Supporting Information
Electron-Rotor Interaction in Organic-Inorganic Lead Iodide Perovskites Discovered by Isotope Effect
Jue Gong,1‡ Mengjin Yang,2‡ Xiangchao Ma,3 Richard D. Schaller,4 Gang Liu,5* Lingping Kong,5 Ye Yang,2 Matthew C. Beard,2 Michael Lesslie,1 Ying Dai,3 Baibiao Huang,3 Kai Zhu,2* Tao Xu1* 1
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, United States 2
Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, CO 80401, United States
3
School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, China
4
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, United States
5
Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China
*
Corresponding authors:
[email protected] (G.L.);
[email protected] (K.Z.);
[email protected]
(T.X.) ‡
The authors contribute equally to this work.
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Figure S1. 1H NMR spectrum of CH3NH3I.
CH3NH3I was dissolved in DMSO-D6 (D, 99.9%, Cambridge Isotope Laboratories, Inc.). The peak at 7.4817 ppm corresponds to hydrogen in –NH3 of CH3NH3I compound; peak at 2.3752 ppm corresponds to hydrogen in –CH3 of CH3NH3I compound; peak at 2.5014 ppm corresponds to signal of DMSO-D6 solvent; peak at 3.3245 ppm refers to hydrogen of water content from air. The approximate 1:1 ratio of –NH3 and –CH3 determined by peak integrations substantiates the existence of CH3NH3I. The trace amount of water indicated by peak at 3.3245 ppm may be caused by moisture in DMSO-D6 or be involved during the transferring sample to NMR tubes.
S2
Figure S2. 1H NMR spectrum of CH3ND3I.
CH3ND3I was dissolved in DMSO-D6 (D, 99.9%, Cambridge Isotope Laboratories, Inc.). The peak at 3.8642 ppm corresponds to H2O; peak at 2.5032 ppm corresponds to signal of DMSO-D6 solvent; peak at 2.3496 ppm corresponds to hydrogen of -CH3 in CH3ND3I. The absence of a peak in the range of 7.4–7.5 ppm indicates the fully deuterated nature of ammonium in CH3ND3I.
S3
Figure S3. 1H NMR spectrum of CD3NH3I.
CD3NH3I was dissolved in DMSO-D6 (D, 99.9%, Cambridge Isotope Laboratories, Inc.). The peak at 7.4602 ppm corresponds to hydrogen in -NH3 of CD3NH3I; peak at 3.3334 ppm corresponds to hydrogen of water content; peak at 2.5010 ppm corresponds to signal of DMSOD6 solvent. The absence of a peak in the range of 2.3–2.4 ppm indicates that all the hydrogens in the methyl group are replaced by deuterium.
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Figure S4. 1H NMR spectrum of CD3ND3I.
CD3ND3I was dissolved in DMSO-D6 (D, 99.9%, Cambridge Isotope Laboratories, Inc.). No hydrogen peaks associated with CD3ND3I were detected. Peak at 3.3810 ppm is assigned for water, and the peak at 2.5011 ppm is signal of DMSO-D6 solvent. The presence of trace amount of water may be caused by moisture in DMSO-D6 or due to transferring sample to NMR tube.
S5
Figure S5. 1H NMR spectrum of the pristine DMSO-D6 solvent without any samples dissolved.
Peak at 3.3217 ppm is assigned for water, and peak at 2.5013 ppm is signal for DMSOD6 solvent. This control experiment suggests that the presence of the water peak in DMSO-D6 is the origin of the water peaks that appeared in all four methylammonium iodide spectra.
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Figure S6. Mass spectra of CH3NH3I (black trace), CH3ND3I (red trace), CD3NH3I (blue trace), and CD3ND3I (pink trace) displayed from 15 to 225 m/z.
For each compound, ions were formed representing both the methylammonium ion and a complex of two methylammonium and iodide ions. To be specific, for CH3NH3I spectrum, peak at 32 m/z represents [CH3NH3]+, and peak at 191 m/z represents [(CH3NH3)-I-(NH3CH3)]+ complex ion; for CH3ND3I spectrum, the peak at 35 m/z represents [CH3ND3]+, and peak at 197 m/z represents [(CH3ND3)-I-(ND3CH3)]+; for CD3NH3I spectrum, peak at 35 m/z is for [CD3NH3]+, and peak at 197 m/z is for [(CD3NH3)-I-(NH3CD3)]+; for CD3ND3I spectrum, peak at 38 m/z is for [CD3ND3]+, and peak at 203 m/z represents [(CD3ND3)-I-(ND3CD3)]+. Shifts in the mass of both sets of ions for each species confirm the expected H/D exchange.
S7
Figure S7. XRD powder diffraction of CH3NH3PbI3 and CH3ND3PbI3 thin films. Red spectrum is for CH3NH3PbI3, and blue spectrum is for CH3ND3PbI3.
The same peak positions and intensities verify that deuteration of ammonium did not alter crystal structure. Major peaks, 14.10o and 28.43o, are assigned to (110) and (220) of the tetragonal phase (space group I4/mcm), respectively, indicating a relatively strong texture of perovskite film.1,2
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Figure S8. Surface morphology of CH3NH3PbI3 thin film (left), CH3ND3PbI3 thin film (right) measured by SEM.
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Figure S9. UV-Vis absorbance of thin-film CH3NH3PbI3 (red), CD3ND3PbI3 (magenta), CD3NH3PbI3 (violet) and CH3ND3PbI3 (blue). The onsets of absorption edges of all four types of perovskites converge at around 825 nm, indicating that four types of perovskite thin films have nearly the same bandgap.
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Figure S10. Stabilized output of power conversion efficiency (PCE) and current density at maximum power point as a function of time for the CH3ND3PbI3-based device shown in Figure 2d under simulated one-sun illumination.
AM 1.5 solar-simulated light illuminated on CH3ND3PbI3-based solar cell at 12 s, and the power conversion efficiency was maintained at about 15.4% with stable short-circuit current density of about 17.90 mA/cm2.
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Figure S11 a-i. Cleaved CH3NH3PbI3 single-crystal SEM image (a); CH3NH3PbI3 single crystal after continuous growth in 1 M CH3NH3I/PbI2 solution for 48 hours (b); cleaved CH3ND3PbI3 single-crystal SEM image (c); CH3ND3PbI3 single crystal after continuous growth in 1 M CH3ND3I/PbI2 solution in an argon glovebox for 48 hours (d); cleaved CD3NH3PbI3 singlecrystal SEM image (e); CD3NH3PbI3 single crystal after continuous growth in 1 M CD3NH3I/PbI2 solution for 48 hours (f); cleaved CD3ND3PbI3 single-crystal SEM image (g);
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CD3ND3PbI3 single crystal after continuous growth in 1 M CD3ND3I/PbI2 solution in an argon glovebox for 48 hours (h); high-resolution X-ray diffraction spectra of CH3NH3PbI3 (purple), CH3ND3PbI3 (pink), CD3NH3PbI3 (red), and CD3ND3PbI3 (blue) (i). The concurrence of the same peak positions across these four compounds indicates that these four materials have the same crystal structure. Sharpness of the peaks nearly matches each other and verifies the high crystallinity of the four types of crystals. Crystals were first broken into smaller grains and annealed at 80 ˚C for 15 min to relieve the possible structural strain during cracking of the crystals, then were loaded into Kapton tubes compactly for subsequent XRD measurements. The absence of grain boundaries, cross-section voids, and defects, along with XRD results, indicate the comparable crystallinities across the four types of grown crystals.
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0.8 N-H
Infrared Absorbance (a.u.)
2846 2917
0.6 CH3NH3PbI3
0.4
2846 2917
0.2
0.0
CH3ND3PbI3
2600
2800
3000
3200
3400
Wave Number (cm-1) Figure S12. Infrared spectra for CH3NH3PbI3 (red) and CH3ND3PbI3 (blue) single crystals. For the IR spectrum of CH3NH3PbI3, the broad peak at ~3158 cm-1 is assigned to the N-H symmetric stretching mode, and the broad peak at 3190 cm-1 refers to asymmetric N-H stretching mode. Peak at 2917 cm-1 is assigned to C-H asymmetric stretching mode, and the peak at 2846 cm-1 refers to C-H symmetric stretching mode. For CH3ND3PbI3, the broad peaks due to N-H nearly disappeared, whereas the peak at 2846 cm-1 corresponds to C-H symmetric stretching mode, and the peak at 2916 cm-1 corresponds to C-H asymmetric stretching motion. These peak positions closely match the literature values.3-5
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N-H 1.5
Absorbance (a.u.)
CD3NH3PbI3 1.0
0.5
CD3ND3PbI3 0.0
2600
2800
3000
3200
3400
-1
Wavenumber (cm )
Figure S13. Infrared spectra for CD3NH3PbI3 and CD3ND3PbI3 thin films. N-H stretching can still be observed in CD3NH3PbI3, but no N-H or C-H can be observed in CD3ND3PbI3. (The slight bump in the N-H stretching region is due to the inevitable H-D exchanged between the film and the humidity in air during sample transportation.)
Table S1. Statistic photovoltaic parameters based on 8~10 devices for CH3NH3PbI3 and CH3ND3PbI3 perovskite materials. Jsc (mA/cm2)
Voc (V)
FF
PCE (%)
CH3NH3PbI3
21.58 ± 0.39
1.060 ± 0.006
0.742 ± 0.015
16.96 ± 0.48
CH3ND3PbI3
21.24 ± 0.44
1.039 ± 0.018
0.716 ± 0.011
15.81 ± 0.61
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Calculation on ratio of rotational frequencies of MA+ The estimation of the ratio of the in-plane rotation frequency along the C-N axis of the four isotope MA+ ν(CH3NH3+) : ν(CH3ND3+) : ν(CD3NH3+) : ν(CD3ND3+) is depicted as follows. If we treat MA+ as a rigid rotor about its center of mass with the methyl group as a whole entity, ammonium as another, the moment of inertia of this bi-unit cationic molecule can be modeled through equation (1),6 𝐼𝐼 = 𝑚𝑚1 ∗ 𝑅𝑅12 + 𝑚𝑚2 ∗ 𝑅𝑅22 ,
(1)
where m1 is mass of methyl group and m2 is mass of ammonium group; R1 is distance from the center of mass of MA+ to the center of mass of methyl group, and R2 is distance from the center of mass of MA+ to the center of mass of ammonium group. Likewise, it can be rewritten as equation (2),6 I=µ·Re2 ,
(2)
where Re is the distance between the center of mass of methyl group and center of mass of ammonium group, so Re = R1 + R2; μ is the reduced mass of methyl and ammonium groups and μ = (m1*m2)/(m1+m2). Therefore, the ratio for μ(CH3NH3+) : μ(CH3ND3+) : μ(CD3NH3+) : μ(CD3ND3+) ≈ 1 : 1.1 : 1.1 : 1.2. Knowing the bond angles and bond lengths in MA+ (note that isotopes do not change bond length and angle), we estimate the ratio for Re(CH3NH3+) : Re(CH3ND3+): Re(CD3NH3+) : Re(CD3ND3+) ≈ 1 : 1.03 : 1.03 : 1.05; consequently, the ratio for I(CH3NH3+) : I(CH3ND3+): I(CD3NH3+) : I(CD3ND3+) ≈ 1 : 1.17 : 1.17 : 1.32. Furthermore, the molecular rotational constant B can be expressed as equation (3),6 B=h/(8π2I) ,
(3)
where h is Planck’s constant and I is moment of inertia. Thus, the rotational frequency ν can be determined by equation (4),6
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ν=h(J+1)/4 π2I ,
(4)
where J is the rotational quantum number and J=0, 1, 2… Thus, the ratio of their rotational frequencies is ν(CH3NH3+) : ν(CH3ND3+) : ν(CD3NH3+) : ν(CD3ND3+) ≈ 1 : 0.85 : 0.85 : 0.76 with the assumption that they take on the same rotational quantum state.
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(6) McQuarrie, D. A.; Simon, J. D. Molecular Thermodynamics (University Science Books, Sausalito, 1999).
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