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Supporting Information

Slow Hot Carrier Cooling in Cesium Lead Iodide Perovskites

Qing Shen,^*,1 Teresa S. Ripolles,^*,2 Jacky Even,^*,3 Yuhei Ogomi,² Koji Nishinaka,² Takuya Izuishi,¹ Naoki Nakazawa,¹ Yaohong Zhang,¹ Chao Ding,¹ Feng Liu, ¹ Taro Toyoda,¹ Kenji Yoshino,⁴ Takashi Minemoto, ⁵ Kenji Katayama,⁶ Shuzi Hayase^*,2

¹ Department of Engineering Science, Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan.

² Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu 808-0196, Japan.

³ Fonctions Optiques pour les Technologies de l’information, UMR 6082, INSA, 35708 Rennes, France

⁴ Department of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuen, Kibanadai-nishi, Miyazaki 889-2192, Japan

⁵ Department of Electrical and Electronic Engineering, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan

⁶ Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo, Tokyo 112-8551, Japan

Experimental Methods:

Sample preparation. CsPbI₃ perovskite samples deposited on Al₂O₃ were fabricated using the following processes and materials. First, mesoporous Al₂O₃ scaffold films were deposited on glass substrates. The alumina solution was diluted in 2-propanol (2:3 by vol.) and spin coated at 2000 rpm for 60 s. Subsequently, the Al₂O₃ substrates were heated at 60 ºC for 10 min and 130 ºC for 30 min. The Al₂O₃ substrates were then transferred into a glove box and CsPbI₃ films were prepared on them using a one-step solution deposition method.¹ A mixture of CsI and PbI₂ (wt. ratio 1:1) dissolved in DMF with a concentration of 20 wt. % was prepared at 60 ºC until complete dissolution. The substrates were pre-heated at 60 ºC for 15 min, and an aliquot of the CsPbI₃ solution was spin-coated at 2000 rpm for 30 s on the Al₂O₃ surfaces, followed by thermal annealing on a hot plate at 60 ºC and then 350 ºC for 30 min each. Finally, the substrates were encapsulated with polymethyl methacrylate (PMMA) on a spin coater at 3000 rpm for 60 s in order to isolate the sample from air and keep them stable.

Transient absorption (TA) measurements. A femtosecond TA setup was used to study the photoexcited carrier dynamics, especially the hot carrier cooling dynamics in CsPbI₃.^2-5 The laser source was a titanium/sapphire laser (CPA-2010, Clark-MXR Inc.) with a wavelength of 775 nm, a repetition rate of 1 kHz, and a pulse width of 150 fs. The light was separated into two parts. One part was incident on a sapphire plate to generate white light for the probe beam. The other part was used to pump an optical parametric amplifier (OPA) (a TOAPS from Quantronix) to generate light pulses with a wavelength tunable from 290 nm to 3 µm. This was used as the pump light to excite the sample. In this study, the pump light wavelengths were 470 nm (2.6 eV) and 650 nm (1.9 eV). The pump light intensity was changed from 1.25 µJ/cm² to 125 µJ/cm². Time-resolved TA spectra from 530 nm (2.34 eV) to 750 nm (1.65 eV) were obtained with a temporal resolution of 100 fs.


Figure S1 XRD patterns of the CsPbI₃ sample measured soon after the preparation and 2 h after the preparation.

Figure S2 SEM image of the CsPbI₃ sample surface.

Figure S3 TA spectra of CsPbI₃ after phase transition from the cubic phase to the yellow phase.

¹ T. S. Ripolles, K. Nishinaka, Y. Ogomi, Y. Miyata, and S. Hayase, Sol. Energy Mater. Sol. Cells 144, 532 (2016).

² Q. Shen, Y. Ogomi, B. W. Park, T. Inoue, S. S. Pandey, A. Miyamoto, S. Fujita, K. Katayama, T. Toyoda, and S. Hayase, Phys. Chem. Chem. Phys. 14, 4605 (2012).

³ Q. Shen, Y. Ogomi, S. K. Das, S. S. Pandey, K. Yoshino, K. Katayama, H. Momose, T. Toyoda, and S. Hayase, Phys. Chem. Chem. Phys. 15, 14370 (2013).

⁴ Q. Shen, Y. Ogomi, J. Chang, S. Tsukamoto, K. Kukihara, T. Oshima, N. Osada, K. Yoshino, K. Katayama, T. Toyoda, and S. Hayase, Phys. Chem. Chem. Phys. 16, 19984 (2014).

⁵ Q. Shen, Y. Ogomi, J. Chang, T. Toyoda, K. Fujiwara, K. Yoshino, K. Sato, K. Yamazaki, M. Akimoto, Y. Kuga, K. Katayama, and S. Hayase, J. Mater. Chem. A 3, 9308 (2015).