Supporting Information. Femtosecond Time-Resolved Transient Absorption. Passivation Effect of PbI 2

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1 Supporting Information Femtosecond Time-Resolved Transient Absorption Spectroscopy of CH 3 NH 3 PbI 3 -Perovskite Films: Evidence for Passivation Effect of PbI 2 Lili Wang a, Christopher McCleese a, Anton Kovalsky a, Yixin Zhao b,* and Clemens Burda a * a Department of Chemistry, Case Western Reserve University, Euclid Ave., Cleveland, OH 44106, USA b School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Rd., Shanghai , China *Address correspondence to: burda@case.edu; yixin.zhao@sjtu.edu.cn S1

2 XRD Diffraction Patterns of PbI 2 on FTO glass and bare glass respectively indicate that the peaks at 12.5 o and 25.8 o are assigned to PbI 2. Figure S1. XRD diffraction pattern of PbI2 on FTO glass (blue) and bare glass (magenta). The peaks of FTO are labelled by asterisk. Both the two patterns demonstrate strong peak at 12.6o. The pattern of PbI2 on bare glass also shows peaks at 25.8o, 38.8o and 52.5 (indicated by green dashed-line) which are assigned to PbI 2. S2

3 A Absorption / normalized PL Intensity / normalized Optical Properties of PbI 2. To provide additional evidence that the sharp peak at ~500 nm in the perovskite samples (Figure 2 of the text) results from PbI 2, PbI 2 films coated on an FTO substrate were prepared and measured under identical conditions. Figure S1 shows steady state absorption and PL spectra in the top panel and fs-ta spectra in the bottom panel. From the fs-ta spectra of PbI 2 we find a transient bleach that occurs at ~500 nm, similar to the perovskite samples coated on mesoporous TiO 2 (Figure 2C and D). PbI 2 /FTO Absorption PL ps 1.6 ps 2.9 ps 5.3 ps 11.7 ps Figure S2. Top Panel: Steady state absorption (black) and PL (red) spectra of PbI2 coated on FTO. Bottom Panel: fs-ta spectra at various probe time delays (noted in legend) after 390 nm excitation. The grey dashed lines are a guide for indicating the band edge absorption and PL peak positions. S3

4 A / normalized A / normalized A / normalized A / normalized fs-ta excited at 600 nm. Since laser excitation at 390 nm excites both the perovskite and any present PbI 2, the samples were additionally excited with a wavelength of 600 nm, Figure S3, in order to monitor the TA spectra of the perovskite. The spectra shown were taken immediately after excitation when the bleach amplitudes were most intense. The laser pulse has been removed from the spectra for the samples excited with 600 nm. Upon excitation with 600 nm, we see that the peak intensity at ~510 nm is greatly diminished. The excitation energy at 600 nm (~2.1 ev) is less than the band gap of PbI 2 (2.3 ev). Thus the observed transient signal after 600 nm excitation is mainly due to perovskite. In order to identify the presence of PbI 2, a pump wavelength of < 510 nm is necessary. A) FTO / Perovskite B) Perovskite / Comp C) FTO / Meso / Perovskite D) FTO / Compact / Meso / Perovskite Figure S3. TA spectra of four PbI 2 containing perovskite architectures (noted in the panels) excited at 390 nm (black) and 600 nm (red). The spectra were taken immediately after excitation when the bleaches were most intense. The laser pulse appeared in the samples excited with 600 nm, therefore it has been cut out of the spectra for clarity. S4

5 Perovskite Pump Power Dependence. To confirm that the pump powers used in this work do not result in multiple carrier effects, we studied the relaxation dynamics at the pump power used in the presented experiments (7.4 x photons*cm -3 ) as well as half the pump power. The fluence at half power is assumed to be an acceptable fluence to use based on the literature. 1,2 If multiple-carrier relaxation would be at play, the kinetics should drastically slow down at half the previously mentioned pump fluence. However, our observation is that the same relaxation dynamics is observed. This is strong evidence for single excitations being observed in our experiments. Figure S4. Kinetic traces for perovskite on glass excited with 390 nm light at a pump fluence of 3.3x10 17 photons*cm -3 *pulse -1 (black squares) and 7.4x10 17 photons*cm -3 *pulse -1 (red circles). S5

6 Intensity / Normalized Intensity / Normalized PL Intenisty / Normalized Intensity / Normalized Intensity / Normalzied Time-Resolved Photoluminescence (TR-PL). TR-PL was performed to further verify our interpretation of the fs-ta decay dynamics. It is quite obvious from the decay of the PL that the lifetime is much longer than those measured in the fs-ta study. Since the PL decay is indicative of the rate at which electrons and holes radiatively recombine, it is not possible that the much faster time constants from the fs-ta measurements would be due to recombination. Therefore we attribute the two fs components to trap state population (τ 1 ) and injection (τ 2 ) into TiO 2 /FTO. Also, Yang and coworkers have shown that charge carrier injection can happen on time scales from ps for perovskite coated on mesoporous TiO 2. 3 This corroborates our results which show TA lifetimes of ps for perovskite on mesoporous TiO 2. The reason that injection rates for the samples without mesoporous TiO 2 are faster (~39 ps) can be explained by the fact that there is no blocking layer for the perovskite/fto sample and there is only a very thin layer of compact TiO 2 in the perovskite/comp/fto samples. 1.0 A) Perovskite / FTO PL Intensity / normalized1.0 B) Perovskite / comp / FTO C) PL Intensity / normalized1.0perovskite / meso / FTO D) PL Intensity / Normalized1.0Perovskite / meso / comp / FTO Figure S5. TR-PL of the various perovskite architectures (noted in the panels). The PL lifetime of A) is ± 3.7 ps, B) is ± 5.0 ps, C) is ± 4.4 ps, and D) is ± 3.9 ps. The inset shows normalized PL spectra. S6

7 References (1) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Science 2013, 342, (2) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C. Science 2013, 342, (3) Zhu, Z.; Ma, J.; Wang, Z.; Mu, C.; Fan, Z.; Du, L.; Bai, Y.; Fan, L.; Yan, H.; Phillips, D. L.; Yang, S. J. Am. Chem. Soc. 2014, 136, S7