovskite solar cell are shown in Supporting Information. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].

Author Contributions ‡These authors contributed equally.

Notes The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (21373083, 21573068 and 51602103), SRF for ROCS, SEM, SRFDP, Fundamental Research Funds for the Central Universities (WD1514301), China Postdoctoral Science Foundation


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Funded Project (2015M581547, 2016T90342), “Chen Guang” Project supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation (15CG26), the Major Research plan of the National Natural Science Foundation of China (91534202), 111 Project (B14018), Shanghai Sailing Program (16YF1402100) and ARC Discovery Projects (DP150103775).

REFERENCES (1) Shi, D.; Adinolfi, V.; Comin. R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsive, K.; Losovyj, Y.; 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, 519-522. (2) Zhao, Y.; Nardes, A. M.; Zhu, K. Solid-State Mesostructured Perovskite CH3NH3PbI3 Solar Cells: Charge Transport, Recombination, and Diffusion Length. J. Phys. Chem. Lett. 2014, 5, 490-494. (3) Han, Q.; Bae, S.; Sun, P.; Hsieh, Y.; Yang, Y. (Michael); Rim, Y. S.; Zhao, H.; Chen, Q.; Shi, W.; Li, G.; Yang, Y. Single Crystal Formamidinium Lead Iodide (FAPbI3): Insight into the Structural, Optical, and Electrical Properties. Adv. Mater. 2016, 28, 2253-2258. (4) Liu, Y. C.; Sun, J. K.; Yang, Z.; Yang, D.; Ren, X. D.; Xu, H.; Yang, Z. P.; Liu, S. Z. (Frank) 20-mm-Large Single-Crystalline Formamidinium-Perovskite Wafer for Mass Production

of

Integrated

Photodetectors.

Adv.

Optical

Mater.

2016,

DOI:

10.1002/adom.201600327. (5) Liu, Y. C.; Yang, Z.; Cui, D.; Ren, X. D.; Sun, J. K.; Liu, X. J.; Zhang, J. R.; Wei, Q. B.; Fan, H. B.; Yu, F. Y.; Zhang, X.; Zhao, C. M.; Liu, S. Z. (Frank) Two-Inch-Sized Perovskite


19


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 20 of 24

CH3NH3PbX3 (X = Cl, Br, I) Crystals: Growth and Characterization. Adv. Mater. 2015, 27, 5176-5183. (6) Liu, Y. C.; Zhang, Y. X.; Yang, Z.; Yang, D.; Ren, X. D.; Pang, L. Q.; Liu, S. Z. (Frank) Thinness- and Shape-Controlled Growth for Ultrathin Single-Crystalline Perovskite Wafers for Mass Production of Superior Photoelectronic Devices. Adv. Mater. 2016, 28, 9204-9209. (7) Dong, Q.; Song, J.; Fang, Y.; Shao, Y.; Ducharme, S.; Huang, J. Lateral-Structure SingleCrystal Hybrid Perovskite Solar Cells via Piezoelectric Poling. Adv. Mater. 2016, 28, 28162821. (8) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 2012, 338, 643-647. (9) Etgar, L.; Gao, P.; Xue, Z.; Peng, Q.; Chandiran, A. K.; Liu, B.; Nazeeruddin, M. K.; Grätzel, M. Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells. J. Am. Chem. Soc. 2012, 134, 17396-17399. (10) Burschka, J.; Pellet, N.; Moon, S. J.; Humphry Baker, R.; Gao, P.; Nazeeruddin, M. K.; Grätzel, M. Sequential Deposition as a Route to High-Performance Perovskite Sensitized Solar Cells. Nature 2013, 499, 316-319. (11) Liu, M.; Johnston, M. B.; Snaith, H. J. Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501, 395-398. (12) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Solvent Engineering for High-Performance Inorganic-Organic Hybrid Perovskite Solar Cells. Nat. Mater. 2014, 13, 897-903.


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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) Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Compositional Engineering of Perovskite Materials for High-Performance Solar Cells. Nature 2015, 517, 476-480. (14) National

Renewable

Energy

Laboratory

Best

Research-Cell

Efficiencies

www.nrel.gov/ncpv/images/efficiency chart.jpg (accessed 17 May 2016). (15) Kim, H. D.; Ohkita, H.; Benten, H.; Ito, S. Photovoltaic Performance of Perovskite Solar Cells with Different Grain Sizes. Adv. Mater. 2016, 28, 917-922. (16) Wu, B.; Nguyen,H. T.; Ku, Z.; Han, G.; Giovanni, D.; Mathews, N.; Fan, H.; Sum, T. C. Discerning the Surface and Bulk Recombination Kinetics of Organic-Inorganic Halide Perovskite Single Crystals. Adv. Energy Mater. 2016, 6, 1600551. (17) Wang, Z.; Kathiraser, Y.; Ang, M. L.; Kawi, S. High Purity Oxygen Production via BBCN Perovskite Hollow Fiber Membrane Swept by Steam. Ind. Eng. Chem. Res. 2015, 54, 63716377. (18) Ren, X.; Yang, Y.; Yang, D.; Zhang, X.; Cui, D.; Liu, Y.; Wei, Q.; Fan, H.; Liu, S. Reaction Temperature Modulating Crystal Grain Size and Optoelectronic Properties of Perovskite Film for Solar Cell Application. Nanoscale 2016, 8, 3816-3822. (19) Im, J.; Jang, I.; Pellet, N.; Grätzel, M.; Park, N. Growth of CH3NH3PbI3 Cuboids with Controlled Size for High-Efficiency Perovskite Solar Cells. Nat. Nanotechnol. 2014, 9, 927932. (20) Hou, Y.; Yang, S.; Li, C. Z.; Zhao, H. J.; Yang, H. G. TiO2 Cement for High-Performance Dye-Sensitized Solar Cells. RSC Adv. 2016, 6, 83802-83807.


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(21) Chen, X.; Yang, S.; Zheng, Y. C.; Chen, Y.; Hou, Y.; Yang, X. H.; Yang. H. G. Multifunctional Inverse Opal-Like TiO2 Electron Transport Layer for Efficient Hybrid Perovskite Solar Cells. Adv. Sci. 2015, 2, 1500105. (22) Zheng, Y. C.; Yang, S.; Chen, X.; Chen, Y.; Hou, Y.; Yang, H. G. Themal-Induced VolmerWeber Growth Behavior for Planar Heterojunction Perovskites Solar Cells. Chem. Mater. 2015, 27, 5116-5121. (23) 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, 683-686. (24) Li, X.; Bi, D. Q.; Yi, C. Y.; Décoppet, J. D.; Luo, J. S.; Zakeeruddin, S. M.; Hagfeldt, A.; Grätzel, M. A Vacuum Flash-Assisted Solution Process for High-Efficiency Large-Area Perovskite Solar Cells. Science 2016, 353, 58-62. (25) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Electron-Hole Diffusion Lengths > 175 µm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347, 967-970. (26) Wang, L.; McCleese, C.; Kovalsky, A.; Zhao, Y.; Burda, C. Femtosecond Time-Resolved Transient Absorption Spectroscopy of CH3NH3PbI3 Perovskite Films: Evidence for Passivation Effect of PbI2. J. Am. Chem. Soc. 2014, 136, 12205-12208. (27) Zhou, Z.; Wang, Z.; Zhou, Y.; Pang, S.; Wang, D.; Xu, H.; Liu, Z.; Padture, N. P.; Cui, G. Methylamine-Gas-Induced Defect-Healing Behavior of CH3NH3PbI3 Thin Films for Perovskite Solar Cells. Angew. Chem. Int. Ed. 2015, 54, 9705-9709. (28) Shao, Y.; Fang, Y.; Li, T.; Wang, Q.; Dong, Q.; Deng, Y.; Yuan, Y.; Wei, H.; Wang, M.; Gruverman, A.; Shield, J.; Huang, J. Grain Boundary Dominated Ion Migration in


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Polycrystalline Organic-Inorganic Halide Perovskite Films. Energy Environ. Sci. 2016, 9, 1752-1759. (29) Long, R.; Liu, J.; Prezhdo, O. V. Unravelling the Effects of Grain Boundary and Chemical Doping on Electron-Hole Recombination in CH3NH3PbI3 Perovskite by Time-Domain Atomistic Simulation. J. Am. Chem. Soc. 2016, 138, 3884-3890. (30) Saidaminov, M. I.; Abdelhady, A. L.; Maculan, G.; Bakr, O. M. Retrograde Solubility of Formamidinium and Methylammonium Lead Halide Perovskites Enabling Rapid Single Crystal Growth. Chem. Commun. 2015, 51, 17658-17661. (31) Yang, S.; Zheng, Y. C.; Hou, Y.; Chen, X.; Chen, Y.; Wang, Y.; Zhao, H. J.; Yang, H. G. Formation Mechanism of Freestanding CH3NH3PbI3 Functional Crystals: In Situ Transformation vs Dissolution-Crystallization. Chem. Mater. 2014, 26, 6705-6710. (32) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341-344. (33) Baikie, T.; Fang, Y.; Kadro, J. M.; Schreyer, M.; Wei, F.; Mhaisalkar, S. G.; Grätzel M.; White, T. J. Synthesis and Crystal Chemistry of the Hybrid Perovskite (CH3NH3)PbI3 for Solid-State Sensitised Solar Cell Applications. J. Mater. Chem. A 2013, 1, 5628-5641. (34) Yu, H.; Wang, F.; Xie, F. Y.; Li, W. W.; Chen, J.; Zhao, N. The Role of Chlorine in the Formation Process of “CH3NH3PbI3-xClx” Perovskite. Adv. Funct. Mater. 2014, 24, 71027108. (35) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341-344.


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(36) Yuan, Z.; Wu, Z.; Bai, S.; Xia, Z.; Xu, W.; Song, T.; Wu, H.; Xu, L.; Si, J.; Jin, Y.; Sun, B. Perovskite Solar Cells: Hot-Electron Injection in a Sandwiched TiOx-Au-TiOx Structure for High-Performance Planar Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500038.

Table of Contents Graphic

A molten salt assisted method is applied to efficiently control the growth of perovskite crystals by using excess ammonium salt. The perovskite crystal does not have obvious grain boundaries with large single crystal domains. Photovoltaic devices based on this film exhibit a power conversion efficiency of 10.12%. This synthetic strategy, for the first time, enable the formation of submillimeter sized perovskite films and would also provide effective means in boosting the efficiency of perovskite solar cells.

CH3NH3Cl CH3NH3l PbI2

Amorphous phase

molten salt

annealing


Perovskite

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Molten Salt-Assisted Growth of Perovskite Films ... - ACS Publications

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