Supporting Information. Surface Ligand Engineering for Near-Unity Quantum Yield. Inorganic Halide Perovskite QDs and High-Performance QLEDs

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1 Supporting Information Surface Ligand Engineering for Near-Unity Quantum Yield Inorganic Halide Perovskite QDs and High-Performance QLEDs Guopeng Li, a Jingsheng Huang, b Hanwen Zhu, a Yanqing Li,*,b Jian-Xin Tang,*,b Yang Jiang*,a a School of Materials Science and Engineering, Hefei University of Technology (HFUT), Hefei, Anhui, , P. R. China. b Institute of Functional Nano & Soft Materials (FUNSOM), Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu , P. R. China Experimental Section Materials Oleic acid (OA, 85 %), oleylamine (OAm, 90%), 1-octadecene (ODE, >90 %), octane (>99%), hexane (>98%), hydrobromic acid (48 wt. % in H 2 O, 99.99%) and ethanol (99.5%) were purchased from Aladdin. Cesium carbonate (Cs 2 CO 3, %), lead bromide (PbBr 2, 98%) and PEA were purchased from Sigma-Aldrich. Methyl acetate (MeOAc, 99%), ethyl acetate (EtOAc, 99%) and lithium fluoride (LiF, 99.99%) were purchased from Macklin. Poly(3,4-ethylenedioxythiophene) 1

2 polystyrene sulfonate (PEDOT:PSS, 4083) was purchased from Heraeus. Poly[N,N -bis(4-butylphenyl)-n,n -bisphenylbenzidine] (Poly-TPD), poly(9,9-dioctylfluorene-co-n-(4-butylphenyl)-diphenylamine) (TFB), poly(9 vinlycarbazole) (PVK) and 1,3,5-tri(phenyl-2-benzimi-dazolyl)-benzene (TPBi) were purchased from Nichem. Diethyl ether was purchased from Sinopharm Chemical Reagent. All the chemicals were used directly without further purification. Synthesis of PEA-modified CsPbX 3 (X=Br, I) QDs The Cs-oleate was prepared as the method reported in the reference (Nano Lett., 2015, 15, ). PbBr 2 (0.8 g), OA (5 ml) and ODE (50 ml) were mixed into 200 ml round bottom flask with stirring. For different PEA-modified QDs, 5 ml OAm was partially substituted by PEA with the content from 0.1 to 0.4 molar fraction, and added into the flask. The flask was degassed under vacuum at 120 C for 1 hour, and heated to 170 C under the nitrogen flow environment. Then, 8 ml Cs-oleate was quickly injected, and the reaction was stopped by the ice-water bath after 5 seconds. 200 ml MeOAc were added into the crude solution and centrifuged at 8000 rpm for 5 min. The precipitate was collected and dispersed in 10 ml hexane. 10 ml MeOAc was added and centrifuged at 8000 rpm for 2 min. The precipitated was dispersed into 20 ml of hexane and centrifuged at 4000 rpm for 5 min. Finally, the hexane was dried and the QDs were dispersed in octane as a concentration of 20 mg ml -1 for the device fabrication. Synthesis of PEABr and PEAI 2

3 PEABr/PEAI was prepared by dissolving PEA (1 g) in ethanol (15 ml) and stirred at 0 C. Then the equal molar of hydrobromic acid/hydroiodic acid was added by drop and stirred for 2 hours. PEABr/PEAI was obtained by evaporating the solution at 50 C, washing the samples three times with diethyl ether, and finally drying them under vacuum for 24 hours. The PEABr/PEAI solution was prepared by mixing 0.06 mmol PEABr/PEAI and 400 µl OA into 32 ml EtOAc. The PEABr/PEAI ligand solution was obtained by ultrasonically treating the mixture for 5 min. Device Fabrication a. The untreated CsPbX 3 (X=Br or I) QLEDs with a structure of ITO/ PEDOT:PSS /poly-tpd/qds/tpbi/lif/al: The PEDOT:PSS solution (filtered through a 0.45 µm filter) was spin-coated onto ITO-coated glass substrates at 4000 rmp for 40 s and baked at 140 C for 10 min. The hole transport layer of Poly-TPD (8 mg ml -1 chlorobenzene solution) was deposited by spin-coating at 4000 rpm for 60 s. The CsPbBr 3 QD layer was prepared by spin-coating at 2000 rpm for 60 s and baked at 80 C for 5 min. TPBi (40 nm) and LiF/Al electrodes (1 nm/100 nm) were deposited using a thermal evaporation system through a shadow mask under high vacuum. b. The treated CsPbX 3 (X=Br or I) QLEDs with a structure of ITO/PEDOT:PSS /poly-tpd/qds/tpbi/lif/al: Except for that CsPbX 3 (X=Br or I) QDs films was treated with PEABr or PEAI, other steps were same to the a process. The ligand-exchange process was executed by dipping the CsPbBr 3 QD films into the 3

4 ligand solution for 30 s, rinsing them with neat EtOAc, and finally baking at 80 C for 5 min. c. The treated CsPbBr 3 QLEDs with a structure of ITO/PEDOT:PSS /TFB/PVK/QDs/TPBi/LiF/Al: Except for that the Poly-TPD layer was instead by TFB and PVK, other steps were same to the b process. The deposition of the TFB (or PVK) layers was performed by spin-coating the TFB (or PVK) chlorobenzene solution of 8 mg ml -1 (or 2 mg ml -1 ) at 3000 rpm for 60 s, and baked at 170 C for 30 min. d. Electron-only and hole-only CsPbX 3 QDs devices of: The electron-only and hole-only devices adopt the structures of ITO/ZnO/QDs/TPBi/LiF/Al and ITO/PEDOT:PSS/poly-TPD/QDs/MoO 3 /Al respectively. The zinc oxide (ZnO) layer in electron-only devices was prepared by spin-coating the ZnO precursor solution at 4000 rpm for 40 s and then baked at 150 C for 15 min. The ZnO precursor solution was obtained by mixing 220 mg zinc acetate dihydrate (Zn(CH 3 coo) 2 2H 2 O, 99.5%; Sigma-Aldrich) with 2 ml 2-methoxyethanol (CH 3 OCH 2 CH 2 OH, 99.8%; Sigma-Aldrich) and 61 µl ethanolamine (NH 2 CH 2 CH 2 OH; Sigma-Aldrich), and stirring for 12 hours under ambient conditions. The MoO 3 layer (15 nm) in hole-only devices was deposited using a thermal evaporation system through a shadow mask under high vacuum. Other layers were prepared as abovementioned process. Material and Device Characterization UV-vis absorption and PL spectra were recorded with the LAMBDA-750 absorption spectrophotometer from Perkinelmer and FL3 spectrometer from Horiba. 4

5 FTIR spectra were measured with the Bruker Hyperion spectrometer. The FTIR spectrum of 0.2 PEA CsPbBr 3 QDs was measured by using the purfied QDs powder directly. And the FTIR spectrum of 0.2 PEA CsPbBr 3 QDs was measured by the following process: firstly, spinning 0.2 PEA CsPbBr 3 QDs on the substrate, and executing the ligand-exchange process with PEABr. Secondly, separating the treated CsPbBr 3 QDs from the substrate and performing the measurement. High-resolution transmission electron microscopy (HRTEM) images were taken by an FEI Tecnai G2 F20 X-TWIN operated at an accelerating voltage of 200 kv. SEM images were measured with the Zeiss Supra 55. XRD patterns were recorded with a Rigaku D/MaxrB diffraction using Cu Kα radiation. Time-resolved PL decay spectra were collected on a Horib-FM-2015 spectrometer. The PLQY of the QD films was obtained by using an absolute PLQY measurement system (FL3, Horiba). The EL spectra and J-V-L characteristics were measured using a programmable source meter (Keithley model 2400) and a luminance meter/spectrometer (PhotoResearch PR670). Note S1. The marked results of different functional groups of FTIR spectra in Figure 3(b) In Figure 3(b), the FTIR spectra of two samples have the peaks at 2924, 2854 and 1468 cm -1, which are resigned as the -CH 2 - symmetric and asymmetric stretching vibration peaks, and bending vibration peak. And the peak at 2960 cm -1 represents the asymmetric stretching vibration peak of -CH 3. The peaks at 1533 and 1406, and 3004 cm -1 observed in 0.2 PEA CsPbBr 3 QDs are related to the symmetric vibration and 5

6 symmetric stretching vibration of the carboxylate group, and the -C=C- stretching vibration, which are absent in the samples treated with PEABr. The peaks at 1640 cm -1 presented in both samples is ascribed to the bending vibration of -NH 2 group. And two samples present the absorption at 3067, 3029, 1032, and 1573 cm -1, which could be assigned to the =C-H stretching vibration and bending vibration, and the -C=C- stretching vibration of the benzene ring. 6

7 Figure S1. Chemical structures of PEA and PEABr. Figure S2. (a) TEM image, (b) time-resolved PL decay curve (c) optical spectra of CsPbBr 3 QDs without PEA. 7

8 Figure S3. The histogram graphs of the size distribution for CsPbBr 3 QDs with different PEA content: a. 0.1 PEA, b. 0.2 PEA, c. 0.3 PEA, d. 0.4 PEA. Figure S4. N 1s core level spectra of the CsPbBr 3 QDs without PEA (a) and with 0.2 PEA (b), and (c) the TGA curves. In XPS spectra, the peaks centred at ev and ev correspond to protonated amine groups (-NH + 3 ) and amine group, 8

9 respectively. The area ratio (peak-401.6/peak-399.9) of these peaks changes from (a) to (b) indicating that the protonation degree of amine ligand increases by adding PEA. The TGA curves suggest that the ligand content decreases from 27% to 21% in the presence of PEA, which is in agreement with smaller molecular mass of PEA compared to that of OAm. Figure S5. TEM image of CsPbBr3 QDs with 0.1 PEA. 9

10 Table S1. The summary of PLQY, average lifetime (τ ave ), radiative recombination lifetime (τ r ), radiative (k r ) and nonradiative (k nr ) decay rates of the CsPbBr 3 QDs with different PEA contents. The τ ave, τ r, k r and k nr are calculated based on the following formulas: τ ave = =, τ r =, k r=, k nr = normalized coefficients and time constants, respectively). k r (B n and τ n are PEA PLQY τ ave τ r k r k nr content [%] [ns] [ns] [ns -1 ] [ns -1 ]

11 Figure S6. Device performance of CsPbBr 3 QLEDs with different PEA contents. (a) J-V and L-V curves. (b) CE as a function of luminance. (c) EQE as a function of luminance. 11

12 Table S2. Device performance of CsPbBr 3 QLEDs with different PEA contents, including maximum luminance (max. L), current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE). PEA V on Max. L Max. CE Max. PE Max. EQE content [V] [cd m -2 ] [cd A -1 ] [lm W -1 ] [%]

13 Figure S7. (a) The XPS spectra and (b) the corresponding atom content of 0.2 PEA CsPbBr 3 QDs without and with EX. Figure S8. SEM images of 0.2 PEA-modified CsPbBr 3 QDs layers before and after the ligand-exchange process. Scar bar: 200 nm. 13

14 Figure S9. Current density-voltage characteristics of hole-only (a) and electron-only (b) devices of 0.2 PEA CsPbX 3 QDs before (Br or I) and after ligand-exchange (Br-EX or I-EX), and the corresponding structures. The electrical performance of all CsPbX 3 (X=Br, I) devices is improved significantly after ligand-exchange, indicating the enhanced injection and transport of electrons and holes. 14

15 Figure S10. Device performance of the CsPbBr 3 QLED treated with PEABr, which consists of a structure of ITO/PEDOT:PSS/TFB/PVK/0.2 PEA-modified CsPbBr 3 QDs/TPBi/LiF/Al. (a) J-V and L-V characteristics. (b) EL spectrum at the maximum luminance. (c) EQE and CE curves as a function of luminance. (d) CIE coordinates. 15

16 Figure S11. (a) The optical spectra of CsPbI 3 QDs without and with 0.1 PEA. (b) The XRD patterns of CsPbI 3 QDs with no PEA, 0.1 PEA and 0.2 PEA. (c) The TEM (left), HRTEM (middle) and size distribution (right) of CsPbI 3 QDs with no PEA (upper), 0.1 PEA (middle) and 0.2 PEA (lower). In the Figure S11a, the PL spectrum is red shifted from 679 nm to 683 nm and 687 nm with the PEA content increasing from 0 to 0.1 and 0.2, which is consistent with the CsPbI 3 QD size increase with the increase of PEA content as shown in Figure 16

17 S11c. The XRD peaks in Figure S11b have been identified as the peaks of cubic perovskite structure, which indicates that the addition of PEA would not change the structure of CsPbI 3 QDs. The structure of CsPbI 3 could also been confirmed from the HRTEM images in Figure S11c. The lattice spacing of 0.62 nm corresponds to the (100) crystal plane of cubic perovskite phase. Figure S11c indicates that the CsPbI 3 QDs have a narrow size distribution and high crystallinity, which would not change with the addition of PEA. Figure S12. Time-resolved PL decay spectrum of 0.2 PEA modified CsPbI 3 QDs (insert: photograph of QDs octane solution under UV-365 nm lamp) 17

18 Figure S13. The histograms of (a) peak luminance of CsPbBr 3 QLEDs and (b) EQE of CsPbI 3 QLEDs show the average values of 19,211 cd/m 2 and 12.6 % for 20 devices. 18