Evolution of Chemical Composition, Morphology, and Photovoltaic

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1 Evolution of Chemical Composition, Morphology, and Photovoltaic Efficiency of CH 3 NH 3 PbI 3 Perovskite under Ambient Conditions Weixin Huang 1,2, Joseph S. Manser 1,3, Prashant V. Kamat 1,2,3, and Sylwia Ptasinska 1,4 1 Radiation Laboratory, 2 Department of Chemistry and Biochemistry, 3 Department of Chemical and Biomolecular Engineering, and 4 Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA Supporting Information Figure S1. X-ray photoelectron spectroscopy survey spectra (left), and high-resolution I 3d 5/2 and Pb 4f spectra (right) for CH 3 NH 3 PbI 3 films stored under ambient laboratory conditions for (a) 0 days and (b) 21 days. Pass energy was set at 100 ev for the survey spectra, and at 45 ev for the I 3d 5/2 and Pb 4f spectra. 1

2 Figure S2. Spectral fitting and peak assignments for CH 3 NH 3 PbI 3 perovskite films exposed to ambient conditions. (a) I 3d 5/2, (b) Pb 4f, (c) C 1s, and (d) O 1s. Peak assignments: (A) ± 0.1 ev (Pb-I), (B) ± 0.1 ev (Pb-I, Pb(OH) 2 ), (C) ± 0.1 ev (PbCO 3 ), and (D) ± 0.1 ev (PbO), (E) ± 0.1 ev (adventitious carbon), (F) ± 0.1 ev (CH 3 NH + 3 ), (G) ev ± 0.2 ev (PbCO 3 ), (H) ± 0.1 ev (PbCO 3, β-pbo, SnO 2 ), (I) ± 0.1 ev (adventitious oxygen, Pb(OH) 2 ), (J) ev ± 0.1 ev (adventitious oxygen), and (K) ± 0.2 ev (α-pbo). 2

3 Figure S3. X-ray photoelectron spectroscopy survey spectra for PbI 2 powder stored under ambient laboratory conditions for (a) 0 days and (b) 8 days. Evolutions of Pb 4f and C 1s spectra for PbI 2 powder (bottom). 3

4 Figure S4. Spectral fitting and peak assignments for PbI 2 powder exposed to ambient conditions (a) C 1s, and (b) O 1s. Each spectrum is normalized with respect to y-axis: (A) ± 0.1 ev (adventitious carbon), (B) ± 0.1 ev (adventitious carbon), (C) ev ± 0.2 ev (PbCO 3 ), and (D) ± 0.2 ev (adventitious oxygen, PbCO 3, β-pbo), (E) ± 0.1 ev (Pb(OH) 2 ), and (F) ± 0.2 ev (α-pbo). 4

5 Figure S5. Summarized photovoltaic parameters for perovskite solar cells prepared from CH 3 NH 3 PbI 3 films stored under ambient conditions for the specified duration (J SC short-circuit current density, V OC open-circuit voltage, ff fill factor, η power conversion efficiency). The middle line represents the median of the data set, the solid circle the mean, the lower and upper box edges are the 25 th and 75 th percentile, respectively, and the whiskers show the maximum and minimum value for each parameter. Red boxes are derived from reverse J-V scans (V OC to J SC ), while the black boxes represent data from forward scans (J SC to V OC ). The number of devices included in the statistical analysis for each data set was between 9 and 12. Figure S6. Optical emission spectrum of fluorescent tube bulb used in the laboratory. 5

6 Table S1. N/Pb, I/Pb, CO 3 2- /Pb and O 529.3eV /Pb ratios for CH 3 NH 3 PbI 3 films stored under ambient conditions. Table S2. I/Pb, CO 3 2- /Pb and O 529.3eV /Pb ratios for PbI 2 powder stored under ambient conditions. Table S3. Hysteresis index for perovskite solar cells prepared from CH 3 NH 3 PbI 3 films stored under ambient conditions. The average of six devices is shown along with the 95% confidence interval (α = 0.05). 6

7 The Gibbs free energy of proposed reactions Since sample degradation is under standard state conditions of 1 atm pressure and 298 K, the Gibbs free energy change of reactions can be calculated from the standard formation Gibbs free energy of the substances. The reversible hydration and dehydration of CH 3 NH 3 PbI 3 films in Steps (1) and (2) have been discussed in detailed in the literature. 1-3 Additionally, the formation Gibbs free energy of hydrate, (CH 3 NH 3 ) 4 PbI 6 2H 2 O, is still unknown. Therefore, only the Gibbs free energy of proposed reactions (3) - (5) was calculated. We assume the transient state (CH 3 NH 3 ) x PbI 2+x is lead iodide (x=0) with lattice strain and that it has the same formation Gibbs free energy of lead iodide. Reaction (3), equivalent to 2(CH 3 NH 3 ) x PbI 2+x + 2CO 2 + O 2 2PbCO 3 + 2I 2 + 2xCH 3 NH 2 + 2xHI 2PbI 2 + 2CO 2 + O 2 2PbCO 3 + 2I 2 (when x=0) r G(3) = 2 f G θ (PbCO 3 ) + 2 f G (I 2 (s) ) - 2 f G (PbI 2 ) - 2 f G (CO 2 ) - f G (O 2 ) = 2(-626.3) + 0 2(-173) 2 (-394) = kj mol -1 Reaction (4), equivalent to (CH 3 NH 3 ) x PbI 2+x + H 2 O + 1/2 O 2 Pb(OH) 2 + I 2 + xhi + xch 3 NH 2 PbI 2 + H 2 O + 1/2 O 2 Pb(OH) 2 + I 2 (when x=0) r G(4) = f G θ (Pb(OH) 2 ) + f G (I 2 (s) ) - f G (PbI 2 ) - f G (H 2 O (g) ) = (-173) (-228.6) = kj mol -1 Reaction (5), Pb(OH) 2 PbO + H 2 O r G(5) = f G θ (PbO) + f G (H 2 O (l) ) - f G (Pb(OH) 2 ) = (-237.1) (-420.9) = kj mol -1 REFERENCES [1] Christians, J. A.; Miranda Herrera, P. A.; Kamat, P. V. Transformation of the Excited State and Photovoltaic Efficiency of CH 3 NH 3 PbI 3 Perovskite upon Controlled Exposure to Humidified Air. J. Am. Chem. Soc. 2015, 137, [2] 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.; Docampo, P.; Barnes, P. R. F. Reversible Hydration of CH 3 NH 3 PbI 3 in Films, Single Crystals, and Solar Cells. Chem. Mater. 2015, 27, [3] Yang, J.; Siempelkamp, B. D.; Liu, D.; Kelly, T. L. An Investigation of CH 3 NH 3 PbI 3 Degradation Rates and Mechanisms in Controlled Humidity Environments Using in Situ Techniques. ACS Nano 2015, 9,