3,4-Dihydroxybenzhydrazide as an additive to improve the morphology of perovskite films for efficient and stable perovskite solar cells

3,4-Dihydroxybenzhydrazide as an additive to improve the morphology of perovskite films for efficient and stable perovskite solar cells

Accepted Manuscript 3,4-dihydroxybenzhydrazide as an additive to improve the morphology of perovskite films for efficient and stable perovskite solar ...

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Accepted Manuscript 3,4-dihydroxybenzhydrazide as an additive to improve the morphology of perovskite films for efficient and stable perovskite solar cells Huiya Li, Kai Zhu, Kaicheng Zhang, Peng Huang, Dahua Li, Ligang Yuan, Tiantian Cao, Ziqi Sun, Zhendong Li, Qiaoyun Chen, Bo Song, Huifang Zhu, Yi Zhou PII:

S1566-1199(18)30644-X

DOI:

https://doi.org/10.1016/j.orgel.2018.12.012

Reference:

ORGELE 5021

To appear in:

Organic Electronics

Received Date: 15 September 2018 Revised Date:

1 December 2018

Accepted Date: 10 December 2018

Please cite this article as: Huiya Li, Kai Zhu, Kaicheng Zhang, Peng Huang, Dahua Li, Ligang Yuan, Tiantian Cao, Ziqi Sun, Zhendong Li, Qiaoyun Chen, Bo Song, Huifang Zhu, Yi Zhou, 3,4dihydroxybenzhydrazide as an additive to improve the morphology of perovskite films for efficient and stable perovskite solar cells, Organic Electronics (2018), doi: 10.1016/j.orgel.2018.12.012 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

3,4-dihydroxybenzhydrazide as an additive to improve the morphology of perovskite films for efficient and stable perovskite solar cells a

a

a

a

a

a

a

a

Huiya Li,† Kai Zhu,† Kaicheng Zhang,† Peng Huang, Dahua Li, Ligang Yuan, Tiantian Cao, Ziqi Sun, a

a

b

a

a.

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China. E-mail: [email protected], [email protected], [email protected]

b.

RI PT

a

Zhendong Li, Qiaoyun Chen, Bo Song,* Huifang Zhu* and Yi Zhou*

Analysis and Testing Center, Soochow University, Suzhou, 215123, P. R. China

SC

†These authors contributed equally to this work.



M AN U

HIGHLIGHT

3,4-dihydroxybenzhydrazide containing

GRAPHICAL ABSTR ACT

Lewis base C=O was employed as additive to control the crystallizxation kinetics of perovskite. The grain size of peroveskite enlarged dramatically

with

doping

of

3,4-

dihydroxybenzhydrazide. The power conversion efficiencies of perovskite

solar

cell

dihydroxybenzhydrazide

with

3,4-

incrased

EP



TE D



dramatically and the stability of Pero-

AC C

SCs was also enhanced.

ARTICLEINFO Keywords:

ABSTRACT Morphological engineering plays a very important role to the

perovskite solar cells

perf orm ance of p er ovskite solar cells. In this stud y, 3 ,4-

additive

dihydroxybenzhydrazide employes as an additive in the perovskite

3,4-dihydroxybenzhydrazide mophology

precursor to control the crystallization kinetics. It is found that the doping of 3,4-dihydroxybenzhydrazide led to increase of grain size and decrease of grain boundaries, both of which facilitate charge transportation and suppress charge recombination within the

* Corresponding author E-mail: [email protected], [email protected], [email protected]

1

ACCEPTED MANUSCRIPT photoactive layers. Consequently, the power conversion efficiencies

Among them, Lewis acid or base that can interact with

of the corresponding perovskite solar cells are significantly enhanced,

perovskite (e.g. coordination between C=O or S=O and

and a champion power conversion efficiencies of 17.58% with open

2+

Pb ), are widely applied to control the perovskite

circuit voltage of 1.06 V, short circuit current density of 21.40 mA cm-2

crystallization

or

defect

passivation.

For

example,

and fill factor of 79.1% is achieved, which is 21.5% higher than that

Namyoung Ahn et al. firstly introduced DMSO into the without 3,4-dihydroxybenzhydrazide (14.47%). Moreover, upon doping

solution of perovskite precursor, where adducts of

the stability of the perovskite solar cells is also improved. We believe

PbI2·DMSO and CH3NH3I·PbI2·DMSO due to interaction

other lead-based perovskite systems.

between S=O and Pb / MA were generated. The

RI PT

that the idea demonstrated in this research can also be applied to

formation of intermediate product slowed down the 1. Introduction

crystallization, and thus led to high-quality perovskite films and consequently a high performance of the

organic-inorganic hybrid perovskite, the perovskite solar

corresponding devic [35]. Zhifang Wu et al. reported a

cells (Pero-SCs) have shown great potentials as the next

cationic

SC

Owing to the excellent optoelectronic properties of

2-(6-bromo-1,3-dioxo-1H-

M AN U

additive,

benzo[de]isoquinolin-2(3H)-yl)ethan-1- ammonium iodide

photovoltaic devices, the performance of Pero-SCs relies

(2-NAM), which possesses a planar aromatic group and

very much on the morphology of the photoactive layers.

C=O groups. This molecule can effectively decrease the

The film morphologies including film uniformities, film

crystallization rate, and thus increasing the grain size and

coverage, and crystal size can be effectively improved by

consequently reducing the charge recombination within

annealing in the presence of additives [6, 7]. Besides, it’s

the perovskite films [34]. In addition, the hysteresis

known that the majority of the charge recombination and

behavior of the corresponding Pero-SC was suppressed,

perovskite degradation occur at the grain boundaries and

and the stability was improved. To give a more detailed

interfaces [8-12]. Therefore, the enhanced film qualities of

overview

EP

TE D

generation of photovoltaic technology [1-5]. Like the other

of

the

contribution

of

additives

to

the

morphology of the perovskite films as well as the

charge transportation, suppress charge recombination

performance of the corresponding Pero-SCs, studies

and improve the stability of the devices. As known,

using Lewis bases as additives are summarized, as

additives

high

shown in Table 1. PbI2 is a Lewis acid, and the presence

performance Pero-SCs. Up to now, additives reported in

of Lewis base will result in the formation of adduct of

the literature can be divided into several categories:

them two.

AC C

perovskite by utilizing additives are expected to facilitate

can

promote

the

development

of

polymers [13-16], fullerenes [17-19], metal halide salts

The weak interaction between the acid and base plays

[20,21], organic halide salts [22-24], solvent [25-27],

a key role in regulating the crystallinity of the perovskite

inorganic acid [28,29], nanoparticles [30,31] and so on

films. A number of small molecules bearing S, O, N,

[32,33].

especially organic solvents, were employed as additives

2

ACCEPTED MANUSCRIPT Efficiency (%) Device configuration

Addictive

Increasing

Functional group

Ref. Before

After

ratio (%)

16.46

19.7

19.7

16.17

32.0

FTO/bl-TiO2/mp-TiO2/MAPbI3/spiroDMSO

S=O

DMSO

S=O

35

MeOTAD/Ag FTO/bl-TiO2/mp-TiO2/MAPbI3/spiroMeOTAD/Au

NMP

C=O

thiophene

thiophene

37

RI PT

12.25

FTO/c-TiO2/MAPbI3-xClx/spiro-MeOTAD/Au

14.66

19.7

15.3

16.8

16.5

25.9

18.25

8.6

39

19.2

368.3

40

13.1 pyridine

pyridine

urea

C=O

caprolactam

C=O

FTO/c-TiO2/PCBA/FA0.85MA0.15Pb (I0.85Br0.15)3/spiro-MeOTAD/Au

4.1

M AN U

FTO/c-TiO2/mp-

16.80

SC

ITO/SnO2/MAPbI3/spiro-MeOTAD/Ag

TiO2/FA0.83MA0.17PbI2.51Br0.49/spiroMeOTAD/Au FTO/bl-TiO2/FAPbI3/spiro-MeOTAD/Au

38

2-NAM

C=O

18.0

19.33

7.4

36

thiourea

C=S

11.5

13.6

18.26

41

15.92

18.3

15.0

42

C=O,

IT-4F

TE D

FTP/Li-NiOx/MAPbI3/PCBM/BCP/Ag

CN, thiophene

Table 1. Comparisons of perovskite solar cells added with different Lewis bases.

derivative

DMSO [35, 37], pyridine [38] NMP [37], may leave

DOBD) was doped in PEDOT:PSS [43]. As being

residue

applied

after

thermo-annealing,

AC C

even

EP

in the literatures [37]. The organic solvents, such as

which

is

detrimental to the stability of the resulting devices. Only

3,4-dihydroxybenzhydrazide

as

hole

transport

materials,

(denoted

the

by

device

performance was greatly enhanced.

a handful of non-solvent small molecules are reported

In

this

study,

we

introduced

DOBD

into

the

by now. For example, Fang et al.’s study demonstrated

preparation of perovskite precursor. Our results indicate

that IT-4F can improve both the PCE and the stability of

that upon addition of DOBD, the grain size of the

the Pero-SCs. Therefore, exploring small Lewis base as

crystals became bigger and the grain boundaries got

additives is highly required to the development of Pero-

less

SCs [42].

corresponding Pero-SCs was significantly improved due

In our previous study, an easy-accessible catechol

after

annealing.

The

performance

of

the

to the improved charge transportation and suppressed

3

Scheme 1. Schematic illustration of the procedure to prepare perovskite films.

charge recombination. A champion PCE of 17.58%

current density (Jsc) of 21.40 mA cm

-2

SC

with open circuit voltage (Voc) of 1.06 V, short circuit

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ACCEPTED MANUSCRIPT

and fill factor

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(FF) of 79.1% was achieved. The PCE is 21.5% higher than that (14.47%) without DOBD In addition, the stability was also improved.

2. Results and discussion

Fig. 1 Photos of PbI2 solution in presence of different

concentration of DOBD. The numbers correspond to

TE D

The p-i-n type Pero-SCs with the configuration of

ITO/PEDOT:PSS/perovskite/C60/BCP/Al were fabricated. The details of the device fabrication were

presented in the experimental section. The procedure

EP

to prepare perovskite films was schematically illustrated in Scheme. 1. Briefly, solution 2 was quickly

the concentrations and all the unit is

mg mL-1

Upon addition of DOBD, the solution became clear and

transparent,

which

implies

that

interaction

between DOBD and PbI2 should happen, and the formation of the complex improved the solubility of

dropped on the PbI2 surface without stopping spinning

AC C

PbI2 in DMF (vide infra). In fact, the transparent

of the substrates. Annealing of the substrates at 100

solution is a colloid with nanoparticles, which is

°C for 3 min led to the formation of the crystalize d

confirmed by the observation of Tyndall effect.

perovskite. It is worth to note that an interesting

Furthermore, as the concentration of DOBD was

phenomenon happened during preparation of solution

-1

increased to 5 mg mL , the light pathway became

neat PbI21. As shown in the up row of Fig. 1, the DMF

apparently wider, suggesting the formation of bigger

solution of neat PbI2 was opaque even after being

colloidal particles in the solution. DOBD additives also

stirred at 70 °C for 12 h. This should be attribute d to

made differences on the morphology and diffraction of

t h e r el a tiv el y p o o r s ol u bilit y of P b I 2 i n D M F .

the spin-coated PbI2 films.

4

ACCEPTED MANUSCRIPT

Fig. 3 (a) XRD patterns of annealed and unannealed Fig. 2 SEM images of neat PbI2 (a) and PbI2 with 3 mg -1

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mL

perovskite films with or without DOBD. (b) FTIR of

DOBD (b); (c) the corresponding X-ray diffraction

DOBD and DOBD+PbI2 for the C=O vibrations.

(XRD) patterns (a) & (b).

film based on PbI2 doped with DOBD increased significantly after annealing. The variation of the peak

(SEM) images in Fig. 2a & 2b, upon addition of 3 mg

intensity and width both are consistent with the other

-1

DOBD, the PbI2 grains became smaller with

results. Without annealing, the peak intensity of the

M AN U

mL

SC

As shown in the scanning electron microscopy

perovskite films decreased upon addition of DOBD,

DOBD). These results are in good agreement with the

and the full-width half-maximum (FWHM) of the peaks

transparency changes. The addition of DOBD caused

increased from 0.12° to 0.19°, both of which indica te

the decrease of grain size of PbI2 in the DMF solution.

that the crystal grains in the film became smaller. With

According to Yang’s research results, the reduced PbI2

annealing, the peak intensity greatly increased and the

particle size should be propitious to the formation of

peak width decreased from 0.12° to 0.09°, both of

high quality of perovskite films [44]. Fig. 2c shows that

which indicate that the crystal size was greatly

the diffraction signal of the samples with DOBD was

increased and crystallinity was improved. It is clear that

much weaker than that without. And according to the

DOBD

EP

TE D

average size of 140 nm (250 nm for PbI2 grains without

can

definitely

regulate

the

crystallization

process of the perovskite films, and this effect should

grains with or without DOBD. The average grain size of

be related to the interactions between DOBD and PbI2.

PbI2 doped with DOBD (18 ± 1 nm) was approximately

In order to investigate the interactions between PbI2

half of PbI2 nanoparticles without doping of DOBD (33

and DOBD, Fourier transform infrared spectroscopy

± 3 nm). The trend was in good accordance to SEM

(FTIR) of DOBD and DOBD + PbI2 were measured,

results.

and the results were shown in Fig. 3b. The sample of

AC C

Scherrer equation, we calculated the size of PbI2

Doping of DOBD also caused great differences to

DOBD+PbI2 was prepared according to the literature -1

the crystallinity of the resulting perovskite films. As

[35]. The peak at 1660 cm

shown in Fig. 3a, the diffraction signal of the perovskite

stretching vibration of C=O bonds of neat DOBD.

film based on neat PbI2 changed slightly after

Being mixed with PbI2, the vibration of C=O bond

annealing, while the diffraction signal of the perovskite

shifted to 1654 cm , which should be attributed to the

-1

5

should be ascribed to the

ACCEPTED MANUSCRIPT weakened bond strength between carbon and oxygen

Nevertheless, as varying the concentration of DOBD

[35], due to the Lewis acid and base adduction

from 0 to 5 mg mL , the peak intensities first increased

interaction

The

and then decreased, and a maximum appeared as the

complexation between DOBD and PbI2 should be

concentration of DOBD was 3 mg mL . The FWHM of

responsible to the passivation of the defects of

the peaks were first decreased and then increased, a

perovskite films during annealing [36].

minimum width was obtained when the concentration

between

Pb

and

C=O

[36,45].

-1

-1

-1

RI PT

of DOBD was 3 mg mL . Both the peak intensity and width of the XRD pattern indicate that 3 mg mL

-1

of

DOBD dopant should be the best in terms of crystallinity and grain size. These results imply that the

SC

crystallinity of the films should be different, and the films doped with 3 mg mL

-1

DOBD may lead to a

M AN U

higher performance.

The effect of DOBD on the morphological change

of perovskite films were investigated by SEM. As shown in Fig. 4c, the perovskite film without DOBD additives consists of many small crystals. Upon

perovskite films doped with different concentrations of

addition of DOBD, the grain size apparently increased,

DOBD. (c) SEM images of the perovskite films

and it reaches to a maximum as the concentration of

prepared with different amount of DOBD additives: 0,

DOBD was 3 mg mL , and further increasing the

1, 2, 3, 4 and 5 mg mL .Scale bar: 2 μm.

concentration did not cause increase of the size. The

-1

TE D

Fig. 4 (a) The UV-vis spectra and (b) XRD patterns of

-1

maximum average diameter was approximately 500

EP

In the following, we systematically studied the

nm. And according to the Scherrer equation, the

dosage effect of DOBD on the perovskite films. As maximum average diameter was 34 ± 3 nm when the

shown in Fig. 4a, the concentrations variation of DOBD

-1

AC C

concentration of DOBD was 3 mg mL . The grain size

did not cause significant change of the UV-vis spectra was increased comparing to the PbI2 nanoparticles

of the resulting perovskite films (after being annealed). doped with DOBD, which is also calculated with

The results indicate that addition of DOBD has very Scherrer equation. Due to the increase of the gain

little effect on the final perovskite, and it is very size,

the

boundaries

per

unit

area

were

possible that interaction between DOBD and PbI2 has correspondingly decreased. According to the study of been replaced by forming perovskite structures. As Wu et al., the grain boundaries act as trap centers and shown in Fig.4b, the diffraction peaks located at 14.08° decelerate the charger transportation from one grain to and 28.45° should be assigned to [110] and [220]

another [36]. Therefore, the reduced grain boundaries

crystal planes of CH3NH3PbI3−xClx perovskite [46].

6

ACCEPTED MANUSCRIPT per

unit

area

result

in

the

improvement

of

the

device

the

device

configuration

was

performances [41]. There is no doubt that the grain

ITO/PEDOT:PSS/perovskite/C60/BCP/Al. The current

size in the horizontal direction was greatly increased.

density- voltage (J-V) and external quantum efficiency

In the normal direction, we can only rely on the XRD

(EQE) curves were shown in Fig. 5a and 5b,

and SEM result to deduce the scale change. Since the

respectively,

XRD results (according to the variation of FWHM)

parameters were listed in Table 2. For the Pero-SCs

implies a increased grain size, and the SEM images

without DOBD, the best PCE achieved was 14.47%

also indicate a increased grain size in the horizontal

with Voc of 0.95 V, Jsc of 20.60 mA cm , and FF of

direction, we assume that the perovskite grains in the

74.7%. For the Pero-SCs with DOBD, the PCE showed

normal direction might also increase accordingly. The

a significant improvement, and a champion PCE of

increase of grain size should facilitate the charge

17.58% with Voc of 1.06 V, Jsc of 21.40 mA cm , and

transportation in the perovskite films.

FF of 79.1% was obtained as 3 mg mL

the

corresponding

photovoltaic

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and

-2

-1

DOBD was

M AN U

SC

-2

added in the preparation of perovskite precursor. The

propose a possible model for the regulation of

enhancement of PCE of the devices was mainly

perovskite films: (1) The interaction between DOBD

attributed to the enhanced Voc and FF. The Jscs of the

and PbI2 resulted in smaller particles of PbI2, and the

Pero-SCs with or without DOBD didn’t have obvious

reduced size, according to Yang’s study, should be

improvements, and the values were confirmed with

propitious to the formation of high quality perovskite

EQE spectra, as shown in Fig. 5b. The steady-state

films;(2) The formation of adduct between DOBD and

photocurrents and efficiencies of the Pero-SCs were

PbI2 retarded the kinetics for crystal growth instead of

investigated to compare with those indicated by the J-

generating multiple nucleation points, finally resulting

V curves. As shown in Fig. 5c, the bias voltages for the

EP

TE D

Combining the FTIR, XRD and SEM results, we

in larger crystal grain sizes [45]. The model for the

Pero-SCs with and without DOBD were 0.9 and 0.85

formation of perovskite was presented in Scheme. 2.

V, and the steady-state efficiencies were 17.24% and 14.60%, respectively.

AC C

The effect of the DOBD additive on the photovoltaic performance of the Pero-SCs was investigated, where

Scheme 2 The model for the formation of perovskite doped with DOBD.

7

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ACCEPTED MANUSCRIPT

Fig. 5 (a) J−V and (b) EQE curves of the Pero-SCs doped with different amount of DOBD. (c) steady-state photocurrents and efficiencies of the Pero-SCs measured at bias voltage of 0.90 and 0.85 V, respectively.

PCE

To figure out why the addition of DOBD can improve

DOBD (mg mL ) (V) (mA cm ) (%)

(%)

the performance of Pero-SCs, the dark J-V curves and

Jsc

-1

-2

SC

FF

Concentration of Voc

0.95

20.60

74.7 14.47 (14.35 ± 0.28)

photocurrent density-effective voltage (Jph-Veff) plots

1

0.98

20.58

77.4 15.67 (15.48 ± 0.15)

were measured. As shown in Fig. 6a, the Pero-SC

2

1.01

20.94

77.2 16.15 (16.00 ± 0.10)

3

1.06

21.40

79.1 17.58 (17.46 ± 0.11)

4

1.06

20.95

77.2 17.20 (17.14 ± 0.08)

5

1.07

20.81

74.8 16.58 (16.45 ± 0.11)

TE D

M AN U

0

Table 2. Photovoltaic parameters of the Pero-SC with

different concentrations of DOBD additive. The data in

Fig. 6 (a) J-V curves measured in the Dark and (b) JphVeff curves for the Pero-SCs doped with and without DOBD.

EP

the brackets are the average PCEs and deviations.

doped with 3 mg mL-1 DOBD had relatively low leakage current compared with that without DOBD at the

in Table 2. Moreover, the values of steady-state

negative voltages, suggesting that the addition of DOBD

efficiency and photocurrent showed a slight decrease for

in perovskite can effectively suppress the charge

Pero-SC without DOBD under simulation of AM 1.5G

recombination and increase charge extraction, and thus

illumination for 300 s. On the contrary, these two values

resulting in improvement of FF [43,47,48]. Fig. 6b shows

for the Pero-SC doped with DOBD kept constant with

the Jph-Veff plots in double-logarithmic coordinates,

time. The results imply that addition of DOBD in

where Jph was determined by the equation Jph = JL – JD,

perovskite was likely to improve the stability of Pero-SCs

and Veff was calculated from the equation Veff = V0 – V.

under illumination, which

Among the equations, JL and JD were the current

AC C

These results were consistent with the values presented

mainly

results

from

the

densities under illumination and in the dark, respectively,

enhanced quality of the erovskite films.

8

ACCEPTED MANUSCRIPT

RI PT

Fig. 7 (a) Nyquist plots of the Pero-SCs with and without DOBD. (b) Steady-state and (c) transient PL spectra of the perovskite films on PEDOT:PSS surface.

wires, and the arc at the high & low frequency region V is applied voltage and V0 is the voltage at Jph = 0

were regarded as transportation resistance (Rtr) and the [49,50]. As shown in Fig. 6b, the values of Jph increased

SC

recombination resistance (Rrec), respectively [51,52]. linearly with Veff before ~ 0.1 V, and reached to a plateau

Upon the addition of DOBD, the Rtr of Pero-SCs as Veff was ~ 0.3 V. It is clear that Jph of the Pero-SC

decreased drastically from 149.4 to 105.5 Ω, which

M AN U

doped with DOBD was higher than that of Pero-SC

makes a good explanation for the improved charge

without DOBD, leading to a high charge extraction

transportation. Meanwhile, the Rrec was increased

efficiency and consequently a high FF.

from12.5 to 13.6 Ω, which should be responsible for the

The

measurements

of

the

alternating

current

suppression of charge recombination [41]. High Jsc and

impedance spectrometry (ACIS) were performed in the

FF were consequently acquired. The increase in Rrec

dark to analyze the charge transportation abilities of the

TE D

also agrees well with the enhancement of Vocs. Voc is Pero-SCs. The corresponding Nyquist plots and the

function of Jsc and the charge recombination current

corresponding parameters are shown in Fig. 7a and Table 3, respectively. Rtr

(Ω)

(Ω)

Pero-SCs

18.5 149.4 2.2 × 10

With 3 mg mL DOBD 13.3 105.5 1.6 × 10 -1

Rrec

(F)

AC C

Without DOBD

C1

EP

Rs

(Ω)

density (J0), as presented in Equation 1 [53], where A is the ideal factor of a device,

C2

(F)

-8

12.5 1.9 × 10

-6

-8

13.6 1.4 × 10

-6

Kb is the Boltzmann constant, T is the temperature, and e is the elementary charge. Herein, A, Kb, T and e are constants, and Jsc and J0 are variables. The Jsc for Pero-

Table 3. The detailed parameters of the equivalent SCs with and without DOBD were very close to each

circuit obtained by fitting the Nyquist plots of Pero-SCs other. Therefore, the Voc should have a reverse relation with J0. In addition, J0 is a function of Rrec, and they also The data were fitted with the equivalent circuit, as

have a reverse relation [53]. That is to say, Voc should

shown in the inset of Fig. 7a, where the series

be proportional to Rrec..Pero-SCs doped with DOBD

resistances (Rs) was the resistance of electrodes and

showed a higher Rrec, suggesting that the corresponding

9

ACCEPTED MANUSCRIPT Voc should be higher, too. This result was in good

being stored in glove box filled with nitrogen atmosphere

agreement with the device performance.

for 35 days, the PCE of Pero-SC doped with DOBD retained 85%, whereas the Pero-SC without DOBD

photoluminescence (PL) spectra were also used to

decreased down to 70% of its initial efficiency, as shown

investigate the charge extraction and transportation of

in Fig. 8. These results indicated that the stabilities of

the perovskite films. The steady-state PL spectra of the

Pero-SCs were dramatically improved with the doping of

perovskite@PEDOT:PSS were presented in Fig. 7b. For

DOBD.

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Apart from ACIS, the steady-state and transient

the perovskite films prepared under parallel conditions, the one with DOBD showed much weaker PL intensity, suggesting that the non-emissive decay of fluorescence

SC

increased. These results indicate that DOBD could passivate the defects in the perovskite film effectively. A1 (%) τ1 (ns) A2 (%)τ2 (ns) τavg (ns)

Without DOBD

24.20 16.94 76.81 91.82 87.71

M AN U

Perovskite films

-1

Fig. 8 Normalized PCEs of the Pero-SCs with and

With 3 mg mL DOBD41.07 3.87 58.93 24.36 22.32

without DOBD.

Table 4. The lifetimes and the corresponding portions of

The

transient

PL

TE D

the Pero-SCs with and without DOBD.

spectra

and

3. Conclusions

corresponding

In conclusion, we introduce an additive DOBD

in Fig. 7c and Table 4, respectively. The average charge

containing Lewis base C=O group into perovskite to

carrier lifetimes (τavg) were calculated from the decay

control the crystallization behavior. With the addition of

times (τi) and amplitudes (Ai) using Equation 2 [55]. The

DOBD, the perovskite presented large grain size and

for

the

perovskite

AC C

τavgs

EP

parameters of perovskite@PEDOT:PSS are presented

films

few grain boundaries, which were beneficial to facilitate

without

charge

the

addition

of

DOBD

suppress

charge

skyrocketed to 17.58% with huge enhanced Voc of 1.06 V, Jsc of 21.40 mA cm

Both the quenched emission and shortened τavg indicate upon

and

recombination. The PCE of DOBD doped-Pero-SC

and with DOBD were 87.71 and 22.32 ns, respectively.

that

transportation

the

-2

and FF of 79.1%, which was up

to 21.5% higher than that without DOBD (14.47%). The

charge

conspicuous improvement of PCE mainly resulted from

transportation between the perovskite and PEDOT:PSS

the enhanced Voc and FF. Besides, the DOBD doped-

were improved. At last, the storage stabilities of the

Pero-SCs were much more stable after storing in

Pero-SCs with and without DOBD were compared. After

10

ACCEPTED MANUSCRIPT and stirred at 70 °C for 12

glovebox for 35 days. The PCE of DOBD doped-Pero-

concentration of 460 mg mL

-1

SC retained 85%, whereas the Pero-SC without DOBD

h.

into

decreased down to 70% of its initial efficiency.

concentrations of 0, 1, 2, 3, 4 and 5 mg mL

DOBD

was

added

DMF

with

different

-1

to form a

series of PbI2 / DOBD mixture solutions. These series of 4. Experimental section

solutions are noted as solution 1. The solution of MAI and MACl was prepared by mixing MAI and MACl in

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4.1 Materials isopropanol (IPA, J&K) with the concentration of 50 mg −1

ITO-coated glass (10 Ω sq ) was purchased from

mL and 5 mg mL , respectively, and stirred at 70 °C for

CSG Holding Co., Ltd. PEDOT:PSS (Clevios P VP AI

12 h. This solution is noted as solution 2. The above

4083) was acquired from Nichem Co., and the possible

solution was filtrated with a polyvinyl difluoride (PVDF)

deposition was removed by running through a syringe

filter with typical pore size of 0.45 µm before use. The

-1

SC

-1

PbI2 solution was firstly spin-coated on the above

Methylammonium iodide (MAI) was prepared according

prepared PEDOT:PSS surface at 4500 rpm for 45 s, and

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filter with typical pinholes of 0.45 µm before use.

to the literature [56]. Methylammonium chloride (MACl)

then approximately 45 mL of mixed solution of MAI and

was purchased from Xi’an Polymer Light Technology

MACl was dropped onto the spinning substrate in 20 s.

Crop. PbI2 (99.999%) and 3,4-dihydroxybenzhydrazide

The substrate was then heated at 100 °C for 3 min,

(DOBD) were both acquired from Alfa Aesar. C60 and

obtaining a resulting perovskite film of ∼ 320 nm. Finally,

BCP were purchased from Puyang Yongxin Fullerene

the perovskite films were capped with C60 (∼ 30 nm),

TE D

Technology Co., Ltd. and Alfa Aesar, respectively. 4.2 Device fabrication

BCP (∼ 8 nm) and Al (∼ 80 nm) by thermal evaporation under vacuum of 1.0 × 10

-5

pa with a shadow mask

covered on the slides to define the active area (0.0757

All devices were fabricated on ITO-coated glass

EP

slides with size of 1.5 cm × 1.5 cm. The ITO slides were

2

cm ). The stabilities of Pero-SCs were tested with samples (without encapsulation) stored in glove box

washed in detergent, deionized water, acetone, ethanol filled with nitrogen atmosphere for 35 days.

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and isopropanol for 20 min twice each solvent under 4.3 Characterization

ultrasonification. Then the slides were dried in nitrogen flow, followed by treating with UV-ozone for 20 min.

The surface morphologies of perovskite films were

PEDOT:PSS was spin-coated on the cleaned ITO slides characterized by scanning electron microscopy (SEM, S-

at 5000 rpm for 40 s, and the slides were annealed at 8010, Hitachi) with applied acceleration voltage of 5 kV. 150 °C in air for 15 min.

The crystallinities of PbI2 and perovskite films were

The perovskite films were prepared by a two-step deposition method. PbI2 dimethylformamide

(DMF,

was

collected by X-ray diffraction (XRD) patterns performed

dissolved in N, N-

99.8%,

J&K)

with

on a diffractometer (D2 PHASER, Bruker). The UV-vis

the

absorption spectra were measured using a UV-visible

11

ACCEPTED MANUSCRIPT Notes and references

spectrophotometer (Cary 5000, Agilent Technology). Fourier transform infrared spectroscopy (FTIR) spectra

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-2

[3] A. (SAN_EI

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SC

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15

ACCEPTED MANUSCRIPT Fig. 6 (a) J-V curves measured in the Dark and (b) Jph-Veff curves for the Pero-SCs doped with and without DOBD. Fig. 7 (a) Nyquist plots of the Pero-SCs with and without DOBD. (b) Steady-state and (c) transient PL spectra of Figure Captions the perovskite films on PEDOT:PSS surface. Scam 1 Schematic illustration of the procedure to

without DOBD. Scam 2 The model for the formation of perovskite doped

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Fig. 8 Normalized PCEs of the Pero-SCs with and prepare perovskite films.

Table 1. Comparisons of perovskite solar cells added with DOBD.

SC

with different Lewis bases. Fig.1 Photos of PbI2 solution in presence of different

Table 2. Photovoltaic parameters of the Pero-SC with concentration of DOBD.

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different concentrations of DOBD additive. The data in Fig. 2 SEM images of neat PbI2 (a) and PbI2 with 3 mg -1

the brackets are the average PCEs and deviations.

mL DOBD (b); (c) the corresponding X-ray diffraction

Table 3. The detailed parameters of the equivalent

(XRD) patterns (a) & (b).

circuit obtained by fitting the Nyquist plots of Pero-SCs.

Fig. 3 (a) XRD patterns of annealed and unannealed

Table 4. The lifetimes and the corresponding portions of

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perovskite films with or without DOBD. (b) FTIR of

DOBD (powder) and DOBD+PbI2 (powder) for the C=O vibrations.

Fig. 4 (a) The UV-vis spectra and (b) XRD patterns of

EP

perovskite films doped with different concentrations of DOBD. (c) SEM images of the perovskite films prepared

AC C

with different amount of DOBD additives: 0, 1, 2, 3, 4 and 5 mg mL . Scale bar: 2 μm. -1

Fig. 5 (a) J−V and (b) EQE curves of the Pero-SCs doped with different amount of DOBD. (c) steady-state photocurrents and efficiencies of the Pero-SCs measured at bias voltage of 0.90 and 0.85 V, respectively.

16

the Pero-SCs with and without DOBD.

ACCEPTED MANUSCRIPT

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M AN U

SC

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Huiya Li, Kai Zhu and Kaicheng Zhang carried out the device fabrication and characterization. Peng Huang and Ligang Yuan carried out the SEM test and analysis. Dahua Li and Tiantian Cao carried out the FTIR characterization and analysis. Ziqi Sun, Zhendong Li and Qiaoyun Chen carried out the ACIS test and analysis. Bo Song, Yi Zhou and Huifang Zhu supervised the work. Bo Song and Kai Zhu analyzed the data and wrote the manuscript with contributions from all the co-authors.