Improved performance of perovskite light-emitting diodes by dual

Subscriber access provided by Queen Mary, University of London

Article

Improved performance of perovskite light-emitting diodes by dual passivation with an ionic additive Huijun Zhang, Fanghao Ye, Wei Li, Robert S Gurney, Dan Liu, Chuanxi Xiong, and Tao Wang ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00186 • Publication Date (Web): 03 Apr 2019 Downloaded from http://pubs.acs.org on April 3, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Energy Materials

Improved performance of perovskite light-emitting diodes by dual passivation with an ionic additive Huijun Zhang1,2, Fanghao Ye1,2, Wei Li1,2, Robert S. Gurney1,2, Dan Liu1,2, Chuanxi Xiong1*, Tao Wang1,2* 1School

of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070,

China 2State

Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology,

Wuhan 430070, China

ABSTRACT: Metal halide perovskites are considered as the new generation semiconductors for optoelectronic devices due to their low material cost, superior optical and electrical properties such as narrow emission linewidth, tunable emission wavelength and high charge carrier mobility. However the morphological and energetic defects of perovskites grown from solution casting hinder the maximum achievable performance of devices. Additive strategy has been demonstrated as a facile and effective method to acquire high quality perovskite films. In this work, we introduce three ionic additives, namely tetrabutylammonium bromide (TBABr), benzyltriethylammonium bromide (BTEABr) and benzyltributylammonium bromide (BTBABr), into CH3NH3Br3 (MAPbBr3) precursor solution respectively to prepare pinhole-free perovskite films with reduced defect density. Perovskite light-emitting diodes (PeLEDs) incorporating BTBABr modified MAPbBr3 emitter exhibits a significantly reduced turn-on voltage from 4.6 to 2.6 V and improved maximum luminance, current efficiency of 23646 cd/m2, 3.39 cd/A compared with those of 3926 cd/m2, 0.27 cd/A of pristine MAPbBr3 based device.

KEYWORDS: Perovskite, light-emitting diode, ionic additive, defect passivation, morphology

1

ACS Paragon Plus Environment

ACS Applied Energy Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 15

1. INTRODUCTION Metal halide perovskites have been established as an important class of semiconductor that exhibit promising magnetic, electrical and optical properties, and have been applied in a large range of optoelectronic applications[1], such as solar cells

[2,3]

and light emitting diodes (LEDs)[4-7]. For

example, Wei et al reported perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency (EQE) of 20.3% though forming CsPbBr3-MA (MA=CH3NH3) quasi-core-shell structure to reduce nonradiative defects and balance the hole-electron injections[5]. Huang et al introduced amino-acid as passivation additive into CH(NH2)2PbI3 (FAPbI3) precursor and spontaneously formed submicrometer-scale structures, which had been found to reduce current leakage and enhance light outcoupling, acquiring a high EQE of 20.7%[6]. Kido et al applied an anion-exchange method with alkyl ammonium and aryl ammonium salts to synthesize CsPbI3 quantum dots for red PeLEDs with a high EQE of 21.3% [7]. PeLEDs incorporating MAPbBr3 emitters have been demonstrated to generate high color purity and luminance, after carefully optimizing the composition and morphology of the perovskite film

[8,9]

as well as the device architecture

[10].

However, a large amount of morphological and

energetic defects are present in the perovskite films due to the polycrystalline nature and poor thermal stability of MAPbBr3, which decrease the radiative recombination and reduce the device performance [11,12]. Furthermore, the huge leakage current induced by pinholes in the discontinuous perovskite film could cut down the device efficiency and even results in short circuit. Hence, it is crucial to deposit a dense MAPbBr3 film with passivated defects for high performance PeLEDs. Additive strategy has been demonstrated as an effective means to overcome these issues whilst avoiding the introduction of complex device fabrication operations. Ionic additives containing both anions and cations could occupy the vacancies from under-coordinated metal cations and halide anions at the perovskite crystal surface

[13],

as well as influence the crystal structure of perovskite

grains. The efficient dual passivation effect of ionic additives has been demonstrated in perovskite solar cells[14],15]. A number of ionic additives have also been investigated to achieve high performance quasi 2D-3D hybrid and nanocrystal PeLEDs, for instance methylammonium bromide (MABr)[4], butylammonium halide salts (BiX, X=Br or I)[16,17], phenethylammonium halide salts (PEAX, X=Br or I)[18], 1-naphthymethylamine iodide (NMAI)[19], phenylalanine bromide (PPABr)[20], tetraoctylammonium bromide (TOAB) and didodecyldimethylammonium bromide (DDAB)[21]. 2


Page 3 of 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In this work, we introduce three new ionic additives, namely tetrabutylammonium bromide (TBABr), benzyltriethylammonium bromide (BTEABr), benzyltributylammonium bromide (BTBABr), into MAPbBr3 precursor solution respectively to reduce defects in perovskite films using one-step spin-coating and fabricate LEDs incorporating these modified emitters. The BTBABr additive modified PeLED exhibits an improved maximum luminance, current efficiency (CE) and EQE of 23646 cd/m2, 3.39 cd/A and 0.82 % compared with those of 3926 cd/m2, 0.27 cd/A and 0.13% of pristine MAPbBr3 based device.

2. EXPERIMENTAL SECTION The patterned indium tin oxid (ITO) glass (resistance ca. 15Ω sq-1) was cleaned by ultra-sonication sequentially in water, ethanol, and isopropyl alcohol for 10 min followed by further treatment with ultraviolet-ozone

for

10

min

to

remove

any

organic

contaminants.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) solution (Clevios Al4083, Heraeus, Germany) was filtered through an 0.45 µm PVDF filter before being spin-cast onto ITO-coated glass substrates (15 mm x 20 mm) at 5000 rpm for 30 s, then baked at 135 °C for 30 min. The perovskite precursor solution was prepared by dissolving additive (98%, Macklin Biochemical Inc., China), MABr and PbBr2 (99.9%, You Xuan Ltd., China) in anhydrous dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (8:2, v/v). The perovskite layer was deposited on top of PEDOT:PSS by spin-coating from 40 wt.% precursor solution at 3000 rpm for 30 s in a N2-filled glove box. All perovskite films were annealed at 60 oC for 30 mins resulting in the formation of high quality perovskite crystals. Then 40 nm 1, 3, 5-Tris (1-phenyl-1Hbenzimidazol-2-yl) benzene (TPBi), 5 nm Ca and 100 nm Ag were thermally evaporated sequentially onto the perovskite film under high vacuum. The devices were encapsulated by pieces of glasses. Electron-only device (ITO/TiO2/MAPbBr3/TPBi/Ca/Ag) and hole-only devices (ITO/PEDOT:PSS/MAPbBr3/TFB/Ag) were also fabricated to calculate the trap density in single-carrier devices. Titanium dioxide (TiO2) was synthesized and coated following our previous report[22]. The thickness of TFB was 40 nm by spin-coated on perovskite films. The current-voltage-luminance characteristics of PeLEDs were measured by using a computer-controlled source-measurement unit (Keithley 2612B) and a luminance meter (Minolta LS-160, Japan). EQEs were calculated assuming a Lambertian emission profile [23]. The steady-state 3



photoluminescence (PL) spectra were obtained using a PL microscopic spectrometer (Flex One, Zolix, China), and the excitation source of PL utilizes a 405 nm CW laser. The electroluminescence (EL) spectra were obtained using the same spectrometer with the power source from Keithley 2612B (USA). The PL lifetime was measured using a time correlated single-photon counting (TCSPC) spectroﬂuorometer (PicoQuant, Germany). The absorption spectra were measured using UV-Visible spectrophotometer (HITACHI, Japan). Film thickness was measured using spectroscopic ellipsometer (J. A. Woollam, USA). Synchrotron grazing incidence wide-angle X-ray scattering (GIWAXS) measurements were conducted using the beamline BL14B1 at the Shanghai Synchrotron Radiation Facility in China. Impedance measurements were made using the ModuLab XM electrochemical workstation (AMETEK, UK) under a series of voltages with the amplitude of 10 mV from 1MHz to 100Hz under one AM 1.5G illumination conditions. Equivalent circuit simulations were conducted using the software package ZView (Scribner Associate, Inc.).

3. RESULTS AND DISCUSSION The one-step solution-casting process of MAPbBr3 films incorporating additives is illustrated in Figure 1(a), with the molecular structures of three additives shown in Figure 1(b). The precursor solution was prepared by dissolving additive, MABr and PbBr2 with a mole ratio of x:1.05:1 in a mixed solvent of anhydrous DMF and DMSO. The perovskite layer was deposited on top of 40 nm PEDOT:PSS by spin-coating from precursor solution at 3000 rpm for 30 s in a N2-filled glove box, and then annealed on a hot plate at 60 oC for 30 min. Figure 1(c) shows the energy level alignments of ITO/PEDOT:PSS/MAPbBr3/TPBi/Ca/Ag device.

H3 C

3000 rpm 30 s

Hot plate 60 oC 30 min

H3 C N

Br

CH3 H3C

N

CH3 Br

H3C

N

CH3 Br

H3 C

-4.7

TBABr

BTEABr

BTBABr

-5.1

-2.7 -3.4

-5.7

-2.9 Ca/Ag

H 3C

TPBi

additive:MABr:PbBr2=x:1.05:1 (mol:mol:mol)

-2.1

(c)

H3C

MAPbBr3

(b)

PEDOT:PSS

(a)

ITO

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 15

-6.2

Figure 1. (a) Schematic diagram of the additive-assisted solution-casting of perovskite films. (b) Molecular structures of TBABr, BTEABr, and BTBABr. (c) Energy-level diagram of the devices. Inset shows an emitting device with an applied bias of 4 V. 4


Page 5 of 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The diagrams of device performance containing luminance, current density, CE and EQE with varying voltage are exhibited in Figure 2(a)-(d). We summarized the detail data of device performance in Table  PeLEDs incorporating additive modified MAPbBr3 emitters show much higher luminance and efficiency, confirming that the ionic additives TBABr, BTEABr and BTBABr can improve device performance. It should be noted that the optimized contents of TBABr and BTBABr were determined as 0.035 mol, whilst that of BTEABr was less at 0.015 mol only due to the poor solubility of BTEABr in solvent as a result of its shorter alkane chains. The BTBABr additive, which contains a bulky benzyl and longer paraffin compared with TBABr and BTEABr, performs the best by reducing the turn-on voltage from 4.6 to 2.6 V and enhancing the luminance, CE, and EQE from 3502 cd/m2, 0.20 cd/A and 0.13 % of the pristine device to 23646 cd/m2, 3.39 cd/A and 0.82 % respectively.

Figure 2. (a) Current density, (b) luminance, (c) CE, and (d) EQE versus voltage characteristics of MAPbBr3 LEDs without and with optimized contents of TBABr, BTEABr and BTBABr.

5



Page 6 of 15

Table 1. Performance of MAPbBr3 LEDs prepared with different contents of additives. additive:MABr:PbBr2=x:1.05:1

Von (V)

Lmax (cd/m2)

CEmax (cd/A)

EQEmax (%)

0 0.03 0.035 0.04 0.01 0.015 0.02 0.03 0.035 0.04

4.6 2.6 2.4 2.4 3.0 3.0 3.0 3.2 2.6 2.4

[email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected]



Reference TBABr

BTEABr

BTBABr

To investigate the influence of additives on the morphology of MAPbBr3 perovskite film, scanning electron microscopy (SEM) images were obtained. SEM images of MAPbBr3 films without and with different additives are shown in Figure 3(a)-(h). Statistical diagrams of grain size obtained from Figure 3(a)-(h) are shown in Figure 3(i)-(l). Obviously, perovskite films prepared with the presence of additives exhibit a higher coverage and reduced grain size comparing with the reference film which is discontinuous with the presence of numerous pinholes. The increased film coverage could reduce the contact barrier at the interface between perovskite and carrier injection layer to reduce the turn-on voltage. The grain size of pristine perovskite ranges from 800 to 1600 nm, showing a wide range of size distribution. The average size of perovskite crystals is reduced from ca. 1100 to 900 nm after adding the optimum contents of TBABr, BTEABr and BTBABr into the MAPbBr3 films respectively. We speculate that the cations of these additives within the precursors have a steric hindrance effect to suppress the growth of perovskite crystals and reduce grain size. The elimination of pinholes will reduce the current leakage, whilst the smaller grains can restrain the dissociation of excitons though limiting the diffusion of excitons[24], so that higher device performance can be acquired after adding these additives. Comparing the SEM images of perovskite films grown with the presence of optimized contents of different additives, their average grain sizes are close, but the film coverage and the proportion of grain size less than 800 nm are highest with BTBABr acting as the additive, which has the largest cation with longer alkyl chains (see Figure 1b) and demonstrating the highest steric hindrance effect towards the growth of perovskite grains. 6


Page 7 of 15

w/o additive (b)

with TBABr (g)

(f)

w/o additive

(i)

50

60

w/o additive

(j)

50

Proportion (%)

40 30 20

60

with TBABr

30 20

30 20

10

10

0

0

0

200 400 600 800 1000 1200 1400 1600

Grain Size (nm)

0

200 400 600 800 1000 1200 1400 1600

60

(l)

50

40

10 0

5m

with BTEABr

(k)

50

40

with BTBABr

5m

Proportion (%)

60

2m

with BTEABr (h)

5m

5m

with BTBABr

2m

2m

2m

(e)

with BTEABr (d)

with TBABr (c)

Proportion (%)

(a)

Proportion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with BTBABr

40 30 20 10

0

200 400 600 800 1000 1200 1400 1600

Grain Size (nm)

Grain Size (nm)

0

0

200 400 600 800 1000 1200 1400 1600

Grain Size (nm)

Figure 3. (a)-(h) SEM images of perovskite films prepared without additive and with an optimum concentration of additives. Scale bars were 2m for (a)-(d) and 5m for (e)-(h). (i)-(l) Statistical histograms of grain size distribution obtained from (e)-(h). The crystalline characteristics of MAPbBr3 films were evaluated by synchrotron based grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. Two-dimensional (2D) GIWAXS patterns of various MAPbBr3 films are shown in Figure 4(a)-(d), and the one-dimensional (1D) profiles of these 2D images are plotted in Figure 4(e). The diffraction rings locating at the scattering vector Q = 1.08, 1.53, 2.16, 2.41 and 2.63 Å−1 correspond to d-spaces of 5.9, 4.2, 3.0, 2.6 and 2.4 Å respectively, and are associated with the (100), (110), (200), (210), and (220) facets of 3D MAPbBr3[15]. The GIWAXS diffraction patterns confirm that the crystal structures of perovskite films have not been changed after adding the optimum amounts of TBABr, BTEABr or BTBABr. Figure 4(e) illustrates that the crystallinity of MAPbBr3 films modified with additives are all increased comparing with the pristine film (with BTBABr modified MAPbBr3 showing the highest crystallinity), indicating the formation of high quality crystals during the additive assisted deposition process. Steady-state photoluminescence (PL) and absorption spectra have also been obtained to explore the optical properties of perovskite film. The optical bandgaps of MAPbBr3 films are 2.3 eV estimated from the absorption spectra in Fig. 4(f), demonstrating the same crystal structure of all 7



Page 8 of 15

films, which is consistent with the GIWAXS results. As shown in Fig. 4(g), the intensities of PL spectra are all increased with the addition of additives due to the higher crystallinity of MAPbBr3 perovskite and the suppressed nonradiative recombination which is induced by high defects density. The PL peaks are found slightly blue-shifted from 548 nm in the pristine MAPbBr3 film to 545 nm in MAPbBr3 with additives, which might be induced by a change in the dielectric screening of excitons induced by the presence of these additives or a strain effect that a stronger distortion exists in Pb-X bond. [25] Electroluminescence (EL) spectra of MAPbBr3 LEDs with an applied bias of 5 V are shown in Fig. 4(h), and illustrate a high color purity with a full width at half maximum (FWHM) value of ca. 25 nm only. The peak of the EL curve blue-shifts from 547 nm of the pristine device to 544 nm after adding additives, exhibiting the same tendency of the PL spectrum.

Figure 4. 2D GIWAXS patterns of perovskite films prepared (a) without additive, and with an optimum concentration of (b) TBABr, (c) BTEABr and (d) BTBABr additives. (e) 1D GIWAXS profiles, (f) absorption and (g) photoluminescence spectra of perovskite films. (h) EL spectra of PeLEDs devices with an applied bias of 5 V. We speculate that anions and cations in TBABr, BTEABr and BTBABr additives could passivate the defects in MAPbBr3 perovskite films by occupying the vacancies of under-coordinated metal cations as well as halide anions at the perovskite crystal surface. We investigate the dual-passivation effect of these additives on MAPbBr3 films by analyzing the trap density in electron- and hole- only devices incorporating pristine and BTBABr modified MAPbBr3 films, 8


Page 9 of 15

which is the best-performing additive in this work. Trap density can be obtained using the equation VTFL=qntL2/2εε0,

[26]

where q is the elementary charge (1.6×10-19 Coulombs), L is the thickness of

the perovskite film (about 500 nm tested by surface profilometer), ε is the relative dielectric constant of MAPbBr3 (taken as 25.5 from a previous report[27]), and ε0 is the vacuum permittivity (8.854×10-12 F m-1). We define the trap-filling limited voltage (VTFL) from the dark J-V curves of electron- and hole- only devices shown in Figure 5(a)-(b). A typical dark J-V curve of electron- or hole- only device can be divided into three regions: the Ohmic region, the trap-filling limited region and the space-charge-limited-current region (SCLC) region[28,29]. VTFL corresponds to the voltage determined from the intersection of the Ohmic and trap-filling limited regions. It can be concluded that the BTBABr modified MAPbBr3 device contains lower electron and hole trap densities of 2.36×1018 and 1.21×1018 cm-3 respectively, compared to values of 2.82×1018 and 3.17×1018 cm-3 of the reference device. It should be noted here that the VTFL values are influenced by both ionic and electronic transportations, therefore the defect density changes here result from the synergistic contribution of both ionic defect passivation as well as improved electronic transport due to morphological improvements. Nevertheless, these reduced electron and hole trap densities confirm the dual-passivation effect of BTBABr in MAPbBr3 films.

(b)

(a)

103

3

102 101 100 10

VTFL

-1

w/o additive with BTBABr

10-2

0.1

Current density (A/m2)

Current density (A/m2)

10

2

10

1

10

100 -1

10

VTFL

-2

10


-3

10

10-4 0.1

1

(c)

1

(d)

Voltage (V)

Voltage (V)

100


w/o additive Fitting curve with BTBABr Fitting curve

6.0k

-1

10

-Z'' (ohm)

Normalized PL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10-2

4.0k

2.0k

10-3 0

100

200

300

0.0

400

Lifetime (ns)

4.0k

8.0k

12.0k

Z' (ohm)

Figure 5. Dark current-voltage curves from (a) electron- and (b) hole- only MAPbBr3 devices with the device structure shown in the insets. (c) Time resolved PL lifetimes of MAPbBr3 films and (d) 9



Page 10 of 15

EIS measurements of perovskite devices, without and with the presence of an optimum amount of BTBABr.

Time resolved PL lifetime was measured to further verify the passivating effects of BTBABr to perovskites. The PL lifetime spectra of MAPbBr3 without and with an optimized content of BTBABr are shown in Figure 5c. The fast PL lifetime τ1, slow PL lifetime τ2 and the average PL lifetime τave obtained from fitting the experimental spectra using a bi-exponential decay model are listed in Table 2. χ2 values of ca. 1.1 only confirm the validiaty of our fitting. The increased τave of MAPbBr3 film from 8.2 to 64.2 ns after incorporating BTBABr also confirms the effective defect passivation of additive. The fast-decay process is related to trap-assisted non-radiative recombination and the slow decay can be related to radiative recombination.[30] The fraction of radiative recombination (f2) of BTBABr-modified MAPbBr3 film is 72.8%, a value that is much higher than 59.7% of the pure MAPbBr3 film and therefore the radiative recombination rate in PeLEDs is enhanced after adding the additive.

Table 2. PL lifetimes and fractions of MAPbBr3 films without and with an optimized content of BTBABr, obtained by fitting the experimental data using a bi-exponential decay model

1(ns)

f1(%)

2(ns)

f2(%)

average(ns)

χ2

w/o additive

0.33

40.3

8.4

59.7

8.2

1.06

with BTBABr

37.3

27.2

69.6

72.8

64.2

1.12

To further evaluate the effects of additives on the performance of PeLEDs, electrical impedance spectroscopy (EIS) measurements were characterized. PeLEDs devices incorporating MAPbBr3 films with and without BTBABr were measured under dark with an applied bias of 0.4 V in the frequency range from 1 MHz to 100 Hz. As shown in Figure 5(d), the typical Nyquist plots can be fitted well using equivalent circuit model consisted of a series resistance (Rs), a recombination resistance (Rrec) and a correlated capacitance shown in the inset of Figure 5(d) [31,32]. Rs is attributed to resistances from device interfaces, while Rrec is associated with the recombination resistance of the MAPbBr3 layer. PeLED incorporating the BTBABr modified MAPbBr3 emitter 10


Page 11 of 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


has a lower Rs of 39  and a higher Rrec of 11080 , comparing with 47  and 1380  in devices with the pristine perovskite film. The reduced Rs here originates from the improved interfacial contact due to the reduced surface roughness and improved uniformity of films containing smaller perovskite grains which are demonstrated through SEM characterization. The significantly increased Rrec, which will restrict the nonradiative recombination as a result of reduced trap density, will contribute to an enhanced performance of PeLEDs.

CONCLUTION In summary, we report on a dual passivation strategy to reduce trap density and improve the morphology of MAPbBr3 films, using three ionic salts contains different cations, to improve the device performance of PeLEDs. All these additives help to deposit high quality perovskite films with higher film coverage and reduced grain size. The additive BTBABr, which exhibits the largest steric hindrance and a better solubility in solvent, effectively passivated the defects in the MAPbBr3 film, and increased maximum luminance, CE, and EQE of 23646 cd/m2, 3.39 cd/A and 0.82 % were achieved. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (C.X.X.) [email protected] (T. W.) ORCID Tao Wang: 0000-0002-5887-534X Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 51861145101). All authors thank the beamline BL14B1 crew at Shanghai Synchrotron Radiation Facility (China) for providing the beam time and helping conduct corresponding experiments. 11



Page 12 of 15

REFERENCE (1) Quan L. N.; Arquer F. P. G.; Sabatini R. P.; Sargent E. H. Adv. Mater. Perovskites for Light Emission. 2018, 30, 1801996. (2) Yang L., Barrows A. T., Lidzey D. G.; Wang T. Recent Progress and Challenges of Organometal Halide Perovskite Solar Cells. Rep. Prog. Phys. 2016, 79, 26501. (3) Yang W. S.; Park B. W.; Jung E. H.; Jeon N. J.; Kim Y. C.; Lee D. U.; Shin S. S.; Seo J.; Kim E. K.; Noh J. H.; Seok S. I. Iodide Management in Formamidinium-Lead-Halide–Based Perovskite Layers for Efficient Solar Cells. Science 2017, 356, 1376-1379. (4) Tan Z. K.; Moghaddam R. S.; Lai M. L., Docampo P.; Higler R.; Deschler F.; Price M.; Sadhanla A.; Pazos L. M.; Credgington D.; Hanusch F.; Bein T.; Snaith H. J.; Friend R. H. Bright Light-Emitting Diodes based on Organometal Halide Perovskite. Nature 2014, 9, 687-692. (5) Lin K.; Xing J.; Quan L. N.; Arquer F. P. G.; Gong X.; Lu J.; Xie L.; Zhao W.; Zhang D.; Yan C.; Li W.; Liu X.; Lu Y.; Kirman J.; Sargent E. H.; Xiong Q.; Wei Z. Perovskite Light-Emitting Diodes with External Quantum Efficiency Exceeding 20 Percent. Nature 2018, 562, 245-248. (6) Cao Y.; Wang N.; Tian H.; Guo J.; Wei Y.; Chen H.; Miao Y.; Zou W.; Pan K.; He Y.; Cao H.; Ke Y.; Xu M.; Wang Y.; Yang M.; Du K.; Fu Z.; Kong D.; Dai D.; Jin Y.; Li G.; Li H.; Peng Q.; Wang J.; Huang W. Perovskite Light-Emitting Diodes Based on Spontaneously Formed Submicrometre-Scale Structures. Nature 2018, 562, 249-253. (7) Chiba T.; Hayashi Y.; Ebe H.; Hoshi K.; Sato J.; Sato S.; Pu Y. J.; Ohisa S.; Kido J. Anion-Exchange Red Perovskite Quantum Dots with Ammonium Iodine Salts for Highly Efficient Light-Emitting Devices. Nat. Photonics 2018, 12, 681-687. (8) Kerner R. A.; Zhao L.; Xiao Z.; Rand B. P. Ultrasmooth Metal Halide Perovskite Thin Films via Sol–Gel Processing. J. Mater. Chem. A 2016, 4, 8308-8315. (9) Zheng G.; Zhu C.; Ma J.; Zhang X.; Tang G.; Li R.; Chen Y.; Li L.; Hu J.; Hong J.; Chen Q.; Gao X.; Zhou H. Manipulation of Facet Orientation in Hybrid Perovskite Polycrystalline Films by Cation Cascade. Nat. Commun. 2018, 9, 2793. (10) Shi Y.; Wu W.; Dong H.; Li G.; Xi K.; Divitini G.; Ran C.; Yuan F.; Zhang M.; Jiao B.; Hou X.; Wu Z. A Strategy for Architecture Design of Crystalline Perovskite Light-Emitting Diodes with High Performance. Adv. Mater. 2018, 30, 1800251. (11) Son D.; Lee J.; Choi Y. J.; Jang I.; Lee S.; Yoo P. J.; Shin H.; Ahn N.; Choi M.; Kim D.; Park N. Self-Formed Grain Boundary Healing Layer for Highly Efficient CH3NH3PbI3 Perovskite Solar Cells. Nat. Energy 2016, 1, 16081. (12) Huang J.; Yuan Y.; Shao Y.; Yan Y. Understanding the Physical Properties of Hybrid

12


Page 13 of 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Perovskites for Photovoltaic Applications. Nat. Rev. Mater. 2017, 2, 17042. (13) Ye S.; Rao H.; Zhao Z.; Zhang L.; Bao H.; Sun W.; Li Y.; Gu F.; Wang J.; Liu Z.; Bian Z.; Huang C. A Breakthrough Efficiency of 19.9% Obtained in Inverted PerovskiteSolar Cells by Using An Efficient Trap State Passivator Cu (Thiourea) I. J. Am. Chem. Soc. 2017, 139, 7504-7512. (14) Zheng X.; Chen B.; Dai J.; Fang Y.; Bai Y.; Lin Y.; Wei H.; Zeng X. C.; Huang J. Defect Passivation in Hybrid Perovskite Solar Cells Using Quaternary Ammonium Halide Anions and Cations. Nat. Energy 2017, 2, 17102. (15) Wang Q.; Zheng X.; Deng Y.; Zhao J.; Cheng Z.; Huang J. Stabilizing the -Phase of CsPbI3 Perovskite by Sulfobetaine Zwitterions in One-Step Spin-Coating Films. Joule 2018, 1, 371-382. (16) Xiao Z.; Kerner R. A.; Zhao L.; Tran N. L.; Lee K. M.; Koh T. W.; Scholes G. D.; Rand B. P. Efficient Perovskite Light-Emitting Diodes Featuring Nanometer-Sized Crystallites. Nat. Photonics 2017, 11, 108-115. (17) Zhao L.; Rolston N.; Lee K. M.; Zhao X.; Martinez M. A. R.; Tran N. L.; Yeh Y. W.; Yao N.; Scholes G. D.; Loo Y. L.; Selloni A.; Dauskardt R. H.; Rand B. P. Influence of Bulky Organo-Ammonium Halide Additive Choice on the Flexibility and Efficiency of Perovskite Light-Emitting Devices. Adv. Funct. Mater. 2018, 28, 1802060. (18) Ban M.; Zou Y.; Rivett J. P. H.; Yang Y.; Thomas T. H.; Tan Y.; Song; X. Gao T.; Credington D.; Deschler F.; Sirringhaus H.; Sun B. Solution-Processed Perovskite Light Emitting Diodes with Efficiency Exceeding 15% through Additive-Controlled Nanostructure Tailoring. Nat. Commun. 2018, 9, 3892. (19) Wang N.; Cheng L.; Ge R.; Zhang S.; Miao Y.; Zou W.; Yi C.; Sun Y.; Cao Y.; Yang R.; Wei Y.; Guo Q.; Ke Y.; Yu M.; Jin Y.; Liu Y.; Ding Q.; Di D.; Yang L.; Xing G.; Tian H.; Jin C.; Gao F.; Friend R. H.; Wang J.; Huang W. Perovskite Light-Emitting Diodes based on Solution-Processed Self-Organized Multiple Quantum Wells. Nat. Photonics 2016, 10, 699-704. (20) Yuan S.; Wang. Z. K.; Zhuo M. P.; Tian Q. S.; Jin Y.; Liao L. S. Self-Assembled High Quality CsPbBr3 Quantum Dot Films toward Highly Efficient Light-Emitting Diodes. ACS Nano 2018, 12, 9541-9548. (21) Song J.; Li J.; Xu L.; Li J.; Zhang F.; Han B.; Shan Q.; Zeng H. Room-Temperature Triple-Ligand Surface Engineering Synergistically Boosts Ink Stability, Recombination Dynamics, and Charge Injection toward EQE-11.6% Perovskite QLEDs. Adv. Mater. 2018, 30, 1800764. (22) Cai F.; Yang L.; Yan Y.; Zhang J.; Qin F.; Liu D.; Cheng Y.; Zhou Y.; Wang T. J. Mater. Chem. A 2017, 5, 9402. (23) Forrest S. R.; Bradley D .D. C.; Thompson M. E. Measuring the Efficiency of Organic

13



Page 14 of 15

Light-Emitting Devices. Adv. Mater. 2003, 15, 1043-1048. (24) Cho H.; Jeong S. H.; Park M. H.; Kim Y. H.; Wolf C.; Lee C. L.; Heo J. H.; Sadahanala A.; Myoung N.; Yoo S.; Im S. H.; Friend R. H.; Lee T. W. Overcoming the Electroluminescence Efficiency Limitations of Perovskite Light-Emitting Diodes Science 2015, 350, 1222-1225. (25) Byun J.; Cho H.; Wolf C.; Jiang M.; Sadhanala A.; Friend R. H.; Yang H.; Lee T. W. Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes Adv. Mater. 2016, 28, 7515-7520 (26) Mark P.; Helfrich W. Space-Charge-Limited Currents in Organic Crystals. J. Appl. Phys. 1962, 33, 205. (27) Liu Y.; Zhang Y.; Zhao K.; Yang Z.; Feng J.; Zhang X.; Wang K.; Meng L.; Ye H.; Liu M.; Liu S. A 1300 mm2 Ultrahigh-Performance Digital Imaging Assembly using High-Quality Perovskite Single Crystals. Adv. Mater. 2018, 30, 1707314. (28) Bube R. H. Trap density determination by space-charge-limited currents. J. Appl. Phys. 1962, 33, 1733-1737. (29) Dong Q.; Fang Y.; Shao Y.; Mulligan P.; Qiu J.; Cao L.; Huang J. Electron-hole diffusion lengths > 175 m in solution grown CH3NH3PbI3 single crystals. Science 2015, 347, 967-970. (30) Park M. H.; Jeong S. H.; Seo H. K.; Wolf C.; King Y. H.; Kim H.; Byun J.; Kim J. S.; Cho H.; Lee T. W. Unravelling additive-based nanocrystal pinning for high efficiency organic-inorganic halide perovskite light-emitting diodes. Nano Energy 2017, 42, 157-165. (31) Liu Y.; Bag M.; Renna L. A.; Page Z. A.; Kim P.; Emrick T.; Venkataraman D.; Russell T. P. Dual functional zwitterionic fullerene interlayer for efficient inverted polymer solar cells. Adv. Energy Mater. 2016, 6, 1501606. (32) Todinova A.; Contreras-Bernal L.; Salado M.; Ahmad S.; Morillo N. Idígoras J.; Anta J. A. Towards a Universal Approach for the Analysis of Impedance Spectra of Perovskite Solar Cells: Equivalent Circuits and Empirical Analysis. Chemelectrochem 2017, 4, 2891-2901.

14


Page 15 of 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphics

additive:MABr:PbBr2=x:1.05:1 (mol:mol:mol) H3 C

3000 rpm 30 s

Hot plate 60 oC 30 min

H3C

H3 C

H3C

N

CH3 H3C Br

CH3

N

Br

H3C

CH3

N Br

H3C

TBABr

w/o additive

BTEABr

BTBABr

with BTBABr

15


Improved performance of perovskite light-emitting diodes by dual

Recommend Documents