Supporting Information. Photoinduced Anion Exchange in Cesium Lead Halide Perovskite Nanocrystals

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1 Supporting Information Photoinduced Anion Exchange in Cesium Lead Halide Perovskite Nanocrystals David Parobek, Yitong Dong, Tian Qiao, Daniel Rossi, Dong Hee Son* Department of Chemistry, Texas A&M University, College Station, Texas United States S1

2 Synthesis Materials and chemicals. Cesium carbonate (Cs 2 CO 3, Alfa Aesar, 99% trace metals basis), lead (II) bromide (PbBr 2, puratronic % trace metals basis, Alfa Aesar), lead (II) chloride (PbCl 2, puratronic % trace metals basis, Alfa Aesar), cadmium oxide (CdO, puratronic % trace metals basis, Alfa Aesar), sulfur (99.98%, Aldich), selenium (200 mesh % trace metals basis, Alfa Aesar), zinc stearate (ZnO %, Alfa Aesar), octylamine (99%, Aldrich), oleylamine (OAm, technical grade 70%, Aldrich), oleic acid (OA, technical grade 90%, Aldrich), 1-octadecene (ODE, technical grade 90%, Aldrich), tributyl phosphine (TBP, 95%, Alfa Aesar), dichloromethane (DCM, 99.5%, Millipore), dibromomethane (DBM, 99%, Acros Organic), acetone (Certified ACS, Fischer), hexanes (ACS grade, Millipore), toluene (HPLC grade, Fischer), methanol (99.5%, Millipore). Preparation of Cs-oleate. Cs-oleate was synthesized by adding Cs 2 CO 3 (0.234 g), OA (0.75 g), and ODE (7.04 g) to a 50-mL 3 neck round bottom flask and was evacuated and refilled with N 2 3 times before being heated to 150 C for at least 10 minutes before using. Synthesis of CsPbCl 3 and CsPbBr 3 NCs. PbCl 2 ( g) or PbBr 2 ( g), OAm (0.8 ml), OA (0.8 ml), and ODE (5 ml) were added to a 25-mL 3 neck round bottom flask. The solution was evacuated and refilled with N 2 followed by heating to 120 C for 30 minutes. The solution was then increased to 165 C and then 200 C for 10 minutes each where at 200 C, dried OAm (0.8 ml) and dried OA (0.8 ml) were consecutively injected to solubilize the solution. Then the Cs-oleate (0.4 ml) was injected and after 1 minute the solution was cooled with an ice bath. The NCs were precipitated with acetone and then centrifuged followed by dissolving in hexanes. Synthesis of CdSSe/ZnS QD. The core shell quantum dot nanocrystals were synthesized following a previously reported method. 1 The CdSSe core was synthesized by first injecting a TBP-selenium solution (0.3 ml, 29 M) into an ODE-sulfur solution (0.25 M). Then 2 ml of the mixture was injected into a solution of CdO (128 mg), ODE (12 ml) and OA (2.02g) at 250 C under N 2 protection where the reaction proceeded at 240 C for 1 minute until it was quenched. The nanocrystals were precipitated with acetone, centrifuged, and dispersed in toluene followed by additional cleaning with methanol precipitation. The ZnS shell was deposited on the prepared core following the SILAR method. The CdSSe QD was dissolved in an ODE (6 ml) and OAm (2 ml) solution and heated to 220 C under N 2 protection. Then in successive 10 minute intervals solutions of ODE-sulfur (0.25 M) and ODE-zinc stearate (0.25 M, ~5% octylamine) were added dropwise. The solution was then quenched and precipitated with acetone and dispersed in toluene followed by further precipitation with methanol. Anion Exchange Reactions. The anion exchange reactions were conducted with a home built optical setup using a 405 nm diode laser and a 445 nm diode laser with intensities of 21 mw/cm 2. For CsPbBr 3 anion exchange a mixture of DCM/hexane (2:1) with 25 μl was used and for CsPbCl 3 anion exchange a mixture of DBM/hexane (1:1) with 25 μl of oleylamine was used. All reactions were done under ambient conditions without stirring. Photoluminescence measurements were taken with a fiberoptic-coupled CCD spectrometer (Ocean Optics, QE65pro) with a 365 nm LED excitation source. The absorption S2

3 measurements were taken with an Ocean Optics USB2000 spectrometer. Control experiments were conducted for CsPbCl 3 (Figure S1a) and CsPbBr 3 (Figure S1b). Figure S1. Absence of the anion exchange under dark condition. (a) CsPbCl 3 NCs in DBM/hexane, (b) CsPbBr 3 NCs in DCM/hexane. TEM images of CsPbX 3 NCs before and after anion exchange All TEM images of CsPbX 3 NCs were collected using a FEI Tecnai G2 F20 ST FE-TEM microscope operated at 4100 kv. Figure S2. TEM image of NCs before (a) and after (b) the photoinduced anion exchange in DBM/hexane solution under 405 nm excitation. Figure S3. TEM images of CsPbBr 3 NCs before (a) and after (b) the photoinduced anion exchange in DCM/hexane solution under 405 nm excitation. S3

4 Powder X-ray Diffraction (XRD) of CsPbX 3 NCs before and after anion exchange Sample\hkl 121/ / /123 Cl Cl Br Br Figure S4. XRD patterns of CsPbCl 3 before (blue) and after (red) anion exchange in DBM/hexane solution. XRD pattern of the freshly synthesized CsPbBr 3 is shown in green. XRD patterns were obtained using a Bruker-AXS GADDS MWPC diffractometer equipped with Cu K-α x-ray radiation and a multi-wire proportional counter. Intensity dependent photoinduced anion exchange reaction Figure S5. PL emission peak shift from anion exchange of CsPbCl 3 in DBM/hexane at two different 405 nm excitation intensities. S4

5 Two-photon excitation induced anion exchange Figure S6. PL emission peak shift from anion exchange of CsPbCl 3 in DBM/hexane mixture induced by two-photon excitation at 800 nm from Titanium Sapphire laser. Exchange between CsPbBr 3 and CH 2 I 2 /toluene Figure S7. Photoinduced anion exchange from CsPbBr 3 to CsPbI 3 in diiodomethane/toluene mixture using two-photon excitation. S5

6 Energy Level Diagram of CsPbX 3 Figure S8. Energy level diagram with respect to vacuum of CsPbCl 3 and CsPbBr 3 2 compared to the reduction potential of common halogenated solvents 3. Patterning of thin film with photoinduced anion exchange Figure S9. Photoinduced anion exchange of a thin film of CsPbCl 3 in a DBM/PMMA matrix to CsPbBr 3 with spatial patterning. Three bright dots are the locations where the beam impinge on. References (1) Chen, H.-Y.; Maiti, S.; Son, D. H. ACS Nano 2012, 6, 583. (2) Ravi, V. K.; Markad, G. B.; Nag, A. ACS Energy Lett. 2016, 1, 665. (3) Isse, A. A.; Lin, C. Y.; Coote, M. L.; Gennaro, A. J. Phys. Chem. B 2010, 115, 678. S6