Supporting Information Photocarrier Recombination and Injection Dynamics in Long-Term Stable Lead-Free CH 3 NH 3 SnI 3 Perovskite Thin Films and Solar Cells Taketo Handa, + Takumi Yamada, + Hirofumi Kubota, Shogo Ise, Yoshihiro Miyamoto, and Yoshihiko Kanemitsu*,+ + Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan Chemical Materials Evaluation and Research Base (CEREBA), Tsukuba, Ibaraki 305-8565, Japan Corresponding author *E-mail: kanemitu@scl.kyoto-u.ac.jp. Phone: +81 774 38 4510. S1
Scanning electron microscope image and film morphology For lead-free tin-halide perovskites, previous works demonstrated that the choice of solvent is very important to fabricate high-quality films. S1-S3 In this study, we used DMSO as a solvent, which has been reported to retard the crystallization of perovskites and thus contributes to an improved morphology. S1-S3 Figure S1 shows a SEM image of the solar-cell device prepared with 20 mol% SnF 2 using toluene dripping. We can confirm that the perovskite grains are dense, i.e., almost all in-plane positions exhibit a single grain structure in vertical direction. The small inhomogeneities in the coverage are a possible reason for the relatively low V OC and FF. It has been reported that the excess SnF 2 can lead to rod-like SnF 2 residues in the film with size of several hundreds of nanometers to micrometer, for the case of FASnI 3 [FA=CH(NH 2 ) 2 ]. S2,S3 In this study, however, we found no indications for SnF 2 residues in the SEM images. In addition, the interfacial contacts between the perovskite and transport layers formed properly. From the above discussion, along with the PL results in the main text, we consider that the samples are optically homogeneous and suited for discussing injection and recombination processes. Figure S1. A representative SEM image of the MASnI 3 solar cell using SnF 2 as an additive. Figure S2 shows a photo of the encapsulated solar cell device used for the optical measurements, taken from (a) the light-incident side and (b) the backside with the Au electrode. The current-voltage curves of this device are provided in Fig. 1a in the main text. Figure S3 shows the current-voltage curves of the CH 3 NH 3 SnI 3 (MASnI 3 ) solar cell prepared without SnF 2 S2
additive, recorded under AM 1.5G 1-sun illumination. As evident from the rather metallic behavior, the device prepared without SnF 2 was not able to generate electric power. Figure S2. A photo of a MASnI 3 -based solar cell device, taken from (a) the light-incident side and (b) the backside with the Au electrode. The ruler scale is centimeter. Figure S3. Current-voltage curves of the MASnI 3 solar cell device prepared without SnF 2 additive, recorded under AM 1.5G 1-sun irradiation. Red (black) circles represent the forward (reverse) scan. S3
Transient photo-response of MASnI 3 thin films and devices The lead perovskite MAPbI 3 thin-films and devices are well-known for showing a slow transient photo-response under light irradiation, which usually occurs on a scale of seconds to minutes. S4-S6 In analogy to MAPbI 3, we expected a similar transient response for MASnI 3, and thus investigated the evolution of the PL intensity of the samples upon laser irradiation. Figure S4 shows the change of the PL intensities for (a) MASnI 3 thin films without and (b) with SnF 2, and (c) the solar cell device (which was prepared with SnF 2 ) against the laser irradiation time. The film prepared without SnF 2 showed almost no change in this time window (Fig. S4a), while the film and device with SnF 2 showed an increase of the PL intensity in the initial time region (Figs. S4b,c). Although a more detailed study is required to confirm the details, the presence of SnF 2 is considered to be the cause for the observed transient photo-response. Due to the slow transient behavior, we show the PL spectrum obtained after 120 s illumination time in Fig. 2a, where the intensity change has almost settled. Figure S4. (a) The time evolution of the PL intensities for the thin film without SnF 2, (b) the thin film with SnF 2, and (c) the solar cell device, plotted against the laser irradiation time. The PL intensities were obtained by integrating the PL spectra from 1.15 ev to 1.35 ev. The excitation wavelength and intensity were 650 nm and 10 nj/cm 2, respectively. Resonantly excited PL spectroscopy, light-soaking, and the power-dependence of PL decay In this section, we show the additional details of the experiments performed in the main text. In Fig. S5, it is clear that the PL width is independent on the excitation photon energy by directly comparing the normalized spectra. Figure S6 evidences that the PL decays are unchanged for S4
prolonged light illumination, which demonstrates the stability of our samples. Figure S7 clarifies the subtle details of the change in the PL decay for different excitation fluences by comparing the normalized data. Figure S5. The normalized PL spectra of the MASnI 3 film prepared with SnF 2 obtained for different excitation energies. The excitation laser energy is shown in the figure. The scattered laser light is visible as a sharp divergent peak. Figure S6. (a) PL decay curves of the MASnI 3 thin film with SnF 2 and (b) solar cell device (with SnF 2 ) obtained for prolonged laser irradiation, i.e., light soaking time. The excitation fluence was 100 nj/cm 2. No significant change of the decay curves was observed upon prolonged irradiation time. S5
Figure S7. (a) The normalized PL decay curves of the MASnI 3 thin film without and (b) with SnF 2, and (c) the solar cell device. References (S1) Hao, F.; Stoumpos, C. C.; Guo, P.; Zhou, N.; Marks, T. J.; Chang, R. P. H.; Kanatzidis, M. G. Solvent-Mediated Crystallization of CH 3 NH 3 SnI 3 Films for Heterojunction Depleted Perovskite Solar Cells. J. Am. Chem. Soc. 2015, 137, 11445-11452. (S2) Lee, S. J.; Shin, S. S.; Kim, Y. C.; Kim, D.; Ahn, T. K.; Noh, J. H.; Seo, J.; Seok, S, Il, Fabrication of Efficient Formamidinium Tin Iodide Perovskite Solar Cells through SnF 2 Pyrazine Complex. J. Am. Chem. Soc. 2016, 138, 3974-3977. (S3) Liao, W.; Zhao, D.; Yu, Y.; Grice, C. R.; Wang, C.; Cimaroli, A. J.; Schulz, P; Meng, W.; Zhu, K.; Yan, Y. Lead-Free Inverted Planar Formamidinium Tin Triiodide Perovskite Solar Cells Achieving Power Conversion Efficiencies up to 6.22%. Adv. Mater. 2016, 28, 9333-9340. (S4) Stranks, S. D.; Burlakov, V. M.; Leijtens, T.; Ball, J. M.; Goriely, A.; Snaith, H. J. Recombination Kinetics in Organic-Inorganic Perovskites: Excitons, Free Charge, and Subgap States. Phys. Rev. Applied 2014, 2, 034007. (S5) dequilettes, D. W.; Zhang, W.; Burlakov, V. M.; Graham, D. J.; Leijtens, T.; Osherov, A.; Bulović, V.; Snaith, H. J.; Ginger, D. S.; Stranks, S. D. Photo-Induced Halide Redistribution in Organic Inorganic Perovskite Films. Nat. Commun. 2016, 7, 11683. (S6) Sanchez, R. S.; Gonzalez-Pedro, V.; Lee, J. W.; Park, N. G.; Kang, Y. S.; Mora-Sero, I.; Bisquert, J. Slow Dynamic Processes in Lead Halide Perovskite Solar Cells. Characteristic Times and Hysteresis. J. Phys. Chem. Lett. 2014, 5, 2357 2363. S6