Quantifying the Composition of Methylammonium Lead Iodide

Subscriber access provided by BOSTON UNIV

C: Energy Conversion and Storage; Energy and Charge Transport

Quantifying the Composition of Methylammonium Lead Iodide Perovskite Thin Films with Infrared Spectroscopy Xiaokun Huang, Michael Sendner, Christian Müller, Michele Sessolo, Lidon GilEscrig, Wolfgang Kowalsky, Annemarie Pucci, Sebastian Beck, and Robert Lovrincic J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b07194 • Publication Date (Web): 19 Aug 2019 Downloaded from pubs.acs.org on August 19, 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 16 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

Quantifying the Composition of Methylammonium Lead Iodide Perovskite Thin Films with Infrared Spectroscopy Xiaokun Huang1,2,3#, Michael Sendner1,3#, Christian Müller1,2, Michele Sessolo4, Lidón GilEscrig4, Wolfgang Kowalsky1,2,3, Annemarie Pucci1,3, Sebastian Beck1,3, and Robert Lovrinčić1,2*+ 1InnovationLab, 2Institute

Heidelberg, Germany

for High-Frequency Technology, Braunschweig Technical University, Germany

3Kirchhoff-Institute 4Instituto

for Physics, Heidelberg University, Germany

de Ciencia Molecular, Universidad de Valencia, C/Catedrático J. Beltrán 2, 46980

Paterna, Spain +New

affiliation: trinamiX GmbH, Ludwigshafen, Germany

AUTHOR INFORMATION # These authors contributed equally to this work. Corresponding Author *E-mail: [email protected]

ACS Paragon Plus Environment

1

The Journal of Physical Chemistry 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 2 of 16

ABSTRACT Lead halide perovskites (ABX3) are generally formed from a reaction of the lead halide salt (BX2) with the halide salt of the A cation (AX). The effects of varying film compositions as result of non-stoichiometric precursor ratios on electronic properties of halide perovskites are currently under debate. It is imperative, but experimentally challenging, to determine the chemical composition of thin films as a function of precursor ratio for a full understanding of the effect. Herein we report a precise quantification of the methylammonium (MA) content in differently fabricated films of MAPbI3 via infrared (IR) spectroscopy. We compare the thin film data to the first high quality dielectric function obtained from single crystals with IR ellipsometry. For spincoated samples, we find that the MAI/PbI2 ratio in solution has an effect on the MA content in the resulting thin films which is in the range of 77-106% compared to single crystals. For coevaporated samples, we show that a very similar range of MA content variation is accessible. Interestingly, co-evaporated films prepared like those for high efficiency solar cells have a significantly lower MA content than single crystals.


2

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




INTRODUCTION

Lead halide perovskites are currently being investigated as active material in thin film devices for a variety of applications. This interest is a result of their intriguing optoelectronic properties.1,2 To unlock the full technological potential of this material class, a complete understanding of how processing parameters determine electronic properties is mandatory but not yet achieved. One aspect that has come under scrutiny is the effect of varying precursor ratios on material properties and device performance.3–9

In the most studied case of methylammonium lead iodide

(CH3NH3PbI3, MAPI), non-stoichiometric ratios in solution of the precursor materials PbI2 and MAI are usually investigated. A multitude of studies has shown that a small amount of excess PbI2 in the precursor solution is beneficial for device performance5,10–17, and an influence on doping level has been found in several studies3,4,7. However, some reports have highlighted detrimental effects due to excess PbI2, such as hysteresis in the I-V curves or faster degradation.18,19 To complicate things further, other studies clearly showed improved device performance due to excess of MAI in the precursor solution.20,21 One necessary step towards clarifying this situation is obtaining accurate values for the stoichiometry of MAPI films formed via different routes in different laboratories. While it is easily possible to control the desired non-stoichiometric precursor ratio in the solution, it is far more challenging to determine the composition of the resulting film. The most common technique to do this is photoelectron spectroscopy (PES).4,6 PES is a very powerful method and provides information on electronic properties (e.g. ionization potential and work function) in addition to chemical composition. However, PES is very surface sensitive (~some nm) and can therefore not probe the bulk of thin films relevant for device applications with typical thicknesses of several hundred nanometers. In addition, whereas the Pb/I ratio of film surfaces can be determined with high accuracy using PES, MA is more challenging to quantify as organic impurities on the sample will alter the C and N content.6,22 In contrast, infrared (IR) spectroscopy lacks the surface sensitivity of PES, but can be utilized to probe the composition of the entire film. This has been demonstrated for halide perovskites in a number of studies over the last years.7,23–28 The low surface sensitivity of IR spectroscopy at normal transmittance is a drawback if the intention is to study surfaces or buried interfaces, for which PES is ideally suited,29 but offers the possibility to characterize the bulk of the film.


3


Page 4 of 16

We measured the IR spectra of MAPI films fabricated (i) via spin-coating from solutions with different precursor ratios and, (ii), via co-evaporation with different relative evaporation rates of the precursors. To establish a baseline value for the MA content, we performed for the first time mid-IR ellipsometry on high quality MAPI single crystals. We then compared the thin film dielectric functions to the single crystal standard. We found significant deviations of the thin film compositions from the single crystal baseline. For spin-coated films made from precursor ratios (MAI/PbI2) of 0.8 to 1.2 in solution, the MA content is 77 - 106% relative to the single crystal. Co-evaporated films fall in a very similar range, with MA contents from 75% to 110%. Our results are the first detailed analysis of MA contents in halide perovskite single crystals and thin films and highlight the structural flexibility30 of this material class. 

EXPERIMENTAL METHODS

Single crystal preparation. MAPbI3 single crystals were prepared as described elsewhere.31 Thin film preparation. SiO2 substrates were cut and cleaned by sonication in acetone and isopropanol followed by drying in a N2 stream. The thin MAPbI3 films were prepared using 2 different methods, namely spin coating and co-evaporation. For solution-processed thin films, we used the previously reported solvent quenching method.36,37 In brief, PbI2 and CH3NH3I (MAI) with a molar ratio of 1:1 were dissolved in a solvent mixture of DMF and DMSO (4:1) with a total concentration of 1M. For the non-stoichiometric precursors, the concentration of MAI was varied. The as-prepared precursor solutions were dropped onto the silicon substrates and spin cast at 4000 rpm for 30 s in the N2 containing glovebox. A drop of 300 μL chlorobenzene was applied 12 s before the end of the procedure. The resulting yellowish transparent adduct films were converted to perovskite films by heating at 100 °C for 10 min. The evaporated MAPbI3 films were fabricated using thermal co-evaporation of either PbCl2 or PbI2 (Sigma-Aldrich) and MAI as described in detail elsewhere.7,23 By varying the MA background pressure during the PbCl2 evaporation the MA content in the evaporated thin films was varied. Ex-situ X-ray diffraction measurements on co-evaporated films showed only peaks corresponding to the perovskite structure and no traces of PbCl2. IR spectroscopic ellipsometry (IRSE) of a single crystal. IRSE measurements of a CH3NH3PbI3 single crystal at different angles of incidence were performed with a Woollam IR-VASE 𝑟𝑝 ellipsometer. Ellipsometry measures the complex reflectance ratio 𝜌 = 𝑟𝑠 = tan (𝛹)exp (𝑖𝛥), where rp and rs are the reflection coefficients for light polarized parallel and perpendicular to the plane of incidence and Ψ and Δ are the standard ellipsometric parameters.


4

Page 5 of 16 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


IR spectroscopy of thin films. The MAPbI3 thin films were transferred to a Bruker Vertex 80v Fourier transform IR (FTIR) spectrometer in ambient air. All spectra were measured in transmission geometry near normal angle of incidence (10°) with the samples in vacuum (~2 mbar) using a DLaTGS detector and are referenced to the spectrum of the bare Si-substrate with natural oxide layer. The spectral resolution was set to 4 cm-1 and at least 500 scans were averaged for each spectrum. Optical modeling of single crystal IR ellipsometric data. Modeling was done using the commercial J.A. Woollam WVASE-32 software package. The modeling is based on the Fresnel equations which depend only on the dielectric function of the perovskite single crystal 𝜀(𝜔) for a certain angle of incidence 𝜗. If the initial medium is air (𝜀air = 1), the reflection coefficients for the air/perovskite interface are: 𝜀(𝜔)cos (𝜗) ― 𝜀(𝜔) ― sin2 (𝜗)

𝑟p = 𝜀(𝜔)cos (𝜗) +

cos (𝜗) ― 𝜀(𝜔) ― sin2 (𝜗)

, 𝑟s = cos (𝜗) ― 𝜀(𝜔) ― sin2 (𝜗)

𝜀(𝜔) ― sin2 (𝜗)

.

By simultaneously modeling the experimentally obtained values for Ψ and Δ for various angles of incidence, a best-fit parameterized description of the dielectric function can be achieved, including anisotropy.38 As previously shown, MAPI is optically isotropic in the mid-IR at room temperature due to the rapid rotation of the MA cation.23 The dielectric function model of the MAPI3 single crystal consisted of a dielectric background 𝜀∞ 𝑀𝐴𝑃𝑏𝐼3 = 5.02 and Lorentz oscillators as given in formula (1). Optical modeling of thin film IR transmission spectra. The experimental thin film transmission spectra were modeled using the commercial software package Scout.39 The optical model consisted of a 1 mm thick silicon substrate with the perovskite layer on top. Both materials were described by models of their dielectric function. For the silicon substrate the dielectric function model consisted of a dielectric background 𝜀∞ Si = 11.69 and Brendel oscillators to account for phonon absorptions, while the dielectric function model of the MAPbI film consisted of a dielectric background 𝜀∞ 𝑀𝐴𝑃𝑏𝐼3 = 5.02 and Lorentz oscillators as given in formula (1). The layer thickness and the parameters of the Lorentz oscillators (position, strength, and damping) were all fitted to the experimental spectrum of the corresponding perovskite layer. Kelvin probe measurements. Work function measurements were performed with a macroscopic Kelvin probe from KP Technology in ambient air. The work function of the gold probe was calibrated with highly-oriented pyrolitic graphite (HOPG, WF of 4.47 eV) directly before each measurement. Perovskite films were spin-coated on C60/ITO substrates. We prepared 8 samples for each precursor solution to test, and three spots of each sample were tested during the measurement.



RESULTS AND DISCUSSION


5


180

 

a)

Experiment Fit

175 170 165

b)  

10 8 Experiment Fit

6 c) dielectric function 

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 6 of 16

5.0 Re() 4.5

Im()

0.6 0.4 0.2 0.0 500

1000

1500

2000 2500 wavenumber [cm-1]

3000

3500

4000

Figure 1. (a) Measured ellipsometric angle Δ (orange) of a MAPbI3 single crystal (60° angle of incidence) and best-fit modeled data (black). (b) Measured ellipsometric angle Ψ (green) of a MAPbI3 single crystal and best-fit modeled data (black). (c) Real (purple) and imaginary part (black) of the fitted dielectric function of the MAPbI3 single crystal.

MAPI thin films were fabricated either by co-evaporation of the corresponding precursor materials in a high vacuum chamber, or by spin coating from solution. We used IR transparent Si wafers as substrates (see Methods for details). The film morphology was examined with SEM measurements (see Methods and Supporting Information for details. Film thicknesses were measured with a profilometer and corroborated by optical modelling of the IR spectra (accuracy +/- 10 nm). Single crystals were grown according to a procedure described in detail elsewhere.31 All IR measurements were performed in vacuum (thin films) or in dry air (single crystals). Figure 1(a) and (b) show the result of an IR ellipsometric measurement of a MAPI single crystal, together with the result of an optical model of the measurement (black). To model the experimental data, a dielectric function 𝜀(𝜔) = 𝜀∞ + ∑𝑗𝜔2

0,𝑗

𝜔2p,j ― 𝜔2 ― i𝛾𝑗𝜔

(1)


6

Page 7 of 16

was fitted (see Methods for details) to the measured spectrum. The sum over j Lorentz oscillators accounts for vibrational excitations with resonance frequency 𝜔0, oscillator strength 𝜔p, and damping 𝛾. We find an 𝜀∞ of 5.02, corresponding to a refractive index of n = 2.24, which is in excellent agreement with data obtained via ellipsometry in the near IR32. The resulting 𝜀(𝜔) is shown in Figure 1(c). All peaks in the measured mid-IR frequency range are attributed to internal MA cation vibrations.33 We refer to our earlier work for a detailed peak assignment.23 The obtained oscillator strengths are a direct measure of the MA concentration in the single crystal and will be used in the following as a standard to compare to the MA concentrations in thin films. c) 115 0.8M MA 1.0M MA 1.2M MA fit

110 105

5%

0.6

0.2

95 90 85 80

100% (single crystal) 77% 84% 106%

0.4

100

75

MA M 1 .2

4000

MA

3500

M

2000 2500 3000 wavenumber [cm-1]

1 .0

1500

M

1000

MA

70

0.0

0 .8

b)

relative MA content [%]

relative transmission

a)

Im(

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. (a) Measured relative transmission spectra of solution processed MAPbI3 thin films on silicon with varying MA content in the precursor solution. Film thicknesses as derived from the spectral fits are 333 nm, 390 nm, and 372 nm for the precursor ratios of 0.8, 1, and 1.2, respectively. The fitted spectra are given in dashed black lines. (b) Imaginary part of the fitted dielectric functions used for the fit in Figure 2 (a) together with the imaginary part of the dielectric function of the MAPbI3 single crystal given in Figure 1(c). (c) Relative MA contents normalized to the MA content of the single crystal.

Figure 2(a) shows the experimental relative transmission spectra of spin coated MAPI layers on silicon. The layers were prepared from precursor solutions with three different MA/PbI2 ratios, namely 0.8, 1, and 1.2. The curved baseline is related to thin film interferences and thus essentially depends on the film thickness as well as on the dielectric background 𝜀∞ of the MAPI films. The


7


Page 8 of 16

spectra were fitted by using dielectric function models for the MAPI thin films consisting of a dielectric background 𝜀∞ of 5.02 and harmonic oscillators for the MA vibrations. The imaginary part of the fitted dielectric function models is given in Figure 2(b). Since all vibrational modes in the mid IR range are evoked by the MA and not by the lead halide framework of the perovskite, the relative MA amount can be determined by comparing the imaginary part of the dielectric functions of the thin films with the single crystal data. The peak areas in the imaginary part of the dielectric functions in the MIR range (500 cm-1 – 6000 cm-1) normalized to the value of the single crystal give a measure for the relative MA content. For the spin coated layers prepared in a nitrogen glovebox the relative MA contents are 77%, 84%, and 106% for the precursor ratios of 0.8, 1, and 1.2, respectively.

Figure 3. Work function (WF) of solution processed MAPbI3 thin films with varying MA content in the precursor solution measured by Kelvin Probe. The samples were processed in nitrogen, measurements were performed in ambient air. Only small changes in WF are observed.

Additionally, we measured the work function (WF) of these films with a Kelvin probe in air (Figure 3, see experimental section for details). We do find a slightly increased WF for the films made with a 1.2 MAI/PbI2 ratio (WF=4.85 eV), but no significant change between 0.8 and 1 (WF=4.7 eV). Yin et al.’s calculations show that in MAPI, dominant defects are Pb vacancies (VPb) and MA interstitials (MAi) acting as acceptor and donor due to energetically unfavorable sp antibonding coupling and weak van der Walls interaction of MA to the inorganic Pb-I framework, respectively.34 They both have transition energy levels very close to the band edges. As is shown


8

Page 9 of 16

in Figure 2(b), perovskite films made with 1.2 MAI/PbI2 ratio have significantly higher amount of MA than that of 0.8 and 1(106% compared to 77% and 84%). Given that in the MA excess case, VPb has much less formation energy than MAi, we deduce that it is mainly these negatively charged defects that contribute to the downward shift of the Fermi level of perovskites with 1.2 MAI/PbI2 ratio. However, we note that the small changes in work function we found are in apparent contradiction to an earlier report that found a much more pronounced change of the Fermi level as a function of the precursor ratio.3 This earlier work used UPS in vacuum to determine the work function of the perovskite films, whereas we measured with a Kelvin probe in air. This might explain the different findings to some extent. However, our new findings here are in good agreement to our recent work on WF differences in stoichiometrically tuned co-evaporated MAPI films.7 Furthermore, this finding is in accordance with a large defect tolerance of the electronic structure of MAPI. a)

336 nm 342 nm 581 nm 344 nm 473 nm fit

relative transmission

10%

b)

100% (single crystal) 75% 79% 83% 89% 110%

0.6 0.4

Im(

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


0.2 0.0 1000

1500

2000

2500

3000

3500

4000

wavenumber (cm-1)

Figure 4. (a) Measured relative transmission spectra of co-evaporated MAPI thin films on silicon for various MA background pressure during film formation. The film thicknesses as fit results are given in the legend and the fitted spectra are given in dashed black lines. (b) Imaginary part of the dielectric functions for the fits in (a) together with the imaginary part of the dielectric function of the MAPbI3 single crystal given in Figure 1(c). The relative MA contents normalized to the MA content of the single crystal are given in the legend.


9


Page 10 of 16

In Figure 4(a) the experimental relative transmission spectra of evaporated MAPI layers on silicon and the result of corresponding fits (vide infra) are shown. The fitted layer thicknesses of the investigated layers varied between 300 and 600 nm and are given in the legend. The fit results for the imaginary part of the dielectric function together with the relative MA content are given in Figure 4(b) (see legend). The variation of the MA background pressure during evaporation in vacuum strongly influences the relative MA content in the formed thin film. With this preparation method the relative MA content can be varied between 75% and 110%. For layers with above 100%, the additional MA molecules are believed to be located in the grain boundaries between MAPI grains. Interestingly, the film with 83% relative MA content was prepared under conditions that yield highly efficient MAPI solar cells.35 This result aligns well with the PbI2 excess typically used in solution processed MAPI solar cell and points to a very general important role that PbI2 excess plays for solar cell performance, independent of the fabrication method. 

CONCLUSION

In summary, we report a precise quantification of the methylammonium (MA) content in differently fabricated films of MAPI via IR spectroscopy and compare the thin film findings to the first high quality dielectric function obtained from single crystals with IR ellipsometry. The MAI/PbI2 ratio in solution has an effect on the MA content in the resulting thin films, with an MA content in the range of 77-106% compared to single crystals. However, the effect on the work function of the films is small, contradicting earlier results. Slightly larger variations of the MA content are achieved for co-evaporated films. Interestingly, films from co-evaporated high efficiency solar cells have a 16% lower MA content than single crystals. Our experiments clearly show that it is possible to fabricate films with relative MA contents between 75% and 110%, independent of the fabrication method.



NOTES

The authors declare no competing financial interests. 

ACKNOWLEDGMENTS


10

Page 11 of 16 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


We thank the German Federal Ministry of Education and Research for financial support within the InterPhase project (FKZ 13N13656, 13N13657). X.H. thanks the Chinese Scholarship Council (CSC) for support.


11


Page 12 of 16

 REFERENCES (1) Brenner, T. M.; Egger, D. A.; Kronik, L.; Hodes, G.; Cahen, D. Hybrid Organic—Inorganic Perovskites: Low-Cost Semiconductors with Intriguing Charge-Transport Properties. Nat. Rev. Mater. 2016, 1 (1), 15007. https://doi.org/10.1038/natrevmats.2015.7. (2) Egger, D. A.; Bera, A.; Cahen, D.; Hodes, G.; Kirchartz, T.; Kronik, L.; Lovrincic, R.; Rappe, A. M.; Reichman, D. R.; Yaffe, O. What Remains Unexplained about the Properties of Halide Perovskites? Adv. Mater. 2018, 30 (20), 1800691. https://doi.org/10.1002/adma.201800691. (3) Wang, Q.; Shao, Y.; Xie, H.; Lyu, L.; Liu, X.; Gao, Y.; Huang, J. Qualifying Composition Dependent p and n Self-Doping in CH3NH3PbI3. Appl. Phys. Lett. 2014, 105 (16), 163508. https://doi.org/10.1063/1.4899051. (4) Emara, J.; Schnier, T.; Pourdavoud, N.; Riedl, T.; Meerholz, K.; Olthof, S. Impact of Film Stoichiometry on the Ionization Energy and Electronic Structure of CH3NH3PbI3 Perovskites. Adv. Mater. 2016, 28 (3), 553–559. https://doi.org/10.1002/adma.201503406. (5) Park, B.; Kedem, N.; Kulbak, M.; Lee, D. Y.; Yang, W. S.; Jeon, N. J.; Seo, J.; Kim, G.; Kim, K. J.; Shin, T. J.; et al. Understanding How Excess Lead Iodide Precursor Improves Halide Perovskite Solar Cell Performance. Nat. Commun. 2018, 9 (1), 3301. https://doi.org/10.1038/s41467-018-05583-w. (6) Fassl, P.; Lami, V.; Bausch, A.; Wang, Z.; Klug, M. T.; Snaith, H. J.; Vaynzof, Y. Fractional Deviations in Precursor Stoichiometry Dictate the Properties, Performance and Stability of Perovskite Photovoltaic Devices. Energy Environ. Sci. 2018, 11 (12), 3380–3391. https://doi.org/10.1039/C8EE01136B. (7) Dänekamp, B.; Müller, C.; Sendner, M.; Boix, P. P.; Sessolo, M.; Lovrincic, R.; Bolink, H. J. Perovskite–Perovskite Homojunctions via Compositional Doping. J. Phys. Chem. Lett. 2018, 9 (11), 2770–2775. https://doi.org/10.1021/acs.jpclett.8b00964. (8) Carmona, C. R.; Gratia, P.; Zimmermann, I.; Grancini, G.; Gao, P.; Grätzel, M.; Nazeeruddin, M. K. High Efficiency Methylammonium Lead Triiodide Perovskite Solar Cells: The Relevance of Non-Stoichiometric Precursors. Energy Environ. Sci. 2015. https://doi.org/10.1039/C5EE02555A. (9) Jung, M.; Ji, S.-G.; Kim, G.; Il Seok, S. Perovskite Precursor Solution Chemistry: From Fundamentals to Photovoltaic Applications. Chem. Soc. Rev. 2019, 48 (7), 2011–2038. https://doi.org/10.1039/C8CS00656C. (10) Cao, D. H.; Stoumpos, C. C.; Malliakas, C. D.; Katz, M. J.; Farha, O. K.; Hupp, J. T.; Kanatzidis, M. G. Remnant PbI2, an Unforeseen Necessity in High-Efficiency Hybrid PerovskiteBased Solar Cells?A). APL Mater. 2014, 2 (9), 091101. https://doi.org/10.1063/1.4895038.


12

Page 13 of 16 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


(11) Bi, D.; Tress, W.; Dar, M. I.; Gao, P.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Baena, J.-P. C.; et al. Efficient Luminescent Solar Cells Based on Tailored MixedCation Perovskites. Sci. Adv. 2016, 2 (1), e1501170. https://doi.org/10.1126/sciadv.1501170. (12) Jacobsson, T. J.; Correa-Baena, J.-P.; Anaraki, E. H.; Philippe, B.; Stranks, S. D.; Bouduban, M. E. F.; Tress, W.; Schenk, K.; Teuscher, J.; Moser, J.-E.; et al. Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells. J. Am. Chem. Soc. 2016, 138 (32), 10331. https://doi.org/10.1021/jacs.6b06320. (13) Kim, Y. C.; Jeon, N. J.; Noh, J. H.; Yang, W. S.; Seo, J.; Yun, J. S.; Ho‐Baillie, A.; Huang, S.; Green, M. A.; Seidel, J.; et al. Beneficial Effects of PbI2 Incorporated in Organo-Lead Halide Perovskite Solar Cells. Adv. Energy Mater. 2016, 6 (4), 1502104. https://doi.org/10.1002/aenm.201502104. (14) Song, D.; Cui, P.; Wang, T.; Wei, D.; Li, M.; Cao, F.; Yue, X.; Fu, P.; Li, Y.; He, Y.; et al. Managing Carrier Lifetime and Doping Property of Lead Halide Perovskite by Postannealing Processes for Highly Efficient Perovskite Solar Cells. J. Phys. Chem. C 2015, 119 (40), 22812– 22819. https://doi.org/10.1021/acs.jpcc.5b06859. (15) Cui, P.; Wei, D.; Ji, J.; Song, D.; Li, Y.; Liu, X.; Huang, J.; Wang, T.; You, J.; Li, M. Highly Efficient Electron-Selective Layer Free Perovskite Solar Cells by Constructing Effective p–n Heterojunction. Sol. RRL 2017, 1 (2), 1600027. https://doi.org/10.1002/solr.201600027. (16) Bi, D.; El-Zohry, A. M.; Hagfeldt, A.; Boschloo, G. Unraveling the Effect of PbI2 Concentration on Charge Recombination Kinetics in Perovskite Solar Cells. ACS Photonics 2015, 2 (5), 589–594. https://doi.org/10.1021/ph500255t. (17) Petrus, M. L.; Hu, Y.; Moia, D.; Calado, P.; Leguy, A. M. A.; Barnes, P. R. F.; Docampo, P. The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non-Stoichiometric Precursor Mixtures. ChemSusChem 2016, 9 (18), 2699–2707. https://doi.org/10.1002/cssc.201600999. (18) Liu, F.; Dong, Q.; Wong, M. K.; Djurišić, A. B.; Ng, A.; Ren, Z.; Shen, Q.; Surya, C.; Chan, W. K.; Wang, J.; et al. Is Excess PbI2 Beneficial for Perovskite Solar Cell Performance? Adv. Energy Mater. 2016, 6 (7), 1502206. https://doi.org/10.1002/aenm.201502206. (19) Yu, H.; Lu, H.; Xie, F.; Zhou, S.; Zhao, N. Native Defect-Induced Hysteresis Behavior in Organolead Iodide Perovskite Solar Cells. Adv. Funct. Mater. 2016, 26 (9), 1411–1419. https://doi.org/10.1002/adfm.201504997. (20) Son, D.-Y.; Lee, J.-W.; Choi, Y. J.; Jang, I.-H.; Lee, S.; Yoo, P. J.; Shin, H.; Ahn, N.; Choi, M.; Kim, D.; et al. Self-Formed Grain Boundary Healing Layer for Highly Efficient CH3 NH3 PbI3 Perovskite Solar Cells. Nat. Energy 2016, 1 (7), 16081. https://doi.org/10.1038/nenergy.2016.81.


13


Page 14 of 16

(21) Ham, S.; Choi, Y. J.; Lee, J.-W.; Park, N.-G.; Kim, D. Impact of Excess CH3NH3I on Free Carrier Dynamics in High-Performance Nonstoichiometric Perovskites. J. Phys. Chem. C 2017, 121 (5), 3143–3148. https://doi.org/10.1021/acs.jpcc.6b11984. (22) Xie, H.; Liu, X.; Lyu, L.; Niu, D.; Wang, Q.; Huang, J.; Gao, Y. Effects of Precursor Ratios and Annealing on Electronic Structure and Surface Composition of CH3NH3PbI3 Perovskite Films. J. Phys. Chem. C 2016, 120 (1), 215–220. https://doi.org/10.1021/acs.jpcc.5b07728. (23) Glaser, T.; Müller, C.; Sendner, M.; Krekeler, C.; Semonin, O. E.; Hull, T. D.; Yaffe, O.; Owen, J. S.; Kowalsky, W.; Pucci, A.; et al. Infrared Spectroscopic Study of Vibrational Modes in Methylammonium Lead Halide Perovskites. J. Phys. Chem. Lett. 2015, 6 (15), 2913–2918. https://doi.org/10.1021/acs.jpclett.5b01309. (24) Patel, J. B.; Milot, R. L.; Wright, A. D.; Herz, L. M.; Johnston, M. B. Formation Dynamics of CH3NH3PbI3 Perovskite Following Two-Step Layer Deposition. J. Phys. Chem. Lett. 2016, 7 (1), 96–102. https://doi.org/10.1021/acs.jpclett.5b02495. (25) Müller, C.; Glaser, T.; Plogmeyer, M.; Sendner, M.; Döring, S.; Bakulin, A. A.; Brzuska, C.; Scheer, R.; Pshenichnikov, M. S.; Kowalsky, W.; et al. Water Infiltration in Methylammonium Lead Iodide Perovskite: Fast and Inconspicuous. Chem. Mater. 2015, 27 (22), 7835–7841. https://doi.org/10.1021/acs.chemmater.5b03883. (26) Gallop, N. P.; Selig, O.; Giubertoni, G.; Bakker, H. J.; Rezus, Y. L. A.; Frost, J. M.; Jansen, T. L. C.; Lovrincic, R.; Bakulin, A. A. Rotational Cation Dynamics in Metal Halide Perovskites: Effect on Phonons and Material Properties. J. Phys. Chem. Lett. 2018, 9 (20), 5987–5997. https://doi.org/10.1021/acs.jpclett.8b02227. (27) Brivio, F.; Frost, J. M.; Skelton, J. M.; Jackson, A. J.; Weber, O. J.; Weller, M. T.; Goñi, A. R.; Leguy, A. M. A.; Barnes, P. R. F.; Walsh, A. Lattice Dynamics and Vibrational Spectra of the Orthorhombic, Tetragonal, and Cubic Phases of Methylammonium Lead Iodide. Phys. Rev. B 2015, 92 (14), 144308. https://doi.org/10.1103/PhysRevB.92.144308. (28) Pérez-Osorio, M. A.; Milot, R. L.; Filip, M. R.; Patel, J. B.; Herz, L. M.; Johnston, M. B.; Giustino, F. Vibrational Properties of the Organic–Inorganic Halide Perovskite CH3NH3PbI3 from Theory and Experiment: Factor Group Analysis, First-Principles Calculations, and LowTemperature Infrared Spectra. J. Phys. Chem. C 2015, 119 (46), 25703–25718. https://doi.org/10.1021/acs.jpcc.5b07432. (29) Olthof, S.; Meerholz, K. Substrate-Dependent Electronic Structure and Film Formation of MAPbI3 Perovskites. Sci. Rep. 2017, 7, 40267. https://doi.org/10.1038/srep40267. (30) Frost, J. M.; Walsh, A. What Is Moving in Hybrid Halide Perovskite Solar Cells? Acc. Chem. Res. 2016, 49 (3), 528–535. https://doi.org/10.1021/acs.accounts.5b00431. (31) 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–


14

Page 15 of 16 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


Inorganic Halide Perovskite Crystals. https://doi.org/10.1038/ncomms13303.

Nat.

Commun.

2016,

7,

13303.

(32) Löper, P.; Stuckelberger, M.; Niesen, B.; Werner, J.; Filipič, M.; Moon, S.-J.; Yum, J.-H.; Topič, M.; De Wolf, S.; Ballif, C. Complex Refractive Index Spectra of CH3NH3PbI3 Perovskite Thin Films Determined by Spectroscopic Ellipsometry and Spectrophotometry. J. Phys. Chem. Lett. 2015, 6 (1), 66–71. https://doi.org/10.1021/jz502471h. (33) Onoda-Yamamuro, N.; Matsuo, T.; Suga, H. Calorimetric and IR Spectroscopic Studies of Phase Transitions in Methylammonium Trihalogenoplumbates (II)†. J. Phys. Chem. Solids 1990, 51 (12), 1383–1395. https://doi.org/10.1016/0022-3697(90)90021-7. (34) Yin, W.-J.; Shi, T.; Yan, Y. Unusual Defect Physics in CH3NH3PbI3 Perovskite Solar Cell Absorber. Appl. Phys. Lett. 2014, 104 (6), 063903. https://doi.org/10.1063/1.4864778. (35) Momblona, C.; Gil-Escrig, L.; Bandiello, E.; Hutter, E. M.; Sessolo, M.; Lederer, K.; Blochwitz-Nimoth, J.; Bolink, H. J. Efficient Vacuum Deposited P-i-n and n-i-p Perovskite Solar Cells Employing Doped Charge Transport Layers. Energy Environ. Sci. 2016, 9 (11), 3456–3463. https://doi.org/10.1039/C6EE02100J. (36) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Solvent Engineering for High-Performance Inorganic–Organic Hybrid Perovskite Solar Cells. Nat. Mater. 2014, 13 (9), 897–903. https://doi.org/10.1038/nmat4014. (37) 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. https://doi.org/10.1021/jacs.5b04930. (38) Schubert, M. Infrared Ellipsometry on Semiconductor Layer Structures; Springer Tracts in Modern Physics; Springer-Verlag Berlin: Berlin, Heidelberg, 2005; Vol. 209. (39)

Theiss, W. Scout; W. Theiss Hard- und Software, 2015.

TOC GRAPHICS


15


Page 16 of 16


16

Quantifying the Composition of Methylammonium Lead Iodide

Recommend Documents