Electronic Supplementary Material

Synthesis of CsPbX3 (X = Cl/Br, Br, and Br/I)@SiO2/PMMA composite films as color-conversion materials for achieving tunable multi-color and white light emission

Varnakavi Naresh1 (), Byung Hyo Kim2, and Nohyun Lee1 ()

1 School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea 2 Department of Organic Materials and Fiber Engineering, Soongsil University, Seoul 06978, Republic of Korea

Supporting information to https://doi.org/10.1007/s12274-020-3170-5

Experimental Materials and methods: Reagents

Lead chloride (PbCl2, 99.99% Sigma-Aldrich ), carbonate (Cs2CO3, 99.99% Sigma-Aldrich), 1-octadecene (ODE, 90% Sigma-Aldrich ), oleic acid (OA, 90% Sigma-Aldrich), oleylamine (OLA, 80-90% Sigma-Aldrich), Methyl acetate (MeOAc, 99.5% Sigma-Aldrich) and n-hexane (95.0% Samchun), (99.99% Samchun) and Poly(methyl methacrylate) (PMMA, Mw: 350,000 by GPC, Sigma-Aldrich) were purchased and used without further purification.

Synthesis methodology: Caesium-oleate preparation

To synthesize caesium-oleate, Cs2CO3 (0.133 g, 1.25 mmol), 5 mL ODE, and 1 mL OA were loaded into a 50 mL 3-neck flask, heated to 120 °C under vacuum for 1 h, and then heated under Ar gas flow at 150 °C until Cs2CO3 was completely dissolved, and a clear solution was obtained. The Cs-oleate solution was kept at this temperature (150 °C) before it was injected.

Synthesis of colloidal solution of pristine CsPbX3 (X = Cl, Br, and I) PNCs

CsPbX3 PNCs solutions were synthesized by loading ODE (5 mL) and 0.188 mmol of PbX2 (PbCl2 – 0.052 g, PbBr2 – 0.069 g, and PbI2 – 0.086 g) into a 50 mL 3-neck flask and dried under vacuum at 120 °C for 1h and then followed by heating the solution to 150 °C under Ar gas. Dried OA (0.5 mL for PbCl2, 0.5 mL for PbBr2 and 0.7 mL for PbI2) and OAm (0.5 mL for PbCl2, 0.5 mL for PbBr2 and 0.7 mL for PbI2) at 100 °C were injected at 120 °C under Ar flow. After complete solubilisation of a PbX2 salt, the temperature was raised to 160-200 °C and Cs-oleate solution (0.5 mL) was swiftly injected into the PbX2-ODE solution and after 60 s the solution was immediately cooled down to room temperature by immersing the flask in an ice- bath. For obtaining CsPbCl3 PNCs, at 150 °C, TOP (2mL) was swiftly injected and stirred until PbCl2 salt was completely dissolved. After the reaction, the aggregated NCs were separated by centrifugation. After centrifugation, the supernatant was discarded and the precipitate was redispersed in dried toluene for further use.

Mixed anion synthesis of colloidal solution of pristine CsPbX3 (X = (Cl0.5/Br0.5) and Br0.4/I0.6) PNCs

The mixed anion compositions of CsPb(Cl0.5/Br0.5)3 and CsPb(Br0.4/I0.6)3 PNCs were synthesized as described above, for the synthesis of CsPb(Cl0.5/Br0.5)3 PNCs, PbCl2 (0.094 mmol; 0.026 g) PbBr2 (0.094 mmol; 0.035 g) and for the synthesis of CsPb(Br0.4/I0.6)3, PbBr2 (0.076 mmol; 0.0261 g) and PbI2 (0.112 mmol; 0.0516 g) were added into a 50 mL three-necked flask containing 5 mL of ODE and heated at 120 °C for 1 h under vacuum. Dried OLA (0.5 mL) and OA (0.5 mL) at 100 °C were injected into the PbX2-ODE solution at 120 °C under Ar flow. After the solution turned clear, the temperature was raised to 140–160 °C and the Cs-oleate solution (0.5 mL) was quickly injected into the PbX2-ODE solution, and 30 s later, the reaction mixture was cooled by an ice-water bath. As the synthesized solution was purified by centrifuging for 5 min at 8000 rpm, and the supernatant was discarded and the process is repeated for a couple of times. Subsequently, the particles in the centrifuge tube were dispersed again in 5 ml of toluene.

Purification of as-synthesized PNCs

As-synthesized CsPbX3 (X = Cl, Br, I, (Cl0.5/Br0.5), and (Br0.4/I0.6)) PNCs were extracted from the crude solution by centrifuging at 8000 rpm for 5 min, and the supernatant is discarded. This process was repeated for one more time by adding 3 ml MeOAc and centrifuged to remove the residual mixture. Then, the precipitate was redispersed in 2 ml MeOAc and 2 ml n-hexane and centrifuged again for 5 min at 8000 rpm, and the supernatant was discarded. Subsequently, the particles in the centrifuge tube were dispersed again in 4 ml n-hexane and centrifuged for 5 min at 5000 rpm supernatant was discarded. Finally, the precipitate was re-dispersed in toluene (or n-hexane for optical characterization) forming stable colloidal solutions. For solid NCs, the

Address correspondence to Varnakavi Naresh, [email protected]; Nohyun Lee, [email protected]

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precipitate obtained in the above step was dried under vacuum at 60 °C overnight. (MeOAc was added only for CsPbCl3, CsPbBr3 and CsPb(Cl0.5/Br0.5)3 PNCs).

Synthesis of SiO2 encapsulated PNCs

For the synthesis of SiO2 encapsulated PNCs, TMOS and colloidal PNCs toluene solution were taken in the molar ratio of 1:10 into 25 mL single neck flask and stirred continuously at room temperature for 10-12 h. Then, the solution was centrifuged at 10000 rpm for 10 min, the precipitate was collected and dried in vacuum at room temperature overnight. Thus, obtained PNCs @ SiO2 composite powder can be dispersed in n-hexane or toluene for further use.

Preparation of PNCs@SiO2/PMMA composite films

For the preparation of PNCs @SiO2/PMMA composite films, 1.5 g PMMA powder (Mw 350, 000) and 10 ml toluene were taken into 25 ml flask and stirred vigorously at 80 °C (overnight) until the PMMA powder dissolves completely and the solution becomes transparent and colorless. Then, CsPbX3 (X = Cl, Br, I, (Cl0.5/Br0.5), and (Br0.4/I0.6)) PNCs @SiO2 composite powders were added to PMMA dissolved toluene solution and stirred vigorously homogeneously dispersed NCs in PMMA solution blend. Thus, the resultant solution blend was drop-casted on a concave 'U' shaped mold and pressed with a convex 'D'' shaped mold to remove the excess , later dried in a vacuum chamber for polymerization. Finally, curvved PNCs-blended solid PMMA films were obtained (PNCs @SiO2/PMMA composite films).

Designing of PNCs @SiO2/PMMA coated LED

For the construction of the prototype, white LED device, individually blue-green-red emitting CsPb(Cl0.5/Br0.5)3, CsPbBr3 and CsPb(Br0.4/I0.6)3 PNCs @SiO2/PMMA composite layers were integrated to the 365 nm UV LED. Schematic diagram of fabricated LED is shown in the inset of Fig. S9(a).

Characterizations XRD patterns were recorded on a Bruker DE/D8 Advance X-ray Diffractometer equipped with Cu Kߙ (ߣ = 1.541 Å) radiation source operated at 60kV and 60 mA at room temperature. The samples were provided in dry powder form and scanned within the range of 2θ from 10 to 60°. The morphology of the as-synthesized perovskite nanocrystals was investigated from the transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) images acquired on a JEM-2100/ JEOL/ JP operated at 200 kV accelerating voltage. The 300 mesh copper Formvar/carbon grid was dipped into the PNCs dispersed toluene solution and allowed to dry in ambient conditions overnight. The X-ray photoelectron spectroscopy (XPS) measurement was conducted on an Ulvac PHI/X-tool spectrometer with Al Kߙ radiation source (1486.6 eV, 24.1W, 15kV) and a beam diameter of 100μm×100μm. UV-Vis absorption spectra were measured in the range of 300-700 nm on a Shimadzu UV-2600 spectrometer. The CsPbX3 (X = C, Br, I) NCs dispersed in toluene were used for the absorption measurement. The steady-state fluorescence spectra (PL and PLE) were recorded using a Shimadzu RF-6000 Spectro-fluoro-photometer equipped with a 150 W Xe lamp as an excitation and scanning speed 60,000 nm/min. The time-resolved decay curves of the samples were measured on a HORIBA Jobin Yvon FluoroMax-4 fluorescence spectrometer equipped with a 150 W Xe lamp as an excitation source at room temperature. The PLQY of the PNCs dispersed toluene solutions were measured by employing an integrated sphere unit attached to Shimadzu RF-6000 Spectro-fluoro- photometer according to the standard procedure using Toluene as a reference under ambient conditions. Electroluminescence spectra were measured on Labsphere CdS-610 spectrometer. The Photo-stability measurement was carried for freshly synthesized CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) PNCs solutions and CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) @SiO2/ PMMA composite films by continuous irradiating with a UV lamp (365 nm, 6W) placed at a distance of 10 cm for 25 days under vacuum condition. The effect of moisture (water-stability test) on the bare and coated PNCs were evaluated by soaking 2.5 mL of PNCs solution in 2.5 mL of deionized water for 25 days and films are immersed in 15 ml of water under vacuum condition.

Fig. S1 (a) EDS signals and elemental mapping images of Cs, Pb, Cl, Br, Si and O in SiO2 coated CsPb(Cl0.5/Br0.5)3 PNCs.

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Fig. S2 (b) EDS signals and elemental mapping images of Cs, Pb, Br, Si and O in SiO2 coated CsPbBr3 PNCs.

Fig. S3 (c) EDS signals and elemental mapping images of Cs, Pb, Br, I, Si and O in SiO2 coated CsPb(Br0.4/I0.6)3 PNCs.

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Table S1 The elemental composition of pristine CsPb(Cl0.5/Br0.5)3, CsPbBr3, and CsPb(Br0.4/I0.6)3 PNCs PNCs Cs Pb Cl Br I Composition (At %) (At %) (At %) (At %) (At %)

CsPb(Cl0.5/Br0.5)3 19 21 30 30 -

CsPbBr3 18 20 - 62 -

CsPb(Br0.4/I0.6)3 20 17 - 25.2 37.8

Fig. S4 (a) Diffraction patterns of pristine CsPb(Cl0.5/Br0.5)3, CsPbBr3 and CsPb(Br0.4/I0.6)3 PNCs compared with the standard ICSD pattern (b) SiO2/PMMA

composite film.

Fig. S5 (a-c) Spectral overlap of PL spectra of pristine CsPbX3 (X = Cl0.5/Br0.5, Br, and (Br0.4/I0.6)) PNCs and CsPbX3 (X = Cl, (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) PNCs @SiO2/PMMA composites exhibiting shift in peak positions.

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Fig. S6 (a-c) The emission decay curves of all-inorganic CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) PNCs immersed in the solution, PNCs @PMMA films, PNCs @SiO2, and PNCs @SiO2/PMMA composites.

Table S2 The average lifetimes of all-inorganic CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) PNCs immersed in the solution, PNCs @PMMA films, PNCs

@SiO2, and PNCs @SiO2/PMMA composites.

@solution @PMMA film @SiO2 @SiO2/PMMA Sample avg (ns) avg (ns) avg (ns) avg (ns)

CsPb(Cl0.5/Br0.5)3 PNCs 4.26 3.35 10.28 10.10

CsPbBr3 PNCs 14.12 10.68 23.62 21.82

CsPb(Br0.4/I0.6)3 PNCs 19.83 16.78 38.75 35.46

Fig. S7 PLQY measurement of of pristine CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6))PNCs and CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) PNCs @SiO2/PMMA composites

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Table S3 Average lifetimes (τavg) of PL decay curves, PLQYs, radiative (τr) and non-radiative (τnr) decay rates of CsPbX3 (X = (Cl0.5/Br0.5), Br and

(Br0.4/I0.6)) PNCs @SiO2/PMMA Composite films.

τavg PLQY τr τnr Sample (ns) (%) (ns-1) (ns-1)

CsPb(Cl0.5/Br0.5)3 @ SiO2/PMMA 10.10 36.53 0.036 0.0062

CsPbBr3@ SiO2/PMMA 21.82 85.53 0.039 0.0066

CsPb(Br0.4/I0.6)3@ SiO2/PMMA 35.46 71.27 0.020 0.0081 2 aii PLQY (%) 1(%) PLQY , where  avg  ,  r  ,  nr  . aii  avg  avg

Fig. S8 TEM micrographs of pristine CsPbBr3 PNCs at different temperatures, (a) @ room temperature, (b) @ 40 ºC, (c) @ 60 ºC, (d) @ 80 ºC, (e) @ 100 ºC, (f) @ 100 ºC for 5 min, (g) @ 100 ºC for 10 min, and (h) @ 100 ºC for 15 min.

Fig. S9 (a-c) Photo-stability test (relative PL intensity depending on time) of pristine CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6))PNCs and CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6)) PNCs @SiO2/PMMA composite films.

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Fig. S10 Digital images of CsPbX3 (X = (Cl0.5/Br0.5), Br, and (Br0.4/I0.6))PNCs dispersed in toluene, PNCs@SiO2 composite in dry powder form and PNCs@SiO2/PMMA composite films

Table S4 Summary and comparison of thermal-, photo (UV)-, and water (moisture) stability tests conducted for CsPbX3 (X = Cl/Br, Br and Br/I) PNCs

@SiO2/PMMA composite films representing relative PL intensity remained relative to pristine CsPbX3 (X = Cl/Br, Br and Br/I) PNCs.

Photo Stability Water stability PLQY Thermal stability Composite (365 nm, 6W for (in Di water References (%) (at 100 ºC) 25 days) For 25 days)

CsPb(Cl0.5/Br0.5)3 @ SiO2/PMMA 36.53 % 54.61% 67.36% 76.2% Present work

CsPbBr3 @ SiO2/PMMA 78.53 % 69.88% 83.48% 86.5% Present work

CsPb(Br0.4/I0.6)3 @ SiO2/PMMA 71.27 % 58.34% 79.18% 77.4% Present work

CsPbBr3 @ PMMA 70 % - - 90% (12 h) 1

SR/PVP-CsPbBr3 45 % 65% 85% (120 h) - 2 PMMA-SQD thin film 62.3% 62.8% (54 h) 91% 3

CsPbBr3 @PVDF composite film 80% (7 days) 4

CsPb(Cl/Br)3 @PVDF thin film CsPb(Br/I)3 @PVDF 18% (7 days) 4 thin film 42% (7 days)

CsPbBr3/SiO2 QD 66% 72% 95% 5

Fig. S11 (a) Photographs of the CsPbX3 (X = Cl, (Cl0.5/Br0.5), Br, (Br0.4/I0.6) and I) PNCs @SiO2/PMMA composite films upon irradiating with 365 nm UV lamp and their corresponding electroluminescence spectra (inset fig: schematic diagram of the constructed white LED unit). (b) EL spectrum of combined CsPb(Cl/Br)3 and CsPbBr3 composite films, (c) EL spectrum of combined CsPbBr3 and CsPb(Br/I)3 composite films, (d) CIE coordinates of CsPbX3 (X = Cl, (Cl0.5/Br0.5), Br, (Br0.4/I0.6) and I) PNCs @SiO2/PMMA composite films. Inset figures are the combination of CsPb(Cl0.5/Br0.5)3 and CsPbBr3 composite films and combination of CsPbBr3 and CsPb(Br0.4/I0.6)3 composite films under UV lamp.

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Fig. S12 Correlated color temperature (CCT(K)), color rendering index (CRI), and luminescence efficiency (LE (lm/W)) versus driving current (mA) for the designed white-LED device.

Table S5 Electroluminescence parameter of the designed white-LED device Driving CCT LE CIE Coordinates CRI Current (mA) (K) (lm/W) 20 (0.3497,0.3505) 4821 84.8 39.2 40 (0.3393,0.3592) 5240 85.6 31.6 60 (0.3348, 0.3563) 5409 86.3 26.9 80 (0.3336, 0.3559) 5453 86.9 20.7 100 (0.3325,0.3597) 5497 87.4 15.8

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