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Reversible and Irreversible Electric Field Induced Morphological and Interfacial Transformations of Hybrid Lead Iodide Perovskites Sergey Yu. Luchkin,† Azat F. Akbulatov,§ Lyubov A. Frolova,§ Monroe P. Griffin,‡ Andrei Dolocan,# Raluca Gearba,# David A. Vanden Bout,‡ Pavel A. Troshin,†,§ and Keith J. Stevenson*,† †
Center for Electrochemical Energy Storage, Skolkovo Institute of Science and Technology, Nobel Street 3, Moscow 143026, Russian Federation § The Institute for Problems of Chemical Physics of the Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka 141432, Russian Federation ‡ Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States # Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States S Supporting Information *
ABSTRACT: We report reversible and irreversible strain effects and interfacial atomic mixing in MAPbI3/ITO under influence of external electric bias and photoillumination. Using conductive-probe atomic force microscopy, we locally applied a bias voltage between the MAPbI3/ITO and the conductive tip and observed local dynamic strain effects and current under conditions of forward bias. We found that the reversible part of the strain is associated with a current spike at the current onset stage and can therefore be related to an electrochemical process accompanied by local molar volume change. Similar partly reversible surface deformation was observed when the tip−sample contact was illuminated by light. Time-of-flight secondary ion mass spectrometry of electrically biased regions revealed massive atomic mixing at the buried MAPbI3/ITO interface, while the top MAPbI3 surface, subjected to strong morphological damage at the tip−surface contact, revealed less significant chemical decomposition. KEYWORDS: MAPbI3, solar cells, hybrid perovskites, electric field, degradation
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INTRODUCTION Exceptional photovoltaic properties of solution processed hybrid perovskite materials have spurred intensive investigations. Currently, the power conversion efficiency (PCE) of perovskite solar cells exceeds 22% on the best laboratory samples.1−3 Despite the rapid PCE improvement, practical use of hybrid perovskite solar cells is hindered by fast environmental degradation.4,5 While degradation from humid atmosphere can be suppressed by proper cell encapsulation, degradation processes under photon flux and electric field (built-in, externally applied, or photoinduced) are intrinsic and can hardly be prevented. Elucidation of these degradation processes is an essential step to overcome current limitations. Additionally, there is the need to understand how these degradations occur throughout the entire 3D configuration and specifically at interfaces. Electric field studies have reported to cause both functional and structural transformations of hybrid perovskite solar cells.6,7 MAPbI3 itself is thermodynamically unstable.8 It is also kinetically unstable due to low activation energies for I− and MA+ migration.9−13 Therefore, it is not surprising that under electric bias MAPbI3 is subjected to irreversible decomposition, as previously reported.7,14,15 Similar effects besides photolysis16 © XXXX American Chemical Society
may be caused by light generated photovoltage, which acts in similar ways as an externally applied voltage.17,18 However, electric bias does not always cause irreversible degradation. For example, a switchable photovoltaic effect,6 which is associated with migration of ions within the perovskite layer, can be reversed by applying opposite bias voltage. Reversible conversion between MAPbI3 and PbI2 was also experimentally observed at small voltages.19 I−V hysteresis has irreversible and reversible parts20 and also strongly depends on contact material.21,22 These observations raise a question about a role of MAPbI3 interfaces with contact materials in these processes. In this paper, we report both reversible and irreversible morphological changes of MAPbI3 and MAPbI3/ITO interface under influence of bias voltage. We used an atomic force microscope (AFM) installed inside an Ar filled glovebox to locally apply electric field to the samples and observe dynamic processes such as local current flow and surface deformation Special Issue: Hupp 60th Birthday Forum Received: February 10, 2017 Accepted: May 1, 2017
A
DOI: 10.1021/acsami.7b01960 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces without exposure to ambient atmosphere. We found that surface deformation has reversible and irreversible parts and that the reversible part is greater than 10 nm for 150 nm-thick MAPbI3 film. Similar partly reversible surface deformation was observed when the tip−sample contact was illuminated by light. These conductive-probe studies in concert with time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies revealed massive atomic mixing at the buried MAPbI3/ITO interface, while the MAPbI3 surface, subjected to strong morphological damage at the tip−surface contact, showed no significant chemical decomposition.
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RESULTS AND DISCUSSION Figure 1 shows MAPbI3 topography and amplitude before (a and b) and after (c and d) application of triangular bias voltage
Figure 2. I−V curves (a and b) and simultaneous deformations (c and d) recorded while applying triangular voltage pulses (the pulse shape is shown in the inset in panel a).
that, upon consequent cycling, the current deteriorated much faster at the points where spikes appeared (Figure S1). The spikes rapidly disappear with further increases in the applied voltage, which is accompanied by a significant partially reversible surface deformation (Figures 2c and d). It is rather remarkable that a 150 nm-thick perovskite film undergoes the local expansion by more than 10 nm, which constitutes more than 6% of the total layer thickness. The reversible part of the deformation disappears upon application of the reverse bias. One can see from Figures 2c and d that more negative voltage is needed to reverse changes induced by applying a more positive bias. The irreversible part of the deformation results in the appearance of voids (for higher voltages) and protrusions (in the case of lower voltages) on the film surface (Figure 1c and d). Such deformation behavior might be due to generation and annihilation of vacancies and vacancy clusters at the MAPbI3/ITO interface.24 Similar partly reversible strain effect correlating with the generated photocurrent was observed when the tip−sample junction was illuminated by sufficiently intense light (see Figure S2 in the Supporting Information). The voltage and light-induced reversible perovskite film deformations were quite large. Therefore, to exclude possible instrumental contributions, we performed test measurements on Si with a native SiO2 (Si/SiO2) sample (see Figure S3). The measurements revealed that under the same experimental conditions no strain was detected except at moments when the blue laser was switched on and off. This strain, however, was significantly smaller than the one measured on the perovskite samples. Therefore, the instrumental contributions to the strain are negligible. At this point, it is important to mention that cantilever heating by laser light can notably influence measurements if the cantilever has a nonuniform coating. We tested a top-view silicon VIT_P_C-A cantilever with Al reflecting coating and no front coating. In this case, the laser illumination and resulting thermal heating leads to cantilever buckling due to the bimorph effect caused by different thermal expansion coefficients of the Si cantilever body and the Al reflective coating (see Figure S4). In contrast, the top-view VIT_P/Pt cantilever with Pt coating
Figure 1. AFM topography (a and c) and amplitude (b and d) images of the MAPbI3 film grown on ITO/glass substrates before (top) and after (bottom) application of bias voltage (from −2 to +2 V to −5 to +5 V). The bias was applied in the dark when the tip was landed on the sample surface and a firm contact was established.
between the conductive Pt coated AFM tip and the sample. New topography elements with vertical size of several nanometers and lateral size of 1−10 nanometers appeared on the surface in the local points where the tip was placed during the voltage application. The emergence of these new features such as protrusions or voids correlates well with the dark current behavior as shown in Figure 2, where the current and simultaneous surface deformation are plotted as a function of the applied bias voltage. The I−V profile in Figure 2a demonstrates a typical dark I−V shape with two particular features: a current spike at the current onset stage and strong hysteresis. The I−V hysteresis in hybrid perovskite solar cells is a well-documented phenomenon and is mainly attributed to ionic migration within the MAPbI3 layer21 and across interfaces.22 The current spike, taking into account the early reported reversible interconversion between MAPbI3 and PbI2,19 may be an indication of onset of an electrochemical process taking place on the surface or in the bulk, including at the buried MAPbI3/ITO interface.23 The electrochemical origin of strain is partially supported by the fact B
DOI: 10.1021/acsami.7b01960 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces on both front and reflective sides possessed no notable bimorph effect (see Figure S3). To further elucidate the observed phenomena, we assessed information about chemical composition of the MAPbI3 film grown on ITO/glass substrates by ToF-SIMS. Because the described above point measurements gave tiny surface features with the lateral size on the order of one-tenth of a nanometer, prior to the ToF-SIMS measurements, we applied voltage between the moving tip and the sample over 5 × 5 μm square regions (Figure 3).
Figure 5. MAPbI3 surface topography after applying different bias voltages between the tip and the sample while scanning. The film surface is severely affected only at the forward bias.
formation of some soft sticky substance that is difficult to image. The ToF-SIMS data are presented in Figure 6, where the PbI2− and SnO2− ion fragments represent the MAPbI3 and ITO, respectively. To start, in the 3D reconstruction of the sputtered volume, we note significant chemical variations appearing in the lithographic regions at the MAPbI3/ITO buried interface (Figure 6a). Regions of interest (ROIs) corresponding to the AFM lithographic regions were identified based on the PbI2− secondary ion map (Figure 6b), and depth profiles (Figure 6c) for each of these ROIs were reconstructed. All profiles were normalized to their corresponding ROI area, while the depth conversion was calculated by employing a sputtering rate model that assumes the sputtering rate at the MAPbI3/ITO interface as a linear combination between the individual sputtering rates.25 The broadening of the MAPbI3/ITO interface suggests mutual diffusion (percolation) of the MAPbI3-derived species into the ITO and vice versa. To quantify the extent of this molecular mixing, we use the so-called mixing-roughnessinformation (MRI) model,26,27 which simulates depth profiles of interfaces while accounting for the sputtering-induced mixing (w), the information depth (λ), and corrugation (σ) effects to determine the molecular mixing length (w0), that is, the length of the real interface between MAPb3 and ITO. For the pristine case (Figure 7a), we simulate and fit the PbI2− ion fragment profile at the ITO interface to determine the w and λ parameters and calculate minimal molecular mixing (w0 = 1.1 nm) with an interfacial corrugation, σ, of ∼1.9 nm. When fitting the lithographic regions, for example, the −4 V ROI (Figure 7b), we fix the w and λ parameters to the values determined from the pristine profile and allow the corrugation and real mixing parameters to vary freely. The calculations yield large corrugation increases in the lithographic regions, as expected from the AFM surface topography measurements. Of note, the corrugation at an interface between two materials is, most times, an average between the corrugation of the substrate and that of the surface of the overlayer. Even with the large corrugation change (∼2× that of pristine case), we calculate a large extent of mixing, ∼5× the mixing in the pristine case for the −4 V ROI. A summary of the calculated molecular mixing length, w0, is given in Figure 7d. The general trend in the forward bias voltage direction is that mixing increases with applied voltage. What is important here is that, unlike the MAPbI3/ITO interface, Pt(tip coating)/MAPbI3 interface was subjected to less significant chemical transformation (Figure 6c) even though the electric field at the tip−sample contact was higher due to the electric field constraint at the tip. This observation is
Figure 3. Schematic overview of the lithography pattern. Sixteen consequent scans of 5 × 5 μm areas within a 30 × 30 μm area were done. The bias voltage was applied to the sample while the tip was grounded; therefore, the voltage sign is opposite to the one for point measurements. Notable changes appeared only on regions toned green.
Figure 4 shows a part of the modified area where the applied voltage caused visible morphological changes. As in the case of
Figure 4. Modified MAPbI3 surface after applying bias voltage while scanning. (a) Area with 4 regions subjected to the lithography with the bias of −3, −4, −5, and −6 V at the tip, and (b) magnified boundary between the modified and pristine regions.
the aforementioned point measurements, the topographical changes appeared only under the forward bias, as seen from Figures 4 and 5. Note that in this case the bias voltage is negative because the bias was applied to the sample while the tip was grounded. Forward bias up to −3 V did not cause notable surface changes. Surface transformations appeared at −4 V (27 mV/nm) (Figure 4b), while applying even higher bias resulted in the C
DOI: 10.1021/acsami.7b01960 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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Figure 6. 3D ToF-SIMS depth profiling studies of lithographically defined regions. (a) 3D reconstruction of the sputtered volume, including the lithography regions. Representing the MAPbI3 and ITO layers, respectively, the PbI2− (red) and SnO2− (blue) secondary ion fragments are displayed in a dual color overlay. A significant chemical variation is observed at the MAPbI3/ITO buried interface in the lithography regions with respect to the pristine region. (b) The total PbI2− ion signal map indicates the lithography modified areas and provides the ROIs denoted in the individual depth profiles shown in panel c. The pristine profile is taken from outside the modified regions in the four corners of the analyzed area. The unlabeled area corresponding to +1 V lithographic region seems to be an artifact because the other areas corresponding to +2 to +8 V lithographic regions do not show topographical changes.
deformation was observed when the tip−sample contact was illuminated by light, thus suggesting that light-induced electric field leads to very similar effects as externally applied electric bias. Time-of-flight secondary ion mass spectrometry reveals massive atomic mixing at the buried MAPbI3/ITO interface. On the contrary, the MAPbI3 surface, subjected to a strong electric field-induced morphological evolution while being in contact with the Pt-coated tip, showed less significant changes in the chemical composition.
in agreement with the previously reported results. Indeed, the reversible reaction was reported in MAPbI3 deposited on glass and when bias is applied between Au electrodes,19 while the irreversible one was reported in MAPbI3 sandwiched between ETL and HTL functional layers.7 Thus, it is reasonable to suggest that the appearance and magnitude of the irreversible field-induced chemical decomposition of MAPbI3 depends on the materials used for the contact and/or functional ETL and HTL layers. These findings strongly suggest that the MAPbI3 interfaces with adjacent functional layers influence not only the solar cell efficiency while controlling the extraction and surface recombination of charge carriers but also the electrochemical stability of the perovskite absorber and the entire device. Improper choice of contact materials and HTL and ETL layers might significantly reduce the lifetime of perovskite solar cells.
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EXPERIMENTAL SECTION
Sample Preparation. ITO/glass substrates (5 Ω square, Luminescence Technology Corp.) were precleaned with organic solvents and then washed consequently with deionized water, acetone, and isopropanol (each for 15 min in ultrasonic bath). The solution of MAPbI3 precursor in DMF (∼45 wt %) was deposited on the substrate by spin-coating at 5000 rpm inside a nitrogen filled glovebox using toluene (200 μL) as antisolvent quencher, inducing film crystallization. After 45 s of spinning, the deposited films were annealed at 100 °C for 15 min on a hot plate inside a nitrogen glovebox. AFM Measurements. Measurements were performed using Cypher EX AFM (Asylum Research, CA, US) operating under inert Ar atmosphere in a MBraun glovebox with O2 < 0.1 ppm and H2O < 1 ppm. Bias voltage was applied in conductive (ORCA) and PFM voltage lithography modes. Surface deformation was obtained as the deflection signal of the cantilever. Topography before and after surface
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CONCLUSION In conclusion, we observed both reversible and irreversible field-induced morphological changes in the MAPbI3 films and at the MAPbI3/ITO interface. Using conductive-probe atomic force microscopy, we locally applied bias voltage between MAPbI3/ITO and the Pt-coated tip and observed local dynamic strain correlating well with the behavior of the dark current. We found that the field-induced surface deformation has reversible and irreversible components. Similar partially reversible surface D
DOI: 10.1021/acsami.7b01960 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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Germany, 2010). During depth profiling, the sputtering ion beam (Cs+ at 500 eV ion energy and ∼40 nA measured sample current) was raster scanned over an area of 300 × 300 μm2. The analysis ion beam consisting of Bi1+ pulses (30 keV ion energy, 100 ns pulse duration, 0.04 pA measured sample current) was set in the burst alignment (BA) mode and raster scanned over a 60 × 60 μm2 area (256 × 256 pixels) centered within the Cs+ sputtered area at the regressing surface. The depth profiles were acquired in noninterlaced mode, that is, sequential sputtering and analysis, at a base pressure of 10−9 Torr. All mass spectra were acquired in negative polarity while the mass resolution was >300 (m/δm) for all fragments of interest. After data collection, the different ROIs, e.g., the −4 V lithography area, were individually reconstructed and analyzed. The reconstructed depth profiles were normalized to their corresponding ROI area to allow for a fair comparison of signal acquired from the different ROIs. The sputtering rates were calculated at 0.72 and 0.18 nm/s for the MAPbI3 perovskite and ITO, respectively.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b01960. Evolution of the dark current in a series of consequent scans in two different points on the MAPbI3, current generation and the surface deformation of the ITO/ MAPbI3 sample under illumination and corresponding topography changes with short description, and testing of instrumental contributions (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Andrei Dolocan: 0000-0001-5653-0439 Pavel A. Troshin: 0000-0001-9957-4140 Keith J. Stevenson: 0000-0002-1799-5177 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS K.J.S. congratulates J.T.H. on the occasion of his 60th birthday. This work was performed in the frame of the Next Generation Skoltech-MIT collaboration program.
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Figure 7. Atomic mixing at the buried MAPbI3/ITO interface. (a and b) MRI simulations, using the PbI2− ion fragment, through the MAPbI3/ITO interface for the pristine (a) and −4 V (b) ROIs. The real interface is broadened by sputtering effects which are accounted for in the simulated profile (see text). (c) Summary of the calculated mixing lengths for the pristine MAPbI3/ITO interface versus the different areas of lithography performed at various bias voltages.
REFERENCES
(1) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. Il. High-Performance Photovoltaic Perovskite Layers Fabricated through Intramolecular Exchange. Science 2015, 348, 1234−1237. (2) Saliba, M.; Matsui, T.; Seo, J.-Y.; Domanski, K.; Correa-Baena, J.P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Grätzel, M. Cesium-Containing Triple Cation Perovskite Solar Cells: Improved Stability, Reproducibility and High Efficiency. Energy Environ. Sci. 2016, 9, 1989−1997. (3) Eperon, G. E.; Leijtens, T.; Bush, K. A.; Prasanna, R.; Green, T.; Wang, J. T.-W.; McMeekin, D. P.; Volonakis, G.; Milot, R. L.; May, R.; Palmstrom, A.; Slotcavage, D. J.; Belisle, R. A.; Patel, J. B.; Parrott, E. S.; Sutton, R. J.; Ma, W.; Moghadam, F.; Conings, B.; Babayigit, A.; Boyen, H.-G.; Bent, S.; Giustino, F.; Herz, L. M.; Johnston, M. B.; McGehee, M. D.; Snaith, H. J. Perovskite-Perovskite Tandem Photovoltaics with Optimized Band Gaps. Science 2016, 354, 861−865. (4) Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.; Chen, L.-Y.; Dubale, A. A.; Hwang, B.-J. Organometal Halide Perovskite Solar Cells: Degradation and Stability. Energy Environ. Sci. 2016, 9, 323−356.
modification was measured in a standard semicontact mode. Pt-coated cantilevers with conventional geometry, 143 kHz resonance frequency, and 4.5 N/m spring constant were used. Electrical contact to the sample was provided by painting conductive Ag paint on ITO. The effect of light exposure was measured by pointing the Cypher Blue Drive laser light with 405 nm wavelength at the tip−MAPbI3/ ITO junction. To allow direct light exposure of the tip−sample junction, the top-view Pt coated VIT_P/Pt cantilever was used. The top-view cantilever geometry allowed direct expose of the Pt-coated tip-MAPbI3/ITO contact area to the laser light without shading from the cantilever. ToF-SIMS Measurements. For depth profiling and chemical analysis, we used a TOF.SIMS 5 instrument (ION-TOF GmbH, E
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Microscopy: Environmental and Current Spreading Effects. ACS Nano 2013, 7, 8175−8182. (24) Kalinin, S. V.; Jesse, S.; Tselev, A.; Baddorf, A. P.; Balke, N. The Role of Electrochemical Phenomena in Scanning Probe Microscopy of Ferroelectric Thin Films. ACS Nano 2011, 5, 5683−5691. (25) Elko-Hansen, T. D.-M.; Dolocan, A.; Ekerdt, J. G. Atomic Interdiffusion and Diffusive Stabilization of Cobalt by Copper During Atomic Layer Deposition from Bis(N - Tert -Butyl- N ′-Ethylpropionamidinato) Cobalt(II). J. Phys. Chem. Lett. 2014, 5, 1091− 1095. (26) Hofmann, S. Profile Reconstruction in Sputter Depth Profiling. Thin Solid Films 2001, 398, 336−342. (27) Chou, H.; Ismach, A.; Ghosh, R.; Ruoff, R. S.; Dolocan. Revealing the Planar Chemistry of Two-Dimensional Heterostructures at the Atomic Level. Nat. Commun. 2015, 6, 7482.
(5) Bryant, D.; Aristidou, N.; Pont, S.; Sanchez-Molina, I.; Chotchunangatchaval, T.; Wheeler, S.; Durrant, J. R.; Haque, S. A. Light and Oxygen Induced Degradation Limits the Operational Stability of Methylammonium Lead Triiodide Perovskite Solar Cells. Energy Environ. Sci. 2016, 9, 1655−1660. (6) Xiao, Z.; Yuan, Y.; Shao, Y.; Wang, Q.; Dong, Q.; Bi, C.; Sharma, P.; Gruverman, A.; Huang, J. Giant Switchable Photovoltaic Effect in Organometal Trihalide Perovskite Devices. Nat. Mater. 2014, 14, 193− 198. (7) Jeangros, Q.; Duchamp, M.; Werner, J.; Kruth, M.; DuninBorkowski, R. E.; Niesen, B.; Ballif, C.; Hessler-Wyser, A. In Situ TEM Analysis of Organic-Inorganic Metal-Halide Perovskite Solar Cells under Electrical Bias. Nano Lett. 2016, 16, 7013−7018. (8) Nagabhushana, G. P.; Shivaramaiah, R.; Navrotsky, A. Direct Calorimetric Verification of Thermodynamic Instability of Lead Halide Hybrid Perovskites. Proc. Natl. Acad. Sci. U. S. A. 2016, 113, 7717− 7721. (9) Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic Transport in Hybrid Lead Iodide Perovskite Solar Cells. Nat. Commun. 2015, 6, 7497. (10) Yuan, Y.; Chae, J.; Shao, Y.; Wang, Q.; Xiao, Z.; Centrone, A.; Huang, J. Photovoltaic Switching Mechanism in Lateral Structure Hybrid Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500615. (11) Azpiroz, J. M.; Mosconi, E.; Bisquert, J.; De Angelis, F. Defect Migration in Methylammonium Lead Iodide and Its Role in Perovskite Solar Cell Operation. Energy Environ. Sci. 2015, 8, 2118−2127. (12) Yang, T.-Y.; Gregori, G.; Pellet, N.; Grätzel, M.; Maier, J. The Significance of Ion Conduction in a Hybrid Organic-Inorganic LeadIodide-Based Perovskite Photosensitizer. Angew. Chem., Int. Ed. 2015, 54, 7905−7910. (13) Yuan, Y.; Huang, J. Ion Migration in Organometal Trihalide Perovskite and Its Impact on Photovoltaic Efficiency and Stability. Acc. Chem. Res. 2016, 49, 286−293. (14) Frolova, L. A.; Dremova, N. N.; Troshin, P. A. The Chemical Origin of the P-Type and N-Type Doping Effects in the Hybrid Methylammonium−lead Iodide (MAPbI 3) Perovskite Solar Cells. Chem. Commun. 2015, 51, 14917−14920. (15) Bae, S.; Kim, S.; Lee, S.-W.; Cho, K. J.; Park, S.; Lee, S.; Kang, Y.; Lee, H.-S.; Kim, D. Electric-Field-Induced Degradation of Methylammonium Lead Iodide Perovskite Solar Cells. J. Phys. Chem. Lett. 2016, 7, 3091−3096. (16) Verwey, J. F. Time and Intensity Dependence of the Photolysis of Lead Halides. J. Phys. Chem. Solids 1970, 31, 163−168. (17) Deng, Y.; Xiao, Z.; Huang, J. Light-Induced Self-Poling Effect on Organometal Trihalide Perovskite Solar Cells for Increased Device Efficiency and Stability. Adv. Energy Mater. 2015, 5, 1500721. (18) Xing, J.; Wang, Q.; Dong, Q.; Yuan, Y.; Fang, Y.; Huang, J. Ultrafast Ion Migration in Hybrid Perovskite Polycrystalline Thin Films under Light and Suppressing in Single Crystals. Phys. Chem. Chem. Phys. 2016, 18, 30484−30490. (19) Yuan, Y.; Wang, Q.; Shao, Y.; Lu, H.; Li, T.; Gruverman, A.; Huang, J. Electric-Field-Driven Reversible Conversion Between Methylammonium Lead Triiodide Perovskites and Lead Iodide at Elevated Temperatures. Adv. Energy Mater. 2016, 6, 1501803. (20) Garcia-Belmonte, G.; Bisquert, J. Distinction between Capacitive and Noncapacitive Hysteretic Currents in Operation and Degradation of Perovskite Solar Cells. ACS Energy Lett. 2016, 1, 683− 688. (21) Kim, H.-S.; Jang, I.-H.; Ahn, N.; Choi, M.; Guerrero, A.; Bisquert, J.; Park, N.-G. Control of I − V Hysteresis in CH 3 NH 3 PbI 3 Perovskite Solar Cell. J. Phys. Chem. Lett. 2015, 6, 4633−4639. (22) Levine, I.; Nayak, P. K.; Wang, J. T.-W.; Sakai, N.; Van Reenen, S.; Brenner, T. M.; Mukhopadhyay, S.; Snaith, H. J.; Hodes, G.; Cahen, D. Interface-Dependent Ion Migration/Accumulation Controls Hysteresis in MAPbI 3 Solar Cells. J. Phys. Chem. C 2016, 120, 16399− 16411. (23) Arruda, T. M.; Kumar, A.; Jesse, S.; Veith, G. M.; Tselev, A.; Baddorf, A. P.; Balke, N.; Kalinin, S. V. Toward Quantitative Electrochemical Measurements on the Nanoscale by Scanning Probe F
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