*Corresponding author.

Transcription

1 Supporting Information for: Ligand-Free, Quantum-Confined Cs 2 SnI 6 Perovskite Nanocrystals Dmitriy S. Dolzhnikov, Chen Wang, Yadong Xu, Mercouri G. Kanatzidis, and Emily A. Weiss * Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, IL Argonne-Northwestern Solar Energy Research Center, 2145 Sheridan Rd., M490, Evanston, IL *Corresponding author. e-weiss@northwestern.edu METHODS Diffuse Reflectance Measurements. Optical diffuse reflectance measurements were performed on films of Cs2SnI6 NCs drop-casted on glass substrates at room temperature using a Shimadzu UV-3600 PC spectrometer operating in the nm region. The reflectance versus wavelength data were used to estimate the band gap of the material by converting reflectance to absorption data using the Kubelka Munk equation: α/s = (1-R) 2 /2R, where R is the reflectance and α and S are the absorption and scattering coefficients, respectively. Transient Absorption Spectroscopy. Details of the TA setup are reported in previous work. 1 Briefly, TA measurements were carried out with a commercial system (Ultrafast Systems LLC, Helios) powered by an 800 nm, 2.5 mj, 100 pulse train generated from a Ti:sapphire amplifier (Spectra-Physics, Solstice). The 800 nm beam was split into pump and probe arms. The pump beam was directed through an optical parametric amplifier (Light Conversion, TOPAS-C) with sum-frequency generation kit to produce pump pulses at wavelengths of 470 nm. A small portion of the amplifier output was directed through a 3 mm sapphire window to generate the white light continuum probe in the visible. The residual 800 nm fundamental in the probe arm was blocked with two KG3 color glass filter (Thorlabs, FGS900). The pump and the probe were focused onto the surface of the drop-cast NC films, which were contained in a 2-mm quartz cuvette. The instrument response function (IRF) of the TA setup was determined as 250 fs by measuring the full-width-at-half-maximum of the optical Kerr effect response of CCl4 in the same quartz cuvette. Kinetic traces were fit by convoluting this IRF with three exponential decay terms. Particle Imaging. All TEM images were acquired on samples drop-cast on a 400 mesh carbonon-copper TEM grid (Ted Pella). We drop-cast aliquots of the Cs2SnI6 NCs in toluene onto the S1

2 TEM grids supported on vacuum filtration paper. Particles were imaged using a JEOL JEM-2100 FasTEM and Hitachi HD-2300 Dual EDS Cryo STEM. The JEOL is equipped with high brightness Schottky FEG emitter operated at 200kV and a Gatan GIF camera. Hitachi is equipped with high brightness FEG operated at 80, 120 and 200 kv. Scanning electron microscopy (SEM) imaging was performed using cold source Field Emission SEM Hitachi SU8030 equipped with an electron beam accelerated at 500 V 30 kv. The films were deposited on glass and sputtered with a palladium/gold mixture before imaging. X-ray Diffraction Measurements. The XRD measurements were carried out on a RigakuMini-Flex600 X-ray diffractometer (CuKα radiation, λ = Å) operating at 40 kv and 15 ma. The films were prepared by drop-casting suspension of Cs2SnI6 NCs in toluene onto glass substrates that were cleaned with acetone and toluene before deposition. Photoluminescence Measurements. Photoluminescence measurements were carried out using a Witec alpha300 confocal imaging system at 532 nm. The films were prepared with a procedure identical to that for the XRD measurements. Infrared Spectroscopy Measurements. The Nexus 870 spectrometer is equipped with a tabletop optics module (TOM) that is used for Polarization Modulation Infrared Reflection Absorption Spectroscopy. It has an extended spectral range from 25,000 cm -1 to 400 cm -1 with a resolution of cm -1. The attenuated total reflection (ATR) capability of a Thermo Nicolet FTIR system was used for the measurements on the films drop-casted on glass substrates S2

3 Figure S1. A) XRD patterns (black curve) of Cs2SnI6 NCs synthesized at 190 with Rietveld fitting (red curve) and their difference (blue curve). B) XRD patterns of Cs2SnI6 NCs films synthesized at various temperatures. The numbers on the left indicate the weight percentage of the product that is CsI. Figure S2. ATR FT-IR spectra of films of Cs2SnI6 NCs synthesized at 120 (blue curve) and190 (red curve). The background spectrum (black curve) only shows peaks corresponding to CO2 and H2O. S3

4 Figure S3. STEM images of Cs2SnI6 NCs synthesized at 100 Ԩ(A), 120 Ԩ(C), 150 Ԩ(E), 220 Ԩ(G) and corresponding size histograms (B, D, F, H). S4

5 Figure S4. A) HRTEM image of a Cs2SnI6 NC and its B) gray scale intensity profile Figure S5. Photographic image of an as-deposited Cs2SnI6 NCs film. S5

6 Figure S6. SEM images of electrosprayed Cs2SnI6 films prepared by deposition of a solution of SnI4 and CsI in methanol show A) rings forming in the film at the edge of the spray area and B) large vacancies from non-uniform crystal growth. Figure S7. A) Dependence of the average diameter of Cs2SnI6 NCs, calculated with Scherrer equation from powder XRD patterns, on the injection temperature. B) Dependence of the band gap energy, measured by diffuse reflectance, on injection temperature. The error bars in both plots are calculated from 4 separate measurements on separately prepared samples. S6

7 Figure S8. A) Steady state absorption spectra (acquired in transmission mode) and B) photoluminescence spectra (acquired in reflection mode) of the Cs2SnI6 NC films prepared with different injection temperatures. REFERENCES (1) McArthur, E. A.; Morris-Cohen, A. J.; Knowles, K. E.; Weiss, E. A. Charge Carrier Resolved Relaxation of the First Excitonic State in CdSe Quantum Dots Probed with Near-Infrared Transient Absorption Spectroscopy. J. Phys. Chem. B 2010, 114, S7