Supplementary Material
The presence of CH3NH2 neutral species in organometal halide perovskite films Min-Cherl Jung,1 Young Mi Lee,2 Han-Koo Lee,2 Jinwoo Park,3 Sonia R. Raga,1 Luis K. Ono,1 Shenghao Wang,1 Matthew R. Leyden,1 Byung Deok Yu,4 Suklyun Hong3 and Yabing Qi1,*
1
Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology
Graduate University (OIST), 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan 2
Pohang Accelerator Laboratory, POSTECH, Pohang, 790-784, Republic of Korea
3
Graphene Research Institute and Department of Physics, Sejong University, Seoul 143-747, Republic
of Korea 4
Department of Physics, University of Seoul, Seoul 130-743, Republic of Korea
* Author to whom correspondence should be addressed. Electronic mail:
[email protected]
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1. Structural confirmation of solution-prepared MAPbI3. We performed atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-Visible spectrometer (UV-Vis), and x-ray diffraction (XRD) to confirm the formation of organometal halide perovskite from solution-processing: MAPbI3 thin film on TiO2(cl)/FTO. AFM and SEM confirmed the film thickness of ~50 nm and the typical surface morphology of MAPbI3 perovskite (Figures S1a and b). The samples showed a brown color (Figure S1b) corresponding to an optical bandgap of ~1.55 eV extracted from UV-Vis measurements and typical diffraction peaks corresponding to the (110), (220), and (330) planes in XRD measurements (Figure S1c and d). All measurements corroborate the formation of MAPbI3 perovskite thin film.1-3
2. Figures
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Figure S1. Surface morphology, absorption properties, and crystallinity. (a) 50-nm MAPbI3/TiO2/FTO film measured by AFM. (b) SEM image of an identical sample (same batch) to that prepared for the synchrotron radiation measurements. (c) UV-Vis spectra where optical band gap of ~1.55 eV was extracted. (d) x-ray diffraction pattern of MAPbI3 showing the main (110), (220) and (330) planes.
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Figure S2. HRXPS results after air exposure. Changes in the intensity ratio of CH3-NH3+ and CH3NH2 in C 1s core-level spectra are shown. The intensity of N 1s core-level decreases with air exposure time. Oxygen signal was below instrument sensitivity limits in the as-received sample inferring sample cleanness. Physisorbed oxygen species was observed to evolve as a function of air exposure time.
Figure S3. Electronic density of states (DOS) of CH3NH3PbI3 (a) and CH3NH2PbI3 (b). In (a), total DOS is shown, while in (b), partial DOS projected to yellow colored atoms (Pb and I) is shown to represent where the band gap closing occurs.
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Table S1. Calculated binding energy Esafe for various ratios of CH3NH3 (m) and CH3NH2 (n) in the supercell of PbI3, where m and n denote the number of CH3NH3 and CH3NH2 molecules in the supercell, respectively. In the tetragonal structure, all values of Esafe are positive. This indicates that CH3NH2 molecules cannot exist in the interior region of PbI3. m, n
Esafe (eV)
15, 1
0.312
14, 2
0.779
13, 3
1.350
12, 4
1.831
11, 5
2.298
10, 6
2.799
9, 7
3.324
8, 8
3.776
7, 9
2.041
6, 10
3.012
5, 11
Unstable (Not converged)
4, 12
2.711
3, 13
3.304
2, 14
Unstable (Not converged)
1, 15
1.381
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References 1
M. Grätzel, Nature Materials 13, 838 (2014).
2
T.-B. Song, Q. Chen, H. Zhou, C. Jiang, H.-H. Wang, Y.M. Yang, Y. Liu, J. You, and Y. Yang,
Journal of Materials Chemistry A 3, 9032 (2015). 3
P. Gao, M. Grätzel, and M.K. Nazeeruddin, Energy Environ. Sci. 7, 2448 (2014).
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