Supporting Information for

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1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C. This journal is The Royal Society of Chemistry 2018 Supporting Information for Correlating Nano Black Spots and Optical Stability in Mixed Halide Perovskite Quantum Dots Yun-Hyuk Ko, a,b Prem Prabhakaran, b Mohammed Jalalah, a Seung-Jae Lee, a Kwang-Sup Lee,* b and Jea-Gun Park* a a Department of Electronics and Computer Engineering Hanyang University Seoul Republic of Korea. parkjgl@hanhyang.ac.kr; Fax: ; Tel: b Department of Advanced Materials, Hannam University, Daejeon , Republic of Korea. kslee@hnu.kr; Fax: ; Tel:

2 Experimental Section Chemicals Cesium carbonate (Cs 2 CO 3, Aldrich, 99.9%), lead(ii) bromide (PbBr 2, ABCR, 98%), lead(ii) iodide (PbI 2, ABCR, %), 1-octadecene (ODE, Sigma-Aldrich, 90%), oleic acid (OA, Sigma-Aldrich, 90%), oleylamine (OAm, Acros, 80-90%), tert-butanol (t-buoh 99.0 %), acetone (anhydrous, 99.8%), and toluene (anhydrous, 99.8%). Synthesis and purification of CsPbBr 3-x I x QDs Schematic illustration of Br - :I - molar fractions used in synthesizing of samples: (A) CsPbBr 2.0 I 1.0, (B) CsPbBr 1.8 I 1.2, (C) CsPbBr 1.5 I 1.5, (D) CsPbBr 1.2 I 1.8, and (E) CsPbBr 1.0 I 2.0 QDs. The CsPbBr 3-x I x QDs were synthesized by adaptation of the synthesis process developed by Protesescu et al. 1 In summary, firstly, Cs 2 CO 3 (0.814g), ODE (40mL) and OA (2.5 ml) were loaded directly into 50 ml 3-neck flask inside the glove-box filled with N 2, degassed inside the fume hood for an hour at 110 ºC, and then heated under N 2 environment to 150 ºC until the solution became clear and formed Cs-oleate. The Cs-oleate solution was kept at 150 ºC to be injected freshly into the main 3-neck flask. In the meantime, the main 50 ml 3-neck flask was set in the glove-box, loaded with ODE (5 ml), OAm (0.5 ml), OA (0.5 ml), and a mmol mixture of PbBr 2 and PbI 2, such as PbBr 2 :PbI 2 = 0.063: mmol, degassed inside the fume hood for an hour at 110 ºC, and then heated under N 2 environment to 165 ºC. At 165 ºC, 0.4 ml of fresh Cs-oleate solution was swiftly injected. 30 seconds later, the crude solution was taken out quickly by syringe and divided into two 20 ml-size vials. For 2

3 purification, 3 ml of tert-butanol was added to each vial and centrifuged at 6000 rpm for 15 min. After discarding of supernatant liquid, the final precipitated QDs powder was re-dispersed in toluene. Characterizations PXRD measurements were performed using a Rigaku-denki XRD (Tokyo, Japan) with a Cu-Kα source of wavelength λ = Å operating at 45 kv and 40 ma. Data were collected over a 2θ angular range of at a scan rate of 0.01 /step and speed of 10 s/point. Highresolution TEM (HR-TEM) images were obtained using a JEM-2100F TEM (JEOL, Tokyo, Japan) equipped with an electron beam gun operated at 200 kv. The TEM samples were prepared by dropping the colloidal QDs, dispersed in toluene, onto 400-mesh carbon-coated copper grids. The chemical compositions of prepared QDs were determined using EDX, attached to TEM JEM-2100F. The HAADF and EF TEM measurements were carried out using Thermo Scientific Talos F200S Scanning/Transmission electron microscope. The absorbance spectra were taken on UV-Vis-IR Varian Cary 5000 spectrometer over the range nm. The PL spectra were obtained using a Dongwoo Optron spectrometer (Vector-01FX) with excitation wavelengths of 325 nm, HeCd laser, and an optical density of The absolute PL-QYs were recorded using a 6-inch diameter integrating sphere (K Sphere-B) with excitation wavelengths of 450 nm. The relative PL-QYs were calculated according to previous reports. 2 All measurements were performed at clean room temperature. Bragg s law: 2d sin θ = nλ (S1) Scherrer s formula: 3

4 λ L = βcos θ (S2) where L is the mean size of crystalline domains in nm, λ is the X-ray wavelength ( nm), θ is the half of Bragg angle (2θ) in radian, β is the integral breadth (integrated area under diffraction peak divided by its height) in radian. We used the integral breadth here instead of FWHM in Scherrer s formula to be independent of the shape of Bragg peaks, such as Gaussian or Lorentzian, especially that some peaks showing an asymmetrical shape. The particle size and lattice parameter were calculated for 2θ=20. Figure S1. Selected area electron diffraction (SAED) pattern for the samples: (A) CsPbBr 2.0 I 1.0, (B) CsPbBr 1.8 I 1.2, (C) CsPbBr 1.5 I 1.5, (D) CsPbBr 1.2 I 1.8, and (E) CsPbBr 1.0 I 2.0 QDs. 4

5 Figure S2. Transmission electron microscopy (TEM) images (scale bar = 10 nm) for the perovskite QD samples: (a) CsPbBr 2.0 I 1.0 taken after the optical degradation initiated, (b) CsPbI 3, taken a few days after preparation. Figure S3. Energy-dispersive X-ray (EDX) results for the samples: (A) CsPbBr 2.0 I 1.0, (B) CsPbBr 1.8 I 1.2, (C) CsPbBr 1.5 I 1.5, (D) CsPbBr 1.2 I 1.8, (E) CsPbBr 1.0 I 2.0 QDs, and (F) comparison of EDX data for all five samples. 5

6 Table S 1. Summary of energy-dispersive X-ray (EDX) results for the samples: (A) CsPbBr 2.0 I 1.0, (B) CsPbBr 1.8 I 1.2, (C) CsPbBr 1.5 I 1.5, (D) CsPbBr 1.2 I 1.8, and (E) CsPbBr 1.0 I 2.0 QDs. Sample A B C D E Br - :I - 2:1 1.8: : :1.8 1:2 Elements Atomic % Br I Cs Pb Calculation of relative PL-QY: Briefly, after collecting the PL and UV-vis spectra of all samples and dye references, the areas of luminescence peaks are integrated and then plotted versus the values of absorbance in order to get a straight line with a gradient (m), used to calculate the relative PL-QY of samples using this equation: PL QY s = PL QY r m s m r ( η s η r ) 2 (S3) where the subscripts r and s in Equation S3 denote the dye reference and tested sample, respectively, and η is the reflective index of solvent. The colloidal QDs samples and dye references are excited at the same wavelength (325 nm) as well as they have the similar relative absorbance values (optical density = 0.046) which were kept below 0.1 to avoid the issue of reabsorption phenomenon between the QDs. Optical Band Gap Tauc equation: 6

7 αhv (hν Eg) n (S4) where α is the absorption coefficient or absorbance, h is the Planck constant, ν is the frequency, hν = 1240/wavelength, and E g is the optical band gap of QDs. Exponent n is a constant and denotes the nature of the transition in the band gap and can have values of 1/2, 2, 3 or 3/2 for direct allowed, indirect allowed, indirect forbidden, and direct forbidden transition, respectively (A) CsPbBr 2.0 I 1.0 ( h (ev 2 cm -2 ) (B) CsPbBr 1.8 I 1.2 (C) CsPbBr 1.5 I 1.5 (D) CsPbBr 1.2 I 1.8 (E) CsPbBr 1.0 I ev 2.01 ev 2.13 ev D C E B A 2.37 ev 2.39 ev h (ev) Figure S4. Tauc plot of the samples: (A) CsPbBr 2.0 I 1.0, (B) CsPbBr 1.8 I 1.2, (C) CsPbBr 1.5 I 1.5, (D) CsPbBr 1.2 I 1.8, and (E) CsPbBr 1.0 I 2.0 QDs to find their optical band gap as presented in the figure. 7

8 Table S 2. Compares QDs A-E with cubic perovskite phase (black) and the orthorhombic phase (yellow) the tolerance factor, crystal structure and crystal distortion. phase tolerance factor (t) Crystal Structure Distortion Black t c = cubic no CsPbBr 2.0 I 1.0 (A) cubic slightly CsPbBr 1.8 I 1.2 (B) cubic slightly CsPbBr 1.5 I 1.5 (C) cubic slightly CsPbBr 1.2 I 1.8 (D) cubic slightly CsPbBr 1.0 I 2.0 (E) cubic slightly Yellow < 0.8 orthorhombic yes HAADF-TEM and EF-TEM imaging Figure S5.1. (a) Bright field TEM images of CsPbI 3 sample (b) HAADF-images of the same sample showing contrast between regions on the nanoparticles with different compositions (c) merged HAADF-EF TEM image showing the phase contrast of HAADF and the local composition from EF TEM measurements. (d) Cs is mapped in red (e) I is mapped in yellow and (f) Pb is mapped in green. Higher concentration of Pb at the locations of the NBSs can be seen in (c) 8

9 Figure S5.2. Merged HAADF-EF TEM images, guiding lines in the merged image demarkattes nanoparticle boundary and NBSs, particle highlighted in the HAADF image in the inset is marked in the merged image. Figure S5.3. (a) Bright field TEM images of CsPbBr 1 I 2 sample (b) HAADF-images of the same sample (c) Br is mapped in blue (d) Pb is mapped in green (e) I is mapped in yellow and (f) Cs 9

10 is mapped in red (g) merged HAADF-EF TEM image showing the phase contrast of HAADF and the local composition from EF TEM measurements. Figure S6. Summarizes the properties of the PET barrier film which is crucial for highly efficient operation of the QD enhancement film. The QD enhancement film is sandwitched between two PET barrier films each of structure PET/Al 2 O 3 /SiO 2 as seen in (a). The PET barrier film should have high transmittance to first allow light from the blue LED into the film, and later transmit the emitted light out of the PQDEF. A TEM image of the PET barrier films can be seen in (b) and its optical transmittance in the range of nm can be seen in (c). 10

11 Table S 3. CIE coordinates (x,y) and (u,v ) for 1976 CIE u v and 1931CIE xy systems, respectively, for the samples: (A) CsPbBr 2.0 I 1.0, (B) CsPbBr 1.8 I 1.2, (C) CsPbBr 1.5 I 1.5, (D) CsPbBr 1.2 I 1.8, and (E) CsPbBr 1.0 I 2.0 QDs. Sample Tristimulus Values CIE coordinates(x,y) CIE coordinates(u,v ) X Y Z x y u y A B C D E References (1) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nano Lett. 2015, 15, (2) Baek, S.-W.; Shim, J.-H.; Ko, Y.-H.; Park, J.-S.; Lee, G.-S.; Jalalah, M.; Al-Assiri, M. S.; Park, J.-G. J. Mater. Chem. A 2015, 3,