Supporting Information. Ce 3+ -Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr 3 Nanocrystals Based Light-Emitting Diodes

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1 Supporting Information Ce 3+ -Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr 3 Nanocrystals Based Light-Emitting Diodes Ji-Song Yao 1,2,, Jing Ge 1,3,, Bo-Ning Han 4, Kun-Hua Wang 1,2, Hong-Bin Yao 1,2,*, Hao-Lei Yu 2, Jian-Hai Li 4, Bai-Sheng Zhu 2, Ji-Zhong Song 4, Chen Chen 2, Qun Zhang 1,3,*, Hai-Bo Zeng 4,*, Yi Luo 1,3 and Shu-Hong Yu 1,2,5 1 Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui , China 2 Department of Chemistry, CAS Center for Excellence in Nanoscience, Hefei Science Center of CAS, University of Science and Technology of China, Hefei, Anhui , China 3 Synergetic Innovation Center of Quantum Information and Quantum Physics, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui , China 4 MIIT Key Laboratory of Advanced Display Materials and Devices, Institute of Optoelectronics & Nanomaterials, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing , China 5 Collaborative Innovation Center of Suzhou Nano Science and Technology, University of Science and Technology of China, Hefei, Anhui , China yhb@ustc.edu.cn, qunzh@ustc.edu.cn, or zeng.haibo@njust.edu.cn S1

2 Figure S1. The experimental setup used for LED performance test. Figure S2. Energy Dispersive X-ray Spectroscopy of Ce 3+ -doped nanocrystals at 30% of CeBr 3 concentration. Inset: quantification of the EDS spectrum showing a Cs:Pb:Ce:Br atomic ratio of 0.75:1.0:0.05:2.6. S2

3 Figure S3. (a) SEM image of Ce 3+ -doped nanocrystals at 30% of CeBr 3 concentrations. (b-e) Elemental mappings of Cs, Pb, Br, and Ce in Ce 3+ -doped CsPbBr 3 NCs. Figure S4. (a) Survey XPS spectra for the undoped and 2.88 mol% Ce 3+ ions doped CsPbBr 3 perovskite NCs. (b e) The high-resolution XPS analysis corresponding to Ce 3+ 3d, Cs + 3d, Pb 2+ 4f, and Br - 3d, respectively. S3

4 Figure S5. PL spectrum of colloidal (a) undoped and (b) doped NCs in toluene solution. Inset: magnified view of the PL data ( nm). Figure S6. Histograms showing the Size distribution of the Ce 3+ -doped CsPbBr 3 NCs prepared with different concentrations of CeBr 3. S4

5 Figure S7. (a) XRD patterns and (b) TEM image of NCs prepared by using cerium bromide to replace lead bromide without adding any PbBr 2. Figure S8. (a f) Plots of (Ahν) 2 vs photon energy (ev) for CsPbBr 3 NCs with different Ce 3+ doping amounts. S5

6 Figure S9. (a) The PL spectra (excitation at 365 nm) and (b) PLQY of Ce 3+ -doped NCs with different concentrations of CeBr 3 precursor, respectively. Photographs of colloidal Ce 3+ -doped NCs solution in toluene after 30-day storage (c) under ambient conditions and the corresponding (d) UV-light irradiation (365 nm), respectively. Figure S10. (a) Evolution of the UV-vis absorption and PL spectra of Ce 3+ -CsPbBr 3 NCs with different extent of anion-exchange of HAI and HACl, respectively. Photographs of as-obtained anion exchanged Ce 3+ -CsPbBr 3 NCs suspension (b) under ambient conditions and (c) the UV-light irradiation (365 nm), respectively. S6

7 Figure S11. PL kinetics recorded on a representative Ce 3+ -doped CsPbBr 3 NCs (30% in terms of CeBr 3 ratio). The PL was excited at 400 nm and monitored at 515 nm. The average PL lifetime can be estimated to be ± 0.10 ns, based on the bi-exponential fitting results (τ1 = 6.43 ± 0.05 ns and τ2 = ± 0.17 ns). The average PL lifetimes for all of the doped samples are collected in Table S2. Figure S12. The corresponding CIE coordinate for the EL spectrum of Ce 3+ -doped CsPbBr 3 NCs based QLED under an applied voltage of 5 V. S7

8 Table S1. The Lattice Constant and Ce/Pb ratio of CsPbBr 3 nanocrystals (NCs) after reaction with different cerium bromide concentrations. CeBr 3 ratio 0% 10% 20% 30% 40% 50% Ce/Pb ratio 0% 0.43% 0.51% 2.88% 0.82% 0.53% Lattice Constant (Å) Table S2. The PL lifetimes for the Ce 3+ -doped CsPbBr 3 NCs with different CeBr 3 ratios. a CeBr 3 ratio 0% 10% 20% 30% 40% 50% τ 1 (ns) τ 2 (ns) 7.58(6) [74%] 20.03(19) [26%] 5.73(4) [78%] 25.58(17) [22%] 5.96(5) [79%] 21.59(16) [21%] 6.43(5) [80%] 20.52(17) [20%] 5.93(9) [78%] 20.73(32) [22%] 5.41(7) [87%] 22.08(46) [13%] τ avg (ns) 18.35(13) 16.78(11) 13.56(10) 12.69(10) 13.17(12) 11.56(26) a The PL was excited at 400 nm and monitored at 515 nm. The average PL lifetimes (τ avg ) were obtained by τ avg = (A 1 τ A 2 τ 2 2 )/(A 1 τ 1 + A 2 τ 2 ), where A 1 and A 2 stand for the statistical weights of the corresponding lifetime components (given in the square parentheses). The errors for the fitted PL lifetimes are given in parentheses in units of the last digits quoted. Table S3. Summary of the performance of CsPbBr 3 NCs-based QLEDs. Previous reports Publication year/month Maximum CE (cd A -1 ) Maximum EQE (%) This work Song et al.(16) 2015/ Li et al.(20) 2016/3 Not reported 0.19 Pan et al.(6) 2016/8 Not reported 3.0 Li et al.(5) 2016/ Wei et al.(17) 2017/ Shan et al.(15) 2017/ Kim et al.(14) 2017/ *The reference number is noted here according the references in the main text. S8