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Supporting Information

Unveiling the Critical Role of Ammonium Bromide in Blue Emissive Perovskite Films

Xuechun Wanga, Lei Caia, Yatao Zou*a, Dong Lianga, b, Lu Wanga, Ya Lia, Jiaqing Zanga, Guilin Baia,

Xingyu Gaob, Tao Song*a, Baoquan Sun*a, c

a. Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano

& Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional

Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, 215123, Jiangsu, China.

E-mail: yataozousuda@163.com; tsong@suda.edu.cn; bqsun@suda.edu.cnb. Shanghai Synchrotron Radiation Facility (SSRF), Shanghai Institute of Applied Physics, Chinese

Academy of Sciences, 239 Zhangheng Road, Pudong New Area, Shanghai 201204, China.c. Macao Institute of Materials Science and Engineering, Macau University of Science and Technology,

Taipa 999078, Macau SAR, China.

Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2021

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Figure S1. Optical characterizations of CsPbBr3 films with different ammonium bromides and proportions.

a, Molecular structure of BDA2+ , BA+ and MA+ cations. b, UV-vis absorption (dash line) and PL spectra

(solid line) of the perovskite films. c, The corresponding digital images of the perovskite films under a 365

nm UV lamp. All the perovskite films were annealed before the test.

Since the incorporation of different ammonium cations may also result in the loading of different

proportions of Br- at the same time, one may concern that the Br- will also affect the bandgap, crystal lattice,

luminescence characteristics of the perovskite films. Although we could not completely exclude this

possibility, we may rule out the main factor of different Br- ratios determining the quality of perovskite

emitters as below. Firstly, in these monoammonium bromides loaded perovskite films, such as PEABr,

BABr, and EABr, when keeping the proportion of Br- same, the perovskite films show quite different

properties, as shown in Figure 1, Figure S1, Figure 2a, and Figure S2. In addition, the emission wavelength

of the MABr-based films shows negligible difference with increasing the ratio of MABr, which may

indicate that the Br- has no impacts on the bandgap and crystal lattice of perovskites. Accordingly, it is safe

for us to conclude that the ammonium cations should be the main factor determining the characteristics of

the perovskite films rather than the proportion of Br- anions.

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400 450 500 550 600 650 700

10 min

20 min

30 min

1 h

2 h

Wavelength (nm)

HDABr2

400 450 500 550 600 650 700

2 h

1 h

30 min

20 min

10 min

Wavelength (nm)

EDABr2

400 450 500 550 600 650 700

1 h

30 min

20 min

10 min

2 h

Nor

mal

ized

PL

Inte

nsity

(a.u

.)

Wavelength (nm)

EABra b c

Figure S2. Normalized PL spectra of perovskite films with different ammonium bromides annealed at 80

℃ for different time to estimate their thermal stability. a, EABr; b, EDABr2; c, HDABr2.

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20

30

40

50

60

70

80

90

HDABr2EDABr2PEABr

PLQ

E (%

)

EABr 50 100 150 200 250 300101

102

103

104 CsPbBr3

EABr PEABr EDABr2

HDABr2

Inte

nsity

(cou

nts)

Time (ns)

a b

Figure S3. a, PLQEs of the sky-blue perovskite films with different ammonium bromides. The PLQEs

were conducted with a 405 nm laser under a light intensity of ~0.2 mW cm-2. b, TCSPC measurement of

the sky-blue perovskite films. The fitted average lifetime were sumarrized in Table S3.

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Figure S4. Characterizations of the PEA2PbBr4 (n = 1) and HDAPbBr4 (n = 1) perovskite films. a, XRD

patterns. b, Schematic illustration of structure and d-spacing of n = 1 low-dimensional R-P (left) and D-J

(right) perovskites.

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10 20 30

EABr

EDABr2

Inte

nsity

(a.u

.)

2Theta (degree)

CsPbBr3

(101)(121) (202)

Figure S5. XRD patterns of control films and perovskite films with EABr and EDABr2.

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-3

-2

-1

0

1

2

3

E-E f (

eV) Eg=1.80 eV

ΓΓ U XZ

a b

c

-3

-2

-1

0

1

2

3

Eg=2.56 eV

E-E f (

eV)

ΓΓ U XZ

d

-1

0

1

2

3

Eg=2.32 eV

E-E f (

eV)

ΓΓ U XZ

e f

Figure S6. Simulated density of states (PDOS) and band structures from DFT calculations for a-b, CsPbBr3

perovskite, c-d, EDA2+ incorporated and e-f, BDA2+ incorporated CsPbBr3 perovskites. The Fermi level is

defined at zero.

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18 17 16 15 14 4 3 2 1 0

Inte

nsity

(a.u

.)

Binding energy (eV)

CsPbBr3

CsPbBr3+EDABr2

-6

-5

-4

-3

CsP

bBr 2

+ED

AB

r 2

-3.61

-6.09

-3.51

Ener

gy (e

V)

-5.84

CsP

bBr 3

a b

Figure S7. Characterization of the band structure of the control sample and EDA2+ incorporated “hollow”

perovskite. a, UPS data. b, Schematic illustration of the VB and CB values of control and EDA2+

incorporated “hollow” perovskite.

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20 40 60 80 100 120

PEABr

EABr

In

tens

ity (a

.u.)

HDABr2

Azimuth (degree)

EDABr2

Figure S8. Azimuthal integration of (020) plane GIWAXS patterns in the CsPbBr3 perovskite films with

different ammonium bromides.

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Figure S9. Characterizations of the performance of PeLEDs with different ammonium bromides. a, Device

structure. b, Energy alignment. c, J-V-L curve. d, EQE-J curve. e, The corresponding CIE coordinates.

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400 425 450 475 500 525 550 575 600

4 V 5 V 6 V

40% EDABr2+20% PEABr

Wavelength (nm)400 425 450 475 500 525 550 575 600

4 V 5 V 6 V 7 V 8 V

60% EABr+20% PEABr

Nor

mal

ized

EL

Inte

nsity

(a.u

.)

Wavelength (nm)

a b

Figure S10. EL stability of EABr and EDABr2 based PeELDs with additional PEABr. a, EABr. b, EDABr2.

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Figure S11. The luminance decay curves of blue perovskite devices with different additives. a, EABr or

EDABr; b, Dual additives of PEABr and EABr or EDABr. An initial luminance of around 100 cd m-2 was

set to measure the luminance decay.

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Table S1. Summarized the effective ionic radii (reff) of perovskite and investigated ammonium cations, as

well as the calculated tolerance factor (t) of different ammonium cations-formed perovskite.

Ions Pb2+ Br- Cs+ EDA2+ BDA2+ HDA2+ PEA+ BA+ EA+ MA+

reff (Å) 1.19 1.96 3.93

t

1.67

0.81

3.33

1.19

4.57

1.47

5.82

1.75

4.31

1.41 1.29

2.74

1.05

2.17

0.93

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Table S2. Recipes for perovskite precursor solutions with different ratios of ammonium halides (MBr =

PEABr, EABr, HDABr2, EDABr2, BDABr2, BABr, and MABr).

Sample CsBr

[mmol mL-1]

PbBr2

[mmol mL-1]

MBr

[mmol mL-1]

Control 0.2 0.2 -

20% MBr 0.2 0.2 0.04

40% MBr 0.2 0.2 0.08

60% MBr 0.2 0.2 0.12

80% MBr 0.2 0.2 0.16

100% MBr 0.2 0.2 0.20

120% MBr 0.2 0.2 0.24

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Table S3. Summarized average PL lifetime (τaverage), PLQE, and calculated radiative recombination rate

and nonradiative recombination rate of perovskite films fabricated with different ammonium cations. 𝑘𝑟 𝑘𝑛𝑟

The PLQE measurements were conducted by using a PLQE test setup. The τaverage were extracted from PL

decay curves in Figure S3, while the recombination rate and were calculated from the equation of 𝑘𝑟 𝑘𝑛𝑟

PLQE = and τaverage = .

𝑘𝑟

𝑘𝑟 + 𝑘𝑛𝑟

1 𝑘𝑟

+1

𝑘𝑛𝑟

Sample (ns -1)𝑘𝑟 (ns -1)𝑘𝑛𝑟 τaverage (ns) PLQE (%)

EABr 0.09 0.22 15.4 29

PEABr 0.11 0.15 16.2 41

EDABr2 0.15 0.06 24.2 72

HDABr2 0.28 0.04 30.3 88