Supporting Information

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1 Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near-Unity Photoluminescence Quantum Yield and Efficient Red Light-emitting Diodes Jun Pan, # Yuequn Shang, Jun Yin, Michele De Bastiani, Wei Peng, Ibrahim Dursun, # Lutfan Sinatra, Ahmed M. El-Zohry, # Mohamed N. Hedhili, Abdul-Hamid Emwas, Omar F. Mohammed, Zhijun Ning, *, and Osman M. Bakr *, # King Abdullah University of Science and Technology (KAUST), KAUST Catalysis Center (KCC), # KAUST Solar Center (KSC), Division of Physical Science and Engineering (PSE), Imaging and Characterization Laboratory, Thuwal 23955, Saudi Arabia. School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai , China Experimental Materials Oleic acid (OA, technical grade 90%) was purchased from Alpha Aesar. Cesium carbonate (Cs2CO3, %, metal basis), oleylamine (OAm, technical grade 70%), anhydrous Octane ( 99%), lead iodide (PbI2, powder, 99%), 2,2 -Iminodibenzoic acid (IDA, powder, 95%), ethyl Acetate (EA, HPCL, 99.8%) and 1-octadecene (ODE, technical grade 90%) were purchased from Sigma-Aldrich. Poly(3,4- ethylenedioxythiophene): polystyrene sulphonate (PEDOT: PSS), Poly[bis(4-phenyl) (4- butylphenyl) amine] (Poly-TPD) and 2,2,2 -(1,3,5-Benzinetriyl)-tris(1-phenyl-1-Hbenzimidazole) (TPBi) were purchased from Xi an p-led, Lithium fluoride (LiF) was purchased from Kurt J. Lesker Company. All chemicals were used as procured without further purification. Preparation of cesium oleate solution Cs2CO3 (0.814 g) was loaded into 100 ml 2-neck flask along with ODE (30 ml). Degassed at 120 ºC for 10 min and then switch to nitrogen flow. 2.5 ml of oleic acid (OA) was injected and degassed for 2h at 120 ºC, and then evacuation and N2 refilling were repeated for three times to make sure all the white solid completely dissolved. The solution was kept at 120 ºC to avoid solidification before injection. 1

2 Synthesis and purification of CsPbI3 nanocrystals (NCs) 100 ml of ODE, PbI2 (2g) were stirred in a 500ml flask, degassed at 120 ºC for 10 min and then switch to nitrogen flow. 10 ml of OAm and 10 ml of OA (preheated at 70 ºC) were injected. The flask was put under vacuum again until the powder completely dissolved. 8 ml of cesium oleate solution was quickly injected at 170 ºC. After 5 s, the reaction mixture was cooled using an ice-water bath. The crude solution was divided into three centrifuge tubes, and directly centrifuged at 8000 rpm for 10 min. The precipitate was collected and dispersed in 10 ml anhydrous octane inside glovebox. Then, another centrifugation at 3000 rpm for 5min must be operated to remove the unreacted precursors and larger particles, and the supernatant was sealed in a glass vial for storage in fridge about 24h. Treatment of CsPbI 3 NCs After two days self-purification in the fridge, the solution was centrifuged at 3000 rpm for 5 min inside a glovebox. The collected supernatant was divided into two vials: one was used as control sample, while another one was defined as treated sample by direct adding powder of 2,2 -Iminodibenzoic acid (IDA). After completely mixed the NCs with IDA for 6 hours, high-speed centrifugation (8000 rpm for 5min) was applied to remove the extra powder. Both samples are collected for further characterization condition. For other halide or hybrid halide synthesis and treatment, follows the same method but just modifying the bromide weight to reach equivalent molar ratio as used for pure idodide perovskite synthesis. For purification process, EA was used to precipitate the NCs and then redispersed in octane inside glovebox. Direct synthesis with IDA 100 ml of octadecene (ODE), PbI2 (2g) and IDA (0.1 g) were stirred in a 500 ml flask, degassed at 120 ºC for 10 min and then switch to nitrogen flow. 10 ml of OAm (preheated at 70 ºC) was injected. The flask was put under vacuum again for 4 hours (not completely dissolved). 8 ml of cesium oleate solution was quickly injected at 170 ºC. After 5 s, the reaction mixture was cooled using an ice-water bath. 2

3 The crude solution was divided into three centrifuge tubes, and directly centrifuged at 8000 rpm for 10 min. The precipitate was collected and dispersed in 10 ml anhydrous octane inside glovebox. Then, another centrifugation at 3000 rpm for 5min was operated to remove the unreacted precursors and larger particles, and the supernatant (less amount) was sealed in a glass vial for storage in fridge about 24h. Characterization UV-Vis absorption spectra were obtained using an absorption spectrophotometer from Ocean Optics. Photoluminescence was tested using an FLS920 dedicated fluorescence spectrometer from Edinburgh Instruments. Quantum yield was measured using an Edinburgh Instruments integrating sphere with an FLS920-s fluorescence spectrometer. FTIR was performed using a Nicolet 6700 FT-IR spectrometer. Powder X-ray diffraction (XRD) patterns were recorded using Siemens diffractometer with Cu Kα radiation (λ= Å). TEM analysis was carried out with a Titan TEM (FEI Company) operating at a beam energy of 300 kev and equipped with a Tridiem post-column energy filter (Gatan, INC.). XPS studies were carried out in a Kratos Axis Ultra DLD spectrometer equipped with a monochromatic Al Ka X-ray source (hν = ev) operating at 150 W, a multi-channel plate and delay line detector under 1.0 x10-9 Torr vacuum. Measurements were performed in hybrid mode using electrostatic and magnetic lenses, and the take-off angle (angle between the sample surface normal and the electron optical axis of the spectrometer) was 0º. All spectra were recorded using an aperture slot of 300 µm x 700 µm. The survey and high-resolution spectra were collected at fixed analyzer pass energies of 160 and 20 ev, respectively. Samples were mounted in floating mode in order to avoid differential charging [53]. Charge neutralization was required for all samples. Binding energies were referenced to the C 1s peak (set at ev) of the sp3 hybridized (C-C) carbon from oleyalmine and oleic acid. The data were analyzed with commercially available software, CasaXPS. The individual peaks were fitted by a Gaussian (70%) Lorentzian (30%) (GL30) function after linear or Shirley-type background subtraction. The NMR spectra were acquired using a Bruker 600 MHz AVANACIII NMR spectrometer equipped with 5 mm Bruker BBOF probe (BrukerBioSpin, Rheinstetten, Germany). For comparative analysis, the spectra were 3

4 recorded using 90 one plus sequence with recycle delay of 10 sec. All spectra were recorded at room temperature by collecting 32 scans with 40 ppm spectral width corresponding to Hz digitized into 64k data point. Tetramethylsilane (TMS) was used as internal reference. Bruker Topspin 2.1 software (Bruker BioSpin, Rheinstetten, Germany) was used to collect and analyze the data. Computational Methods The density functional theory (DFT) calculations were performed using PWSCF code implemented in Quantum ESPRESSO package. 1 The generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) method was used to optimize the crystal structure of cubic-phase CsPbI3 bulk and slabs. The ultrasoft scalar-relativistic pseudopotentials were used to describe the electron-ion interactions by explicitly treating electrons for H (1s 1 ), N, O and C (2s 2, 2p 2 ), I (5s 2, 5p 2 ), Cs (5s 2, 5p 6, 6s 1 ), and Pb (5d 10, 6s 2, 6p 2 ). Single-particle wave functions (charges) were expanded on a plane-wave basis set up to a kinetic energy cutoff of 50 Ry (300 Ry) for both CsPbI3 bulk and slab structures. The van der Waals functional vdw-df2 2-3 was also used for the structural optimizations and electronic calculations (projected density of states and charge density redistributions). Monkhorst Pack-type K-meshes of for the bulk CsPbI3 and for slabs exposing the (001) surface with OA and IDA modifications were used. Each structure was optimized until the forces on each single atom were smaller than 0.01 ev/å. Three-dimensional charge density differences were defined as ρdiff = ρtotal ρligand ρcspbi3, where ρtotal is the total charge density of the slab after OA or IDA modification, and ρligand and ρcspbi3 represent the charge densities of the individual parts. The molecular graphics viewer VESTA was used to plot molecular structures and charge densities. PLED Fabrication and Characterization Indium tin oxide (ITO)-coated glass substrates were cleaned consecutively with detergent, isopropanol and deionized water under sonication for 30 min each. The cleaned ITO glasses were treated by oxygen plasma for 10 min before depositing PEDOT: PSS layer. PEDOT: PSS solutions (Clevios PVP Al 4083, filtered through a 0.45 mm filter) were spin-coated onto the substrates at 4000 rpm for 60 s and baked at 140 ºC for 20 min in air. Then all the prepared PEDOT: PSS films were transferred into the 4

5 glovebox immediately for the following fabrication processes. The Poly-TPD layer were spin coated at 3000 rpm for 60 s using an 8mg ml 1 solution in chlorobenzene, followed by baking at 130 C for 30 min. The washed CsPbI3 and CsPbI3-IDA quantum dots were dissolved in toluene (10 mg ml 1 ) and then spin coated at 2000 rpm for 60 s. Finally, TPBi(50nm), LiF(1.2nm) and Al electrodes (120 nm) were deposited by thermal evaporation under a based vacuum of ~ Torr. The device area was 5 mm 2 as defined by the overlapping area of the ITO and Al electrodes. The current density-luminance-voltage (J-V-L) characteristics were acquired by a Keithley 2400 source meter and a PR-655 (Photo Research Inc.) Spectroradiometer. The film electrical properties were measured via the connection to a Keithley 2400 source meter with a threshold detection limit of 10 pa. The scan range is from 0V to 15V with a step length of 0.3V. All of the device test processes were performed in the ambient environment without any encapsulation. Figure S1. Size distribution of untreated (blue dots) and IDA-treated NCs (red dots). 5

6 Figure S2. TEM image and PL spectrum of NCs directly using IDA during synthesis. 6

7 Figure S3. Time-resolved PL for untreated (pink dots) and IDA-treated NCs (sky blue dots). The PL lifetime is extrapolated from averaging the bi-exponential fitting (solid line). The excitation wavelength was 475 nm, and the time-resolved emission was collected on a PMT tube in the spectral range of 600 to 800 nm. 7

8 Figure S4. Cs 3d, Pb 4f, and I 3d core level spectra of untreated (blue) and treated NCs (red). 8

9 Figure S5. N 1s core level spectra of the untreated (blue) and IDA-treated NCs (red). 9

10 Figure S6. 1 H nuclear magnetic resonance (NMR) spectroscopy of IDA (blue), IDA treated NCs (red) and untreated NCs (black). 10

11 Figure S7. 1 H nuclear magnetic resonance (NMR) spectroscopy of IDA treated NCs (red) and untreated NCs (blue). Table 1. Quantity analysis by chemical shift integrate area. Sample Shift 1 Shift 2 OLA/OA Untreated : 2.6 Treated : 1 11

12 Figure S8. FTIR spectra for the untreated (black), IDA-treated NCs (red) and pure IDA (blue). 12

13 Figure S9. XRD pattern of purified NCs film (a) and IDA treated NCs film (b), original and after 40 days. 13

14 Figure S10. FTIR spectra for the untreated (black) and the precipitate of degraded untreated NCs (red). 14

15 Supporting Information Figure S11. N 1s core level spectrum of IDA treated NCs after ethyl acetate washing. 15

16 Supporting Information Figure S12. Emission peak of different halide NCs after IDA treatment. Table S2. Summary of different halide NCs before and after IDA treatment Sample Composition PL Peak CsPbBr3 CsPbBr1.5I1.5 CsPbBr0.9I2.1 CsPbBr0.6I QY before treatment (%) QY after treatment (%)

17 e Figure S13 Electronic calculations (projected density of states). 17

18 Supporting Information Figure S14 I-V curve of film conductivity test for pure IDA film (red) and IDA-treated NC film (black). Al (100 nm) electrode was thermally deposited on the quartz glass substrate through a metal shadow mask with channel width equal to 100 µm. References: 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. J. Phys.: Condens. Matter. 2009, 21, Berland, K.; Cooper, V. R.; Lee, K.; Schroder, E.; Thonhauser, T.; Hyldgaard, P.; Lundqvist, B. I. Rep. Prog. Phys. 2015, 78, Langreth, D. C.; Lundqvist, B. I.; Chakarova-Kack, S. D.; Cooper, V. R.; Dion, M.; Hyldgaard, P.; Kelkkanen, A.; Kleis, J.; Kong, L. Z.; Li, S.; Moses, P. G.; Murray, E.; Puzder, A.; Rydberg, H.; Schroder, E.; Thonhauser, T. J. Phys.: Condens. Matter. 2009, 21,