Electrochemistry and Electrochemiluminescence of Organometal Halide Perovskite Nanocrystals in Aqueous Medium

Article abstract of DOI:10.1021/jacs.7b05073

The redox nature and electrochemiluminescence (ECL) of highly crystallized organometal halide perovskite CH₃NH₃PbBr₃ nanocrystals (NCs) in aqueous medium were investigated for the first time. CH₃NH₃PbBr₃ NCs could be electrochemically reduced to negative charge states by injecting electrons into the lowest unoccupied molecular orbitals and oxidized to positive charge states by removing electrons from the highest occupied molecular orbitals; charge transfer between NCs with positive and negative charge states could produce ECL. The redox sequence of CH₃NH₃PbBr₃ NCs played an important role in the generation of charge-transfer-mediated ECL; transient ECL could be achieved only by electrochemically reducing positive-charged NCs in an annihilation route. A large redox current was unfavorable for ECL. Charge mobility within CH₃NH₃PbBr₃ NCs had an important effect on ECL intensity in a co-reactant route, which is promising for photovoltaic and optoelectronic device applications. Importantly, the ECL spectra of CH₃NH₃PbBr₃ NCs were almost identical to their photoluminescence spectra, with a maximum emission around 535 nm and full width at half-maximum around 25 nm; this might open a way to obtaining monochromatic ECL using highly crystallized NCs as emitters, which makes them promising for use in color-selective ECL analysis.

Full text of DOI:10.1021/jacs.7b05073

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Article
Electrochemistry and Electrochemiluminescence of Organometal
Halide Perovskites Nanocrystals in Aqueous Medium
Xiao Tan, Bin Zhang, and Guizheng Zou
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 09 Jun 2017
Downloaded from http://pubs.acs.org on June 10, 2017
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Electrochemistry and Electrochemiluminescence of Organo-
metal Halide Perovskites Nanocrystals in Aqueous Medium
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Xiao Tan, Bin Zhang, and Guizheng Zou*
School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, China
ABSTRACT: The redox nature and electrochemiluminescence (ECL) of highly crystalized organometal halide perovskites
CH3NH3PbBr3 nanocrystals (NCs) in aqueous medium were investigated for the first time. CH3NH3PbBr3 NCs could be electroꢀ
chemically reduced to negative charged states by injecting electrons onto the lowest unoccupied molecular orbitals and oxidized to
positive charged states by removing electrons from the highest occupied molecular orbitals, the charge transfer between NCs of
positive charged states and negative charged states could bring out ECL. Redox sequence of CH3NH3PbBr3 NCs played an important
role on the generation of charge transfer involved ECL, transient ECL could only be achieved by electrochemically reducing the
positive charged NCs in annihilation route. Large redox current was unfavorable for the ECL, charge mobility within CH3NH3PbBr3
NCs displayed important effect on ECL intensity in coreactant route, which was promising for photovoltaic and optoelectronic deꢀ
vices. Importantly, ECL spectra of CH3NH3PbBr3 NCs were almost identical to the photoluminescence spectrum with maximum
emission around 535 nm and FWHM around 25 nm, which might open a way to monochromatic ECL with highly crystalized NCs as
emitters and was promising for the colorꢀselective ECL analysis.
states.27 Herein, the electrochemical redox and charge transfer
natures of CH3NH3PbBr3 NCs in aqueous medium were invesꢀ
tigated by ECL from CH3NH3PbBr3 NCs modified glass carbon
electrode (GCE), i.e. CH3NH3PbBr3 NCs|GCE.
INTRODUCTION
Hybrid organometal halide perovskites, with the common
formation AMX3 (A is an organic cation, M is a metal cation,
and X is a halogen anion), are of great interest in photovoltaic
and optoelectronic devices.1ꢀ6 A certified power conversion
efficiency as high as 22.1% has been achieved with the orꢀ
ganometal halide perovskite based solar cells.5 Along with
investigation on the charge mobility,7,8 carriers lifetime,9 carrier
diffusion length,10 and carriers recombination dynamics11
within organometal halide perovskites, the high absorption
coefficient,12 high photoluminescence (PL) quantum yield,13,14
narrow full width at half maximum (FWHM), and wide waveꢀ
length tunability13,15 features also made hybrid halide perovꢀ
skites promising for optoelectronic devices.2,4 Unfortunately,
the poor longꢀterm stability against ultraviolet irradiation and
water blocked their possible applications under normal condiꢀ
tion.5 The intrinsic affinity of AMX3 for moisture might lead to
degradation process,16,17 many open questions about their redox
and charge transfer natures in aqueous medium still remain.
Electrochemiluminescence (ECL) was the light emitting
process whose exited states were generated by the energetic
electron transfer occurred in the vicinity of working electrode.18
Ding and Bard first investigated the redox nature of Si NCs
with ECL technology.19 They found that Si NCs could be
electrochemical reduced by injecting electrons onto the lowest
unoccupied molecular orbitals (LUMO) and oxidized by reꢀ
moving electrons from the highest occupied molecular orbitals
(HOMO), Si NCs could store both positive and negative
charges under electrochemical condition, and subsequently lead
to ECL upon charge transfer.19 Although ECL has been extenꢀ
sively utilized to investigate the redox nature of various
NCs,20ꢀ26 only very recently, Huang demonstrated that perovꢀ
skites CsPbBr3 NCs could be electrochemically oxidized (or
reduced) to different charged states and bring out highly monꢀ
ochromatic ECL in organic medium upon the charge transfer
between NCs of positive charged states and negative charged
EXPERIMENTAL SECTION
Chemicals and Materials. All chemicals were of analytiꢀ
cal grade. All aqueous solutions were prepared with doubly
distilled water (DDW). Methylamine (CH3NH2, 30%ꢀ33% in
methyl alcohol), hydrobromic acid (HBr, 40%), lead bromide
(PbBr2, 99%), nꢀoctylamine (C8H19N, 99%,), oleic acid (OA,
AR), triꢀnꢀpropylamine (TPrA, >99%) were purchased from
Aladdin. NꢀNꢀdimethylformamide (DMF, AR), potassium
phosphate monobasic (KH2PO4, AR), diꢀpotassium hydrogen
phosphate trihydrate (K2HPO4•3H2O, AR), potassium chloride
(KCl, AR), ammonium persulfate ((NH4)2S2O8, AR) were
obtained from Sinopharm Chemical Reagent Co., Ltd.
(Shanghai, China). Ether absolute (AR) was obtained from
Fuyu Fine Chemical Co., Ltd. (Tianjin, China). Hydrochloric
acid (HCl, AR) was obtained from Laiyang Economic and
Technological Development Zone Fine Chemical Plant
(Shanghai, China). Toluene (AR) was purchased from Laiyang
Kant Chemical Reagent Co., Ltd. (Shandong, China).
Apparatus and Characterizations. Scanning electron miꢀ
croscopy (SEM) was obtained with a SUPRA 55 field emission
scanning electron microscope (Carl Zeiss AG, Germany). Ulꢀ
travioletꢀvisible (UVꢀvis) absorption spectrum was recorded on
a TUꢀ1901 UVꢀvis spectrophotometer (Beijing Purkinje Genꢀ
eral Instrument Co., Ltd., China). PL analysis was measured
with Fꢀ320 spectrofluorimeter (Tianjin Gangdong Sci&Tech
Development Co., Ltd., China). Xꢀray diffraction (XRD) patꢀ
tern was recorded using an Xꢀray diffractometer (Bruker AXS
D8 Advance, Germany) with Cu Kɑ radiation (λ=1.5418Å).
Differential pulse voltammetry (DPV) was recorded with a CHI
822 electrochemical analyzer (Shanghai, China). The ECL was
conducted on a MPIꢀA ECL analyzer (Xi’an Remex Analytical
Instrument Co., Ltd. China) using a threeꢀelectrode system
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including a GCE working electrode, a Ptꢀwire counter elecꢀ wellꢀdefined perovskites structure. The absorption and PL
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trode, and an Ag/AgCl (saturated) reference electrode. The
photomultiplier tube was biased at 800 V. ECL spectra were
recorded with a homemade ECL spectrum system,28,29 which
could synchronously trigger and operate VersaSTAT 3 analyzer
and CCDꢀcoupled monochromator.
spectra were almost identical to the CH3NH3PbBr3 NCs of the
same size in literature.31
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Preparation of CH3NH3PbBr3 NCs and CH3NH3PbBr3
NCs|GCE. CH3NH3PbBr3 NCs were synthesized according to
literature.30 Briefly, 15 mL of methylamine was cooled to 0 °C
with continuous stirring, and 14.25 mL HBr was added slowly.
After stirring for 1 h, the mixture was rotary evaporated at 50
°C, the precipitate were washed and centrifuged with diethyl
ether for three times, CH3NH3Br was obtained by drying the
precipitate under vacuum. 0.64 mmol CH3NH3Br and PbBr2,
500 ꢁL oleic acid and 25 ꢁL nꢀoctylamine were dissolved into 5
mL DMF, and then slowly transferred into 30 mL toluene under
stirring. 2 h later, the final solution was centrifugation at 6000
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rpm for
5 min, the obtained yellow precipitates, i.e.
CH3NH3PbBr3 NCs, were stored under darkness condition.
The CH3NH3PbBr3 NCs were ultrasonically dispersed into
toluene (0.030 g/mL). Then 10 ꢁL of the suspension was cast
onto GCE to form CH3NH3PbBr3 NCs|GCE.
Figure 2. (A) anodic DPV of (a) GCE and (b) CH3NH3PbBr3
NCs|GCE in airꢀfree 0.10 M pH 7.4 PBS; (B) anodic CV and (C)
ECL of (a) GCE and (b, c) CH3NH3PbBr3 NCs|GCE in airꢀfree
0.10 M pH 7.4 PBS containing (a, b) 10.0 and (c) 0.0 mM TPrA at
100 mV/s. Inset: anodic ECL spectra of (a) GCE and (b)
CH3NH3PbBr3 NCs|GCE in airꢀfree 0.10 M pH 7.4 PBS containing
10 mM TPrA.
Electrochemistry and Coreactant ECL of CH3NH3PbBr3
NCs|GCE
Several groups demonstrated that the deliberately injected
charges in polycrystalline perovskite films could exhibit reꢀ
markably long lifetime, long diffusion length, and high inꢀ
traꢀgrain carrier diffusivity.8ꢀ10,34 When comparted with bare
GCE, DPV of CH3NH3PbBr3 NCs|GCE in phosphate buffer
solution (PBS) displayed a weak anodic process with onset
potential around +0.69 V and maximum response around +0.87
V (Figure 2A), which indicated that CH3NH3PbBr3 NCs could
be electrochemically oxidized to positive charged states (R+,
cation radical) in PBS by removing electrons from HOMO.19
Both DPV (Figure 2A, curve b) and cyclic voltammetry (CV)
response (Figure 2B, curve c) of CH3NH3PbBr3 NCs|GCE were
very weak in blank PBS, the efficiency for removing electrons
from HOMO of CH3NH3PbBr3 NCs might be low. TPrA was
employed to investigate the anodic redox nature of
CH3NH3PbBr3, because TPrA could be oxidized to TPrA+•, then
underwent deprotonation to produce TPrA• (E°= ꢀ1.7 eV),18,35
which could inject electrons onto LUMO of NCs to produce
Figure 1. (A) UV−vis absorption and PL (λex: 380 nm) spectra of
monodispersed CH3NH3PbBr3 NCs in toluene; (B) SEM pattern of
CH3NH3PbBr3 NCs|GCE; Inset: SEM pattern of bare GCE.
RESULTS AND DISCUSSION
Characterization of CH3NH3PbBr3 NCs and CH3NH3PbBr3
NCs|GCE
The perovskites CH3NH3PbBr3 NCs displayed an obvious
excitonic peak at 526 nm (2.35 eV) on absorption spectrum and
a sharp PL peak around 531 nm (2.34 eV) with FWHM of 22
nm on PL spectrum (Figure 1A). The small Stokes shift implied
that the PL was originated from directꢀgap recombination.11
XRD pattern (Figure S1A) of CH3NH3PbBr3 NCs displayed
several peaks at 2θ values of 14.9°, 21.3°, 30.1°, 33.9°, 37.2°,
43.1°, 46.0°, and 48.5°, respectively, which was almost the
same to those of bulk CH3NH3PbBr3 materials.3,10,30,31 The
wellꢀdefined XRD pattern not only indicated the perfect
structure cell of asꢀprepared CH3NH3PbBr3 NCs without obꢀ
vious defects, but also confirmed that CH3NH3PbBr3 NCs were
of cubic crystal structure with the cation lead in the center of an
octahedron formed by six bromide ions, while the methyl
ammonium cations were embedded in the voids of a set of
cornerꢀsharing PbBr6 octahedra (Inset of Figure S1).3,32,33 The
broadness of the peaks on XRD pattern manifested that
CH3NH3PbBr3 NCs was smaller than bulk CH3NH3PbBr3. The
morphology pattern of CH3NH3PbBr3 NCs|GCE (Figure 1B
and Figure S1B) not only demonstrated that CH3NH3PbBr3
NCs were nanowires of 500±300 nm × 50±20 nm size and
uniformly distributed on GCE surface, but also further proved
the CH3NH3PbBr3 NCs were highly crystalized with
negative charged NCs (R̄
, anion radical) for coreactant ECL.20
TPrA displayed strong oxidation current on bare GCE with
onset around +0.60 V and no ECL was detected (Figure
2B&2C, curve a). The oxidation of TPrA was almost comꢀ
pletely blocked between 0.60 and 1.20 V on CH3NH3PbBr3
NCs|GCE (Figure 2B, curve b), the CH3NH3PbBr3 nanocrystal
film of CH3NH3PbBr3 NCs|GCE apparently blocked the direct
charge transfer for oxidizing TPrA on GCE. Interestingly,
CH3NH3PbBr3 NCs|GCE also displayed strong anodic ECL
with onset potential around +0.69 V and the maximum emisꢀ
sion around +1.20 V in the presence of TPrA (Figure 2C, curve
b). The onset potential for ECL of CH3NH3PbBr3 NCs|GCE in
PBS containing TPrA (Figure 2C, curve b) was almost the
same to that for oxidizing CH3NH3PbBr3 NCs|GCE in blank
PBS (Figure 2A, curve b), thus mobility of positive charge
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within CH3NH3PbBr3 nanocrystal film might play an important
3B, curve b), respectively, the generation of R+ by oxidizing
•̄
role on oxidizing TPrA to TPrA•. Eqs1ꢀ5 embodied the coreꢀ
actant ECL at anode:
CH3NH3PbBr3 NCs with SO4 apparently occurred ahead of
generation of Rꢀ by electrochemically reducing CH3NH32PꢀbBr3
NCs at cathode. The reductive current of S2O8 on
CH3NH3PbBr3 NCs|GCE was much stronger than the oxidative
current of TPrA on CH3NH3PbBr3 NCs|GCE, probably due that
mobility of electron was much higher than that of positive
charge within perovskite NCs.40,41 Because CH3NH3PbBr3
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R ꢀ e → R+
(1)
(2)
(3)
(4)
(5)
TPrA ꢀ e → [TPrA•]+ → TPrA• + H+
R + TPrA• → Rꢀ
R+ + Rꢀ → R*
R* → R + hʋ
2ꢀ
NCs|GCE displayed strong cathodic current for reducing S2O8
The increasing current with potential beyond 1.20 V might
due to the accumulation of positive charges within the
CH3NH3PbBr3 nanocrystal film of CH3NH3PbBr3 NCs|GCE
with positive scanned potential. As highꢀcurrentꢀdensity was
unfavorable for the radiative charge transfer36 and elecꢀ
tricꢀfieldꢀinduced light emission,37 lowered ECL was obtained
with potential beyond +1.2 V (Figure 2C, curve b). The anodic
ECL spectrum of CH3NH3PbBr3 NCs|GCE displayed a sole and
symmetric peak around 535 nm with FWHM of 25 nm (Inset of
Figure 2C). The FWHM was smaller than those of traditional
ECL emitters,18 such as luminol and Ru(bpy)32+, and even some
highly passivated NCs with promising monochromatic ECL
emission, such as dualꢀstabilizersꢀcapped CdTe and CdSe
NCs.29,38,39
(Figure 3B, curve b), only weak ECL was observed upon the
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charge transfer between R̄
and R+ at cathode.
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•̄
S2O82ꢀ + e → SO42ꢀ + SO4
(6)
(7)
(8)
(9)
•
̄
SO4 + R → SO42ꢀ + R+
R + e → Rꢀ
Rꢀ + R+ → R*
The charge mobility within CH3NH3PbBr3 NCs demonstrated
unneglectable effects on ECL intensity, both the anodic and
cathodic coreactant ECL manifested that high redox current
would lower the charge transfer involved ECL between R+ and
R̄. Cathodic ECL spectrum of CH3NH3PbBr3 NCs|GCE (inset
of Figure 3C) displayed a sharp and symmetric peak around 535
nm. Both anodic and cathodic coreactant ECL spectra were
almost identical to PL spectrum of CH3NH3PbBr3 NCs (Figure
S2), indicating CH3NH3PbBr3 NCs were highly passivated
without obvious defect surface states. As SEM and XRD have
proved that CH3NH3PbBr3 NCs possessed perfect crystalized
structure without obvious defects (Figure 1 & S1), these results
might open a way towards highly monochromatic ECL with
highly crystalized NCs as emitters.
Figure 3. (A) cathodic DPV of (a) GCE and (b) CH3NH3PbBr3
NCs|GCE in airꢀfree 0.10 M pH 7.4 PBS; (B) cathodic CV and (C)
ECL of (a) GCE and (b, c) CH3NH3PbBr3 NCs|GCE in airꢀfree
0.10 M pH 7.4 PBS containing (a, b) 0.10 and (c) 0.0 M
(NH4)2S2O8 at 100 mV/s. Inset: cathodic ECL spectra of (a) GCE
and (b) CH3NH3PbBr3 NCs|GCE in airꢀfree 0.10 M pH 7.4 PBS
containing 0.10 M (NH4)2S2O8.
Figure 4. Oxidative process started ECL transients of GCE
(black line) and CH3NH3PbBr3 NCs|GCE (red line) in airꢀfree
0.10 M pH 7.4 PBS by repetitively stepping potential from
+1.50 V to (A) ꢀ1.30 V, (B) ꢀ1.0 V, (C) ꢀ0.80 V, and (D) ꢀ0.70 V,
respectively, for 30 s at a frequency of 1 s. The blue lines inꢀ
dicate the stepping potentials. Inset: corresponding ECL spectra
of CH3NH3PbBr3 NCs|GCE by repetitively stepping the potenꢀ
tial for 30 s (the data was accumulated results for three parallel
measurements).
When compared with bare GCE, DPV of CH3NH3PbBr3
NCs|GCE in blank PBS also displayed a cathodic process with
onset potential around ꢀ0.80 V (Figure 3A), indicating that
CH3NH3PbBr3 NCs could be electrochemically reduced to
negative charged states (Rꢀ) by injecting electrons onto
2ꢀ
LUMO.19,27 S2O8 was employed to investigate the cathodic
redox of CH3NH3PbBr3, because S2O82ꢀ could be electrochemꢀ
。
•̄
ically reduced to a strong oxidizing intermediate, i.e. SO4 (E ≥
Annihilation ECL of CH3NH3PbBr3 NCs|GCE
3.15 V vs SCE), and then inject holes onto HOMO of NCs to
2ꢀ
produce R+ for coreactant ECL.19,20 S2O8 displayed strong
The electrochemical energy required for oxidizing or reꢀ
ducing CH3NH3PbBr3 NCs were further verified by ECL tranꢀ
sient technology,27 because annihilation ECL could be generꢀ
ated upon the exergonic electron transfer between electroꢀ
chemically reduced NCs and electrochemically oxidized NCs.19
Figure 4 displayed the oxidative process started ECL transient
reduction current on bare GCE with onset around ꢀ0.30 V and
maximum response around ꢀ1.0 V (Figure 3B, curve a). Altꢀ
hough the reduction of S2O82ꢀ on CH3NH3PbBr3 NCs|GCE was
obviously delayed with the onset negatively moved to ~ ꢀ0.60 V
and maximum response negatively moved to ~ ꢀ1.30 V (Figure
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of CH3NH3PbBr3 NCs|GCE. No ECL was observed by stepping quence of CH3NH3PbBr3 NCs played a crucial role on the
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CH3NH3PbBr3 NCs|GCE at +1.5 V for 1s in the initial step,
because only holes was injected onto HOMO and only NCs of
oxidative states were obtained. Obvious ECL was observed
stepping CH3NH3PbBr3 NCs|GCE from +1.50 V to ꢀ1.30, ꢀ1.0,
and ꢀ0.80 V, by respectively, indicating radiative charge
transfer occurred by reducing CH3NH3PbBr3 NCs of oxidative
states. No ECL was obtained by stepping potential from +1.50
V to ꢀ0.70 V (Figure 4D), the onset potential to electrochemical
reduce CH3NH3PbBr3 NCs|GCE was deduced to be around
ꢀ0.80 V, which was consisted with that obtained with DPV
(Figure 3A). The onset potential for coreactant cathodic ECL of
CH3NH3PbBr3 NCs|GCE was around ꢀ1.0 V (Figure 3C), which
probably because large redox current was unfavorable for the
radiative charge transfer.37 Transient ECL spectra were almost
the same to PL spectrum of CH3NH3PbBr3 NCs, indicating
excited states generated under different electrochemical
bandgaps were the same to those for PL.
generation of radiative charge transfer between CH3NH3PbBr3
NCs of positive charged states and negative charged states.
Transient ECL of CH3NH3PbBr3 NCs|GCE was only achieved
with oxidative process started redox processes, which was
different from that of CsPbBr3 NCs|GCE.27 Importantly,
lifeꢀtime for the transient ECL of CH3NH3PbBr3 NCs|GCE was
less than 80 ms (inset A, Figure S3A), which was also much
shorter than that of CsPbBr3 NCs|GCE (Figure S3B).27 The Cs+
+
or CH3NH3 located between the octahedras of cubic structure
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cell for perovskites NCs might have important effects on the
radiative charge transfer of perovskites NCs. No ECL was
obtained by stepping CH3NH3PbBr3 NCs|GCE from +0.60 V to
ꢀ1.60 V (Figure 5D), the lowest electrochemical energy for
oxidizing CH3NH3PbBr3 NCs was deduced to be around +0.70
V, which was similar to that obtained with DPV (Figure 2A).
Spectra of the reductive process started transient ECL demonꢀ
strated a single peak with maximum intensity around 535 nm,
which were almost the same to aforementioned ECL spectra of
CH3NH3PbBr3 NCs. Fortunately, transient ECL with greatly
enhanced intensity and lifetime was obtained by stepping
CH3NH3PbBr3 NCs|GCE from 0 V to +1.50 V in 0.1 M pH 7.4
PBS containing 10 mM TPrA (Figure S4). The flexible and
adjustable ECL of CH3NH3PbBr3 NCs under varied electroꢀ
chemical conditions was promising for photovoltaic and optoꢀ
electronic devices.
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CONCLUSIONS
The electrochemical redox and ECL of CH3NH3PbBr3 NCs in
aqueous medium were investigated for the first time.
CH3NH3PbBr3 NCs could be electrochemically oxidized to
positive charged states and reduced to negative charged states,
respectively. Both coreactant and annihilation ECL proved that
electrochemical redox reaction sequence played a crucial role
on the ECL of CH3NH3PbBr3 NCs, i.e., the radiative charge
transfer between CH3NH3PbBr3 NCs of positive charged states
and negative charged states, because ECL from CH3NH3PbBr3
NCs were usually achieved by reducing CH3NH3PbBr3 NCs of
positive charged states. CH3NH3PbBr3 NCs display flexible and
adjustable ECL under varied electrochemical conditions, while
spectral of all the ECL generated under different conditions
were almost the same to PL spectrum with unmoved maximum
emission wavelength and similar FWHM. CH3NH3PbBr3 NCs
was promising for photovoltaic and optoelectronic device with
impressive charge transfer and annihilation performance. The
highly monochromatic ECL of CH3NH3PbBr3 NCs might also
open a way to design novel ECL emitter with highly crystalized
NCs for multipleꢀcolored ECL assay.
Figure 5. Reductive process started ECL transients of GCE
(black line) and CH3NH3PbBr3 NCs|GCE (red line) in airꢀfree
0.10 M pH 7.4 PBS by repetitively stepping potential from
ꢀ1.60 V to (A) 1.20 V, (B) 1.0 V, (C) 0.70 V, and (D) 0.60 V
respectively at a frequency of 1 s. The blue lines indicate stepꢀ
ping potentials. Inset: corresponding spectra for the annihilaꢀ
tion ECL from CH3NH3PbBr3 NCs|GCE by repetitively stepꢀ
ping the potential for 30 s (the data was accumulated results for
three parallel measurements).
Figure 5 demonstrated the reductive process started transient
ECL of CH3NH3PbBr3 NCs|GCE. No ECL was observed by
stepping CH3NH3PbBr3 NCs|GCE at ꢀ1.6 V for 1s in the initial
step, because only electron was injected onto LUMO of the
NCs. However, no ECL was detected in all the potential stepꢀ
ping cycle by stepping CH3NH3PbBr3 NCs|GCE from ꢀ1.60 V
to +1.20, +1.0, +0.80 V (Figure S3A) and +0.70 V, respecꢀ
tively, indicating radiative charge transfer could not occur by
ASSOCIATED CONTENT
Supporting Information. XRD and SEM patterns, normalized
ECL and PL spectra, ECL transients in control, and ECL transients
with the presence of coreactant. This material is available free of
charge via the Internet at http://pubs.acs.org.
electrochemically
oxidizing
the
negative
charged
CH3NH3PbBr3 NCs. The obvious ECL was observed in the
followed steps by stepping CH3NH3PbBr3 NCs|GCE from
+1.20, +1.0, +0.80 and +0.70 V to ꢀ1.60 V, respectively, which
eventually proved that transient ECL of CH3NH3PbBr3 NCs
could only be achieved by electrochemicaly reducing the posiꢀ
tive charged NCs. Actually, both anodic and cathodic coreacꢀ
tant ECL also indicated that the oxidation of CH3NH3PbBr3
NCs in advance was important for the charge transfer involved
ECL in coreactant route (Figure 2 & 3). Thus, the redox seꢀ
AUTHOR INFORMATION
Corresponding Author
zouguizheng@sdu.edu.cn. Tel: +86ꢀ531ꢀ88361326. Fax:
+86ꢀ531ꢀ88564464.
ACKNOWLEDGMENT
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This project was supported by the National Natural Science
1
2
3
Foundation of China (Grant Nos. 21427808 and 21375077), the
Fundamental Research Funds of Shandong University (Grant No.
2015JC037), and the Shandong Provincial Natural Science Founꢀ
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