Supporting Information. Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals

Transcription

1 Supporting Information Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals David Parobek, Benjamin J. Roman, Yitong Dong, Ho Jin, Elbert Lee, Matthew Sheldon, * and Dong Hee Son * Department of Chemistry, Texas A&M University, College Station, Texas Department of Materials Science & Engineering, Texas A&M University, College Station, Texas *dhson@chem.tamu.edu *matt.sheldon@chem.tamu.edu 1

2 Materials and Synthesis Materials and chemicals. Cesium carbonate (Cs 2 CO 3, Alfa Aesar, 99% metals basis), lead (II) bromide (PbBr 2, puratronic % metals basis, Alfa Aesar), lead (II) chloride (PbCl 2, puratronic % metals basis, Alfa Aesar), manganese chloride tetrahydrate (MnCl 2 (H 2 O) 4, USP specifications, Aldrich), oleylamine (OAm, technical grade 70%, Aldrich), oleic acid (OA, technical grade 90%, Aldrich), 1- octadecene (ODE, technical grade 90%, Aldrich), acetone (Certified ACS, Fischer), hexanes (ACS grade, Millipore), toluene (ACS grade, Fischer), poly(styrene-divinylbenzene) (2% cross linked, mesh, BeanTown Chemical). Preparation of Cs-oleate: Two separate Cs-oleate solutions were made for the Br/Cl and Cl doped and undoped perovskites. For the Br/Cl and Cl systems respectively, Cs 2 CO 3 (0.402 g/ g), OA (1.74 ml, 1.76 ml), and ODE (18 ml/ 18 ml) were added to a 50-mL 3-neck round bottomed flask and evacuated and refilled with nitrogen 3 times then heated to 150 C for at least 10 minutes before using. Synthesis of CsPbCl 3 NCs: PbCl 2 ( g), OAm (0.8 ml), OA (0.8 ml), and ODE (5 ml) were added to a 25-mL 3-neck round bottomed flask and were evacuated and refilled with N 2 followed by heating the solution to 120 C for 30 minutes. The solution was then increased to 165 C and then 200 C for 10 minutes each. At 200 C, dried OAm (0.8 ml) and dried OA (0.8 ml) were subsequently injected to solubilize the solution. Then the Cs-oleate (0.4 ml) was swiftly injected and after 1 minute the solution was cooled with an ice bath. The NCs were precipitated with acetone and the centrifuged followed by dissolving in hexanes. Synthesis of Mn-doped CsPbCl 3 NCs: PbCl 2 ( g), MnCl 2 (H 2 O) 4 ( g), OAm (0.8 ml), OA (0.8 ml), and ODE (5 ml) were added to a 25-mL 3 neck round bottom flask and were evacuated and refilled with N 2 followed by heating the solution to 120 C for 30 minutes. The solution was then increased to 165 C and then 200 C for 10 minutes each. At 200 C, dried OAm (0.8 ml) and dried OA (0.8 ml) were subsequently injected to solubilize the solution. Then the Cs-oleate (0.4 ml) was swiftly injected and after 1 minute the solution was cooled with an ice bath. The NCs were precipitated with acetone and the centrifuged followed by dissolving in hexanes. Synthesis of CsPb(Cl/Br) 3 NCs: PbCl 2 ( g), PbBr 2 ( g), OAm (0.8 ml), OA (0.8 ml), and ODE (5 ml) were added to a 25-mL 3-neck round bottomed flask and were evacuated and refilled with N 2 followed by heating the solution to 120 C for 30 minutes. The solution was then increased to 165 C and then 200 C for 10 minutes each. At 200 C, dried OAm (0.8 ml) and dried OA (0.8 ml) were subsequently injected to solubilize the solution. Then the Cs-oleate (0.4 ml) was swiftly injected and after 1 second the solution was cooled with an ice bath. The NCs were precipitated with acetone and the centrifuged followed by dissolving in hexanes. Synthesis of Mn-doped CsPb(Cl/Br) 3 NCs: PbBr 2 ( g), MnCl 2 (H 2 O) 4 ( g), OAm (0.8 ml), OA (0.8 ml), and ODE (5 ml) were added to a 25-mL 3 neck round bottom flask and were evacuated 2

3 and refilled with N 2 followed by heating the solution to 120 C for 30 minutes. The solution was then increased to 165 C and then 200 C for 10 minutes each. At 200 C, dried OAm (0.8 ml) and dried OA (0.8 ml) were subsequently injected to solubilize the solution. Then the Cs-oleate (0.4 ml) was swiftly injected and after 1 second the solution was cooled with an ice bath. The NCs were precipitated with acetone and the centrifuged followed by dissolving in hexanes. Purification of perovskite nanocrystals: To purify the nanocrystals, gel permeation chromatography (GPC) was used following a similar method by Shen et al 1. Prior to use, 4 g of poly(styrenedivinylbenzene) gel was soaked in toluene overnight and then packed into a column with toluene as the mobile phase. The perovskite samples were then loaded into the column and run through multiple times to ensure the removal of excess Mn-oleate or Mn-oleylamine complexes. The first 2 ml of the eluent nanocrystals were collected for each run followed by the measurement of the absorption, emission, and Mn doping concentration. The optical properties of the NC show little change after being put through the column multiple times (Figure S1a,b) while the elemental analysis (Figure S1c) also confirms that the excess Mn was removed giving a final doping concentration that converges at 0.2%. Figure S1. a) Absorption spectra of unwashed Mn-doped CsPb(Cl/Br) 3 and after being washed multiple times. b) Emission spectra of of unwashed Mn-doped CsPb(Cl/Br) 3 and after being washed multiple times. c) Elemental analysis of %Mn doping concentration correlated to the amount of times run through the GPC column. Characterization Methods Absorbance: UV-VIS spectra were collected on an Ocean Optics USB2000 spectrometer. Photoluminescence (PL): A fiberoptic-coupled CCD spectrometer (Ocean Optics, QE65pro) with a 365 nm LED light source was used to collect PL spectra of the NC solutions. The PL spectra were obtained by correcting the raw spectra with the spectral response of the entire optical system. Lifetime Measurements: Lifetime of Mn luminescence was measured using a pulsed N 2 laser (NL100 SRS, 337 nm) as the excitation source. The time-dependent luminescence intensity was recorded with a PMT (R928, Hamamatsu Photonics KK) and amplifier (C9663, Hamamatsu Photonics KK) in conjunction with a digital oscilloscope (WaveAce 234, Teledyne Lecroy). 3

4 Transmission Electron Microscopy (TEM): TEM images were collected on a FEI Tecnai G2 F20 ST FE-TEM microscope operated at 4100 kv. Elemental Analysis: Inductively coupled plasma mass spectrometry (ICP-MS) (NexIon 300D) was used to determine the amount of Cs, Pb, and Mn present in undoped and Mn-doped CsPbCl3 and CsPb(Cl/Br)3 perovskite nanocrystals. The nanocrystal solutions were sonicated in concentrated nitric acid to ensure complete digestion of the sample. The ratio between the chloride and bromide in the mixed halide perovskite was determined using SEM/EDS (FEI Quanta 600 FE-SEM) operated at 5 kv. The samples were dried in vacuum overnight and then placed on a carbon substrate where multiple locations similar to that in Figure S2 were scanned giving a consistent Cl/Br ratio of 4.2:1 for the doped CsPb(Cl/Br)3 and 4.4:1 for the undoped CsPb(Cl/Br)3. Figure S2. SEM scan of Mn-doped CsPb(Cl/Br)3 perovskite nanocrystals. 4

5 Figure S3. SEM/EDS atomic composition of Mn-doped CsPb(Cl/Br) 3 perovskite nanocrystals. Powder X-ray Diffraction (XRD): XRD measurements were taken with a Bruker-AXS GADDS MWPC diffractometer equipped with Cu K-α x-ray radiation and a multi-wire proportional counter. Fitting was done using GSAS on data obtained with a Bruker-AXS D8 Advanced Bragg-Brentano diffractometer equipped with Cu K-α x-ray radiation and a Lynxeye position sensitive detector. Table S1. Cell parameters for CsPbCl 3 perovskite nanocrystal through fitting refinement. Space Group: Pnma a= Å b = Å c = Å V = Å 3 χ 2 = x y z Occupancy U iso Cs Pb Cl Cl

6 Figure S4. Reitveld refinement fitting of CsPbCl 3 perovskite nanocrystal carried out using GSAS 2. Electron Paramagnetic Resonance (EPR): Samples were used as prepared in hexanes on a Bruker E1 Exsys with a super CW EPR bridge. Measurements were taken at room temperature with 9.37 MHz microwave frequency and 20 mw microwave power. Single-particle photoluminescence (PL): The single-particle PL spectra from individual perovskite nanocrystals were measured with a home-built wide-field microscope equipped with an imaging spectrograph (Princeton Instruments, Acton SpectraPro SP-2300) and an electron multiplying charge coupled device (EMCCD) (Princeton Instruments, ProEM 16002). A Xe-lamp (Oriel Instrument, 300 W) in conjunction with a monochromator (Newport, Oriel Cornerstone 130) provided the excitation light in the UV region (370 nm). Excitation of perovskite nanocrystals was performed via an attenuated total reflection (ATR) scheme using a quartz prism to minimize the interference from the excitation light during the PL measurement. A highly diluted colloidal suspension of perovskite nanocrystals is drop casted onto a thin quartz plate to deposit well-separated perovskite nanocrystals, and the plate is placed on top of the prism using an index matching liquid. The PL from a single perovskite nanocrystals collected with an objective (Olympus, PLanFL N 40X) is focused on the EMCCD as a spectrum using a tube lens (Nikon) through the imaging spectrograph. 6

7 Additional TEM Images Figure S5: TEM of Mn-doped CsPbCl 3 nanocrystals. Figure S6: TEM of CsPbCl 3 nanocrystals. Figure S7: TEM of CsPb(Br/Cl) 3 nanocrystals. 7

8 Table S2. Size distribution of doped and undoped perovskite samples. Sample CsPbCl 3 CsPbCl 3 :Mn CsPb(Cl/Br) 3 CsPb(Cl/Br) 3 :Mn size 10.4 ± 1.4 nm 8.7 ± 1.3 nm 11.0 ± 2.4 nm 10.6± 1.3 nm References: 1. Shen, Y.; Gee, M. Y.; Tan, R.; Pellechia, P. J.; Greytak, A. B., Purification of Quantum Dots by Gel Permeation Chromatography and the Effect of Excess Ligands on Shell Growth and Ligand Exchange. Chem. Mater. 2013, 25 (14), Larson, A. C.; Dreele, R. B. V., General Structure Analysis System (GSAS). Los Alamos National Laboratory Report LAUR: 2000; Vol