Inside Perovskites: Quantum Luminescence from Bulk Cs 4 PbBr 6 Single Crystals

Transcription

1 Inside Perovskites: Quantum Luminescence from Bulk Cs 4 PbBr 6 Single Crystals Michele De Bastiani -, Ibrahim Dursun -, Yuhai Zhang -, Buthainah A. Alshankiti, Xiao-He Miao, Jun Yin, Emre Yengel, Erkki Alarousu, Bekir Turedi, Jawaher M. Almutlaq, Makhsud I. Saidaminov,±, Somak Mitra, Issam Gereige, Ahmed AlSaggaf, Yihan Zhu, Yu Han, Iman S. Roqan, Jean-Luc Bredas, Omar F. Mohammed * and Osman M. Bakr,# * King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC), Division of Physical Science and Engineering (PSE), Thuwal , Kingdom of Saudi Arabia. # KAUST Catalysis Center (KCC), Division of Physical Science and Engineering (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal , Saudi Arabia. Imaging and Characterization Core Lab, King Abdullah University of Science and Technology (KAUST), Thuwal , Kingdom of Saudi Arabia. Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal , Kingdom of Saudi Arabia. Saudi Aramco Research & Development Center, Dhahran 31311, Kingdom of Saudi Arabia. Advanced Membranes and Porous Materials Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal , Kingdom of Saudi Arabia. Present address: ± Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario M5S 3G4, Canada. 1

2 Supporting Information Experimental methods Materials: all the reagents were used as received. Cesium bromide (99.9%), and lead bromide (PbBr, 98%) were purchased from Sigma Aldrich. All the solvents meet the ACS reagent grade. Optical microscope: Nikon SMA5 stereomicroscope with a green filter cube. SEM images: Scanning Electron Microscopy images were collected with Quanta 00 SEM machine from FEI, Inc. Optical characterization: The absorption spectrum of perovskite crystal is calculated using reflectance data according to the Kubelka-Munk equation, F(R) = K/S = (1 R) /R, where R is the absolute reflectance of the sample, K is the molar absorption coefficient, and S is the scattering coefficient. Edinburg F900 Spectrometer with an integrating sphere and BaSO 4 as non-absorbing reflectance reference were used to acquire diffuse reflectance. The temperature-dependent steady state photoluminescence spectra were characterized using a Horiba JY LabRAM Aramis spectrometer with an Olympus 50x lens in a Linkam THMS600 stage. A 473 nm laser was used as the excitation source. Time Resolved photoluminescence: samples were excited with the second harmonic (410 nm) of a Spectra Physics MaiTai ehp and Inspire HF-100 OPO. Repetition rate of the beam is adjusted to 4 MHz with a APE Pulse Select pulse picker. The sample is excited with the excitation fluence of 0.5 nj/cm. The PL spectra are collected with a streak camera (Hamamatsu C10910) system with a temporal resolution of 1ps. For the temperature dependent photoluminescence lifetime samples were excited with a mode-locked Ti:Sapphire laser (coherent Mira 900) having laser output = 1.90 W at 800nm. Second harmonic generator (APE-SHG/THG) was used to excite the sample by 400nm equipped with a Pulse picker (APE) to reduce the laser repetition rate from 76MHz to MHz having a Pulse width = ~150 fs. The PL spectra are collected with a streak camera Hammatsu attached to single-sweep unit. Emission of the sample was detected by a monochromator attached to a UV-sensitive Hamamatsu C6860 streak camera with a temporal resolution of ps. The samples were mounted in a variable temperature closed-helium cryostat for measurements between 80K and 300K. DFT calculations: Ground State Calculations: The density functional theory (DFT) were performed using PWSCF code implemented in Quantum ESPRESSO (QE) package. 1 The exchange-correlation energy was approximated using the General Gradient Approximation (GGA) proposed by Perdew-Burke-Ernzerhof (PBE) functional. Electron-ion interactions were described by normconserving Troullier-Martins pseudopotentials by treating explicitly electrons for Cs (5s 5p 6 6s 1 ); Pb (5d 10 6s 6p ), and Br (4s 4p 5 ). Single-particle wave functions (charges) are expanded on a plane-wave basis set up to a kinetic energy cutoff of 80 Ry (400 Ry). The Monkhort Pack type K-meshes is for the bulk Cs 4 PbBr 6. The crystal structure was optimized until forces on single atoms are smaller than 0.01 ev/å. The molecular graphics viewer VESTA was used to plot the Cs 4 PbBr 6 crystal structure. Optical Response Calculations: Based on the electronic wavefunctions of the ground state of bulk Cs 4 PbBr 6 obtained from QE, the optical transitions were calculated by solving the Bethe-Salpeter equations (BSE) using YAMBO code: E E A " + vck K v c k A = Ω A " where E and E are the quasiparticle energies of the conduction and valence states, respectively; A " are the expansion coefficients of the excitons and Ω are the eigenenergies. The imaginary part (ε 1 ) of the optical response was calculated by evaluating direct electronic transitions between occupied and higher-energy unoccupied electronic states as obtained from ck p vk ε ω A " ε ε " δ Ω ħω Γ

3 where ck p vk are the dipole matrix elements for electronic transitions from valence to conduction states. Then the absorption coefficient (α) was obtained as: α = ω ε ω + ε ω / ε ω / (1) Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; Dal Corso, A.; de Gironcoli, S.; Fabris, S.; Fratesi, G.; Gebauer, R.; Gerstmann, U.; Gougoussis, C.; Kokalj, A.; Lazzeri, M.; Martin-Samos, L.; Marzari, N.; Mauri, F.; Mazzarello, R.; Paolini, S.; Pasquarello, A.; Paulatto, L.; Sbraccia, C.; Scandolo, S.; Sclauzero, G.; Seitsonen, A. P.; Smogunov, A.; Umari, P.; Wentzcovitch, R. M. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J Phys-Condens Mat, 009, 1. () Marini, A.; Hogan, C.; Gruning, M.; Varsano, D. Yambo: An ab initio tool for excited state calculations. Comput. Phys. Commun., 009, 180, Electron Diffraction: TEM images were acquired using a Tecnai transmission electron microscope with an acceleration voltage of 10 kev. Selected area diffraction was collected on the same microscope with a camera distance of 640 mm. Crystal size calculations: Crystal sizes are calculated from the XRD pattern using the commercial program TOPAS, General Profile and Structure Analysis Software for Powder Diffraction Data, V4., Bruker AXS GmbH, Karlsruhe, Germany. Single Crystal X-Ray Diffraction details Crystal data Chemical formula Br 6 Cs 4 Pb M r Crystal system, space group Trigonal, R -3c Temperature (K) 93 a, c (Å) 13.7 (3), (4) V (Å 3 ) (13) Z 6 Radiation type Mo Kα µ (mm 1 ) 9.31 Crystal size (mm) Data collection Diffractometer Absorption correction SuperNova, Dual, Cu at zero, Atlas diffractometer Multi-scan CrysAlis PRO f (Rigaku Oxford Diffraction, 015) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. 3

4 T min, T max 0.068, No. of measured, independent and observed [I > σ(i)] reflections 15644, 938, 857 R int (sin θ/λ) max (Å 1 ) Refinement R[F > σ(f )], wr(f ), S 0.043, 0.138, 1.07 No. of reflections 938 No. of parameters 19 Δρ max, Δρ min (e Å 3 ) 3.9, 3.37 Computer programs: CrysAlis PRO f (Rigaku OD, 015), SHELXS (Sheldrick, G.M. Acta Crystallographica, 008, A64, 11-1), SHELXL (Sheldrick, G.M. Acta Cryst. 008, A64, 11-1), Olex (Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard J. A. K.; Puschmann, H. OLEX: a complete structure solution, refinement and analysis program. J. Appl. Cryst. 009, 4, ). Figure S1. Absorption spectrum of Cs 4 PbBr 6 0D-PVK in powder form. The steady-state absorption was recorded using a UV-Vis Cary-5000 spectrophotometer equipped with praying mantis diffuse reflectance accessory. 4

5 Figure S. Photoluminescence quantum yield. Black line: reference spectrum, red line: Cs 4 PbBr 6 single crystal. Figure S3. Time-resolved PL map and kinetic trace extracted at 54 nm and fitted with bi-exponential function. PBE 5 PBE+SOC 5 Cs 4 Pb Br 4 A Γ L M H K Eneryg (ev) Energy(eV) Γ A H K Γ M L J PDOS (a.u.) -1 Figure S4. Crystal structure, band structure, and projected density of states of monoclinic Cs 4 PbBr 6 calculated at PBE level without and with spin-orbit coupling (SOC) effects. 5

6 Figure S5. Temperature dependent XRD of the heating process at 700 K and the cooling process at 100 K. A 3D-like feature starts appearing irreversibly by decreasing the temperature at 575 K. 6

7 Figure S6. Photoluminescence lifetime of Cs 4 PbBr 6 single crystal collected at different temperatures for three different excitation powers. Dots: experimental data, lines: bi-exponential fitting. Figure S7. XRD patterns of calculated Cs 4 PbBr 6, emissive Cs 4 PbBr 6, and a mixture of (99.5 wt%) Cs 4 PbBr 6 and (0.5 wt%) CsPbBr 3. Note that trace amount of CsPbBr 3 as low as 0.5 wt% is clearly detectable through XRD measurement, indicating the emitting motif is not CsPbBr 3 impurity. 7