Fabrication of stable and efficient 2D/3D perovskite solar cells through post-treatment with TBABF4

Article abstract of DOI:10.1039/d0tc05010e

Perovskite solar cells (PSCs), with their low cost and simple fabrication, have emerged as promising devices to solve global warming issues. In this study, tetrabutylammonium tetrafluoroborate (TBABF₄) was used as a passivator to boost the performance and the stability of the fabricated PSCs. Through TBABF₄post-treatment, the perovskite film's grain boundaries were passivated, which caused a reduction of charge traps on the surface of the perovskite layer and served as interfacial engineering at the perovskite/hole transport layer (HTL) interface. It was found that TBABF₄can act as a source of TBA⁺cations and cause the formation of a 2D/3D heterostructure layer, which increases the stability of PSCs. Indeed, the 2D/3D structure derived from TBABF₄solution plays the role of a shield layer to protect the surface of the perovskite layer from degradation and facilitates charge transport processes. The post-treatment of perovskite films is, thus, introduced as an approach to address both the stability and the performance of PSCs and as a step forward to commercialize PSCs.

Full text of DOI:10.1039/d0tc05010e

View Article Online
View Journal
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. Dehghanipour,
A. Behjat and H. Amrollahi Bioki, J. Mater. Chem. C, 2020, DOI: 10.1039/D0TC05010E.
Volume
Number
6
5
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
7
February 2018
Pages 911-1266
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
rsc.li/materials-c
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2050-7526
PAPER
Nosang V. Myung, Yong-Ho Choa et al.
A
noble gas sensor platform: linear dense assemblies of
a multi-layered
single-walled carbon nanotubes (LACNTs) in
ceramic/metal electrode system (MLES)
rsc.li/materials-c

Page 1 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
Fabrication of Stable and Efficient 2D/3D Perovskite Solar Cells through Post-treatment with TBABF4
a,b
a,b
a,b
M. Dehghanipour , A. Behjat† , H. Amrollahi Bioki
a
Department of Physics, Faculty of Science, Yazd University, Yazd, Iran
Photonics Research Group, Yazd University, Yazd, Iran
b
† Corresponding author. E-mail: abehjat@yazd.ac.ir
Abstract
7
8
9
Perovskite solar cells (PSCs), with their low cost and simple fabrication, have emerged as promising
devices to solve global warming issues. In this study, tetrabutylammonium tetrafluoroborate (TBABF ) was
4
used as a passivator to boost the performance and the stability of the fabricated PSCs. Through TBABF4
post-treatment, the perovskite film's grain boundaries were passivated, which caused a reduction of
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
charge traps on the surface of the perovskite layer and served as interfacial engineering at the perovskite/
+
hole transport layer (HTL) interface. It was found that TBABF can act as a source of TBA cation and cause
4
to form a 2D/3D heterostructure layer, which increases the stability of PSCs. Indeed, 2D/3D structure
derived from TBABF solution plays the role of a shield layer to protect the surface of perovskite layer
4
from degradation and facilitates charge transport processes. The post-treatment of perovskite films is,
thus, introduced as an approach to address both the stability and the performance of PSCs and as a step
forward to commercialize PSCs.
1
1
2
8
9
0
Keywords: Thermal stability, 2D-3D perovskite, Perovskite solar cells, Mixed-dimensional perovskite
1. Introduction
2
2
2
2
2
2
2
1
2
3
4
5
6
7
In recent years, perovskite solar cells (PSCs) have emerged as a promising application to meet the energy
demands of the world 1-3. The unique optoelectronic properties of perovskite materials 4-6 and their low-
cost fabrication have universally promoted them as appropriate candidates for producing solar cells. In
7
the past decade, the goal of many researchers was the improvement of the photovoltaic (PV) performance
of PSCs by suppressing charge recombination in perovskite layers or at the perovskite/charge interfaces
of transport layers -10, tailoring the composition of perovskite layers 11, 12, passivating grain boundaries
8
1
3-15
and reducing the surface defects of perovskite films 16, 17
.
2
2
3
3
3
3
3
8
9
0
1
2
3
4
Perovskite materials are known with a general ABX formula 18, 19, wherein A is an organic cation
3
+
+
+
+
+
+
(MA (CH NH ), FA (CH(NH ) ) or an inorganic cation (Cs , Rb ) at the hexahedral vertices, B is a metal
3
2
2 2
2
+
2+
2+
-
-
-
-
cation (Pb , Sn , Ge ) in the center, and X is a halide anion (Cl , Br , I , or SCN ) which coordinates the B
cations. Among perovskite materials, MAPbI with a bandgap of ≈1.55 eV is the most extensively used
3
material in PSCs 20-22. The maximum PCE reported for MAPbI -based PSCs is 21.2%, obtained through the
3
2
3
modification of electron transporting layers (ETLs) . FAPbI is another perovskite material widely used as
3
a light-harvesting layer in PSCs. Its desirability is due to the lower bandgap of about ≈1.43 eV 24, 25. This
1

Journal of Materials Chemistry C
Page 2 of 17
View Article Online
DOI: 10.1039/D0TC05010E
2
6
1
2
3
4
5
6
material has two perovskite phases, known as α and δ phases . The black α-phase of FAPbI perovskite
3
is useful for PV application, while its yellow δ-phase, known as the non-perovskite phase, is not favorable
. The partial substitution of Cs , Rb , and MA with FA has been introduced as an effective approach
to stabilize the photoactive α-phase of FAPbI perovskite 6, 28-33. A PCE of 23.4% was reported for FAPbI3-
2
7, 28
+
+
+
+
2
3
based PSCs. It was obtained by the incorporation of methylammonium chloride (MACl) into a FAPbI
3
2
8
precursor solution .
7
8
9
0
1
2
3
4
Both pure MAPbI and FAPbI PSCs have achieved high PCE values, but they suffer from low intrinsic
3
3
stability. The low stability disadvantage of PSCs should be addressed, and further efforts should be made
3
4
to industrialize PSCs. Different ISOS standards , such as, dark storage (ISOS-D), thermal cycling (ISOS-T),
1
1
1
1
1
and light-soaking (ISOS-L) have been considered to study the stability issue of PSCs. Saliba et al. showed
+
that adding a small amount of Cs to the FA/MA perovskite would significantly improve the thermal and
3
5
operational stability of PSCs . Afterwards, the A-site cation engineering of perovskite materials was
developed for PSCs stabilization 36-38. Researchers showed that adding Rb+ 39, K+ 40, or Gu+ 41 to triple-cation
Cs/FA/MA could further boost the PV performance and the stability of Cs/FA/MA PSCs.
1
1
1
1
1
2
2
2
2
2
5
6
7
8
9
0
1
2
3
4
Recently, the dimensional engineering of perovskite materials to form 2D/3D bi-layered structures on the
top of 3D perovskites has served as a most promising approach to improving the efficiency and stability
of PSCs 6, 42. Hu et al., for the first time, combined 2D perovskite (PEA) (MA) Pb I with 3D perovskite
2
4
5 16
MAPbI to form a 2D/3D heterostructure. They showed that the 2D/3D approach could boost the
3
4
3
performance and stability of 3D PSCs . Niu et al. compared different spacer ligands such as FBA, FPEA,
BA and PEA to fabricate 2D perovskite (L) (FA) Pb I (L refer to spacer ligands). They used FAPbI in 3D
2
n−1
n 3n+1
3
perovskite solar cells and deposited different 2D perovskites on the top of it. They also showed that FPEA-
4
4
based 2D/3D PSCs have higher stability than other spacers . Yao et al. employed a 2D/3D bi-layered
structure to improve both the efficiency and the stability of triple-cation PSCs. They incorporated n-
4
5
propylammonium iodide (PAI) in a 3D perovskite layer .
2
2
2
2
2
3
3
3
3
3
3
5
6
7
8
9
0
1
2
3
4
5
Considering the above discussion, this research aims at the fabrication of highly stable and efficient PSCs.
+
For this purpose, tetrabutylammonium tetrafluoroborate (TBABF ) is introduced as a source of TBA 2D
4
cation for the post-treatment of a triple-cation Cs/FA/MA perovskite layer and the formation of a 2D/3D
heterostructure layer. It has been found that TBABF can passivate the grain boundaries of perovskite
4
layers and subsequently improve the PV performance of PSCs. The results show that, through TBABF4
post-treatment, surface defects and non-radiative charges recombination are decreased. Through the
post-treatment approach practiced in this study, a considerable PCE of 17.02% is achieved, which is higher
than that of 14.01% for control devices. Additionally, it has been observed that TBABF -based PSCs are
4
more resistant to heat and humidity than control devices. Overall, the results prove that TBABF post-
4
treatment is a trustworthy approach for boosting the PCE and stability of PSCs through passivating the
grain boundaries and reducing the trap-state density of perovskite films.
3
6
2. Results and discussion
3
3
7
8
In this study, the PV properties and the stability of triple-cation PSCs were improved through the post-
treatment of perovskite films with a TBABF solution. To this end, first, the effects of TBABF concentration
4
4
2

Page 3 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
and the post-annealing temperature of the treated perovskite film on its properties were studied to
optimize the approach. Then, PSCs were fabricated via a two-step sequential deposition method (To find
more details, see the Experimental Section in Supporting Information). Figure 1 presents a schematic
diagram for the fabrication of PSCs without and with TBABF post-treatment (i.e., control devices and
4
treated devices respectively).
6
(a)
(b)
Figure 1. (a) Schematic illustration of the fabrication process for the control perovskite solar cells (PSCs)
top) and the PSCs post-treated with tetrabutylammonium tetrafluoroborate (TBABF ) (bottom). (b)
(
4
Chemical structure of the TBABF salt
4
7
2.1. Probing the effects of TBABF on perovskite film properties
4
8
9
Figure 2a shows the UV-vis absorption spectra of the perovskite films treated with different
concentrations of the TBABF solution. As it was observed, an increase in the concentration of the TBABF
4
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
solution to 4 mg/ml would lead to a remarkable increase in the absorbance capacity of the corresponding
perovskite film within the visible range. Further increase in the TBABF concentration, however, would
4
lead to the reduction of the absorbance of the perovskite film step by step. Figure 2b shows the UV-vis
absorbance spectra of the perovskite film treated with 4 mg/ml of TBABF solution, followed by different
4
post-annealing temperatures. From these spectra, it can be found out that the post-annealing
temperature of the treated film affected the optical properties of the perovskite film. As the results
o
showed, the absorbance of the perovskite film was improved when the temperature of 70 C was selected
for the post-annealing process of the treated perovskite film. Also, from the absorbance spectra of the
perovskite films with and without the post-treatment step, it is clear that TBABF treatment did not
4
change the edge-absorption position of the perovskite film 46, 47. In the literature, high absorbance by PSCs
is usually attributed to the enlarged grains size of the perovskite, but there were no enlarged grains
observed in the present study (Figure 3). The question is, thus, why did the absorbance of the treated
perovskite film increase? As deduced, the lower absorbance in the untreated perovskite film was due to
the non-perovskite phase of FAPbI (δ-FAPbI ) 48, which vanished after the post-treatment of the
3
3
perovskite (Figure 5a).
3

Journal of Materials Chemistry C
Page 4 of 17
View Article Online
DOI: 10.1039/D0TC05010E
o
Control
4 mg/ml
70 C
o
(a)
1
1
00 C
8
1
mg/ml
2 mg/ml
o
30 C
(b)
400
500
600
700
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Figure 2. (a) UV–vis absorption spectra of the control perovskite film and those post-treated with different
concentrations of tetrabutylammonium tetrafluoroborate (TBABF ). (b) UV–vis absorption spectra of the perovskite
4
films post-treated with 4 mg/ml of TBABF at different annealing temperatures
4
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
For a more profound study of the role of concentration and post-annealing temperature in the TBABF4
post-treatment approach, the surface morphology of different perovskite films was examined through
top-view SEM images (Figure 3). As it was found, at the annealing temperature of 100 C for treated
o
perovskite films by increasing the concentration of TBABF solution, the micromorphology of the
4
corresponding perovskite film would change. In the case of the sample treated with concentration of 4
mg/ml, compared to other solution concentrations, a desirable film could be achieved for PV applications.
As another observation, when the post-annealing temperature of the treated perovskite film increased
o
o
o
from 70 C (Figure 3e) to 100 C (Figure 3b) and even to 130 C (Figure 3f), some wrinkles and pinholes
appeared on the film, which would serve as centers for charge accumulation and were not favorable for
1
1
1
1
1
1
1
1
1
PSCs. Figure 3e clearly shows that, upon the TBABF post-treatment in optimized conditions, i.e., 4 mg/ml
4
o
solution of TBABF and a post-annealing temperature of 70 C for treated perovskite film, the grain
4
boundaries (GBs) of the perovskite film were passivated well. This phenomenon led to a decrease of the
trap density in the GBs, resulting in the decline of the monomolecular recombination and the
improvement of the PV performance (Figure 6). To support the results obtained from UV-vis and SEM
measurements, HTL-free PSCs were fabricated with the TBABF post-treatment step. Then, the effects of
4
the TBABF solution concentration and the post-annealing temperature of the treated perovskite films on
4
the PV properties were carefully probed (For more details, see Figure S1 and Table S1). The results shown
in Figure S1 are in full agreement with the findings of this study.
4

Page 5 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
Figure 3. Top-view SEM images of (a) the control and the tetrabutylammonium tetrafluoroborate
(
TBABF ) post-treated perovskite films with different concentrations of (b) 4 mg/ml, (c) 8 mg/ml and
4
(d) 12 mg/ml. The post-annealing temperature of the treated perovskite films for (b), (c) and (d) was
5

Journal of Materials Chemistry C
Page 6 of 17
View Article Online
DOI: 10.1039/D0TC05010E
o
1
00 C. (e) and (f) Top-view SEM images of the 4 mg/ml TBABF -treated perovskite films at the post-
4
o
o
annealing temperatures of 70 C and 130 C respectively
1
2
3
4
5
To further study the effects of the TBABF additive on the morphology of perovskite film, cross-sectional
SEM and AFM were employed (Figure 4). From cross-sectional SEM images was found that the thickness
4
of mixed mp-TiO /perovskite layer in both control and treated devices is about 500 nm. Besides, the root
2
mean square (RMS) roughness of the perovskite film before and after treatment shows a reduction of
16.02 nm to 12.92 nm, indicating a better perovskite film with lower surface traps.
3
D Perovskite
2
D/3D Perovskite
(a)
(b)
mp-TiO2
c-TiO2
FTO
(c)
(d)
Figure 4. (a, b) Cross-sectional SEM images of FTO/c-TiO /mp-TiO /control and treated perovskite films. Scale bar of SEM
2
2
images is 500 nm. (c, d) AFM images of control and the treated perovskite films on FTO/c-TiO /mp-TiO substrate.
2
2
6
7
8
9
0
1
2
3
From here onwards, the fabricated perovskite films with and without optimized post-treatment step were
labeled as ‘treated’ and 'control'. In Figure 5a, the XRD patterns of the control and the treated perovskite
films are compared. The XRD characterizations show that, with the addition of TBABF post-treatment
4
step, the peak intensity of the perovskite layer in the orientation of (001), (111) and (002) clearly
increased, resulting in improved perovskite crystallinity due to the perovskite treatment. This consistent
with the top-view SEM images (Figure 3). As it can be seen in the XRD pattern of the control film, there
are two PbI peaks at 12.56° and 38.56° as well as a light non-perovskite peak for the δ-FAPbI at 11.71°,
1
1
1
1
2
3
none of which is desirable for PSCs. After the perovskite treatment with TBABF , the PbI peaks were
4
2
6

Page 7 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
7
8
suppressed, and the δ-FAPbI peak completely vanished. Besides, in the XRD pattern of the treated
3
perovskite film, a low-angle peak was observed at 7.28°, which might have belonged to the two-
dimensional perovskite TBA PbI (BF ) structure 49, 50. As it was also observed, all the X-ray diffraction
2
4
4 4-x
peaks of the treated perovskite film shifted toward lower angles, considering a slight expansion in the unit
+
cell of perovskite caused by the incorporation of larger TBA cation into the 3D perovskite crystal structure
45, 49, 51. For better insight, the (001) plane for the control and the treated films is presented in Figure 5b.
It can be concluded that the TBABF treatment caused the formation of a 2D/3D bi-layered structure on
4
top of the 3D perovskite layer.
Control
Treated
Control
Treated
(a)
(b)
(111)
(002)
(001)
13.99
1
4.04
(
012)
(003)
022)
■
(
(011)
(112)
♥
♦
♦
♣
♥
♣
▲
13.6
13.8
14.0
14.2
14.4
5
10
15
20
25
30
35
40
45
2
Theta (degree)
2
Theta (degree)
Perovskite
Control
Treated
Control
Treated
(c)
7
50
775
800
825
850
600
650
700
750
800
850
900
Wavelength (nm)
Figure 5. (a) XRD pattern of the perovskite film with (treated) and without (control) TBABF treatment. ♦ denotes the PbI
4
2
phase, ▲ denotes the non-perovskite phase (δ-FAPbI ), ♥ denotes the TiO phase, ♣ denotes the FTO phase, and ■ denotes
3
2
the two-dimensional TBA PbI phase. (c) Steady-state photoluminescence (PL) spectra of the control and the post-treated
2
4
7

Journal of Materials Chemistry C
Page 8 of 17
View Article Online
DOI: 10.1039/D0TC05010E
perovskite films deposited on an FTO substrate. Inset of (c) represents the PL spectra of different perovskite solar cells with
ETL and HTL layers.
1
2
3
4
5
6
7
8
9
0
To further investigate the effect of TBABF post-treatment on the optical properties and the charge
4
recombination processes of perovskite films, steady-state photoluminescence (PL) measurements were
conducted at the excitation wavelength of 405 nm. First, the PL spectra of the control and the treated
perovskite films were measured on the FTO substrate (Figure 5c). It was found that both perovskite films
had a PL peak around 800 nm corresponding to the bandgap of 1.55 eV. This was consistent with previous
reports for triple-cation perovskite solar cells 52, 53. The PL intensity of the treated perovskite film was
higher than that of the control perovskite film, which suggests the reduction of non-radiative
recombination in the perovskite film due to the TBABF treatment. The suppressed non-radiative
4
recombination in the treated perovskite layer also suggests surface defects passivation and GBs
1
passivation after the TBABF treatment (See Figure 3) 46, 54.
4
Table 1. Photovoltaic parameters of different perovskite solar cells.
a
scb (mA/cm2)
c
d
Device
Voc (V)
J
FF (%)
PCE (%)
Average
Best
0.95
0.96
0.98
0.99
21.55
22.60
23.64
24.23
61.71
64.50
68.39
12.59
14.01
14.71
17.02
Control
Average
Best
Treated
71.20
a
b
c
d
Voc: open-circuit voltage; Jsc: short-circuit current density; FF: fill factor; PCE: power conversion
efficiency
1
1
2.2. TBABF effects on photovoltaic properties
4
1
1
1
1
2
3
4
5
To provide better insight, hole-only PSCs were fabricated with the configuration of
FTO/PEDOT:PSS/Perovskite/Spiro-OMeTAD/Au and the dark current-voltage (I-V) response of the control
and the treated hole-only devices were measured to calculate their trap density (푁 ) (Figures 7c and 7d).
푡
The 푁 was determined as follows:
푡
2
푉
휀 휀
푞퐿2
푇퐹퐿 푟 0
푁 =
푡
(1)
1
1
1
1
2
2
2
6
7
8
9
0
1
2
where q is the electric charge, L (400 nm) is the thickness of the perovskite layer, 휀 is the relative dielectric
푟
constant of perovskite (휀 = 47 for FAPbI ), 휀 is the vacuum permittivity, and V is the trap-filled limit
푟
3
0
TFL
voltage. As it can be seen in Figure 6, the VTFL value obtained for the control and the treated devices was
1
4
―3
0.41 V and 0.3 V respectively. The calculated hole trap density was also 2.83 × 10 푐푚 for the control
1
4
―3
and 2.07 × 10 푐푚 for the treated device, which was consistent with the higher PL peak intensity
observed in the treated perovskite film (Figure 5c). The inset of Figure 5c shows the PL spectra of the
control and the treated complete PSCs. It clearly shows a higher PL peak quenching in the treated PSCs,
8

Page 9 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
7
8
9
which implies the reduction of the charge recombination at the perovskite/HTL interface. The formation
of 2D/3D bi-layered due to the TBABF post-treatment approach facilitated the charge transfer process at
4
the perovskite/HTL interface 55, and, as schematically shown in Figure 7a, it blocked the charge
recombination. This was consistent with the higher PL quenching observed in the treated devices (Inset
of Figure 5c). This phenomenon explains the higher current-density in the treated PSCs than in the control
5
6
PSCs (Figure 6a) . To provide evidence for this statement, the dark I-V responses of the control and the
treated PSCs were measured (Figure 7b). The dark current-density of the treated device was significantly
lower than that of the control cells. This indicates that more photogenerated current would flow through
the PSC to reduce direct shunting. It also suggests the suppressed charge recombination and leakage
1
0
current in the treated PSCs 57, 58
.
25
20
15
10
5
0
19
(a)
18 (b)
Control
Treated
17
16
15
14
13
12
11
10
0.0
0.2
0.4
0.6
0.8
1.0
Control
Treated
V (Volt)
2
2
1
1
5
0
5
0
5
0
100
80
60
40
20
0
25
20
15
10
5
(
d)
(
c)
Control-F / PCE: 12.13%
Control-R / PCE: 13.80%
Treated-F / PCE: 15.77%
Treated-R / PCE: 16.69%
Control
Treated
0
900
0
.0
0.2
0.4
0.6
0.8
1.0
400
500
600
700
800
V (Volt)
Wavelength (nm)
Figure 6. (a) The current density–voltage (J-V) curves for the champion control and the treated perovskite solar cells
PSCs). (b) The statistical PCE distribution of all the control and the treated PSCs. (c) J-V characteristics in reverse and
(
forward scans of a typical device for control and treated PSCs. (d) The IPCE spectra of different PSCs and the integrated
current densities from the IPCE.
9

Journal of Materials Chemistry C
Page 10 of 17
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
The current density–voltage (J-V) characteristics of the best-performing PSCs for the control and the
treated devices are shown in Figure 6a. The active area of all PSCs to record J-V curves was 8 mm . The
2
statistical PCE distribution of all the fabricated PSCs is presented in Figure 6b, and all the other
corresponding PV parameters are summarized in Table 1. A champion PCE of 14.01% was achieved for the
control PSCs, with the open-circuit voltage (V ), the short-circuit current density (J ) and the fill factor
OC
SC
2
(FF) of 0.96 V, 22.60 mA/cm and 64.5% respectively. After the post-treatment step, a PCE of 17.02% was
2
obtained with the V , J and FF of 0.99 V, 24.23 mA/cm and 71.2% respectively. Besides, in Figure 6d
OC SC
the IPCE test was employed to show the J improvement. The obtained values of J from IPCE spectra
SC
SC
2
2
were 22.06 mA/cm and 23.40 mA/cm for control and the treated PSCs respectively, consistent with the
1
1
1
1
1
1
average J value calculated from J-V curves (See Table 1).”. All the PV parameters of the treated devices
SC
were higher than those of the control devices. As earlier explained, the higher V obtained in the treated
OC
devices is due to the lower trap density in them and the reduced non-radiative recombination. Also, the
higher J and FF for the treated devices are attributed to the suppressed charge recombination, blocked
SC
direct shunting, and suppressed non-perovskite δ-FAPbI phase caused by the formation of a 2D/3D bi-
3
layered structure in the TBABF post-treatment step. In addition, the hysteresis phenomenon (HI
4
1
6
(%)=((PCEreverse-PCEforward)/PCEreverse)╳100%) of PSCs was studied as shown in Figure 6c. It was found that
1
1
1
2
7
8
9
0
in treated PSCs the hysteresis index (HI) value reduces to 5.5% from 12% of that of the control device. The
lower HI in treated PSCs may be due to the GBs passivation of perovskite layer (Figure 3) and also
smoother perovskite layer (Figures 4c and 4d), which reduces the non-radiative recombination, and
facilitates charge transport processes at the perovskite/HTLs interface.
1E+00
(b)
1
E-01
E-02
E-03
E-04
(a)
1
1
1
Control
Treated
-
1.0
-0.5
0.0
V (Volt)
0.5
1.0
1
0

Page 11 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
1
7
5
2
.00E-05
4.0E-04
Control
Treated
(
c)
(d)
.50E-06
.00E-06
.50E-06
3.0E-04
2.0E-04
1.0E-04
VTFL= 0.41
VTFL= 0.30
0.01
0.1
V (Volt)
1
0.01
0.1
1
Volt (V)
Figure 7. (a) Band diagram of the perovskite solar cells (PSCs) with and without TBABF post-treatment. Bands energy
4
value as reported in 59, 60. (b) The dark current density–voltage (J-V) for the control and the treated PSCs. Dark current–
voltage characteristics of the hole-only device (FTO/PEDOT:PSS/Perovskite/Spiro-OMeTAD/Au) for (c) the control
perovskite film and (d) the treated perovskite film
1
2.3. Stability of the photovoltaic devices
2
3
4
5
6
7
8
9
0
1
As an important parameter, the stability of the PSCs was studied against humidity and heat. At first, the
thermal stability (thermal cycling) of the control and the treated perovskite layers were monitored. For
o
o
o
o
this purpose, the perovskite films were exposed to different temperatures of 85 C, 100 C, 120 C, 140 C
o
and 160 C. The perovskite films were held at each temperature for 30 minutes, and the UV-vis absorption
spectra were measured. Then, the temperature was immediately increased for the next step. This process
o
was repeated up to the temperature of 160 C (See Figure S2). There was a change observed in the edge-
absorption (EDA) position of the control perovskite film when the temperature of the thermal stability
o
o
test rose from 85 C to 160 C, suggesting a composition change in the control perovskite film. By contrast,
no change was observed in the EDA position of the treated perovskite film. So, it can be deduced that the
thermal stability of treated PSCs is higher than that of untreated PSCs.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
3
4
5
6
7
8
9
0
1
2
To investigate the long-term humidity stability (ISOS-D protocols) of the control and the treated PSCs, four
devices in each group were kept in a dry box with a humidity of < 20% (Figure 8e) and ambient air with a
relative humidity of 20-45% (Figure 8d). Figure 8a shows the digital photographs of the control (top) and
the treated (bottom) perovskite films during the stability test in ambient air. For both dry box and ambient
air stability tests, the UV-vis absorbance spectra of the corresponding perovskite films were periodically
measured (Figure S3). After 1440 hours of storage inside the dry box, the treated PV devices retained
about 90% of their initial efficiency, whereas a PCE loss of almost 30% occurred in the control devices.
Also, in the case of the ambient air test, after 600 hours, the treated PSCs had better ambient air stability
with a PCE loss of about 25%, as compared to the control PSCs which were degraded entirely during the
ambient air test. The same trend was observed in the UV-vis absorbance spectra of the devices during the
humidity tests (Figure S3). The observed results in ambient air stability are supported by the static contact-
1
1

Journal of Materials Chemistry C
Page 12 of 17
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
7
8
9
0
angle measurements presented in Figures 8b and 8c. As can be seen, the water droplet contact angle on
the TBABF4 treated perovskite film is larger than that that of the control film, indicating reduced
hygroscopicity and improved water resistance in treated films. The enhanced hydrophobicity behavior of
the treated films is an important factor contributing to the improved stability of TBABF -based PSCs. The
4
stability tests results bring one to the conviction that the stability improvement of treated PSCs is due to
the formation of 2D/3D bi-layered and GBs passivation, caused by the TBABF post-treatment approach.
4
6
1
As reported by Castro-Méndez et al. , the GBs in a perovskite layer are responsible for the unstable
behavior of PSCs. A perovskite film in humidity undergoes a degradation process beginning from the
surface, and the speed of degradation increases through GBs. GBs passivation is, thus, introduced as an
effective method to address the stability issue of PSCs.
1
(a)
(b)
(c)
1
2

Page 13 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
Control
Treated
Control
Treated
1.0
0.8
0.6
0.4
0.2
0.0
1
0
0
0
.0
.8
.6
.4
(d)
(e)
0.2
0
100
200
300
400
500
600
0
200 400 600 800 1000 1200 1400
Time (h)
Time (h)
Figure 8. (a) Digital photographs of the control and the treated perovskite films at 600 h in ambient air with a relative
humidity of 20-45%. The contact-angle measurement of control (b), and treated perovskite film (c). (d) The stability test
of the control and the treated perovskite solar cells at room temperature without encapsulation kept in ambient air
with a relative humidity of 20-45% and (e) those stored in a dry box (< 20% RH) in a dark condition. Four devices of each
type were utilized for the stability tests, and 5% of the error bars were adopted.
1
3. Conclusion
2
3
4
5
6
7
8
9
0
1
In this study, triple-cation PSCs were fabricated, and their performance and stability were improved by
using a TBABF salt solution for the post-treatment of the perovskite layer. The TBABF salt could serve as
a source for the TBA cation to form a 2D/3D heterostructure layer on the top of a 3D perovskite layer. As
4
4
+
it was found, TBABF treatment passivated GBs and reduced the trap density at the perovskite/HTL
4
interface, which improved the charge transport processes and reduced the charge recombination rate.
There was also a shift to a lower angle in the XRD pattern of the treated perovskite film, which proved the
formation of a 2D/3D structure. The results indicated that the presence of the 2D/3D layer on the top of
the 3D perovskite film and the passivation of GBs were both the result of the TBABF post-treatment and
4
1
1
the increased the thermal and ambient air stability of PSCs. In brief, the TBABF post-treatment approach
4
provides a simple way to enhance the PV parameters and the stability of PSCs.
1
1
2
3
Acknowledgments
1
1
4
5
The authors wish to thank Iran National Science Foundation (INSF) for the financial support of this
research (Research proposal No: 96003879).
1
6
References
1
1
1
7
8
9
1.
2.
T. N. Murakami and N. Koumura, Adv. Energy Mater., 2019, 9, 1802967.
M. Thambidurai, S. Foo, K. M. M. Salim, P. C. Harikesh, A. Bruno, N. F. Jamaludin, S. Lie, N.
Mathews and C. Dang, J. Mater. Chem. C, 2019, 7, 5028-5036.
1
3

Journal of Materials Chemistry C
Page 14 of 17
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
3.
4.
5.
M. Li, C. Zhao, Z. K. Wang, C. C. Zhang, H. K. H. Lee, A. Pockett, J. Barbé, W. C. Tsoi, Y. G. Yang and
M. J. Carnie, Adv. Energy Mater., 2018, 8, 1801509.
N. Torabi, A. Behjat, Y. Zhou, P. Docampo, R. J. Stoddard, H. W. Hillhouse and T. Ameri, Mater.
Today Energy, 2019, 12, 70-94.
N. Aeineh, A. s.-F. Castro-Méndez, P. J. Rodriguez-Cantó, R. Abargues, E. Hassanabadi, I. Suarez,
A. Behjat, P. Ortiz, J. P. Martínez-Pastor and I. Mora-Seró, ACS Omega, 2018, 3, 9798-9804.
G. Grancini and M. K. Nazeeruddin, Nat. Rev. Mater., 2019, 4, 4-22.
H. Zarenezhad, M. Askari, M. Halali, N. Solati, T. Balkan and S. Kaya, Sol. Energy Mater. Sol. Cells,
2020, 206, 110318.
M. M. Tavakoli, K.-H. Tsui, Q. Zhang, J. He, Y. Yao, D. Li and Z. Fan, ACS Nano, 2015, 9, 10287-
10295.
H. Wang, F. Li, P. Wang, R. Sun, W. Ma, M. Chen, W. Miao, D. Liu and T. Wang, Adv. Energy Mater.,
2020, 10, 2000615.
D. Aidarkhanov, Z. Ren, C.-K. Lim, Z. Yelzhanova, G. Nigmetova, G. Taltanova, B. Baptayev, F. Liu,
S. H. Cheung and M. Balanay, Sol. Energy Mater. Sol. Cells, 2020, 215, 110648.
F. Valipour, E. Yazdi, N. Torabi, B. F. Mirjalili and A. Behjat, J. Physics D: Appl. Phys., 2020.
J. Tian, J. Wang, Q. Xue, T. Niu, L. Yan, Z. Zhu, N. Li, C. J. Brabec, H. L. Yip and Y. Cao, Adv. Funct.
Mater., 2020, 2001764.
P. Guo, Q. Ye, X. Yang, J. Zhang, F. Xu, D. Shchukin, B. Wei and H. Wang, J. Mater. Chem. A, 2019,
7, 2497-2506.
J. Zhu, B. He, Z. Gong, Y. Ding, W. Zhang, X. Li, Z. Zong, H. Chen and Q. Tang, ChemSusChem, 2020.
Q. Guo, F. Yuan, B. Zhang, S. Zhou, J. Zhang, Y. Bai, L. Fan, T. Hayat, A. Alsaedi and Z. a. Tan,
Nanoscale, 2019, 11, 115-124.
F. Doosthosseini, A. Behjat, A. Karimi Zarchi, N. Taghavinia and B. F. Mirjalili, J. Mater. Sci.: Mater.
Electron., 2020, 1-10.
M. Ouafi, L. Atourki, L. Laânab, E. Vega, B. Mari, M. Mollar and B. Jaber, J. Alloys Compd., 2019,
790, 1101-1107.
M. A. Green, A. Ho-Baillie and H. J. Snaith, Nat. Photonics, 2014, 8, 506-514.
P. Wang, Y. Wu, B. Cai, Q. Ma, X. Zheng and W. H. Zhang, Adv. Funct. Mater., 2019, 29, 1807661.
Z. Chen, B. Turedi, A. Y. Alsalloum, C. Yang, X. Zheng, I. Gereige, A. AlSaggaf, O. F. Mohammed and
O. M. Bakr, ACS Energy Lett., 2019, 4, 1258-1259.
Y. Ma, P. M. Hangoma, W. I. Park, J.-H. Lim, Y. K. Jung, J. H. Jeong, S. H. Park and K. H. Kim,
Nanoscale, 2019, 11, 170-177.
M. B. Islam, M. Yanagida, Y. Shirai, Y. Nabetani and K. Miyano, Sol. Energy Mater. Sol. Cells, 2019,
195, 323-329.
S. S. Shin, E. J. Yeom, W. S. Yang, S. Hur, M. G. Kim, J. Im, J. Seo, J. H. Noh and S. I. Seok, Science,
2017, 356, 167-171.
6.
7.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
G. S. Shin, Y. Zhang and N.-G. Park, ACS Appl. Mater. Interfaces, 2020, 12, 15167-15174.
H.-C. V. Tran, W. Jiang, M. Lyu and H. Chae, J. Phys. Chem. C, 2020.
A. Binek, F. C. Hanusch, P. Docampo and T. Bein, J. Phys. Chem. Lett., 2015, 6, 1249-1253.
D. Barrit, P. Cheng, K. Darabi, M. C. Tang, D. M. Smilgies, S. Liu, T. D. Anthopoulos, K. Zhao and A.
Amassian, Adv. Funct. Mater., 2020, 30, 1907442.
M. Kim, G.-H. Kim, T. K. Lee, I. W. Choi, H. W. Choi, Y. Jo, Y. J. Yoon, J. W. Kim, J. Lee and D. Huh,
Joule, 2019, 3, 2179-2192.
N. Pellet, P. Gao, G. Gregori, T. Y. Yang, M. K. Nazeeruddin, J. Maier and M. Grätzel, Angew. Chem.,
2014, 126, 3215-3221.
28.
29.
30.
N. J. Jeon, J. H. Noh, W. S. Yang, Y. C. Kim, S. Ryu, J. Seo and S. I. Seok, Nature, 2015, 517, 476-480.
1
4

Page 15 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
6
7
8
9
31.
O. A. Syzgantseva, M. Saliba, M. Grätzel and U. Rothlisberger, J. Phys. Chem. Lett., 2017, 8, 1191-
1196.
Z. Li, M. Yang, J.-S. Park, S.-H. Wei, J. J. Berry and K. Zhu, Chem. Mater., 2016, 28, 284-292.
Y. H. Park, I. Jeong, S. Bae, H. J. Son, P. Lee, J. Lee, C. H. Lee and M. J. Ko, Adv. Funct. Mater., 2017,
27, 1605988.
32.
33.
34.
35.
M. V. Khenkin, E. A. Katz, A. Abate, G. Bardizza, J. J. Berry, C. Brabec, F. Brunetti, V. Bulović, Q.
Burlingame and A. Di Carlo, Nat. Energy, 2020, 5, 35-49.
M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa-Baena, M. K. Nazeeruddin, S. M.
Zakeeruddin, W. Tress, A. Abate and A. Hagfeldt, Energy Environ. Sci., 2016, 9, 1989-1997.
S. Tang, S. Huang, G. J. Wilson and A. Ho-Baillie, Trends Chem., 2020.
L. K. Ono, E. J. Juarez-Perez and Y. Qi, ACS Appl. Mater. Interfaces, 2017, 9, 30197-30246.
H. Shahivandi, M. Vaezzadeh and M. Saeidi, Sol. Energy Mater. Sol. Cells, 2020, 218, 110770.
M. Saliba, T. Matsui, K. Domanski, J.-Y. Seo, A. Ummadisingu, S. M. Zakeeruddin, J.-P. Correa-
Baena, W. R. Tress, A. Abate and A. Hagfeldt, Science, 2016, 354, 206-209.
T. Bu, X. Liu, Y. Zhou, J. Yi, X. Huang, L. Luo, J. Xiao, Z. Ku, Y. Peng and F. Huang, Energy Environ.
Sci., 2017, 10, 2509-2515.
S. Wu, Z. Li, J. Zhang, T. Liu, Z. Zhu and A. K. Y. Jen, ChemComm., 2019, 55, 4315-4318.
A. Krishna, S. Gottis, M. K. Nazeeruddin and F. Sauvage, Adv. Funct. Mater., 2019, 29, 1806482.
Y. Hu, J. Schlipf, M. Wussler, M. L. Petrus, W. Jaegermann, T. Bein, P. Müller-Buschbaum and P.
Docampo, ACS Nano, 2016, 10, 5999-6007.
T. Niu, J. Lu, X. Jia, Z. Xu, M.-C. Tang, D. Barrit, N. Yuan, J. Ding, X. Zhang and Y. Fan, Nano Lett.,
2019, 19, 7181-7190.
D. Yao, C. Zhang, S. Zhang, Y. Yang, A. Du, E. Waclawik, X. Yu, G. J. Wilson and H. Wang, ACS Appl.
Mater. Interfaces, 2019, 11, 29753-29764.
M. M. Tavakoli, M. Saliba, P. Yadav, P. Holzhey, A. Hagfeldt, S. M. Zakeeruddin and M. Grätzel,
Adv. Energy Mater., 2019, 9, 1802646.
L. Tian, W. Zhang, H. Yu, C. Peng, H. Mao, Y. Li, Q. Wang and Y. Huang, ACS Appl. Energy Mater.,
2019, 2, 4954-4963.
F. Xie, C.-C. Chen, Y. Wu, X. Li, M. Cai, X. Liu, X. Yang and L. Han, Energy Environ. Sci., 2017, 10,
1942-1949.
I. Poli, S. Eslava and P. Cameron, J. Mater. Chem. A, 2017, 5, 22325-22333.
S. Nagane and S. Ogale, J. Phys. Chem. Lett., 2016, 7, 4757-4762.
S. Shao, J. Dong, H. Duim, H. Gert, G. R. Blake, G. Portale and M. A. Loi, Nano Energy, 2019, 60,
810-816.
X. Zheng, Y. Hou, C. Bao, J. Yin, F. Yuan, Z. Huang, K. Song, J. Liu, J. Troughton and N. Gasparini,
Nat. Energy, 2020, 5, 131-140.
Q. Li, Y. Zhao, W. Zhou, Z. Han, R. Fu, F. Lin, D. Yu and Q. Zhao, Adv. Energy Mater., 2019, 9,
1902239.
M. Chen, P. Li, C. Liang, H. Gu, W. Tong, S. Cheng, W. Li, G. Zhao and G. Shao, J. Energy Chem.,
2020, 45, 103-109.
M. Salado, M. Andresini, P. Huang, M. T. Khan, F. Ciriaco, S. Kazim and S. Ahmad, Adv. Funct.
Mater., 2020, 30, 1910561.
Y. Zhang, J. Chen, X. Lian, M. Qin, J. Li, T. R. Andersen, X. Lu, G. Wu, H. Li and H. Chen, Small
Methods, 2019, 3, 1900375.
K. Chen, Q. Hu, T. Liu, L. Zhao, D. Luo, J. Wu, Y. Zhang, W. Zhang, F. Liu and T. P. Russell, Adv.
Mater., 2016, 28, 10718-10724.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
Z. Li, J. Dong, C. Liu, J. Guo, L. Shen and W. Guo, Nanomicro Lett., 2019, 11, 50.
1
5

Journal of Materials Chemistry C
Page 16 of 17
View Article Online
DOI: 10.1039/D0TC05010E
1
2
3
4
5
59.
60.
61.
Z. Li, J. Chen, H. Li, Q. Zhang, Z. Chen, X. Zheng, G. Fang and Y. Hao, RSC Adv., 2017, 7, 41903-
41908.
S. Wang, J. Jin, Y. Qi, P. Liu, Y. Xia, Y. Jiang, R. X. He, B. Chen, Y. Liu and X. Z. Zhao, Adv. Funct.
Mater., 2020, 30, 1908343.
A. F. Castro-Méndez, J. Hidalgo and J. P. Correa-Baena, Adv. Energy Mater., 2019, 9, 1901489.
6
1
6

Page 17 of 17
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/D0TC05010E
Fabrication of Stable and Efficient 2D/3D Perovskite Solar Cells through Post-
treatment with TBABF4
A promising 2D/3D heterostructure based on TBABF salt to boost the performance and stability
4
of perovskite solar cells
Contents
1
2
. Introduction……………………………………………………………………………………………………………………………1
. Results and discussion…………………………………………………………………………………………………………….2
2
2
2
.1.Probing the effects of TBABF4 on perovskite film properties…………………………………………….3
.2.TBABF effects on photovoltaic properties………………………………………………………………………..9
4
.3.Stability of the photovoltaic devices…………………………………………………………………………………12
3
. Conclusion………………………………………………………………………………………………………………………………13
Acknowledgments…………………………………………………………………………………………………………………………14
References…………………………………………………………………………………………………………………………………….14