Defect-passivation of organometal trihalide perovskite with functionalized organic small molecule for enhanced device performance and stability

Article abstract of DOI:10.1016/j.dyepig.2021.109255

Defects in solution-processed organic and inorganic halide perovskite thin films deteriorate their photovoltaic performance and stability. Here, a bisimidazole-based organic small molecular hole transport material (HTM) that can suppress interfacial defects of the perovskite with its functional groups working as Lewis bases is newly introduced. Surface passivation of perovskite film leads to the reduction in non-radiative recombination trap density as well as the improvement of its crystallinity, consequently enhancing the efficiency of perovskite solar cell (PSC) from 16.3% to 18.3% with superior stability, preserving 92% of its initial efficiency for 500 h in an atmosphere.

Full text of DOI:10.1016/j.dyepig.2021.109255

Dyes and Pigments 189 (2021) 109255
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Defect-passivation of organometal trihalide perovskite with functionalized
organic small molecule for enhanced device performance and stability
,
b
,
,
,
,
,b
Joonhyuk Choia 1, Eswaran Kamarajc 1, Hansol Parka b, Bum Ho Jeonga
,
Hyoung Won Baacd **, Sanghyuk Parkc ***, Hui Joon Parka
,
,b,*
a Department of Organic and Nano Engineering, Hanyang University, Seoul, 04763, Republic of Korea
b Human-Tech Convergence Program, Hanyang University, Seoul, 04763, Republic of Korea
c Department of Chemistry, Kongju National University, Kongju, 32588, Republic of Korea
d Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
Defects in solution-processed organic and inorganic halide perovskite thin films deteriorate their photovoltaic
performance and stability. Here, a bisimidazole-based organic small molecular hole transport material (HTM)
that can suppress interfacial defects of the perovskite with its functional groups working as Lewis bases is newly
introduced. Surface passivation of perovskite film leads to the reduction in non-radiative recombination trap
density as well as the improvement of its crystallinity, consequently enhancing the efficiency of perovskite solar
cell (PSC) from 16.3% to 18.3% with superior stability, preserving 92% of its initial efficiency for 500 h in an
atmosphere.
Perovskite solar cell
Organic hole-transport layer
Defect-passivation
1. Introduction
shown various advantages like low processing temperature, negligible
hysteresis, etc. [6–9].
Organic-inorganic halide perovskite solar cells (PSCs) have shown
tremendous potentials during the last decade for conversion of solar
energy to electrical energy. Correspondingly, the PSCs have gained their
power conversion efficiency (PCE) from 3.8% in 2009 to 25.2% now.
These incredible progresses in PSCs are due to their exceptional opto-
electronic properties such as high absorption coefficient, high defect
tolerable limit, high carrier mobility, and long carrier diffusion length
[1–5]. The PSC devices are generally sandwiched by interfacial electron
transport layer (ETL) and hole transport layer (HTL), and those are
classified as n-i-p and p-i-n, depending on the order of interfacial layers.
The PSCs having n-i-p configuration, of which a ETL has been firstly
deposited on a transparent conducting oxide (TCO) layer, have shown
higher PCE than that of PSCs having p-i-n configuration, but they had
limitations such as high process temperature (>400 ◦C), required for the
annealing of ETL (e.g. TiO2), and hysteretic behaviors, often observed in
this configuration without a mesoporous structure. In comparison, the
p-i-n configuration PSCs, of which a HTL is formed on a TCO, have
The performances of PSCs are largely dependent on the interfacial
characteristics between the charge transport layer (ETL and HTL) and
perovskite photoactive layer. Especially for the hole transport material
(HTM), a superior hole-extracting and electron-blocking capability
along with a low carrier recombination property at the interface with the
perovskite layer are required. Moreover, for the layer to be efficiently
utilized as a HTL in the p-i-n configuration PSC, a chemical robustness
that can help to form a stable perovskite layer on top of the HTL is also
necessary [9–12]. In these aspects, a variety of inorganic HTMs such as
CuOx, MoO3, graphene oxide, CuSCN, CuI, CuS, CuGaO2, V2O5, and
NiOx have been intensively investigated due to their suitable band
alignment, hole mobility, stability, and cost effectiveness [10–12].
Among those, NiOx is one of the widely explored HTMs because of its
high band gap, high transmittance in visible range and deep valance
band edge [13–17]. However, NiOx-based PSCs have often suffered from
a poor interfacial property between NiOx and perovskite layer, because
low temperature solution processed-NiOx usually had high defect
* Corresponding author. Department of Organic and Nano Engineering, Hanyang University, Seoul, 04763, Republic of Korea.
** Corresponding author. Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
*** Corresponding author. Department of Chemistry, Kongju National University, Kongju, 32588, Republic of Korea.
E-mail addresses: hwbaac@skku.edu (H.W. Baac), spark0920@kongju.ac.kr (S. Park), huijoon@hanyang.ac.kr (H.J. Park).
1
J.C and E.K. contributed equally to this work.
https://doi.org/10.1016/j.dyepig.2021.109255
Received 5 January 2021; Received in revised form 18 February 2021; Accepted 19 February 2021
Available online 2 March 2021
0143-7208/© 2021 Elsevier Ltd. All rights reserved.

J. Choi et al.
Dyes and Pigments 189 (2021) 109255
density, which reduced its hole extraction ability [18–22]. This incurred
the accumulation of hole near the interface with the perovskite and
increased the trap-assisted non-radiative recombination losses, conse-
quently decreasing the efficiency of devices. Moreover, a rough surface
of NiOx layer deteriorates the surface morphology and crystallinity of
the following perovskite layer, also degrading their performances.
Therefore, a strategy that can enhance the interfacial properties between
NiOx and perovskite can be an effective approach to achieve high effi-
ciency PSCs.
be tailored with diverse D and A groups on the phenyl ring that present
in the C2, C4 and C5 positions, together with N1 position of the imid-
azole ring (Fig. S1) [17,31,32,41]. These structural modifications can
also be used to modulate the bandgap of imidazole derivatives, which
are suitable for HTMs of PSCs [17,41,43].
Here, aiming at development of robust and facile imidazole-based
HTMs for PSCs, we have introduced D-A-D structures with extended
π
-conjugation. By simple alteration of benzaldehyde into tereph-
thaldehyde, a bisimidazole-based HTMs (1,4-bis(4,5-bis(4-methox-
yphenyl)-1-phenyl-1H-imidazol-2-yl)benzene) was designed and
synthesized through the one-pot condensation of Debus–Radziszewski
imidazole synthetic route [44] with cost-effective high reaction yield
(molecular structure in Fig. 1a, synthetic procedure in Fig. S2, and cost
evaluation chart in Table S1). Compared to asymmetric D-A-structured
monoimidazole HTMs or conventional spiro-OMeTAD molecules, the
Among various heterocyclic aromatic organic materials, imidazole
derivatives have attracted significant attention because of their exclu-
sive optical, thermal, and electronic properties [23,24]. Combination of
electron donating (D) groups and electron accepting (A) moieties are
frequently used to generate dipolar push-pull systems that feature low
bandgap energy as well as intense charge transfer absorption [25,26].
The substitution of various electron D/A groups to initial imidazole
moiety increased polarizability, stability, and thermal or chemical
robustness [27]. Charge transport and balance are key factors for
obtaining high device performances, and bisimidazole derivatives with
proper D/A moieties have showed promising hole transport character-
istics for organic light-emitting diodes (OLEDs), dye-sensitized solar
cells, and PSCs [28–30]. In this work, a bisimidazole-based organic HTM
molecule is newly designed and introduced between NiOx and perov-
skite layer of p-i-n structure PSC devices for improving their interfacial
properties. Especially, methoxy functional groups, attached to the
organic molecule, are shown to passivate non-radiative recombination
trap sites of perovskite as well as to improve its crystallinity, conse-
quently enhancing the performances and stability of PSC devices.
π
-conjugated system of planar bisimidazole makes high density packing
possible in solid state, which is helpful in obtaining higher hole mobility
[45]. Also, the two imidazole rings, which are linked by central phenyl
spacer, effectively lower highest occupied molecular orbital (HOMO,
ꢀ 5.23 eV) and lowest unoccupied molecular orbital (LUMO, ꢀ 2.12 eV)
energy levels, and minimize the energy offset between the valence band
maximum of perovskite and the HOMO of the HTMs (Table S2). Addi-
tionally, its low absorbance in visible wavelength region (Fig. S3a) is
beneficial to increase the amount of photon into the perovskite
photo-absorber in p-i-n structure PSC devices. For reference, cyclic
voltammetry results for energy level calculation are in Fig. S4, and
material characterization data such as photoluminescence (PL)
(Fig. S3b), TGA results along with DSC (Fig. S5), 1H NMR (Fig. S6), and
HR-MS (Fig. S7) are in Supplementary data.
Furthermore, four methoxy groups, introduced to the organic
molecule, are expected to work as Lewis bases due to their excess
electron lone pairs, which can passivate unsaturated bonds such as
under-coordinated Pb2+ ions in the perovskite [46]. The reduced deep
level defects at the interface by the passivation are advantageous to
decrease non-radiative recombination losses [47,48]. Raman spectrum
of the perovskite film, cast on top of the organic HTM, shows a peak at
350 cmꢀ 1 that can be assigned to Pb–O bond stretching (Fig. 1b), and
2. Results and discussion
2.1. Organic HTM with defect-passivating functional groups
Recently, lophine (2,4,5-triphenyl-1H-imidazole) derivatives
showed attractive emitting characteristics for OLEDs [31–36], lasing
materials [37–39], and chemosensors [40], and transporting properties
for HTMs [17,41,42]. Especially, the molecular structure of lophine can
Fig. 1. (a) Molecular structure of designed bisimidazole derivative organic HTM. (b) Raman spectra of perovskite films (bare perovskite and perovskite cast on
organic HTM thin film). (c) SEM image of perovskite cast on organic HTM. (d) X-ray diffraction (XRD) patterns of the perovskite films (NiOx/perovskite and NiOx/
organic/perovskite). (e) Variation of XRD patterns of perovskite films depending on UV illumination time.
2

J. Choi et al.
Dyes and Pigments 189 (2021) 109255
this validates the formation of Lewis adduct between O atom of the
organic HTM and unsaturated Pb2+ ions of the perovskite [49,50]. To
rule out the possibility of oxidation of perovskite, we immediately
characterized the samples, and no peak was observed from the
perovskite-only layer even after its exposure to air for several hours.
X-ray diffraction (XRD) patterns in Fig. 1d, referenced to ITO signals,
show that the crystallinity of perovskite is enhanced on the underlying
organic HTL. The passivation of defect at the interface is believed to
assist the growth of perovskite crystal in the preferred orientation.
characteristics, which were measured under 100 mW cmꢀ 2 AM 1.5G
illumination, at a scan rate of 0.05 V sꢀ 1 for forward scan, in an atmo-
sphere without encapsulation, and with an aperture area of 0.096 cm2,
are represented in Fig. 3a. J-V curves of PSCs show that the efficiency of
the PSC without organic HTM is largely improved from 16.28% [short
circuit current density (Jsc): 21.95 mA cmꢀ 2, open circuit voltage (Voc):
1.04 V, fill factor (FF): 71.44%] to 18.29% (Jsc: 22.41 mA cmꢀ 2, Voc:
1.04 V, and FF: 78.47%) with the addition of organic HTL. For reference,
the average values of PV cell parameters, obtained by J-V characteris-
tics, are summarized in Table 1. The enhancement of photocurrent could
be further confirmed by external quantum efficiency (EQE) spectra
(Fig. 3b), and the Jsc values, obtained by integrating the EQE spectra,
were well-matched to those from the J-V plots. Meanwhile, the PSCs
with organic HTM did not show any hysteretic behaviors, as shown in
Fig. 4a, and the performances of devices, measured at the maximum
power point, were comparable to those from J-V scanning (Fig. 4b),
representing the stable operation of the devices. As mentioned, the
improved interfacial properties along with the superior quality of defect-
passivated perovskite are also expected to enhance the stability of PSC
devices [58], and we confirmed that the PSCs with organic HTM showed
excellent stability (Fig. 4c), preserving 92% of its initial efficiency for
500 h in ambient air (Al2O3-encapsulation, room temperature, and the
relative humidity between 30% and 50%).
Moreover, under UV-irradiation (from perovskite-side), while
a
diffraction peak at 12.6◦, related to (001) plane of PbI2 impurity, is
newly generated from the pristine perovskite, demonstrating the
decomposition of the perovskite, no PbI2-related peak is observed from
the perovskite, grown on the organic HTM, proving its enhanced UV-
stability after passivation (Fig. 1e) [51,52]. The variation of intensity
and full width at half maximum (FWHM) of main XRD peak of perov-
skite at ~ 14◦ is summarized in Table S3, for reference. Additionally, the
perovskite grains with and without organic HTM are shown in scanning
electron microscope (SEM) images in Fig. 1c and Fig. S8.
Fig. 2a shows that photoluminescence (PL) intensity of perovskite is
30% and 54% reduced in NiOx/perovskite and NiOx/organic HTM/
perovskite films, respectively, compared to that of pristine perovskite
film. These reduced PL spectra represent that the recombination loss in
the perovskite photo-absorber is suppressed by the passivation of its
defects with the organic HTM [53–56]. Additionally, charge transfer
dynamics at the interface was further examined by time-resolved pho-
toluminescence (TRPL) measurement (Fig. 2b and Table S4), and it was
confirmed that the carrier lifetime of 202 ns, observed from the
perovskite-only thin film, decreased to 165 ns with NiOx and it was
further reduced to 157 ns with the additional organic HTM on NiOx. The
shortened lifetime could be a proof of improved carrier extraction at the
interface with the passivation. For calculating those lifetimes, the sam-
ples were excited using a picosecond diode laser (510 nm wavelength)
from the perovskite-side, and their carrier lifetimes (τavg) were calcu-
lated by fitting their decay curves to a bi-exponential equation: τavg = A1
2.3. Reduced trap-density at the interface between perovskite and HTL
The trap-density of the perovskite can be calculated by estimating
the trap-filled limited voltages (VTFL) of dark J-V curves of hole-only
devices (ITO/NiOx/organic HTM/perovskite/spiro-OMeTAD/Au) with
the following equation (1) [59,60].
Ntrap = 2εεoVTFL(eL2)ꢀ 1
(1)
where e is elementary charge, εεo is semiconductor permittivity, and L is
the layer thickness. Fig. 5a and Table S5 confirmed that the calculated
static trap-density of the perovskite film was reduced after passivation
exp(-t/τ1) + A2 exp(-t/τ2), where τ1, τ2, A1, and A2 were lifetimes for
slow and fast decay, and their relative amplitudes, respectively
(Table S4) [57].
from 1.18 × 1016 to 0.88 × 1016 cmꢀ 3. The hole-mobility (
μ) was also
obtained by fitting the curves in space-charge-limited-current (SCLC)
regime with the Mott-Gurney law (2) [61].
2.2. Perovskite solar cell performances
J = 9εεoμV2(8L3)ꢀ 1
(2)
The enhanced interfacial properties between perovskite and HTL
with the addition of organic HTM are expected to improve the perfor-
mances and stability of PV devices. To confirm this, we prepared p-i-n
architecture PSC devices with the following structure, ITO/NiOx/
The calculated hole-mobility was enhanced from 1.2 × 10ꢀ 3 to 3.0 ×
10ꢀ 3 cm2 Vꢀ 1 sꢀ 1 with the organic passivation layer (Table S5), indi-
cating that the reduced trap density was beneficial to the efficient charge
transport.
organic
HTM/perovskite[Cs0.04(FA0.92MA0.08 0.96
)
Pb(I0.92Br0.08)3]/
The decreased trap-states are also advantageous to suppress the non-
radiative recombination of photo-generated carrier in the photo-
absorbing layer, consequently increasing its quasi-Fermi level
fullerene(C60)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP)/
silver(Ag) (inset of Fig. 3a), and their current density-voltage (J-V)
Fig. 2. (a) Steady-state photoluminescence (PL) spectra of perovskite films (perovskite, NiOx/perovskite, and NiOx/organic/perovskite). (b) Time-resolved PL (TRPL)
decay curves of perovskite films (perovskite, NiOx/perovskite, and NiOx/organic/perovskite).
3

J. Choi et al.
Dyes and Pigments 189 (2021) 109255
Fig. 3. Performances of perovskite solar cell (PSC) devices: (a) J-V curves and (b) External quantum efficiency (EQE) spectra.
splitting, and thus improving the built-in potential (Vbi) of devices. From
the Mott-Schottky plots of the devices (Fig. 5b), obtained by the recip-
rocal of the square of capacitance-voltage (Cꢀ 2-V) curves, Vbi of PSCs
with and without organic HTM could be estimated using equation (3)
[62,63].
Table 1
Perovskite solar cell performances with and without organic HTM.
Voc (V)
Jsc (mA
FF (%)
PCE (%)
cmꢀ 2
)
Without org.
HTM
1.04
21.95
71.44
16.28
Cꢀ 2 = 2(Vbi-V)(A2eεεoNA)ꢀ 1
(3)
(1.03)
1.04
(21.62)
22.41
(69.85)
78.47
(15.52)
18.29
With org. HTM
where A and NA are device area and doping concentration, respectively.
The calculated Vbi of the device with the organic HTM (1.06V) is higher
than that without the HTM (1.01V), advantageous to better charge
extraction.
(1.05)
(22.35)
(75.83)
(17.64)
Numbers in and out of the parenthesis are average and best values, respectively.
Admittance spectroscopy could be further utilized to prove the
Fig. 4. (a) J-V curves of organic HTM-introduced PSC device depending on the scanning direction. (b) Power conversion efficiencies (PCEs) of PSC devices at
maximum power point (0.84 V). (c) Normalized PCEs of PSC devices (Al2O3-added) depending on the time in an atmosphere.
4

J. Choi et al.
Dyes and Pigments 189 (2021) 109255
Fig. 5. (a) J-V curves of hole-only devices with and without the organic HTM at dark condition. (b) Mott-Schottky plots of PSCs with and without the organic HTM.
(c) Trap density of state of PSCs with and without the organic HTM with respect to the energetic demarcation (Etrap – Eband edge).
reduced trap-density with the organic passivation layer. The trap density
recombination in that device (with and without organic HTM are 0.992
and 0.959, respectively) [67–70]. Meanwhile, the Voc of the PV device
has the following relation with the light-intensity: Voc ≈ nkBT/e ln
of states (Nt) can be estimated from the capacitance-angular frequency
(C-ω) curves using the following equation (4) [64,65].
(Jsc/Jo) ≈
α (nkBT/e) ln(I) + c, where n is the diode ideality factor, Jo is
Nt = -Vbi (ekBTW)ꢀ 1
(
ω
dC/dω
)
(4)
the reverse saturation current density at dark condition, and c is a fitting
parameter, as far as it has high shunt resistance. The estimated diode
ideality factors of PSC devices with and without organic HTM are 1.15
and 1.63, respectively, which represents that Shockley–Read–Hall
(SRH) trap-assisted recombination is significantly reduced after passiv-
ation with organic HTM [71].
where kB is Boltzmann constant and T is temperature. Fig. 5c represents
the trap density of states according to the energetic demarcation (Eω),
the difference between Etrap and Eband
(Eω = Etrap - Eband edge),
edge
defined by Eω = kBTln(ωo/ω), where ωo is the attempt-to-escape fre-
quency, and it is confirmed that the density of deep-level traps, which
generally exist at the interface, is significantly reduced by the passiv-
ation of the organic HTM [66].
Additionally, an electrochemical impedance spectroscopy (EIS) was
further utilized to understand the charge transport and recombination
behaviors in PSC devices. Fig. 6c shows that recombination resistance
(Rrec) of the PV device, measured at low frequency, significantly in-
creases with the organic HTM from 518 to 1451 Ω, and its series resis-
tance (Rs), calculated at high frequency, slightly decreases from 20 to 18
Ω, indicating the enhanced interfacial property of the PV device with the
organic HTM layer [72,73].
2.4. Recombination kinetics in PSCs
Recombination kinetics of the PSC devices can be estimated by
investigating their light intensity(I)-dependent Jsc and Voc characteris-
tics (Fig. 6a and b). The Jsc of PSC generally has a power law dependence
according to the light intensity (Jsc ∝ Iα), and its exponential parameter
3. Conclusion
α
, obtained by fitting its data in a double log scale to a linear curve,
approaches 1, when a bimolecular recombination in the PSC device at
In this work, we represent that the performances of PSC devices can
be enhanced by passivating the defects of perovskite at the interface
with the HTL. For this purpose, a lophine-based bisimidazole derivative
short-circuit condition is not noticeable. The logarithmic dependence in
Fig. 6a shows that the slope
α of the defect-passivated PSC device with
the organic HTM is much closer to 1, representing a reduced bimolecular
5

J. Choi et al.
Dyes and Pigments 189 (2021) 109255
Fig. 6. (a) Light intensity dependent Jsc characteristics of the PSCs with and without the organic HTM. (b) Light intensity dependent Voc characteristics of the PSCs
with and without the organic HTM. (c) Nyquist plots of the PSCs with and without the organic HTM.
organic molecule is newly prepared, and the Lewis-base type functional
groups of this organic HTM are proved to interact with under-
coordinated Pb2+ ions of perovskite. The designed organic molecule is
inserted to the interface between NiOx and perovskite, and it is
confirmed that this modification can not only elaborate the rough sur-
face of NiOx but also passivate the defects existing at the interface with
polycrystalline perovskite, improving its crystallinity and reducing non-
radiative recombination in the devices. Consequently, the performances
and stability of PSCs are significantly enhanced. We believe that our
approach through a molecular design of organic HTM can be an effective
way to complement structural defects of the perovskite for realizing high
performance PSC devices having long-term stability.
4.2. Materials
Foramidinium iodie (FAI) and Methyl ammonium bromide (MABr)
were purchased from the Great Cell Solar Company and Xi’an Polymer
Light Technology Corp, respectively. Cesium iodide (CsI, 99.9%), lead
bromide (PbBr2, 98%), bathocuproine (BCP, sublimed grade, 99.99%),
Octylamine (OA, >99.5%) dimethyl sulfoxide (DMSO, anhydrous),
chlorobenzene (CB, anhydrous), N,N-dimethylmethanamide (DMF,
anhydrous), N-methyl-2-pyrrolidone (NMP, anhydrous) were purchased
from Sigma Aldrich. Lead iodide (PbI2 10-mesh beads, ultra-dry,
99.999%) and Fullerene (C60) were purchased from Alfa Aesar and
Nano C, respectively. All chemicals were used for experiments without
any further purification. NiOx nanoparticles (NPs) synthesis method,
used in this work, was optimized from the previous studies [74–77]. To
prepare the NiOx NPs, Ni(NO3)2∙6H2O (0.04 mol) was dispersed in
deionized water to obtain a dark green solution. NaOH (0.08 mol) was
dispersed in deionized water under the cold condition to prevent pre-
cipitation through reverse reactions. Then, NaOH solution was added
slowly to Ni(NO3)2∙6H2O solution drop by drop until the pH value
reaches 10. During the dropping process, the colloidal precipitate was
produced. The whole reaction process was carried out under stirring
condition. After the reaction, the colloidal precipitate was washed with
deionized water more than three times to remove impurities. And the
4. Experimental section
4.1. Synthesis of organic HTM
The mixture of terephthalaldehyde (1 eq), corresponding aniline (2.1
eq), p-anisil (2.1 eq) and ammonium acetate (7 eq) in glacial acetic acid
were refluxed for 12 h and cooled to room temperature. The resulting
precipitates were filtered and washed with small amount of acetic acid,
sodium carbonate solution followed by copious amount of water and
dried. Then, the crude product was purified by silica gel column chro-
matography (DCM:EtOAc = 90:10) and recrystallized from CHCl3:
EtOAc (70:30) solvent mixture. Pure white spongy solid. Yield: 1.5 g
◦
washed colloidal precipitation was dried at 80 C for overnight. After
drying, green powder was produced, and then calcined at 285 ◦C for 2 h
inside the furnace to get black powder. Finally, the black powder was
pulverized to be small sized particles through a grinder. The NiOx NPs
solution was used by dispersing the black powder in deionized water at
an appropriate concentration.
1
(51%). H NMR (400 MHz, Chloroform-d) δ 7.50 (d, J = 8.9 Hz, 4H),
7.27 (s,4H), 7.25–7.21 (m, 6H), 7.00 (dd, J = 12.6, 7.8 Hz, 8H), 6.79 (d,
J = 8.9 Hz, 4H), 6.74 (d, J = 8.8 Hz, 4H), 3.77 (d, J = 9.8 Hz, 12H).
HRMS-TOF [M+H]+: m/z calcd for [C52H42N4O4+H]+ 787.3284; found
787.3379.
6

J. Choi et al.
Dyes and Pigments 189 (2021) 109255
4.3. Preparation of perovskite precursor
NiOx/perovskite and glass/ITO/NiOx/organic/perovskite. Steady-state
and time-resolved PL (TRPL) curves were depicted via FlouTime 300
(PicoQuant). For steady-state PL, the excitation source was from a
monochromated lamp, and, for time-resolved PL, a green laser diode
was used for the excitation. Steady-state PL and TRPL sample configu-
ration: glass/ITO/perovskite, glass/ITO/NiOx/perovskite, and glass/
ITO/NiOx/organic/perovskite. PL decay curves were fitted with biex-
ponential components to obtain a slow and a fast decay lifetime. SEM
images were taken from Nova Nano SEM 450 (FEI).
The perovskite solution of Cs0.04(FA0.92MA0.08 0.96Pb(I0.92Br0.08)3
)
composition was prepared by dissolving 1.35 M mixed metal lead salts
(0.883 PbI2: 0.077 PbBr2) and 1.35 M mixed organic cation (0.883 FAI:
0.077 MABr) into mixed solvent of DMF/DMSO (4:1 vol ratio). Other
precursor CsI of 0.05 M and alkylammonium ligands (OA) of 0.1 wt%
were added into the prepared solution. The perovskite composition was
well-optimized by tuning the previous work [78].
4.4. Device fabrication
CRediT authorship contribution statement
We prepared a p-i-n architecture PSC device with the following
Joonhyuk Choi: Validation, Formal analysis, Investigation, Data
curation, Writing – original draft. Eswaran Kamaraj: Validation,
Formal analysis, Investigation, Data curation, Writing – original draft.
Hansol Park: Formal analysis, Investigation, Data curation. Bum Ho
Jeong: Formal analysis, Investigation. Hyoung Won Baac: Software,
Validation, Formal analysis, Supervision. Sanghyuk Park: Conceptu-
alization, Methodology, Validation, Formal analysis, Writing – original
draft, Writing – review & editing, Supervision, Project administration.
Hui Joon Park: Conceptualization, Methodology, Validation, Formal
analysis, Writing – original draft, Writing – review & editing, Visuali-
zation, Supervision, Project administration, Funding acquisition.
structure,
MA0.08 0.96
ITO/NiOx/organic
HTM/perovskite[Cs0.04(FA0.92
)
Pb(I0.92Br0.08)3]/fullerene(C60)/2,9-dimethyl-4,7-diphenyl- -
1,10-phenanthroline(BCP)/silver(Ag). Initially, we patterned the ITO
glass substrate and followed the etching process using HCl (35%) and
zinc powder. Further patterned substrates were cleaned sequentially in
deionized water, isopropyl alcohol, and acetone with ultra-sonication.
The substrates were dried with N2 blowing and further treated with
oxygen plasma for 20 min at 60 W. A NiOx hole transport layer of 30 nm
was deposited on the plasma-treated substrate by spin-casting of nano-
particle solution (20 mg NiOx nanoparticles dissolved into 1 mL deion-
ized water) at 2000 r.p.m for the 30s and further annealed at 150 ◦C for
10 min. The process followed for the synthesis of NiOx is reported in our
previous work [74]. Next, organic HTL was deposited on NiOx film by
spin-casting of organic HTL solution (1.5 mg of organic material dis-
solved into 1 mL of NMP) at 2000 r.p.m for 25s and further annealed in a
vacuum oven (1 kPa) at 100 ◦C for 10 min. Perovskite solution was
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
prepared in N2 filled glove box and filtered using PTFE filter of 0.2 μm.
The filtered solution was spin-coated with two-step process (2000 r.p.m
for 10s and then 4500 r.p.m for the 50s) to prepare the perovskite film.
Acknowledgment
Anti-solvent CB of 160 μL was drop-cast on the substrate during the
J.C and E.K. contributed equally to this work. This research was
supported by the National Research Foundation of Korea (NRF) grant
funded by the Korea government (MSIT) (NRF-2020R1A2C2010342).
This work was support by the research fund of Hanyang University
(HY2019).
second step of spinning at 45 s. Further, the perovskite film was
annealed at 100 ◦C for 30 min. Moreover, C60 (19 nm), BCP (4 nm) and
Ag (120 nm) were deposited sequentially using the high vacuum thermal
evaporator. The hole-only devices were prepared by replacing the
C
60/BCP and Ag to spiro-OMeTAD, spin-coated on the perovskite layer at
4000 r.p.m for the 30s, and Au, respectively. The device area of 0.096
cm2 defined using the metal mask.
Appendix A. Supplementary data
4.5. Device characterization
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2021.109255.
A solar simulator with AM 1.5G 100 mW cmꢀ 2 of illumination was
utilized for J-V curves. The intensity was calibrated by an infrared cut-
off filter (KG5)-equipped NREL certified Si photodiode, reducing spec-
tral mismatch. An ABET technology 10,500 solar simulator and a
SPECTRO Mmac-200 were used as light source and light solution. The
EQE was measured at a short-circuit condition. Mott-Schottky plots,
Nyquist plots, and trap density of states were plotted at room temper-
ature using a potentiostat (SP-300, BioLogic). A Mott-Schottky analysis
was performed at fixed frequency (100 kHz). Electrochemical imped-
ance spectroscopy data was measured at 0.3 V DC bias and 30 mV
amplitude with a frequency ranging from 1 MHz to 1 mHz. For trap
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