Acid-Catalyzed Reactions Activate DMSO as a Reagent in Perovskite

Subscriber access provided by Macquarie University

Article

Acid-Catalyzed Reactions Activate DMSO as a Reagent in Perovskite Precursor Inks J. Clay Hamill, Jr., Jeni C. Sorli, István Pelczer, Jeffrey Schwartz, and Yueh-Lin Loo Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b00019 • Publication Date (Web): 25 Feb 2019 Downloaded from http://pubs.acs.org on February 27, 2019

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

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

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

Chemistry of Materials

Acid-catalyzed reactions activate DMSO as a reagent in perovskite precursor inks J. Clay Hamill, Jr.†, Jeni C. Sorli,† István Pelczer,‡ Jeffrey Schwartz‡, and Yueh-Lin Loo†,§* †Department

of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544 of Chemistry, Princeton University, Princeton, NJ 08544 §Andlinger Center for Energy and the Environment, Princeton University, Princeton, NJ 08544 ‡Department

ABSTRACT: Proton transfer from methylammonium (CH3NH3+) to dimethylsulfoxide (DMSO), a common Lewis-base solvent, initiates the production of ammonium (NH4+) and dimethylammonium ([CH3]2NH2+). We propose two parallel reaction pathways initiated by this proton transfer. Using DMSO-d6 to elucidate reaction schemes, we demonstrate that protonation is followed either by methyl group transfer between the resulting CH3NH2 and residual CH3NH3+, or by transmethylation to CH3NH2 from DMSOH+. The former reaction yields NH4+ and (CH3)2NH2+ and is the dominant pathway at processing-relevant temperatures; the latter yields (CH3)2NH2+ in addition to methylsulfonic acid and dimethyl sulfide. In the preparation of hybrid organic-inorganic perovskites (HOIP) thin films for photovoltaic applications, substitution of CH3NH3+ with NH4+ and (CH3)2NH2+ in the HOIP crystal results in deviations from the tetragonal structure expected of phase-pure CH3NH3PbI3, with a deleterious effect on the absorptivity of the resulting films. These results emphasize the importance of elucidating underappreciated precursor/solvent reactivity, the products of which, when incorporated in the solid state, can have profound effects on HOIP composition and structure, with commensurate impact on macroscopic properties and device performance. Hybrid organic-inorganic perovskites (HOIPs) are wellstudied materials for use in photovoltaic (PV) cells, owing to their tunable bandgaps,1 solution processability,2–4 and applicability as singular active layers or as secondary active layers in PV cells.5–7 PV devices comprising HOIP absorbers have achieved excellent power-conversion efficiencies that exceed 22% for single-junction cells,8–10 and approach 24% when paired with silicon cells in multi-junction architectures.6 While precursor-solvent interactions are acknowledged to be problematic for HOIPs,11–14 a comprehensive examination of the chemistry of such interactions has been neglected in favor of implementing mitigating processing approaches, such as dry milling of precursor salts.15 Yet, understanding precursor-solvent chemistries might be key to obviating unfavorable byproduct formation, and can lead to a more precisely controlled composition of the active layers in a PV construct.16–19 Indeed, mixed-cation active layers involving cesium, formamidinium (NH2-CH=H2N+), and + methylammonium (CH3NH3 ) cations show the best performance of any PbI2-based perovskite material tested thus far;9,10 such materials demand precise stochiometric control over the active layers in order to form the desired crystal structure of the resulting HOIP.20,21 Incorporation of impurities in forms of byproducts from precursor-solvent reactions can have a deleterious impact on the structure of the resulting materials, with attendant performance degradation of devices prepared from them.15 Herein, we report precursor-solvent reactions that relate to the most widely studied perovskite materials, which are obtained from solutions of PbI2 and CH3NH3I in DMF or DMF/DMSO.2,22,23 In particular, we find that reactions between CH3NH3+ and DMSO lead to the formation of ammonium (NH4+) and dimethylammonium, (CH3)2NH2+ cations; these reactions are faster than the hydrolysis that

takes place between CH3NH3+ and DMF.15 When the reaction byproducts are incorporated in the solid state as A-site impurities, the structure of the intended perovskite is altered. NH4+ incorporation results in phase segregation forming distinct CH3NH3PbI3 and NH4PbI3 regions, while the incorporation of (CH3)2NH2+ with CH3NH3PbI3 results in a solid solution possessing a cubic structure, as opposed to the intended tetragonal structure of phase-pure CH3NH3PbI3 at minute concentrations, and a hexagonal structure with increasing amounts of (CH3)2NH2+. While it is known that a Brønsted acid, such as HI, or a Lewis acid, such as Pb(II), that is present in a perovskite precursor solution might catalyze the hydrolysis of DMF13,15 to (CH3)2NH2+, the possibility that DMSO – an equally common solvent additive in perovskite processing – might act as a reagent has not been described. As an initial observation, heating 1:1:1 solutions of CH3NH3I:PbI2:DMSO in DMF led to perovskite films with a cubic structure, instead of with the more commonly accessed tetragonal phase, though the morphology of films was not significantly altered by the heating step.22 We hypothesized that precursor-solvent reactions might lead to the eventual formation of byproducts that, when incorporated in the solid state, could be responsible for the observed deviation from the expected structure. Thus, we deemed the formation of the cubic phase to be diagnostic of conditions implicating precursor/solvent reactivity. To determine the reagents that must be present in solution to result in such reactions, we conducted a series of experiments in which we sequentially added various precursors to, and heated, the solutions. XRD traces of films cast from these solutions are shown in Figure 1a. We first thermally annealed a mixture of DMSO and DMF at 150 °C for 24 h; their relative concentrations were consistent with those used in precursor solutions22 to determine if solvent degradation

ACS Paragon Plus Environment

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

alone was responsible for the observed cubic structure. After the solvent mixture had cooled to room temperature, CH3NH3I and PbI2 were added, and perovskite films were prepared by spin coating and subsequent thermal annealing. The XRD pattern of one such film matches that calculated for tetragonal CH3NH3PbI3;24 this observation proves that heating the solvents alone does not result in the formation of the cubic phase. Next, a solution of 1:1 PbI2:DMSO was prepared in DMF, and was heated at 150 °C for 24 h. After the solution had cooled to room temperature, CH3NH3I was added, followed by film formation. The XRD trace of this film also conforms to the calculated XRD trace of tetragonal CH3NH3PbI3.24 Finally, a mixture of 1:1 CH3NH3I:DMSO was prepared in DMF and heated to 150 °C for 40 min. PbI2 was added after the solution had cooled to room temperature. Remarkably, even after this shorter heating time, the XRD trace of films processed from this solution showed the calculated XRD trace of cubic CH3NH3PbI3.24 The magnified XRD traces in Figure S1a highlight the absence of the tetragonal (211) reflection in films cast from heated DMF+DMSO+CH3NH3I; the absence of this reflection is evidence for the extinction of the tetragonal phase following solution heating. Since phasepure cubic CH3NH3PbI3 is normally only accessed > 54 °C25 or under confinement,26 we hypothesized that reactions among CH3NH3I and DMF/DMSO give rise to new speciation whose incorporation leads to a cubic phase of the perovskite.

Figure 1. (a) XRD traces of films cast from solutions under various precursor addition/annealing sequences; (b) XRD traces of films processed from pure solvents annealed with CH3NH3I. Calculated XRD traces of the tetragonal and cubic phases of CH3NH3PbI3 are shown in black and blue, respectively, for reference. Traces are staggered along the y-axis for clarity. We then sought to determine if both or only one of the solvents was required to give rise to the new phases. First, CH3NH3I was added separately to pure DMF and to pure DMSO, and each solution was heated at 150 °C for time periods between 40 min and 6 h. PbI2 was subsequently

added to each annealed solution after they were cooled to room temperature prior to film deposition. Figure 1b shows the XRD traces of films formed by this method. When pure DMF was used and the solution was heated for 40 min, the resulting films adopts the tetragonal phase of CH3NH3PbI3. In contrast, when pure DMSO was used, the XRD trace of film formed was both distinctive and different from that of either the tetragonal or cubic phases, having an intense reflection at 2θ = 11.64° and several weaker reflections in the range of 2θ = 12° – 40°. This XRD trace indicates access of a third phase, different from the tetragonal or cubic phases that we had previously formed. When CH3NH3I was heated in pure DMF for 6 h before the addition of PbI2, the XRD trace of the film produced showed reflections consistent with the coexistence of the cubic phase and the same, new, unidentified phase. Magnified XRD traces in Figure S1b also highlight the absence of the tetragonal (211) reflection in films cast from DMSO+CH3NH3I solutions heated for 40 min and DMF+CH3NH3I solutions heated for 6 h, confirming the absence of the tetragonal phase in these films. Because incorporating a cation larger than CH3NH3+ is known to stabilize the cubic structure of CH3NH3PbI3 at room temperature,27 we hypothesized that heating the precursor solutions prior to deposition led to reactions in solutions that produced such larger cations.

Figure 2. (a) 1H NMR spectra of CH3NH3I in DMSO-d6 after the solution was heated at 150 °C for 40 min and 6 h. Spectra of authentic NH4I, CH3NH3I and (CH)3NH2I in DMSO-d6 are provided for reference. The residual DMSO-d5 peak (*) is observed at 2.5 ppm at various concentrations. (b) Magnified 13C NMR spectra of CH NH I in DMSO-d after the solution was 3 3 6 heated at 150 °C 6 h. Red bars highlight the position of a septet at 34.55 and an isotope-shifted broader singlet at 34.97 ppm, which are attributed to the CD3 and CH3 groups of CH3CD3NH2+, respectively. Inset highlights the location of the magnified region in Figure 2(b) relative to the full spectrum.

Our next objective was to identify new species arising from heating the precursor solutions, which we addressed


Page 2 of 8

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

Chemistry of Materials through NMR analysis of solutions of CH3NH3I in DMSO-d6 that were heated to 150 °C for varying times. Figure 2a shows the 1H NMR spectrum of CH3NH3I solution in DMSOd6 at room temperature, and that of solutions heated at 150 °C for 40 min and 6 h. The signals at 2.30 and 7.47 ppm that are assigned to the protons of CH3- and of N-H of CH3NH3+, respectively, slowly diminish on heating; singlets at 2.51 and 8.14 ppm and a 1:1:1 triplet at 7.09 ppm emerge and grow in intensity. These data indicate consumption of CH3NH3+ on heating to yield products that can be identified by reference to NMR spectra of authentic materials (Figure 2a): The singlets at 2.51 and 8.14 ppm are assigned to the protons of CH3- and N-H, respectively, of (CH3)2NH2+. The triplet observed as a result of solution heating is attributed to NH4+; the triplet is indicative of J (14N, 1H) coupling in the symmetric NH4+ ion, where the quadrupolar moment of 14N has diminished.28 Attenuated total reflectance infrared spectroscopy (ATR-IR) of powders recovered from solutions of CH3NH3I that were heated at 150 °C for 40 min in DMSO provides independent verification of these new species observed by 1H NMR data (Supporting Information Figure S2). We also collected 13C NMR spectra of CH3NH3I/DMSO-d6 solutions; after 6 h heating at 150 °C, peaks for residual CH3NH3+ and (CH3)2NH2+ are observed. Close examination of the singlet at 35.03 ppm attributed to (CH3)2NH2+ (Figure 2b) reveals a septet centered at 34.55 ppm and a companion resonance at 34.97 ppm near the base of the main peak, which we attribute, respectively, to the carbon on C-D of (CH3)(CD3)NH2+ and to an isotope shift on the main peak caused by the deuterated methyl group. That we observe two distinct populations of dimethylammonium cations suggests that two parallel reactions take place: one produces NH4+ and (CH3)2NH2+, and the other involves DMSO-d6 and produces CH3CD3NH2+. Quantification of the 1H NMR further indicates that that (CH ) NH + and NH + are 3 2 2 4 produced in equal amounts, while 13C NMR shows that the ratio of non-deuterated to deuterated dimethylammonium species is ca. 4:1 after 6 h of heating. Importantly, the presence of NH4+, and the two distinct populations of dimethylammonium, imply that the chemical reactions that take place in DMSO are distinct from the hydrolysis reaction that had been reported for CH3NH3+ in DMF.11,15 Given our NMR results, we propose deprotonation of CH3NH3+ by DMSO is followed by methyl group transfer between CH3NH2 and residual CH3NH3+ (Scheme 1) to produce dimethylammonium and ammonium cations. This reaction occurs in parallel with one between DMSO and CH3NH3+ in which proton transfer is followed by transmethylation to yield the dimethylammonium cation (Scheme 2). Only the latter reaction involves DMSO as a reagent; using DMSO-d6 in our NMR experiments allowed us to distinguish between the dimethylammonium cations produced in these two reactions, with those produced in the latter reaction deuterated. Our proposal (Scheme 2) yields methylsulphenic acid (CH3SOH) as the primary product of transmethylation; this species is known29 to react quickly with DMSO to form methylsulfinic acid (CH3SOOH) and dimethylsulfide (CH3SCH3). Methylsulfinic acid can undergo further reaction with DMSO to form methylsulfonic acid (CH3SO3H) and another equivalent of CH3SCH3.29 Consistent with this reaction scheme, we note a

sulfidic odor that is characteristic of CH3SCH330,31 when the precursor solutions are heated. In contrast to reports of transmethylation from DMSO that involve a formic acid adduct,32–34 our observations show that no third species is required. While the reaction shown in Scheme 1 may also occur in DMF, reaction in this solvent is apparently substantially slower than in DMSO; we believe this may be related to relative differences in protonation susceptibility of DMF and DMSO. That formation of (CH)3NH2+ and NH4+ occurs in substantive quantities in the precursor solution and has strong implications on the resulting perovskite thin films. We surmise that (CH)3NH2+ and NH4+ incorporation into the perovskite material is responsible for accessing species whose crystal structures are other than the conventional tetragonal structure of CH3NH3PbI3. When dried films formed from precursor solutions of 1:1 CH3NH3I:PbI2 in DMSO were recovered and dissolved in DMSO-d6, NMR analysis confirmed that both (CH)3NH2+ and NH4+ had been incorporated into the solid state. This discovery prompted us to map the phase diagram of the ternary cation system to elucidate how the presence of (CH)3NH2+ and NH4+ impact the phase behavior of CH3NH3PbI3. Scheme 1. Formation of (CH3)2NH2+ and NH4+ in DMSO. CH3NH3+ undergoes proton transfer to DMSO32,34–37, yielding CH3NH2, which can react with a second equivalent of CH3NH3+. This is followed by methyl group transfer from CH3NH3+ to CH3NH2 with subsequent formation of NH4+ and (CH3)2NH2+.

Scheme 2. Transmethylation from DMSO to CH3NH3+. Proton transfer from CH3NH3+ to DMSO is followed by methyl group transfer to give (CH3)2NH2+, methylsulfonic acid (CH3SO2OH), and dimethylsulfide (CH3SCH3).

We first considered the effects of separately adding prescribed concentrations of authentic (CH3)2NH2I or NH4I to CH3NH3PbI3 precursor solutions to create double-organic



cation perovskite thin films. Figure 3a shows highresolution XRD traces of [(CH3)2NH2]x(CH3NH3)1-xPbI3 films (XRD

Figure 3. (a) HR-XRD traces of [(CH3)2NH2]x(CH3NH3)1-xPbI3 films. Solid and dashed black lines indicate the positions of the (110) reflection of tetragonal CH3NH3PbI3 and the (100) reflection of hexagonal (CH3)2NH2PbI3, respectively. (b) HRXRD traces of (NH4)y(CH3NH3)1-yPbI3 films. Solid and dashed black lines indicate the positions of the (110) reflection of tetragonal CH3NH3PbI3 and the (002) and (102) reflections of hexagonal NH4PbI3, respectively. Traces are stacked along the y-axis for clarity.

survey scans are in Supporting Information Figure S3a). Starting from pure CH3NH3PbI3 (x = 0), we observe a peak at 2θ = 14.10o that is indexed to the (110) reflection of tetragonal CH3NH3PbI3. At low x, this reflection shifts toward lower 2θ, consistent with an expansion of the unit cell dimension along this crystallographic axis. We interpret this to indicate incorporation of (CH3)2NH2+ in the unit cell and the formation of a solid solution at these compositions. At x = 0.05, this reflection is shifted to 2θ = 13.98o, which is coincident with the (100) reflection of cubic CH3NH3PbI3; survey scans confirm that the cubic phase is accessed at this concentration. Collectively, the XRD scans acquired on films with increasing but still low x indicate a gradual transformation from the tetragonal to the cubic structure: the unit cell increases in lattice spacing and decreases in octahedral tilt38–40 to incorporate the larger (CH3)2NH2+ cation. In addition, Figure S4 shows a magnified view of the region of the XRD traces containing the tetragonal (211) reflection; for XRD traces in which x = 0.05 and above, the tetragonal (211) reflection is absent. This observation offers further evidence that that the films adopt a cubic phase. At x = 0.20, a new peak appears at 2θ = 11.64° that persists with increasing x; at x > 0.25, the intensity of this peak increases relative to that of the reflection at higher 2θ.

This new peak, at 2θ = 11.64°, is indexed to the (100) reflection of hexagonal [(CH3)2NH2]x(CH3NH3)1-xPbI3; its coexistence with the reflection at higher 2θ ( 14o) suggests the onset of phase separation: a cubic phase rich in CH3NH3+ and a hexagonal phase that is richer in (CH3)2NH2+.41 Finally, above x = 0.60, only the hexagonal phase is observed. Not coincidentally, comparison of these high resolution XRD traces with the survey scans in Figure 1 shows that the previously unidentified reflection at 2θ = 11.64° agrees with the hexagonal phase observed in Figure 3a, providing further corroboration of the presence of (CH3)2NH2+ incorporation in films cast from heated solutions. Consistent with our XRD data, Figure S5 shows the characteristic spacing of the (100) plane of the cubic phase increasing linearly with increasing (CH3)NH2+ concentration in the single phase region between x = 0.05 and x = 0.20. This characteristic spacing is then invariant within the composition window that we observe phase separation (0.20 < x < 0.80). Figure 3b shows XRD traces of (NH4)y(CH3NH3)1-yPbI3 films (XRD survey scans are in Supporting Information Figure S3b). NH4+ incorporation results in a shift of the (110) reflection of CH3NH3PbI3 to larger 2θ, indicating a contraction of the lattice due to incorporation of the smaller cation. When y  0.25, a new phase emerges whose XRD trace matches the calculated XRD trace of phase-pure NH4PbI3.42 These reflections do not deviate from their calculated positions (Supporting Information Figure S3b), suggesting that CH3NH3+ is not soluble in NH4PbI3. We thus interpret this observation to the coexistence of phase-pure NH4PbI3 and a tetragonal phase that is rich CH3NH3+.

Figure 4. Partial ternary phase diagram of [(CH3)2NH2]x(NH4)y(CH3NH3)1-x-yPbI3. Photographs of tripleorganic cation films are overlaid on corresponding data points in the center of the phase diagram; their border color


Page 4 of 8

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

Chemistry of Materials corresponds to the phase(s) present, which we identified by XRD analysis of the films.

On the basis HR-XRD observations, it was possible to map the phase space of the [(CH3)2NH2]x(NH4)y(CH3NH3)1-x-yPbI3 system (Figure 4; for HR-XRD traces of triple-organic cation films corresponding to data points in the ternary phase diagram, see Supporting Information Figure S6), in which the phase behavior of binary-organic cation systems are incorporated in the ternary phase diagram along its left and bottom axes; the CH3NH3+-rich tetragonal phase is shown as α, the CH3NH3+-rich cubic phase as αꞌ, and the (CH3)2NH2+rich, hexagonal phase as β. As the concentrations of NH4+ and (CH3)2NH2+ increase concurrently (moving towards the center of the ternary diagram), phase segregation becomes increasingly prevalent. In all cases where y ≥ 0.30, a distinct NH4PbI3 phase coexists with the α, αꞌ, or β phases. Datapoints in the diagram’s center also show overlaid photographs of triple-organic cation films, highlighting that incorporation of reaction byproducts can dramatically impact optical properties of perovskite films; they range from highly to poorly absorptive, and this decrease in optical absorption can have significant consequences for devices comprising perovskite active layers. We have shown that the chemistry of perovskite synthesis is dramatically affected by solvent-based interconversions of the CH3NH3+ cation. Methyl group transfer reactions of this cation in DMSO produce NH4+ and, (CH3)2NH2+, which are subsequently incorporated into perovskites as A-site impurities with commensurate effects on the stoichiometry, structure, and absorptivity of the thin film that is ultimately produced. Because DMSO is commonly used as a Lewis-base additive in preparing precursor solutions,2,23,43 and given myriad methods for thin-film processing of active layers, including heating precursor solutions22,44–46 and/or prolonged solution aging,15,47,48 the reactions we have elucidated must pervade perovskite solar cell processing. Thus, it is critical to identify solvents and additives for such processing that do not react with critical precursors if materials with definite, stable structure are to be formed.

Author Contributions The manuscript was written with contributions from all authors. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT The authors acknowledge financial support from the National Science Foundation through award number CMMI-1537011 and DMR-1420541. The latter originates from NSF’s MRSEC program that supports Princeton Center for Complex Materials. Hamill is supported by the Department of Defense (DoD) through a National Defense Science and Engineering Graduate (NDSEG) Fellowship. We also acknowledge Professor Barry Rand (Princeton University, Department of Electrical Engineering) for his helpful input.

REFERENCES (1)

(2)

(3)

(4)

(5)

(6)

ASSOCIATED CONTENT      



Supporting Information Scheme S1: Proposed reaction mechanism of DMF hydrolysis. Supporting Information Figure S1: Magnified view of XRD traces in Figure 1. Supporting Information Figure S2: ATR spectra of CH3NH3I powders heated in DMSO/DMSO. Supporting Information Figure S3: Wide-angle XRD traces of [(CH3)2NH2]x(CH3NH3)1-xPbI3 and (NH4)y(CH3NH3)1-yPbI3 films. Supporting Information Figure S4: Magnified view of XRD traces in Figure S3. Supporting Information Figure S5: Characteristic dspacing associated with the cubic (100) reflection as a function of (CH3)2NH2+ content in [(CH3)2NH2]x(CH3NH3)1-xPbI3 films. Supporting Information Figure S6: HR-XRD traces of [(CH3)2NH2]x(NH4)y(CH3NH3)1-x-yPbI3 films.

AUTHOR INFORMATION Corresponding Author *[email protected]

(7)

(8) (9)

(10)

(11)

Jacobsson, T. J.; Correa-Baena, J.-P.; Pazoki, M.; Saliba, M.; Schenk, K.; Grätzel, M.; Hagfeldt, A. Exploration of the compositional space for mixed lead halogen perovskites for high efficiency solar cells. Energy Environ. Sci. 2016, 9, 1706– 1724 DOI: 10.1039/C6EE00030D. Ahn, N.; Son, D.-Y.; Jang, I.-H.; Kang, S. M.; Choi, M.; Park, N.-G. Highly reproducible perovskite solar cells with average efficiency of 18.3% and best efficiency of 19.7% fabricated via lewis base adduct of lead(II) iodide. J. Am. Chem. Soc. 2015, 137, 8696–8699 DOI: 10.1021/jacs.5b04930. Williams, S. T.; Rajagopal, A.; Chueh, C.-C.; Jen, A. K.-Y. Current challenges and prospective research for upscaling hybrid perovskite photovoltaics. J. Phys. Chem. Lett. 2016, 7, 811– 819 DOI: 10.1021/acs.jpclett.5b02651. Fateev, S. A.; Petrov, A. A.; Khrustalev, V. N.; Pavel, V.; Zubavichus, Y. V; Goodilin, E. A.; Tarasov, A. B. Solution processing of methylammonium lead iodide perovskite from gamma-butyrolactone: crystallization mediated by solvation equilibrium. Chem. Mater. 2018, 30, 5237–5244 DOI: 10.1021/acs.chemmater.8b01906. Albrecht, S.; Saliba, M.; Correa Baena, J. P.; Lang, F.; Kegelmann, L.; Mews, M.; Steier, L.; Abate, A.; Rappich, J.; Korte, L.; et al. Monolithic perovskite/silicon-heterojunction tandem solar cells processed at low temperature. Energy Environ. Sci. 2016, 9, 81–88 DOI: 10.1039/C5EE02965A. Bush, K. A.; Palmstrom, A. F.; Yu, Z. J.; Boccard, M.; Cheacharoen, R.; Mailoa, J. P.; McMeekin, D. P.; Hoye, R. L. Z.; Bailie, C. D.; Leijtens, T.; et al. 23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability. Nat. Energy 2017, 2, 17009 DOI: 10.1038/nenergy.2017.9. McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Horantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; et al. A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells. Science. 2016, 351, 151–155 DOI: 10.1126/science.aad5845. Best Research Cell Efficencies http://www.nrel.gov/ncpv/images/efficiency_chart.jpg (accessed Nov 12, 2018). 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.; et al. Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy Environ. Sci. 2016, 9, 1989–1997 DOI: 10.1039/C5EE03874J. Yang, W. S.; Park, B.-W.; Jung, E. H.; Jeon, N. J.; Kim, Y. C.; Lee, D. U.; Shin, S. S.; Seo, J.; Kim, E. K.; Noh, J. H.; et al. Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells. Science. 2017, 356, 1376–1379 DOI: 10.1126/science.aan2301. Nayak, P. K.; Moore, D. T.; Wenger, B.; Nayak, S.; Haghighirad, A. A.; Fineberg, A.; Noel, N. K.; Reid, O. G.; Rumbles, G.; Kukura, P.; et al. Mechanism for rapid growth of organic–inorganic halide perovskite crystals. Nat. Commun. 2016, 7, 13033 DOI:



(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19) (20)

(21)

(22)

(23) (24)

(25)

(26)

(27)

10.1038/ncomms13303. Noel, N. K.; Congiu, M.; Ramadan, A. J.; Fearn, S.; McMeekin, D. P.; Patel, J. B.; Johnston, M. B.; Wenger, B.; Snaith, H. J. Unveiling the influence of pH on the crystallization of hybrid perovskites, delivering low voltage loss photovoltaics. Joule 2017, 1, 328–343 DOI: 10.1016/j.joule.2017.09.009. Lee, M. V.; Raga, S. R.; Kato, Y.; Leyden, M. R.; Ono, L. K.; Wang, S.; Qi, Y. Transamidation of dimethylformamide during alkylammonium lead triiodide film formation for perovskite solar cells. J. Mater. Res. 2017, 32, 45–55 DOI: 10.1557/jmr.2016.272. Kerner, R.; Schloemer, T. H.; Schulz, P.; Berry, J. J.; Schwartz, J.; Sellinger, A.; Rand, B. P. Amine additive reactions induced by the soft lewis acidity of Pb2+ in halide perovskites. Part I: evidence for Pb-alkylmide formation. J. Mater. Chem. C 2018 DOI: 10.1039/C8TC04871A. Dou, B.; Wheeler, L. M.; Christians, J. A.; Moore, D. T.; Harvey, S.; Berry, J. J.; Barnes, F. S.; Shaheen, S. E.; van Hest, M. F. A. M. Degradation of highly alloyed metal halide perovskite precursor inks: mechanism and storage solutions. ACS Energy Lett. 2018, 3, 979–985 DOI: 10.1021/acsenergylett.8b00305. Hamill, J. C.; Schwartz, J.; Loo, Y.-L. Influence of solvent coordination on hybrid organic–inorganic perovskite formation. ACS Energy Lett. 2017, 3, 92–97 DOI: 10.1021/acsenergylett.7b01057. Stevenson, J.; Sorenson, B.; Subramaniam, V. H.; Raiford, J.; Khlyabich, P. P.; Loo, Y.-L.; Clancy, P. Mayer bond order as a metric of complexation effectiveness in lead halide perovskite solutions. Chem. Mater. 2016, 29, 2435–2444 DOI: 10.1021/acs.chemmater.6b04327. Sharenko, A.; Mackeen, C.; Jewell, L.; Bridges, F.; Toney, M. F. Evolution of iodoplumbate complexes in methylammonium lead iodide perovskite precursor solutions. Chem. Mater. 2017,29, 1315–1320 DOI: 10.1021/acs.chemmater.6b04917. Kerner, R. A.; Zhao, L.; Xiao, Z.; Rand, B. P. Ultrasmooth metal halide perovskite thin films via sol-gel processing. J. Mater. Chem. A 2016, 4, 8308–8315 DOI: 10.1039/c6ta03092k. Zhang, Y.; Grancini, G.; Feng, Y.; Asiri, A. M.; Nazeeruddin, M. K. Optimization of stable quasi-cubic FAxMA1–xPbI3 perovskite structure for solar cells with efficiency beyond 20%. ACS Energy Lett. 2017, 2, 802–806 DOI: 10.1021/acsenergylett.7b00112. Syzgantseva, O. A.; Saliba, M.; Grätzel, M.; Rothlisberger, U. Stabilization of the perovskite phase of formamidinium lead triiodide by methylammonium, Cs, and/or Rb doping. J. Phys. Chem. Lett. 2017, 8, 1191–1196 DOI: 10.1021/acs.jpclett.6b03014. Khlyabich, P. P.; Hamill, J. C.; Loo, Y.-L. Precursor solution annealing forms cubic-phase perovskite and improves humidity resistance of solar cells. Adv. Funct. Mater. 2018, 28, 1801508 DOI: 10.1002/adfm.201801508. Lee, J. W.; Kim, H. S.; Park, N. G. Lewis acid-base adduct approach for high efficiency perovskite solar cells. Acc. Chem. Res. 2016, 49, 311–319 DOI: 10.1021/acs.accounts.5b00440. Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties. Inorg. Chem. 2013, 52, 9019– 9038 DOI: 10.1021/ic401215x. Poglitsch, A.; Weber, D. Dynamic disorder in methylammoniumtrihalogenoplumbates (II) observed by millimeter-wave spectroscopy. J. Chem. Phys. 1987, 87, 6373– 6378 DOI: 10.1063/1.453467. Wang, Q.; Lyu, M.; Zhang, M.; Yun, J.-H.; Chen, H.; Wang, L. Transition from the tetragonal to cubic phase of organohalide perovskite: the role of chlorine in crystal formation of CH3NH3PbI3 on TiO2 substrates. J. Phys. Chem. Lett. 2015, 6, 4379–4384 DOI: 10.1021/acs.jpclett.5b01682. Peng, W.; Miao, X.; Adinolfi, V.; Alarousu, E.; El Tall, O.; Emwas, A. H.; Zhao, C.; Walters, G.; Liu, J.; Ouellette, O.; et al. Engineering of CH3NH3PbI3 perovskite crystals by alloying large organic cations for enhanced thermal stability and transport properties. Angew. Chemie - Int. Ed. 2016, 55, 10686–10690 DOI: 10.1002/anie.201604880.

(28) (29) (30)

(31)

(32) (33) (34)

(35)

(36)

(37)

(38)

(39) (40)

(41)

(42) (43)

(44)

(45)

Field, L. D.; Hazari, N.; Li, H. L. Nitrogen fixation revisited on iron(0) dinitrogen phosphine complexes. Inorg. Chem. 2015, 54, 4768–4776 DOI: 10.1021/acs.inorgchem.5b00211. Gollnick, K.; Stracke, H.-U. Direct and sensitized photolysis of dimethyl sulphoxide in solution. Pure Appl. Chem. 1973, 33, 217–246 DOI: 10.1351/pac197333020217. Zang, B.; Li, S.; Michel, F. C.; Li, G.; Zhang, D.; Li, Y. Control of dimethyl sulfide and dimethyl disulfide odors during pig manure composting using nitrogen amendment. Bioresour. Technol. 2017, 224, 419–427 DOI: 10.1016/j.biortech.2016.11.023. Leonardos, G.; Kendall, D.; Barnard, N. Odor threshold determinations of 53 odorant chemicals. J. Air Pollut. Control Assoc. 1969, 19, 91–95 DOI: 10.1080/00022470.1969.10466465. Wu, X. F.; Natte, K. The applications of dimethyl sulfoxide as reagent in organic synthesis. Adv. Synth. Catal. 2016, 358, 336–352 DOI: 10.1002/adsc.201501007. Jones-Mensah, E.; Karki, M.; Magolan, J. Dimethyl sulfoxide as a synthon in organic chemistry. Synth. 2016, 48, 1421–1436 DOI: 10.1055/s-0035-1560429. Jiang, X.; Wang, C.; Wei, Y.; Xue, D.; Liu, Z.; Xiao, J. A general method for N-methylation of amines and nitro compounds with dimethylsulfoxide. Chem. - a Eur. J. 2014, 20, 58–63 DOI: 10.1002/chem.201303802. Rasul, G.; Prakash, G. K. S.; Olah, G. A. Protonated and methylated dimethyl sulfoxide cations and dications. DFT/GIAO-MP2 NMR studies and comparison with experimental data. J. Org. Chem. 2000, 65, 8786–8789 DOI: 10.1021/jo001366x. Reynolds, W. L.; Lampe, K. A. The dissociation constant of protonated dimethyl sulfoxide in aqueous perchlorate media. J. Inorg. Nucl. Chem. 1968, 30, 2860–2862 DOI: 10.1016/0022-1902(68)80417-8. Yang, J.; Yuan, Q.; Yakobson, B. I. Chemical trends of electronic properties of two-dimensional halide perovskites and their potential applications for electronics and optoelectronics. J. Phys. Chem. C 2016, 120, 24682–24687 DOI: 10.1021/acs.jpcc.6b10162. 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 DOI: 10.1021/acsenergylett.6b00441. Kawamura, Y.; Hiroyuki, M.; Katsuhiko, H. Structural study on cubic – tetragonal transition of CH3NH3PbI3. J. Phys. Soc. Japan 2002, 71, 1694–1697 DOI: 10.1143/JPSJ.71.1694. Lee, J.; Bristowe, N. C.; Lee, J. H.; Lee, S.; Bristowe, P. D.; Cheetham, A. K.; Jang, H. M. Resolving the Physical Origin of Octahedral Tilting in Halide Perovskites. Chem. Mater. 2016, 28, DOI: 10.1021/acs.chemmater.6b00968. Mancini, A.; Quadrelli, P.; Amoroso, G.; Milanese, C.; Boiocchi, M.; Sironi, A.; Patrini, M.; Guizzetti, G.; Malavasi, L. Synthesis, structural and optical characterization of APbX3 (A = methylammonium, dimethylammonium, trimethylammonium; X=I, Br, Cl) hybrid organic-inorganic materials. J. Solid State Chem. 2016, 240, 55–60 DOI: 10.1016/j.jssc.2016.05.015. Fan, L. Q.; Wu, J. H. NH4PbI3. Acta Crystallogr. Sect. E Struct. Reports Online 2007,63, DOI: 10.1107/S1600536807050581. Cao, X. B.; Li, C. L.; Zhi, L. L.; Li, Y. H.; Cui, X.; Yao, Y. W.; Ci, L. J.; Wei, J. Q. Fabrication of high quality perovskite films by modulating the Pb–O bonds in Lewis acid–base adducts. J. Mater. Chem. A 2017, 5, 8416–8422 DOI: 10.1039/C7TA00539C. Yang, H.; Zhang, J.; Zhang, C.; Chang, J.; Lin, Z.; Chen, D.; Xi, H.; Hao, Y. Effects of annealing conditions on mixed lead halide perovskite solar cells and their thermal stability investigation. Materials 2017, 10, 837-848. DOI: 10.3390/ma10070837. 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


Page 6 of 8

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

Chemistry of Materials

(46)

(47)

solution. Energy Environ. Sci. 2016, 9, 2072–2082 DOI: 10.1039/c6ee01047d. Yuan, B.; Zhao, S.; Xu, Z.; Song, D.; Qiao, B.; Li, Y.; Qin, Z.; Meng, J.; Xu, X. Improving the photovoltaic performance of planar heterojunction perovskite solar cells by mixed solvent vapor treatment. RSC Adv. 2018, 8, 11574–11579 DOI: 10.1039/c7ra13289a. Tsai, H.; Nie, W.; Lin, Y. H.; Blancon, J. C.; Tretiak, S.; Even, J.;

(48)

Gupta, G.; Ajayan, P. M.; Mohite, A. D. Effect of precursor solution aging on the crystallinity and photovoltaic performance of perovskite solar cells. Adv. Energy Mater. 2017, 7, 1602159. DOI: 10.1002/aenm.201602159. Boonmongkolras, P.; Kim, D.; Alhabshi, E. M.; Gereige, I.; Shin, B. Understanding effects of precursor solution aging in triple cation lead perovskite. RSC Adv. 2018, 8, 21551–21557 DOI: 10.1039/c8ra03471k.



Page 8 of 8

Insert Table of Contents artwork here


8

Acid-Catalyzed Reactions Activate DMSO as a Reagent in Perovskite

Recommend Documents