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Electronic Supplementary Information (ESI)

The Controllable and Reversible Phase Transformation between

All-inorganic Perovskites for High-quality White Light Emitting

Diodes

Shengnan Liu a, Yifei Yue a, Xiaohua Zhang c, Chenxu Wang* b, Guochun Yang* c and

Dongxia Zhu* a

a Key Laboratory of Nanobiosensing and Nanobioanalysis at Universities of Jilin

Province, Department of Chemistry, Northeast Normal University, 5268 Renmin Street,

Changchun, Jilin Province 130024, P.R. China.

E-mail: zhudx047@nenu.edu.cn.b Public Technical Service Center, Northeast Institute of Geography and Agroecology,

Chinese Academy of Sciences, Changchun 130102, P.R. China.

E-mail: wangchenxu@iga.ac.cnc Center for Advanced Optoelectronic Functional Materials Research and Key

Laboratory for UV Light-Emitting Materials and Technology of Ministry of Education,

Northeast Normal University, Changchun 130024, P. R. China.

E-mail: yanggc468@nenu.edu.cn

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2020

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Table of Contents

1. Experimental Section S3

2. Supporting Figures S7

3. Supporting Tables S25

4. References S28

5. Supporting Movie

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Experimental SectionChemicals and Materials:

Cesium iodide (CsI, 99.0%), Copper iodide (CuI, 99.0%), Dimethylsulfoxide (DMSO,

99.5%), N,N-dimethylformamide (DMF, 99.5%), Dichloromethane (DCM, 99.5%),

Methanol (99.5%), Ethanol (99.7%), Isopropanol (99.7%), n-butanol(99.0%),

Chloroform(99.0%), Toluene (99.0%), Ethyl acetate (EA, 99.5%),

Polymethylmethacrylate (PMMA). All chemicals were directly used without further

purification.

Synthetic Methods:

Synthesis of Cs3Cu2I5: An amount of 1.5588 g (6 mmol) CsI, 0.7618 g (4 mmol) CuI,

5 mL DMSO and 5 mL DMF were loaded into a 50 mL round bottom flask and heated

under N2 in dark at 60°C for 4.5 h. The solution was cooled down to room temperature.

35 mL DCM was added into 5 mL precursor solution and stirred for 30 min. The product

was obtained by centrifugation. Obtained product and DCM (10 mL) were loaded into

a 50 mL centrifuge tube. Then the mixture was ultrasonically shaken for 5 minutes. The

supernatant was removed after centrifugation. The above steps were repeated 3 times.

The product was dried at 68°C for 6h.

Synthesis of CsCu2I3: 0.15 g Cs3Cu2I5 was added into 15 mL methanol and stirred for

1 h. The product was obtained by centrifugation. The supernatant was removed after

centrifugation. The product was dried at 68°C for 6h.

Solvent Treatment:

Ethanol Treatment: 0.15 g Cs3Cu2I5 was added into 15 mL ethanol and stirred for 1 h

and then centrifuged to obtain 1-hour ethanol treated product. 1-hour ethanol treated

product was added into 15 mL ethanol and stirred for 1 h and then centrifuged to obtain

2-hour ethanol treated product. 2-hour ethanol treated product was added into 15 mL

ethanol and stirred for 1 h and then centrifuged to obtain 3-hour ethanol treated product.

3-hour ethanol treated product was added into 15 mL ethanol and stirred for 1 h and

then centrifuged to obtain 4-hour ethanol treated product. 4-hour ethanol treated product

was added into 15 mL ethanol and stirred for 1 h and then centrifuged to obtain 5-hour

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ethanol treated product. 5-hour ethanol treated product was added into 15 mL ethanol

and stirred for 1 h and then centrifuged to obtain 6-hour ethanol treated product. All the

products were dried at 68°C for 6h.

Ethanol and Methanol Treatment: 0.15 g Cs3Cu2I5 was added into 15 mL ethanol and

methanol mixture (the volume ratio of ethanol to methanol is 1: 0, 2: 1, 1: 1, 1: 2 and

0: 1) and stirred for 1 h and then centrifuged to obtain product. All the products were

dried at 68°C for 6h.

Ethanol and Isopropanol Treatment: 0.15 g Cs3Cu2I5 was added into 15 mL ethanol and

isopropanol mixture (the volume ratio of ethanol to isopropanol is 1: 0, 2: 1, 1: 1, 1: 2

and 0: 1) and stirred for 1 h and then centrifuged to obtain product. All the products

were dried at 68°C for 6h.

Ethanol and Water Treatment: 0.15 g Cs3Cu2I5 was added into 15 mL ethanol and water

mixture (the volume ratio of ethanol to water is 1: 0, 1: 1, 1: 2, 1: 3, 1: 4, 1:5 and 0: 1)

and stirred for 1 h and then centrifuged to obtain product. All the products were dried

at 68°C for 6h.

Other Solvent Treatment: 0.15 g Cs3Cu2I5 was added into 15 mL solvent (N-butanol,

chloroform, DCM, toluene and ethyl acetate) and stirred for 1 h and then centrifuged to

obtain product. All the products were dried at 68°C for 6h.

CsI Solution Treatment: 0.9 g CsI was added into 30 mL methanol and stirred to

dissolve. 0.05 g CsCu2I3 was added into CsI solution and stirred for 1 h and then

centrifuged to obtain product. All the products were dried at 68°C for 6h.

Preparation of films with acetonitrile and DMSO: The 10 mg/mL CsCu2I3 solution was

prepared with solvent of acetonitrile or DMSO, respectively. They were used to make

films by drop-casting respectively on quartz plates. The films were dried at 80°C.

Measures and characterization:

Field-emission scanning electron microscope (FESEM) images, the contents of

elements of the samples and energy dispersive X-ray spectroscopy mapping were

obtained using a HITACHI SU8010. Solid-state XRD patterns were recorded using an

X-ray diffractometer with SmartLab system. Absorption spectra were obtained by

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Cary7000 UV-Vis-NIR Spectrophotometer with a calibrated integrating sphere. The

emission spectra were recorded by an F-7000 FL spectrophotometer. The excited-state

lifetime and photoluminescence quantum yields (PLQYs) of the powders were

measured using a transient spectrofluorimeter (Edinburgh FLS920P). The absolute

PLQY of the film was measured using an integrating sphere integrated to HORIBA

FL3C-111. Atomic force microscopy (AFM) was measured using a SPA 300HV with

a SPI 3800 N controller (Seiko Instruments, Inc., Japan) in tapping mode.

Computational method:

Structural optimization and electronic property calculations were carried out within

density functional theory (DFT)1, 2 as implemented in the Vienna Ab initio Simulation

Package (VASP)3. Considering both of accuracy and computational efficiency, the

Perdew-Burke-Ernzerhof generalized gradient approximation (GGA)4 exchange and

correlation functional was used as compromise. The scalar relativistic projector

augmented wave (PAW)5 pseudopotentials were adopted to describe electron-ion

interaction, with 5s25p66s1, 3d104s1, and 5s25p5 valence electrons for Cs, Cu, and I

atoms, respectively. The cutoff energy was set at 800 eV, and a Monkhorst-Pack6 k-

point grids with a reciprocal space resolution of 2π×0.03 Å-1 in the Brillouin zone were

selected to ensure that all enthalpy calculations converged to less than 1 meV per atom.

Device preparation and characterization:

The WLEDs are fabricated with a structure of ITO/PEDOT: PSS (40 nm)/V-NPB (20

nm)/ Cu-based perovskite (20 nm)/SPPO13(50 nm)/LiF(1 nm)/Al (100 nm). The

PEDOT:PSS dispersed in water was spin-coated onto the pre-cleaned and ultraviolet-

ozone (UVO) treated ITO substrates to form a 40 nm thick film, and then baked at 120

oC for 30 min in air condition. After transferring the substrates to glovebox, the hole-

transporting material V-NPB was spin-coated onto PEDOT: PSS from its

chlorobenzene solution, and then annealed at 180 oC for 1 h to complete the cross-

linking and form a 20 nm thick solvent-resistant film. The Cu-based perovskite was

spin-coated onto V-NPB at 1500 rpm for 60 s from its ACN solution with a

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concentration of 15 mg ml-1. After that, the structure of SPPO13(50 nm)/LiF (1 nm)/Al

(100 nm) was deposited with thermal evaporation at a base pressure under 4×10-4 Pa to

complete the device with area of 14 mm2. Before testing, the devices were encapsulated

with glass in glovebox. The current density-voltage-luminance (J-V-L) characteristics

were measured by using a Keithley source measurement unit (calibrated silicon

photodiode, Keithley 2400 and Keithley 2000), and the EL spectra and CRI were

measured by using a CS2000A spectrometer. The EQE was calculated from the

luminance, current density and EL spectra assuming a Lambertian distribution.

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Fig. S1. a) XRD pattern of Cs3Cu2I5 compared to the standard XRD pattern of Cs3Cu2I5.

b) Crystal structure of Cs3Cu2I5 (green, purple and red represent Cs, Cu, and I,

respectively). c) DOS plots of Cs3Cu2I5.

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Fig. S2. Crystal structure of CsCu2I3 (green, purple and red represent Cs, Cu, and I,

respectively).

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Fig. S3. FESEM image of Cs3Cu2I5 (a, b) and CsCu2I3 (c, d).

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Fig. S4. a) DFT calculations of band structures for Cs3Cu2I5. b) Enlarged (from -0.4 to

0.2 eV ) DFT calculations of band structures for Cs3Cu2I5. c) DFT calculations of band

structures for CsCu2I3.

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Fig. S5. a) Normalized UV-vis absorption spectra of CsCu2I3 and Cs3Cu2I5. b) Time-

resolved PL decay curve of CsCu2I3 and Cs3Cu2I5.

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Fig. S6. CIE color coordinates of Cs3Cu2I5 and CsCu2I3 and inset photos of blue

emission Cs3Cu2I5 and yellow emission CsCu2I3 under UV illumination (254 nm).

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Fig. S7. XRD pattern of CsCu2I3 and of CsCu2I3 after 3.5 months placed in the air.

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Fig. S8. a) Enlarged (from 10 to 35 degree) XRD pattern of one-hour ethanol treated

product (blue triangles to Cs3Cu2I5 characteristic peaks and yellow squares to CsCu2I3

characteristic peaks). b) Normalized UV-vis absorption spectrum of ethanol treated

product. c) Energy dispersive X-ray spectroscopy mapping of ethanol treated product.

CsCu2I3 is shown as rod-shaped crystal and another crystal is one representative

Cs3Cu2I5. The same signal strength of I are observed in the two materials, which can be

attributed to the same theoretical content of I in both materials (element content: 50%).

The data obviously shows that the theoretical content of Cs in Cs3Cu2I5 is higher than

that in CsCu2I3 (yellow part in Fig. S8c, Cs content: 30% of Cs3Cu2I5 and 16.7% of

CsCu2I3), and the theoretical content of Cu in CsCu2I3 is higher than that in Cs3Cu2I5

(Cu content: 33.3% of CsCu2I3 and 20% of Cs3Cu2I5).

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Fig. S9. FESEM image of Cs3Cu2I5 (a), product treated by ethanol for 1 h (b), product

treated by ethanol for 6 h (c) and CsCu2I3 (d).

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Fig. S10. a) XRD patterns of ethanol treated products (obtained by stirring Cs3Cu2I5 in

ethanol for different time: 0 h, 1 h, 2 h, 3 h, 4 h, 5 h and 6 h). b) Enlarged (from 10 to

35 degree) XRD patterns of ethanol treated products (blue triangles to Cs3Cu2I5

characteristic peaks and yellow squares to CsCu2I3 characteristic peaks). c) Normalized

PL spectra of ethanol treated products. d) Ratios of the emission peak intensity at 555

nm to that at 437 nm for ethanol treated products. e) XRD patterns of ethanol and

methanol treated products (obtained by stirring Cs3Cu2I5 in different volume ratio of

ethanol and methanol the volume ratio of ethanol to methanol is 1: 0, 2: 1, 1: 1, 1: 2 and

0: 1). f) Enlarged (from 10 to 35 degree) XRD patterns of ethanol and methanol treated

products (blue triangles to Cs3Cu2I5 characteristic peaks and yellow squares to CsCu2I3

characteristic peaks). g) Normalized PL spectra of ethanol and methanol treated

products. λex= 327 nm h) Ratios of the emission peak intensity at 555 nm to that at 437

nm for ethanol and methanol treated products. While the ratios of ethanol to methanol

are 1: 2 and 0: 1，the Cs3Cu2I5 characteristic peaks cannot be observed in the XRD

patterns and the emission peak at 437 nm disappears, suggesting that the transformation

is almost complete in these solvent ratios.

As shown in Fig. S10d and h, the enhanced yellow emission intensity and the reduced

blue emission intensity indicate the increase of phase transformation rate, and content

of Cs3Cu2I5 is reduced in accordance to the increase of reaction time or solvent polarity.

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Fig. S11. a) XRD patterns of ethanol and isopropanol treated products (obtained by

stirring Cs3Cu2I5 in different volume ratio of ethanol and isopropanol the volume ratio

of ethanol to isopropanol is 1: 0, 2: 1, 1: 1, 1: 2 and 0: 1). b) Enlarged (from 10 to 35

degree) XRD patterns of ethanol and isopropanol treated products (blue triangles to

Cs3Cu2I5 characteristic peaks and yellow squares to CsCu2I3 characteristic peaks). c)

Normalized PL spectra of ethanol and isopropanol treated products obtained. λex= 327

nm d) XRD patterns of ethanol and water treated products (obtained by stirring

Cs3Cu2I5 in different volume ratio of ethanol and water the volume ratio of ethanol to

isopropanol is 1: 0, 1: 1, 1: 2, 1: 3, 1: 4, 1: 5 and 0: 1). e) Enlarged (from 10 to 35

degree) XRD patterns of ethanol and water treated products (blue triangles to Cs3Cu2I5

characteristic peaks, yellow squares to CsCu2I3 characteristic peaks and purple

hexagons to CuI characteristic peaks). f) Normalized PL spectra of ethanol and water

treated products. λex= 327 nm The transformation rate gradually decreases with

isopropanol content increasing. Only a few Cs3Cu2I5 can be transformed into CsCu2I3

in pure isopropanol. This incomplete transformation can be caused by weak-polar of

isopropanol. However, while the solvents turn into a mixture of water and ethanol, the

product has a different change. As shown in XRD pattern, a large amount of CuI exist

in the products stirred in high-water-content solvents (ethanol to water < 4: 1). In PL

spectra, the emission at 420-424 nm belongs to CuI, indicating the transformation is

from Cs3Cu2I5 to CsCu2I3 and then to CuI in this two-solvent system. The thorough

transformation can be attributed to the strong-polarity of water.

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Fig. S12. a) Normalized PL spectra of products obtained by stirring Cs3Cu2I5 in

different solvents (n-butanol, chloroform, dichloromethane, toluene and ethyl acetate)

λex= 327 nm. b) Enlarged (from 530 to 580 nm) normalized PL spectra of products

obtained by stirring Cs3Cu2I5 in different solvents. c) Normalized PL spectra of the

products obtained by stirring the same amount of Cs3Cu2I5 in more volume of relevant

solvent. d) Normalized PL spectra of the different solvent-treated products compared

with those of the products treated with the same volume of methanol and ethanol.

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Fig. S13. XRD pattern of CsI obtained by evaporating supernatant compared to the

standard XRD pattern of CsI.

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Fig. S14. a) XRD pattern of product obtained by stirring CsCu2I3 in CsI solution

compared to the standard XRD pattern of Cs3Cu2I5. b) Normalized PL spectra of

products obtained by stirring CsCu2I3 in CsI solution and Cs3Cu2I5. λex= 327 nm

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Fig. S15. Enlarged (from 10 to 35 degree) XRD patterns of the films obtained by drop-

casting the solutions through dissolved CsCu2I3 with DMSO and ACN (blue triangles

to Cs3Cu2I5 characteristic peaks and yellow squares to CsCu2I3 characteristic peaks).

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Fig. S16. The image of CsCu2I3 solutions with DMSO and ACN as solvent, starch

solutions and the starch solutions after CsCu2I3 solutions added. More I2 exist in the

CsCu2I3 solutions with DMSO as solvent than that with ACN as solvent.

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Fig. S17. Performance for the device with the the light emitting layer obtained by spin-

coating the CsCu2I3 solution in DMSO: a) Electroluminescent (EL) spectra at 4.8 V. b)

Current density-voltage-luminance (J-V-L) characteristics. c) Current efficiency and

power efficiency as a function of luminance.

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Fig. S18. AFM images of films prepared with CsCu2I3 solution in ACN (a) and DMSO

(b).

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Table S1. Perovskite-based WLEDs examples.

Device structure Emitting layerLE

(cd/A)

EQE

(%)

Lmax

(cd/m2)

CIE

coordinatesCRI

Refer

-ences

ITO/ZnO/PEI/ZnCdS/ZnS/CsPb(Br1.65/I1.35)/TCTA/MoO3/Au ZnCdS/ZnS/CsPb(Br1.65/I1.35) − 0.015 275 (0.34, 0.34) 75 7

ITO/PEDOT:PSS/PA2CsPb2I7/BIPO:PolyTPD/CsPb(Br, Cl)3/TPBi/LiF/Al PA2CsPb2I7/CsPb(Br, Cl)3 − 0.22 − (0.32, 0.32) − 8

ITO/NiOx/PEDOT:PSS/HFSO/CsPb(Br1.5I1.5)/Ca/Al HFSO/CsPb(Br1.5I1.5) 0.48 − 1200 (0.28, 0.33) − 9

ITO/NiOx/CsPb(Brx/l3-x)/MEH:PPV/TPBi/LiF/Al CsPb(Brx/l3-x)/MEH:PPV − − 105 (0.33,0.34) − 10

ITO/PEDOT:PSS/MAPbBr3/compound 1/compound 2/PBD/ LiF /Al MAPbBr3/compound 1/compound 2 − 0.001 − (0.3, 0.49) 27.5 11

ITO/ PEDOT:PSS/V-NPB / Cu-based perovskites/ SPPO13/LiF /Al Cu-based perovskites 0.11 0.053 352.3 (0.327,0.348) 94This

work

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Table S2. Energy dispersive X-ray spectroscopy (EDS) data

Sample Cs (%) Cu (%) I (%)

Cs3Cu2I5 37.10 18.92 43.98

CsCu2I3 22.54 33.30 44.16

Ethanol-1 h 33.86 22.93 43.21

Ethanol-6 h 22.09 33.39 44.52

Film (ACN) in the device 21.89 32.16 45.95

Film (DMSO) in the

device

26.99 29.47 43.53

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Table S3. Summary of the devices performance for the white and blue light-emitting

diodes.

a: The light emitting layer of the white device is obtained by spin-coating the CsCu2I3

solution in ACN.

b: The light emitting layer of the blue device is obtained by spin-coating the CsCu2I3

solution in DMSO.

Max performance Performance at 100 cd m-2

DevicesVon

(V)L

(cd/m2)

LE

(cd/A)

PE

(lm/W)

EQE

(%)

Vd

(V)

LE

(cd/A)

PE

(lm/W)

EQE

(%)

CIE (x,y)

Whitea

Blueb

2.9

2.9

352.3

1113.3

0.11

0.16

0.083

0.069

0.053

0.12

4.4

4.8

0.11

0.045

0.075

0.030

0.053

0.031

(0.327,0.348)

(0.183,0.203)

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