Direct Observation of Reversible Transformation of CH3NH3PbI3 and

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Letter

Direct Observation of Reversible Transformation of CH3NH3PbI3 and NH4PbI3 Induced by Polar Gaseous Molecules Weixin Huang, Joseph S Manser, Subha Sadhu, Prashant V. Kamat, and Sylwia Ptasinska J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b02499 • Publication Date (Web): 25 Nov 2016 Downloaded from http://pubs.acs.org on November 25, 2016

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

The Journal of Physical Chemistry Letters 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 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

The Journal of Physical Chemistry Letters

Direct Observation of Reversible Transformation of CH3NH3PbI3 and NH4PbI3 Induced by Polar Gaseous Molecules Weixin Huang1,2, Joseph S. Manser1,3, Subha Sadhu1, Prashant V. Kamat1,2,3, and Sylwia Ptasinska1,4* 1 2

Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA

Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA 3

Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA 4

Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA *corresponding author: [email protected]

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Despite its competitive photovoltaic efficiency, the structural transformations of the prototypical hybrid perovskite, methylammonium lead iodide, are facilitated by interactions with polar molecules. Changes in optical and electronic properties upon exposure to ammonia potentially can enable the use of hybrid perovskites in gas-sensing applications. We investigated the effects of ammonia on CH3NH3PbI3 by exposing perovskite films to a wide range of vapor pressures. Spectroscopic analyses indicated that ammonium cations replaced the methylammonium cations in the perovskite crystal, thereby resulting in the formation of NH4PbI3. The transformation of CH3NH3PbI3 to NH4PbI3 caused distinct changes in the morphology of the film and its crystalline structure; however, the introduction of CH3NH2 gas reversed these changes. An in-depth understanding of the reversible chemical and structural alterations resulting from exposure to polar molecules can advance the development of hybrid perovskite sensors and provide insight into mechanisms by which perovskites convert due to interactions with polar molecules.

TOC GRAPHICS

2


Page 2 of 19

Page 3 of 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


Because of the outstanding optoelectronic properties and facile processing ability of inorganicorganic hybrid perovskites, they have proven to be breakthrough materials for next-generation photovoltaics and other applications.1–5 With the general formula of AMX3 (where A is a monovalent organic cation, M is a divalent metal, and X is a halide anion), the structures of 3D metal halide hybrid perovskites are extended inorganic frameworks of corner-sharing [MX6]4octahedra with organic cations that fill the cuboctahedral cavities and balance the charge. In addition, the properties of such materials can be tailored readily by modifying the organic and inorganic submodules in the hybrid perovskite structure.6–11

Despite the successful design of efficient perovskite photovoltaic devices, the chemical and structural labilities of CH3NH3PbI3 lead to its transformation at various environmental and operational conditions, e.g., heat,12,13 low-energy electrons,14 humidity,15,16 concentrated light,17–19 and other factors.20–25 Polar gas-phase compounds react easily with perovskite materials, producing severe and often deleterious alterations to their structures and properties.10,16,17 At 90% relative humidity, unencapsulated films of methylammonium lead iodide (CH3NH3PbI3) perovskite have the propensity to form new, solvated crystal structures (CH3NH3PbI3·H2O and (CH3NH3)4PbI6·2H2O) with dramatically altered optical and electronic properties. Such changes significantly degraded the performances of the devices in which they were used, even though the hydrated perovskite reverted to the original structure after the films were exposed to dry nitrogen.15,16 However, industry can use the rapid transformation of perovskite materials in the presence of polar gaseous compounds to extend their applications as gas sensors. It has been known for some time that CH3NH3PbI3 perovskite is highly sensitive to water, but recently it also was found to be sensitive to another polar molecule, i.e., ammonia (NH3).26 Upon exposure to 3



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

NH3 gas, the resistance of the perovskite film was found to decrease significantly within seconds, but it reverted to its initial value when the NH3 environment was removed. Thus, this sensitivity facilitates the use of perovskite films as electrical NH3 sensors.27 However, poor repeatability, which results from the fact that the continued exposure of perovskites to NH3 gradually results in the transformation of CH3NH3PbI3 to a new and unknown product, has impeded the use of this method.27 Limited understanding of the processes in which halide perovskites interact with NH3 further hinders the improvement and full use of the unique properties of these materials.

We examined the chemical evolution of CH3NH3PbI3 perovskite in the presence of low-pressure NH3 (0.05-5 mbar) using in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS). We performed two types of in situ AP-XPS experiments using the CH3NH3PbI3 films: (1) exposure of the samples for different durations to a constant NH3 pressure (time-dependent study) and (2) exposure of the samples to different NH3 pressures for a set duration (pressure-dependent study). Figures 1(a-d) show the C 1s, N 1s, Pb 4f, and I 3d5/2 photoelectron spectra obtained at a constant NH3 pressure of 1.0 mbar for 0 to 13 h. The C 1s spectra for the pristine CH3NH3PbI3 film showed two features at binding energies (BEs) corresponding to 285.3 and 286.6 eV, see Figures 1(a) and S1(a-c) in the Supporting Information (SI), which are attributed to adventitious carbon and carbon from the methylammonium cation, respectively.22,28 The spectral feature in the N 1s spectra observed at 402.5 eV is characteristic of the methylammonium cation (CH3NH3+).28 The appearance of a new peak at 401.4 eV in the N 1s spectra at an NH3 pressure of 1.0 mbar is attributed to gas-phase NH3, which is consistent with the control NH3 spectrum in Figure S1. As the duration of NH3 treatment increased, the intensity of the characteristic C 1s peak of CH3NH3+ decreased significantly. In contrast, there were no distinguishable changes in the intensities of the 4


Page 4 of 19

Page 5 of 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


peaks or the positions of the BEs of the N 1s, Pb 4f, and I 3d5/2 spectra during treatment with NH3 at 1.0 mbar (0.5-13 h). The similar photoelectron intensity of N 1s corresponding to either CH3NH3+ or NH4+ in Figure 1(b) implies that the nitrogen-containing species remain unchanged within the perovskite structure. We observed similar results in the pressure-dependent study, as presented in Figures S2(a-d).

Figure 1. (a) C 1s, (b) N 1s, (c) Pb 4f, and (d) I 3d5/2 photoelectron spectra of a CH3NH3PbI3 film recorded at an NH3 pressure of 1.0 mbar for 0-13 h and after evacuation of NH3.

Figures 2(a) and (b) show the atomic ratios of C/Pb, N/Pb, and I/Pb obtained from the time- and pressure-dependent studies, which were estimated from the fitted peaks of C 1s (286.6 eV), N 1s (402.5 eV), Pb 4f, and I d5/2. For the pristine samples, the C/Pb, N/Pb, and I/Pb ratios were approximately 1.5, 1, and 3, respectively. Both the time- and pressure-dependent studies (Figs. 2(a) and (b)) showed a decrease in the ratio of the C/Pb from approximately 1.5 to 0.5, which suggested the gradual loss of CH3NH3+ ions. Unlike the C/Pb ratios, the N/Pb ratios remained nearly constant after treatment at either elevated pressures of NH3 or at 1 mbar of NH3 for 13 h. Therefore, the decreasing C/Pb ratios and constant N/Pb ratios in both the time- and pressure5



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

dependent studies indicated that the substitution occurred between equimolar amounts of Ncontaining species and CH3NH3+. Since NH4+ and CH3NH3+ ions have the same BE (402.5 eV) in the N 1s spectra,29-32 the NH4+ ion is the most probable nitrogen-containing ion involved in the substitution. In addition, the constant I/Pb ratio suggested that there was no loss of iodide in the perovskite structure during the reaction. The decrease in the I/Pb ratio in Fig. 2(b) was due to an increase in the scattering cross section of photoelectrons by gaseous NH3 rather than the loss of Iions.33,34 Increasing the NH3 pressure led to a higher attenuation of photoelectrons from the I 3d5/2, which have lower kinetic energy (867.3 eV) than those from Pb 4f7/2 (1348.2 eV). After the evacuation of NH3, the ratio of I/Pb reverted to its initial value, clearly indicating that there was no loss of I- from the perovskite structure (Fig. 2(b)). These results suggested that the presence of NH3 triggered the substitution of CH3NH3+ by NH4+ (NH3 + CH3NH3PbI3 → NH4PbI3 + CH3NH2↑). The transformation of CH3NH3PbI3 to NH4PbI3 occurred through a proton transfer mechanism, in which the nitrogen-bound hydrogen atom of CH3NH3+ transferred to an ammonia molecule. Figure S3 shows a schematic representation of this mechanism.

6


Page 6 of 19

Page 7 of 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


Figure 2. I/Pb, C/Pb, and N/Pb ratios estimated from the CH3NH3PbI3 films upon exposure to relatively low-pressure NH3: (a) time-dependent study; (b) pressure-dependent study; (c) the same atomic ratios from the CH3NH3PbI3 films after exposure to NH3 at 600 mbar for 5 and 60 min; (d) XRD patterns of pristine CH3NH3PbI3 and CH3NH3PbI3 films exposed to NH3 at 600 mbar. Characteristic XRD peaks are indicated by gray squares for CH3NH3PbI3, green circles for NH4PbI3, and orange stars for the fluorine-doped tin oxide (FTO) substrate.

Although the XPS data demonstrated the conversion of CH3NH3PbI3 to NH4PbI3, the XRD patterns of the CH3NH3PbI3 films used in the time- and pressure-dependent experiments under relatively low-pressure NH3 were indicative of the CH3NH3PbI3 perovskite structure (Fig. S4). This observation implies that the substitution may take place only at the surface, because the XPS technique primarily probes the surface. To verify this hypothesis, we investigated the presence of CH3NH3+ in perovskite at the bulk level using nuclear magnetic resonance (NMR) spectroscopy. 7



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 S5 shows the proton NMR spectra for the pristine perovskite film and the spectra after the time-dependent experiment. The spectrum of the pristine perovskite film exhibited the CH3NH3+ signal at 2.59 ppm, which was also detected in the sample after treatment with NH3 at a pressure of 1 mbar for 13 h. This provides evidence that the substitution occurred only in the outermost atomic layers of the material during exposure to low-pressure NH3.

A previous study showed that CH3NH3PbI3 was transformed to a wide band gap material after a few seconds of uncontrolled contact with NH3 vapor.26 Conversely, no observable color change occurred in our controlled experiments with low-pressure NH3, suggesting that the reaction was limited to the near-surface region of the films in our conditions. Therefore, we conducted a highpressure NH3 study, in which we exposed the perovskite samples to NH3 at a pressure of 600 mbar (Figs. S6(a-d)). Figure 2(c) presents the atomic ratios of N/Pb, C/Pb, and I/Pb as a function of NH3 exposure in the quasi-in situ XPS study. (The detailed experimental setup is described in the SI.) After treatment with NH3 at a pressure of 600 mbar, the atomic ratios of N/Pb and I/Pb remained constant, but the atomic ratio of C/Pb decreased rapidly as the exposure time increased, indicating the loss of CH3NH3+ ions in the perovskite structure. In addition, the NMR measurements showed that the CH3NH3+ signal was nearly absent in the perovskite films exposed to NH3 at a pressure of 600 mbar for 60 min (Fig. S7). Therefore, when the samples were exposed to NH3 at the high pressure of 600 mbar, the XPS and NMR results indicated that NH4PbI3 was formed both at the surface and in the bulk.

To analyze the transformation from CH3NH3PbI3 to NH4PbI3, we used scanning electron microscopy to determine the surface structure of the perovskite films after exposure to NH3 at a 8


Page 8 of 19

Page 9 of 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


pressure of 600 mbar. These films exhibited morphologies that were strikingly different from the morphology of the pristine sample. After exposure to NH3 at a pressure of 600 mbar for 5, 60, and 180 min (Fig. S8), the perovskite films underwent a coarsening process and eventually developed large fissures along the previously smooth CH3NH3PbI3 crystallites. Figure S9 shows the UV-vis absorption spectrum of a pristine CH3NH3PbI3 film and the spectrum of the same film exposed to NH3 at a pressure of 600 mbar for 60 min. The sharp absorption edge at ~750 nm is characteristic of CH3NH3PbI3.35,36 In contrast to the pristine film, the CH3NH3PbI3 film treated with highpressure NH3 lacked significant absorption above 500 nm, and the spectrum displayed a distinct absorption feature at shorter wavelengths, which also confirmed the transformation of the bulk structure.

Following the chemical, morphological, and spectroscopic changes of perovskite films due to exposure to high-pressure NH3, we sought to determine the structural properties of bulk perovskites. Figure 2(d) shows the XRD patterns of CH3NH3PbI3 films exposed to NH3 at a pressure of 600 mbar for 5 and 60 min. There were significant differences between the diffraction patterns of the pristine CH3NH3PbI3 film and those exposed to high-pressure NH3. Figure 2(d) shows that a new, prominent peak developed at 9.6° along with other new peaks for 2θ ranging between 22° and 28° after 5- and 60-minute exposures, respectively. The characteristic XRD peaks for tetragonal CH3NH3PbI3 disappeared after exposure to high-pressure NH3 for 60 min. The substantial change in the XRD pattern indicated that the sample did not maintain the original perovskite structure after treatment with high-pressure NH3, which might be due to the low tolerance factor of NH4PbI3 (tf = 0.78).37,38 To better understand the structure of NH4PbI3, we obtained the theoretical XRD patterns of the reported NH4PbI3 structure (Fig. S10) by using the 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 19

visualization software VESTA39 and the cell parameters reported by Fan et al.40 The XRD patterns of the NH3-treated perovskite film and crystalline NH4PbI3 indicated that both samples had intense diffraction peaks at 2θ values of approximately 9.6°, 22.7°, 26.4°, and 28.7°, suggesting that the CH3NH3PbI3 films transformed to crystalline NH4PbI3 throughout the bulk with prolonged exposure to high-pressure NH3. The reduction in the number of diffraction peaks observed in NH3-treated CH3NH3PbI3 compared to as-synthesized NH4PbI3 crystals likely resulted from preferential orientation of the perovskite crystallites formed on the substrate.41 In addition, different synthesis methods also could affect the crystalline structure.42,43 Thus, the new structure can be assigned provisionally to NH4PbI3 as the species most likely to be formed after treating CH3NH3PbI3 with NH3. Our results implied that CH3NH3PbI3 is converted to NH4PbI3 via a cation substitution, but a significant question remains concerning the reversibility of this reaction. To test the scenario of a reverse reaction from NH4PbI3 to CH3NH3PbI3, we performed time-dependent in situ AP-XPS measurements on NH4PbI3 films with methylamine gas (CH3NH2). We fabricated NH4PbI3 films by exposing CH3NH3PbI3 perovskite to NH3 at a pressure of 600 mbar for 1 h. To compare the chemical changes that occurred due to the interactions of CH3NH2 with the NH4PbI3 films, photoelectron spectra for C 1s and N 1s were obtained under a CH3NH2 pressure of 1 mbar (Figs. 3(a) and (b)). In the presence of CH3NH2, the C 1s spectra of NH4PbI3 films became broader and were fitted with three components at BEs of 285.3, 286.6, and 287.6 eV, corresponding to adventitious carbon, CH3NH3+, and gas-phase CH3NH2, respectively. The spectral features in the N 1s observed at 402.5 and 401.3 eV were characteristic of CH3NH3+ or NH4+ cations and the gas-phase CH3NH2, respectively. Figure S11 shows the deconvoluted peaks of the C 1s and N 1s spectra obtained for the perovskite film during treatment with CH3NH2. At a CH3NH2 pressure of 10


Page 11 of 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


1 mbar, the spectra of the NH4PbI3 films showed a strong increase in the C 1s signal intensity at 286.6 eV, which indicated the appearance of CH3NH3+ in the samples. However, the N 1s signal at a BE of 402.5 eV did not increase; instead, it displayed the same intensities before and after treatment with CH3NH2, indicating a constant amount of N-containing ions in the films. Figure 4(a) shows that the C/Pb ratio increased by more than a factor of two and that the N/Pb ratio remained constant, which confirms that equimolar substitution occurred between CH3NH3+ and NH4+. The NMR measurements showed an increase in the CH3NH3+ signal in the films exposed to NH3 at a pressure of 1 mbar for 30 min (Fig. S12), indicating the rapid formation of CH3NH3PbI3 both at the surface and in the bulk upon exposure to CH3NH2 gas at a low pressure.

Figure 3. (a) C 1s and (b) N 1s photoelectron spectra of NH4PbI3 films at a CH3NH2 pressure of 1 mbar for various durations and after the gas was evacuated from the reaction cell.

It is interesting to note that the NH4PbI3 films underwent structural and morphological recoveries during the CH3NH2 treatment. After treatment in CH3NH2 for 30 min, we observed strong diffraction peaks that were characteristic of the perovskite structure (Fig. S13), indicating the 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 19

presence of crystalline CH3NH3PbI3. When NH4PbI3 films were exposed to CH3NH2, the transformation to CH3NH3PbI3 caused a recrystallization process in which surface cracking was reduced significantly and the CH3NH3PbI3 crystallites became smooth and compact (Fig. S14). The change in the morphology of the film most likely resulted from re-growth and grain reconstruction in the perovskite crystal. This is because the exposure of perovskite to methylamine leads to the formation of a densely-packed distribution of nanoscale crystallites.44 The structural and morphological recoveries also were consistent with the observed chemical shift of the absorption edge for the CH3NH2-treated NH4PbI3 sample. The transformation from NH4PbI3 to CH3NH3PbI3 produced broad absorption across the visible range with an absorption edge at 750 nm (Fig. 4(b)). Based on these results, it is evident that the structural changes in NH3treated perovskite films can be reversed rapidly during interactions with a low-pressure CH3NH2 gas, as shown in Figure 4(c).

12


Page 13 of 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


Figure 4. (a) I/Pb, C/Pb, and N/Pb ratios estimated from the NH4PbI3 films at a CH3NH2 pressure of 1 mbar for various durations; (b) UV-vis absorption spectra of perovskite films treated with NH3 at a pressure of 600 mbar for 1 h and of NH3-treated CH3NH3PbI3 films exposed to CH3NH2 at a pressure of 1 mbar for 30 min; (c) Schematic of the reversible transformation of CH3NH3PbI3 into NH4PbI3.

To summarize, a substitution reaction between CH3NH3PbI3 perovskite and NH3 was conducted with in situ AP-XPS and quasi-in situ XPS experiments in which CH3NH3+ was exchanged with NH4+ to form new material (NH4PbI3). The in situ AP-XPS analysis indicated that the presence of NH3 triggered the transformation of CH3NH3PbI3 to NH4PbI3 via cation exchange and a proton transfer mechanism at low pressures. When exposed to high-pressure NH3 (600 mbar), NH4PbI3 was formed both at the surface and in the bulk as detected by the XPS and NMR measurements. When CH3NH3PbI3 was exposed to a high-pressure NH3, the perovskite films exhibited a distinct morphological change and a decrease in absorption across the visible region. Furthermore, the XRD patterns suggested a total conversion of the perovskite to NH4PbI3. We also demonstrated that the NH4PbI3 films could revert to CH3NH3PbI3 after exposure to CH3NH2. These results provided an essential understanding of the reaction between perovskite and polar molecules that can aid in the development of more stable materials for solar cells since perovskite materials are 13



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 14 of 19

vulnerable to phase transformation and morphological changes in the presence of polar molecules. However, the fast response time and recovery of the structure imply that CH3NH3PbI3 and NH4PbI3 potentially could be used as NH3 or CH3NH2 sensors, which might help exploit the unique properties of CH3NH3PbI3 for applications in addition to their use in photovoltaics.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Phone: + 1 (574) 631-12819. Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences under Award Number DE-FC02-04ER15533. This is contribution number NDRL 5153 from the Notre Dame Radiation Laboratory. The authors thank the cSEND Materials Characterization Facility for the use of the Bruker pXRD.

ASSOCIATED CONTENT Supporting Information.

Supporting information include detail experimental and characterization techniques, XPS spectra at different conditions along with detail peak fitting, XRD patterns, 1HNMR spectra, SEM images, and UV-Visible absorption spectra of the pristine CH3NH3PbI3 and CH3NH3PbI3 films treated with NH3. 14


Page 15 of 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


REFERENCES (1)

Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T. -b.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345, 542–546.

(2)

Dou, L.; Wong, A. B.; Yu, Y.; Lai, M.; Kornienko, N.; Eaton, S. W.; Fu, A.; Bischak, C. G.; Ma, J.; Ding, T.; et al. Atomically Thin Two-Dimensional Organic-Inorganic Hybrid Perovskites. Science 2015, 349, 1518–1521.

(3)

Manser, J. S.; Kamat, P. V. Band Filling with Free Charge Carriers in Organometal Halide Perovskites. Nat. Photonics 2014, 8, 737–743.

(4)

Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A. Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells. Nano Lett. 2014, 14, 2584–2590.

(5)

Manser, J. S.; Christians, J. A.; Kamat, P. V. Intriguing Optoelectronic Properties of Metal Halide Perovskites. Chem. Rev. 2016, 116, 12956–13008.

(6)

Park, N.-G. Perovskite Solar Cells: An Emerging Photovoltaic Technology. Mater. Today 2014, 18, 65–72.

(7)

Manser, J. S.; Reid, B.; Kamat, P. V. Evolution of Organic-Inorganic Lead Halide Perovskite from Solid-State Iodoplumbate Complexes. J. Phys. Chem. C 2015, 119, 17065−17073.

(8)

Yoon, S. J.; Stamplecoskie, K. G.; Kamat, P. V. How Lead Halide Complex Chemistry Dictates the Composition of Mixed Halide Perovskites. J. Phys. Chem. Lett. 2016, 7, 1368– 1373.

(9)

Manser, J. S.; Saidaminov, M. I.; Christians, J. A.; Bakr, O. M.; Kamat, P. V. Making and Breaking of Lead Halide Perovskites. Acc. Chem. Res. 2016, 49, 330–338.

(10)

Zhou, Z.; Pang, S.; Ji, F.; Zhang, B.; Cui, G.; Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T.; Kim, H. S.; et al. The Fabrication of Formamidinium Lead Iodide Perovskite Thin Films via Organic Cation Exchange. Chem. Commun. 2016, 52, 3828–3831.

(11)

Frolova, L. A.; Anokhin, D. V.; Gerasimov, K. L.; Dremova, N. N.; Troshin, P. A. Exploring the Effects of the Pb2+ Substitution in MAPbI3 on the Photovoltaic Performance of the Hybrid Perovskite Solar Cells. J. Phys. Chem. Lett. 2016, 7, 4353–4357.

(12)

Dualeh, A.; Tétreault, N.; Moehl, T.; Gao, P.; Nazeeruddin, M. K.; Grätzel, M. Effect of Annealing Temperature on Film Morphology of Organic-Inorganic Hybrid Pervoskite Solid-State Solar Cells. Adv. Funct. Mater. 2014, 24, 3250–3258.

(13)

Divitini, G.; Cacovich, S.; Matteocci, F.; Cinà, L.; Di Carlo, A.; Ducati, C.; Green, M.; Emery, K.; Hishikawa, Y.; Warta, W.; et al. In Situ Observation of Heat-Induced Degradation of Perovskite Solar Cells. Nat. Energy 2016, 1, 15012/1-15012/6.

(14)

Milosavljević, A. R.; Huang, W.; Sadhu, S.; Ptasinska, S. Low-Energy Electron-Induced Transformations in Organolead Halide Perovskite. Angew. Chem. Int. Ed. 2016, 55, 15



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 16 of 19

10083–10087. (15)

Christians, J. A.; Miranda Herrera, P. A.; Kamat, P. V. Transformation of the Excited State and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite upon Controlled Exposure to Humidified Air. J. Am. Chem. Soc. 2015, 137, 1530–1538.

(16)

Leguy, A. M. A.; Hu, Y.; Campoy-Quiles, M.; Alonso, M. I.; Weber, O. J.; Azarhoosh, P.; Schilfgaarde, M. van; Weller, M. T.; Bein, T.; Nelson, J.; et al. Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals, and Solar Cells. Chem. Mater. 2015, 27, 3397– 3407.

(17)

Misra, R. K.; Aharon, S.; Li, B.; Mogilyansky, D.; Visoly-Fisher, I.; Etgar, L.; Katz, E. A. Temperature- and Component-Dependent Degradation of Perovskite Photovoltaic Materials under Concentrated Sunlight. J. Phys. Chem. Lett. 2015, 6, 326–330.

(18)

Hoke, E. T.; Slotcavage, D. J.; Dohner, E. R.; Bowring, A. R.; Karunadasa, H. I.; McGehee, M. D. Reversible Photo-Induced Trap Formation in Mixed-Halide Hybrid Perovskites for Photovoltaics. Chem. Sci. 2014, 6, 613–617.

(19)

Yoon, S. J.; Draguta, S.; Manser, J. S.; Sharia, O.; Schneider, W. F.; Kuno, M.; Kamat, P. V. Tracking Iodide and Bromide Ion Segregation in Mixed Halide Lead Perovskites during Photoirradiation. ACS Energy Lett. 2016, 1, 290–296.

(20)

Nenon, D. P.; Christians, J. A.; Wheeler, L. M.; Blackburn, J. L.; Sanehira, E. M.; Dou, B.; Olsen, M. L.; Zhu, K.; Berry, J. J.; Luther, J. M. Structural and Chemical Evolution of Methylammonium Lead Halide Perovskites during Thermal Processing from Solution. Energy Environ. Sci. 2016, 9, 2072–2082.

(21)

Aristidou, N.; Sanchez-Molina, I.; Chotchuangchutchaval, T.; Brown, M.; Martinez, L.; Rath, T.; Haque, S. A. The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers. Angew. Chem. Int. Ed. 2015, 54, 8208–8212.

(22)

Huang, W.; Manser, J. S.; Kamat, P. V.; Ptasinska, S. Evolution of Chemical Composition, Morphology, and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite under Ambient Conditions. Chem. Mater. 2015, 28, 303–311.

(23)

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.

(24)

Schelhas, L. T.; Christians, J. A.; Berry, J. J.; Toney, M. F.; Tassone, C. J.; Luther, J. M.; Stone, K. H. Monitoring a Silent Phase Transition in CH3NH3PbI3 Solar Cells via Operando X-Ray Diffraction. ACS Energy Lett. 2016, 1, 1007–1012.

(25)

Yang, J.; Siempelkamp, B. D.; Liu, D.; Kelly, T. L. An Investigation of CH3NH3PbI3 Degradation Rates and Mechanisms in Controlled Humidity Environments Using in Situ Techniques. ACS Nano 2015, 9, 1955–1963.

(26)

Zhao, Y.; Zhu, K. Optical Bleaching of Perovskite (CH3NH3)PbI3 through RoomTemperature Phase Transformation Induced by Ammonia. Chem. Commun. 2014, 50, 1605–1607.

(27)

Bao, C.; Yang, J.; Zhu, W.; Zhou, X.; Gao, H.; Li, F.; Fu, G.; Yu, T.; Zou, Z. A Resistance 16


Page 17 of 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


Change Effect in Perovskite CH3NH3PbI3 Films Induced by Ammonia. Chem. Commun. 2015, 51, 15426–15429. (28)

Chen, S.; Goh, T. W.; Sabba, D.; Chua, J.; Mathews, N.; Huan, C. H. A.; Sum, T. C. Energy Level Alignment at the Methylammonium Lead Iodide/Copper Phthalocyanine Interface. APL Mater. 2014, 2, 081512/1−081512/7.

(29)

Bassignana, I. C.; Wagemann, K.; Küppers, J.; Ertl, G. Adsorption and Thermal Decomposition of Ammonia on a Ni(110) Surface: Isolation and Identification of Adsorbed NH2 and NH. Surf. Sci. 1986, 175, 22–44.

(30)

Kiyooka, H.; Matsumoto, O. Reaction Scheme of Ammonia Synthesis in the ECR Plasmas. Plasma Chem. Plasma Process. 1996, 16, 547–562.

(31)

Takeuchi, M.; Shimizu, Y.; Yamagawa, H.; Nakamuro, T.; Anpo, M. Preparation of the Visible Light Responsive N3--Doped WO3 Photocatalyst by a Thermal Decomposition of Ammonium Paratungstate. Appl. Catal. B Environ. 2011, 110, 1–5.

(32)

Guo, C.; Yin, S.; Dong, Q.; Sato, T. Simple Route to (NH4)xWO3 Nanorods for Near Infrared Absorption. Nanoscale 2012, 4, 3394–3398.

(33)

Khare, S. P.; Meath, W. J. Cross Sections for the Direct and Dissociative Ionisation of NH3 , H2O and H2S by Electron Impact. J. Phys. B At. Mol. Phys. 1987, 20, 2101–2116.

(34)

Starr, D. E.; Liu, Z.; Hävecker, M.; Knop-Gericke, A.; Bluhm, H. Investigation of Solid/Vapor Interfaces Using Ambient Pressure X-Ray Photoelectron Spectroscopy. Chem. Soc. Rev. 2013, 42, 5833–5857.

(35)

Zhao, Y.; Zhu, K. Charge Transport and Recombination in Perovskite (CH3NH3)PbI3 Sensitized TiO2 Solar Cells. J. Phys. Chem. Lett. 2013, 4, 2880–2884.

(36)

Zhang, W.; Saliba, M.; Moore, D. T.; Pathak, S. K.; Hörantner, M. T.; Stergiopoulos, T.; Stranks, S. D.; Eperon, G. E.; Alexander-Webber, J. A.; Abate, A.; et al. Ultrasmooth Organic–Inorganic Perovskite Thin-Film Formation and Crystallization for Efficient Planar Heterojunction Solar Cells. Nat. Commun. 2015, 6, 6142–6248.

(37)

Kieslich, G.; Sun, S.; Cheetham, T. An Extended Tolerance Factor Approach for OrganicInorganic Perovskites. Chem. Sci. 2015, 6, 3430–3433.

(38)

Filip, M. R.; Eperon, G. E.; Snaith, H. J.; Giustino, F. Steric Engineering of Metal-Halide Perovskites with Tunable Optical Band Gaps. Nat. Commun. 2014, 5, 5757.

(39)

Momma, K.; Izumi, F. VESTA : A Three-Dimensional Visualization System for Electronic and Structural Analysis. J. Appl. Crystallogr. 2008, 41, 653–658.

(40)

Fan, L.-Q.; Wu, J.-H. NH4PbI3. Acta Crystallogr., Sect. E 2007, 63, 189–191.

(41)

Smith, I. C.; Hoke, E. T.; Solis-Ibarra, D.; McGehee, M. D.; Karunadasa, H. I. A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability. Angew. Chemie 2014, 126, 11414–11417.

(42)

Rosa, I. M. L.; Costa, M. C. S.; Vitto, B. S.; Amorim, L.; Correa, C. C.; Pinheiro, C. B.; Doriguetto, A. C. Influence of Synthetic Methods in the Structure and Dimensionality of Coordination Polymers. Cryst. Growth Des. 2016, 16, 1606–1616.

(43)

Tan, L.; Gu, X.; Yang, L.; Jin, W.; Zhang, L.; Xu, N. Influence of Powder Synthesis 17



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

Methods on Microstructure and Oxygen Permeation Performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ Perovskite-Type Membranes. J. Membr. Sci. 2003, 212, 157–165. (44)

Zhao, T.; Williams, S. T.; Chueh, C.-C.; deQuilettes, D.; Liang, P.-W.; Ginger, D. S.; Jen, A. K.-Y. Design Rules for the Broad Application of Fast (

Direct Observation of Reversible Transformation of CH3NH3PbI3 and

Recommend Documents