Fused ring non-fullerene acceptors with benzothiophene dioxide end groups and their side chain effect investigations

Article abstract of DOI:10.1016/j.dyepig.2020.108452

The development of small molecule-based non-fullerene acceptors (NF-SMAs) greatly advanced the performances of polymer solar cells (PSCs) in recent years. As the foreseeability of commercializing this technology in the future, interest in reducing the materials cost is rising. To this end, efforts have been made in this work on exploring the usage of commercially available chemical segment of benzothiophene dioxide (BC) in constructing efficient NF-SMAs. Thus, we designed and synthesized two BC-based NF-SMAs, which showed high power conversion efficiency (PCE) of 7.59% also by device engineering and side chain engineering. Our work revealed the full potential of using BC end groups in constructing high-performance NF-SMAs and demonstrated the application of side chain engineering in tuning material properties and performances.

Full text of DOI:10.1016/j.dyepig.2020.108452

Journal Pre-proof
Fused ring non-fullerene acceptors with benzothiophene dioxide end groups and their
side chain effect investigations
Min Deng, Xiaopeng Xu, Liyang Yu, Ruipeng Li, Qiang Peng
PII:
S0143-7208(20)30836-6
DOI:
https://doi.org/10.1016/j.dyepig.2020.108452
DYPI 108452
Reference:
To appear in: Dyes and Pigments
Received Date: 2 April 2020
Revised Date: 15 April 2020
Accepted Date: 15 April 2020
Please cite this article as: Deng M, Xu X, Yu L, Li R, Peng Q, Fused ring non-fullerene acceptors with
benzothiophene dioxide end groups and their side chain effect investigations, Dyes and Pigments
(2020), doi: https://doi.org/10.1016/j.dyepig.2020.108452.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
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© 2020 Published by Elsevier Ltd.

Graphic abstract
3
0
PM6:ITTBC
PM6:ITThBC
Ar
S
O
O
CN
Ar
S
NC
S
S
CN
NC
O
S
-3
Ar
O
S
Ar
-6
Ar =
C6H13
ITTBC
-9
C6H13
ITThBC
S
PCE = 6.83%
-12
PCE = 7.59%
-0.2
0.0
0.2
0.4
0.6
0.8
Voltage (V)
The photovoltaic potential and fundamental limitations of commercial dye based on
benzothiophene dioxide (BC) as end group for constructing non-fullerene acceptors has been fully
revealed through device optimization and side chain engineering.

Fused Ring Non-Fullerene Acceptors with Benzothiophene Dioxide End
Groups and Their Side Chain Effect Investigations
Min Deng,a Xiaopeng Xu,a Liyang Yu,a* Ruipeng Li,b Qiang Penga*
a Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of
Chemistry, and State Key Laboratory of Polymer Materials Engineering, Sichuan
University, Chengdu 610064, P. R. China
b National Synchrotron Light Source II, Brookhaven National Lab, Suffolk, Upton, NY
11973, USA
*To whom correspondence should be addressed: Tel: +86-28-85415506; fax: +86-28-85415506;
liyangyu@scu.edu.cn (L.Y. Yu); qiangpengjohnny@yahoo.com (Q. Peng)

Abstract
The development of small molecule-based non-fullerene acceptors (NF-SMAs) greatly
advanced the performances of polymer solar cells (PSCs) in recent years. As the
foreseeability of commercializing this technology in the future, interest in reducing the
materials cost is rising. To this end, efforts have been made in this work on exploring the
usage of commercially available chemical segment of benzothiophene dioxide (BC) in
constructing efficient NF-SMAs. Thus, we designed and synthesized two BC-based
NF-SMAs, which showed high power conversion efficiency (PCE) of 7.59% also by device
engineering and side chain engineering. Our work revealed the full potential of using BC
end groups in constructing high-performance NF-SMAs and demonstrated the application
of side chain engineering in tuning material properties and performances.
Keywords: polymer solar cells, non-fullerene acceptor, commercial dye, side chain
engineering, benzothiophene dioxide

1. Introduction
Remarkable advancement has been made recently for polymer solar cells (PSCs), thanking
for the rapid development of small molecule-based non-fullerene acceptors (NF-SMAs),
which exhibit both excellent solar light-harvesting capability and easily tunable energy
levels [1-5]. The power conversion efficiencies (PCEs) of non-fullerene-based polymer
solar cells (NF-PSCs) have exceeded 16%,[6-14] demonstrating the potential of PSCs as a
viable candidate for the next generation solar energy technology.
The acceptor-donor-acceptor (A-D-A) structure with a fused electron-donating core
plus two electron-accepting end groups and alkylphenol side groups dominates the most
efficient NF-SMAs [15,16]. For example, the famous NF-SMA of ITIC [1] contained
indacenodithieno[3,2-b]thiophene
(IDTT)
core
and
2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene) propanedinitrile (INCN) end groups. Its
derivatives were also some of the working horses for the groundbreaking performances
obtained in the past few years [17-20].
Compared with INCN skeleton, benzothiophene dioxide (BC) showed higher
electron-accepting ability from its commercial application in dye industry, due to its high
photon absorption abilities, availability and cost efficiency [21-23]. Therefore, the energy
levels of NF-SMAs should be lower than those of ITIC, if being linked with BC end groups,
which would provide an improved energetic matching to the developed excellent wide
bandgap donor polymers [24-26]. However, the application of BC as end groups still has
not been used in NF-SMAs for systematic explorations. Thus, it is interesting to investigate
the structure-performance relationship of BC-containing NF-SMAs.
Side group engineering is a versatile and effective stratagem for fine-tuning molecular

structures due to its minor modification on synthesis [27-31]. Halogenation of the side
groups is one viable approach. [32,33] Another approach is the selection of the aromatic
group on the side chain. For example, ITIC with 2-thienyl side groups substitution
(ITIC-Th) was reported with the higher device performances [34]. In comparison to ITIC,
ITIC-Th showed increased crystallinity, which was attributed to the sulfur-sulfur
interactions from the 2-thienyl side groups [1,35,36]. Additionally, ITIC-Th featured with
the deeper energy levels than ITIC due to the stronger electron-withdrawing ability of
2-thienyl group. A lower HOMO is beneficial for matching with donor polymers with a
wider bandgap for complimentary absorption while maintaining efficient charge separation
[37-39]. Also, higher maximum extinction coefficient was recorded for ITIC-Th [34] in
comparison to ITIC [1]. Stronger absorption is a vital foundation for obtaining higher short
current density (Jsc) and PCE.
Based on this understanding, we designed and synthesized two new NF-SMAs based on
BC end groups attached with phenyl side groups (ITTBC) or 2-thienyl side groups
(ITThBC) (Fig. 1). In this work, both ITTBC and ITThBC were found with decent
performances when blended with PM6. In comparison between these two NF-SMAs, thin
films containing ITThBC demonstrated significantly increased crystallinities and electron
transport abilities. The higher PCE of the optimized PSCs containing ITThBC was
improved to 7.59% in comparison to the ITTBC-based devices (PCE = 6.83%), with
simultaneously improved fill factor (FF) and Jsc. Our work revealed the full potential of BC
as the end group for high-performance NF-SMAs and identified the main limiting factor of
these materials to be their limited absorption and charge transport abilities. Additionally,
we confirmed that side chain engineering as a viable method for constructing

high-performance semiconducting materials for PSC applications.
2. Results and discussion
2.1. Materials synthesis and structure characterization
Scheme
Benzo[b]thiophene-3(2H)-one
3-dicyanomethylene-benzo[b]thiophene-
1
shows
the
synthetic
routes
of
ITTBC
(1)
(BC)
and
ITThBC.
[23],
1,1-dioxide
1,1-dioxide
[40],
6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:
5,6-b']dithiophene-2,8-dicarboxaldehyde (IDTT-CHO) [1], and 6,6,12,12-
tetrakis(5-hexyl-2-thienyl)-6,12-dihydrodithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithi
ophene-2,8-dicarboxaldehyde (ITTh-CHO) [41] were synthesized according to previously
reported procedures. The Knoevenagel condensation reaction of IDTT-CHO or ITTh-CHO
with BC unit afforded ITTBC and ITThBC in good yields. The detailed synthetic
procedures were given in the Supporting Information. The molecular structures of the
BC-based NF-SMAs were characterized by NMR spectroscopy and elemental analysis.
These two NF-SMAs can be well dissolved in common organic solvents, such as
chloroform (CF), tetrahydrofuran (THF) and chlorobenzene (CB) at room temperature. The
thermal properties of the two materials were also characterized. Thermalgravimetric
analysis (TGA, Figure S1a) suggested that both materials were stable above 200 ˚C and
differential scanning calorimetry (DSC, Figure S1b) detected no thermal transitions from
room temperature to 140 ˚C.
2.2. Optical absorption properties
UV-vis absorption spectroscopy was applied to study the optical absorption abilities of
ITTBC and ITThBC. The absorption spectra of both NF-SMAs in either dilute chloroform

solution or solid state were shown in Fig. 2a and Fig. 2b. Both NF-SMAs showed vibronic
structures with similar absorption strength in solution state. In comparison to ITTBC with a
0-0 absorption located at 711 nm, ITThBC was found with a blue-shifted 0-0 absorption
peaked at 676 nm reaching a maximum molar extinction coefficient (εmax) of 1.099
M-1 cm-1, which was slightly higher than that of ITTBC (εmax = 1.078 105 M-1 cm-1).
×
105
×
Notably, the absorption of ITThBC had a wider full width at half maximum (FWHM) than
ITTBC (102 vs 99 nm). The 0-1 absorption shoulder of ITThBC was also significantly
stronger than ITTBC (9.02
× ×
104 vs 7.18 104 M-1 cm-1). The combined effect of these
differences led to a higher total photon absorption between 400 nm and 700 nm for ITThBC,
which could be a source for generating a higher Jsc in PSCs. We noticed that the extinction
coefficient of these two NF-SMAs were substantially lower than that of ITIC (εmax = 1.3
×
105 M-1 cm-1) [1] and ITIC-Th (εmax = 1.5 105 M-1 cm-1) [35]. Hence, compared to
×
NF-SMAs with INCN end groups, these two NF-SMAs with BC end groups displayed a
notable shortcoming in photon absorption ability. In solid state, both NF-SMAs displayed
similar vibrionic structures with redshifts. ITThBC was found with a slightly more
red-shifted absorption in solid state, suggesting a higher level of intermolecular interaction.
The optical band gap (Egopt) was 1.53 eV for ITTBC and 1.58 eV for ITThBC, respectively.
Additionally, the absorption ranges of both NF-SMAs were found to be complimentary to
the absorption range of the chosen donor polymer of PM6 as found in Fig. 2b.
2.3. Electrochemical properties
The electrochemical properties of ITTBC and ITThBC were investigated using cyclic
voltammetry (CV, Fig. 2c, Table 1). The highest occupied molecular orbital (HOMO)
energy level was estimated to be -5.71 eV for ITThBC and -5.61 eV for ITTBC,

respectively. And the lowest unoccupied molecular orbital (LUMO) energy level was -4.15
CV
eV for ITThBC and -4.13 eV for ITTBC, respectively. The electrochemical band gaps (Eg
)
was 1.48 eV for ITTBC and 1.56 eV for and ITThBC, respectively. Hence, the energy
levels of both acceptors match those for the donor polymer PM6 (EHOMO/ELUMO
-5.45/-3.51 eV, Figure S2, Table 1).
=
2.4. Theoretical calculations
Density functional theory (DFT) calculations were conducted for both NF-SMAs at the
B3LYP/6-31G* levels (Fig. 3). Both ITTBC and ITThBC exhibited a planar configuration,
which was beneficial for face-to-face packing and thus carrier transport [42,43]. The
calculated HOMO/LUMO were -5.53/-3.55 eV for ITTBC and -5.56/-3.56 eV for ITThBC,
respectively. As expected, ITThBC showed slightly lower energy levels than ITTBC, but
slightly large band gaps (2.0 eV vs 1.98 eV). The variation trend resembled that obtained
from CV.
2.5 Photovoltaic Properties
Inverted device configuration (ITO/ZnO/active layer/MoO3/Al) was fabricated and
evaluated to study the photovoltaic properties. Table 2 summarized the statistics of the
figures of merits for these devices, and Fig. 4a presented the representative current
density-voltage (J-V) characteristics. The optimized device containing ITTBC exhibited an
open-circuit voltage (Voc) of 0.86 V, a low Jsc of 12.52 mA cm-2 and an FF of 63.4%,
leading to a PCE of 6.83%. Devices containing ITThBC displayed obviously improved Jsc
of 13.36 mA cm-2, Voc of 0.87 V and FF of 65.3%, contributing the higher PCE of 7.59%.
The Voc values of the devices containing these two NF-SMAs were comparable, which
agreed with their almost identical LUMO levels. The higher efficiency of the ITThBC

devices was found to be due to the improved Jsc and FF in comparison to ITTBC
counterpart.
2.6. External quantum efficiency
We also measured the external quantum efficiencies (EQEs) to investigate the origin of the
Jsc differences (Fig. 4b). Both devices exhibited photo-current responses from 300 to 780
nm. ITThBC-based devices showed the maximum EQE value reaching 66%, higher than
that of 60% for ITTBC-based devices. The EQE response from ITThBC device was higher
within the wavelength range from 400 nm to 700 nm, which overlapped with the regime
where ITThBC exhibited stronger absorption. Despite ITTBC possessed a more red-shifted
EQE response towards infrared region, the integrated JEQE was much higher for ITThBC
device in comparison to the ITTBC counterpart. In comparison to devices containing ITIC
or ITIC-Th, which delivered the maximum EQE around 80% [1,34], the relatively low
extinction coefficient of ITTBC and ITThBC with BC end groups was identified to be one
of the main limitation factor for the low Jsc as well as PCE in devices.
2.7. Charge carrier mobilities, recombination and collection
The causes for FF differences were firstly studied by measuring hole/electron mobilities
(μh/μe) of ITTBC and ITThBC-based blend films with the space charge limited current
method (SCLC, Fig. 5). The μh/μe of these films were 3.9×10-4/6.7×10-5 cm2 V-1 s-1 for
PM6:ITTBC blend with a ratio of 5.82, and 4.5×10-4/9.4×10-5 cm2 V-1 s-1 for PM6:ITThBC
blend with a ratio of 4.87. Both thin films displayed rather imbalanced charge transport
mobilities with significantly lower electron mobilities. The μe delivered by the NF-SMAs
with BC end groups were about one order of magnitude lower those provided by their
counterparts with INCN end groups [1,44-46]. The limited μe impaired the free electrons

transport from the D/A interfaces to the ZnO electron-transporting layer and the FF of the
devices [47-50]. Hence, the low μe was identified as the other limiting factor for the device
performances of NF-SMAs with BC end groups. In comparison between the two NF-SMAs
with BC end groups, PM6:ITThBC blend delivers a more balanced μh/μe ratio, thanking to
the notably higher μe and thus its higher FF.
Charge recombination mechanism was also investigated to further understand the origin
of the FF differences. The Jsc and Voc dependence on light intensity (Plight) were measured
(Fig. 6). As shown in Fig. 6a, the slope (α) of ln(Jsc) versus ln(Plight) plot was fitted to be
0.82 for ITTBC and 0.85 for ITThBC-based devices, respectively, implying low
bimolecular recombination probability in the PM6:ITThBC blend. As a result, lower carrier
extraction and Jsc could be observed compared to the ITThBC-based devices. The Voc as a
function of ln(Plight) was plotted in Fig. 6b, the slope (S) of Voc versus ln(Plight) was 1.37
kT/q for ITTBC and 1.30 kT/q for ITThBC devices, implying less trap-assisted
recombination in the PM6:ITThBC devices. The lower recombination probabilities of
PM6:ITThBC device was a result of the higher μe of ITThBC, contributing to its higher FF
value in comparison with the PM6:ITTBC device.
The relationship of photocurrent (Jph) versus effective voltage (Veff) was used to analyze
charge carrier transferring and extraction process of the PSCs (Fig. 6c). Jph is defined as the
difference between the light (JL) and dark current (JD, i.e. Jph = JL - JD. Veff is defined by the
equation Veff = V0 - V, where V0 is the voltage at which JL = JD, and V is the applied voltage)
[51-53]. The Jph for the two devices containing either NF-SMAs reached a saturation at Veff
= 2 V, suggesting all charges were swiped at this voltage. This saturation was reached by
the ITThBC device at a lower Veff, and the Jph was found to be higher throughout the

measured Veff range. This was more obvious towards lower Veff where Jph for ITThBC
device decreased steadily and linearly, while Jph dropped rapidly out of the measuring range
with the decrease of Veff for the ITTBC device. These observations suggested a more
efficient charge extraction process in device containing ITThBC than ITTBC likely due to
the higher μe of ITThBC. The charge dissociation probability (P(E,T)) estimated by the
ratio between the Jph at short circuit condition and saturation of the two devices were found
to be 0.78 and 0.82 for PM6:ITTBC and PM6:ITThBC devices, respectively. A higher
P(E,T) for the ITThBC device suggested a more efficient exciton dissociation process
which pointed to a more optimized nanostructure [54,55].
2.8 Morphology characterization
Grazing-incident wide-angle X-ray scattering (GIWAXS) was used to characterize the
morphology NF-SMA based blend films (Fig. 7). Neat ITTBC thin film showed an almost
isotropic weak scattering feature at q = 3.4 nm-1 (d = 1.85 nm), likely associated with its
(100) lamellar stacking. In a contrast, thin film containing ITThBC displayed a
distinguishable (100) lamellar stacking also at qz = 3.4 nm-1 (d = 1.85 nm). A weaker (010)
diffraction from the π-π stacking at qz = 19.5 nm-1 (d = 0.32 nm) suggested that more
crystals existed in the edge-on stacking state than the face-on stacking state. Higher order of
this diffraction could also be observed for both blend films, and the weak (200) diffractions
and strong (300) diffractions appeared. Since the diffraction at q = 3.4 nm-1 overlapped with
the lamellar stacking of PM6, the higher diffraction intensity should come mainly from
PM6 with higher crystallinity. The (010) diffraction of PM6 at qz = 17 nm-1 appeared as a
broad hump with a comparable intensity in both blend films. The (010) diffraction of these
two NF-SMAs at qz = 19.5 nm-1 were found to be stronger than those in the neat films,

indicating that the crystallinity of NF-SMAs could be enhanced by the crystallization
process of PM6. Obviously, the (010) diffraction of ITThBC was stronger than ITTBC,
implying its higher crystallinity. Reasonably, ITThBC should have higher μe and higher FF
in devices.
The higher crystallinity of ITThBC was less pronounced from the atomic force
microscopy (AFM) images (Fig. 8). However, clear nanoscale phase separated structure
could be seen from both height and phase images. The PM6:ITThBC film had a slightly
larger aggregation with a root-mean-square (RMS) roughness of 1.30 nm than that of 1.21
nm for PM6:ITTBC blend. The higher roughness could be a consequence of the higher
crystallinity of ITThBC. The similar morphology observed despite the crystallinity
differences of these two NF-SMAs suggested that the formation process of the phase
separated nanostructure was mainly driven by PM6.
3. Conclusions
In summary, we developed two novel NF-SMAs, namely ITTBC and ITThBC, based on an
uncommon end group of benzothiophene dioxide (BC). The side chain effect was also
studied in detail on their photovoltaic properties. Selecting PM6 as the donor polymer,
ITTBC and ITTBC devices exhibited high PCEs of 6.83% and 7.59%. 7.59% is the highest
efficiency of the BC-containing NF-SMAs reported so far. Such enhanced device
performance was be closely connected with the crystallization process of PM6, which
simultaneously increased the crystallinity of ITTBC in active layer. In comparison with
ITTBC with phenyl side chains, the altered thienyl side chains made ITThBC exhibit an
improved absorption between 400-700 nm and a higher crystallinity. Therefore, ITThBC
device had the higher Jsc, FF and overall PCE than ITTBC counterpart. The primary results

indicated that BC unit was a promising end group for designing high performance
NF-SMAs. The main limiting factors for the adaptation of BC end groups in NF-SMAs
were identified to be the low photon absorption and charge transport abilities. Beside the
side chain engineering used in this work, further work should be performed on the
optimization of the fused ring central core and delivered much higher device performance.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (NSFC,
21825502, 51573107, 91633301 and 21905185), the Foundation of State Key Laboratory of
Polymer Materials Engineering (SKLPME 2017-2-04) and the Fundamental Research
Funds for the Central Universities (YJ201957). The authors thanks NSLS-II (Brookhaven
National Laboratory under Contract No. DE-SC0012704) for the GIWAXS measurements.
Appendix A. Supplementary data
Supplementary data to this article can be found online at XXX.
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Al
MoO3
PM6:ITTBC or ITThBC
ZnO
Glass/ITO
Fig. 1 Chemical structures of the acceptor (a) and donor (b) materials used in this work, including
ITTBC, ITThBC and PM6. (c) Device structure used in this work.

Scheme 1 The synthetic routes of the NF-SMAs.

12
10
8
1.2
1.0
0.8
0.6
0.4
0.2
0.0
ITTBC
ITThBC
ITTBC
ITThBC
PM6
6
4
2
0
300
400
500
600
700
800
900
300
400
500
600
700
800
900
Wavelength (nm)
Wavelength (nm)
-3.0
-3.5
-4.0
-4.5
-5.0
-5.5
-6.0
0.2
0.1
ITTBC
ITThBC
-3.51
-4.13
-4.15
0.0
-0.1
-0.2
-0.3
-5.45
-5.61
-5.71
-1.0 -0.5 0.0 0.5 1.0
1.5 2.0
2.5
Potential (V vs. Ag/AgCl)
Fig. 2 (a) UV-vis absorption spectra of ITTBC and ITThBC in chloroform solution. (b) Normalized
UV-vis absorption spectra of thin films containing ITTBC, ITThBC and PM6. (c) Cyclic
voltammograms for ITTBC and ITThBC. (d) Diagram displaying the energy levels of ITTBC, ITThBC
and PM6.

ITTBC
ITThBC
LUMO = -3.55 eV
LUMO = -3.56 eV
HOMO=-5.53 eV
HOMO=-5.56 eV
Fig 3 The optimal geometries and HOMO and LUMO distributions of ITTBC and ITThBC calculated at
B3LYP/6-31G* level.

3
0
70
60
50
40
30
20
10
0
PM6:ITTBC
PM6:ITThBC
-3
-6
-9
PM6:ITTBC
PM6:ITThBC
-12
-15
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
300
400
500
600
700
800
Voltage (V)
Wavelength (nm)
Fig. 4 J-V characteristics (a) and EQE curves (b) of the optimized PSCs based on PM6:ITTBC and
PM6:ITThBC.

PM6:ITTBC
PM6:ITTBC
PM6:ITThBC
PM6:ITThBC
100
10
1
100
10
0.01
0.01
0.1
1
10
0.1
1
10
Vapp-Vbi-Va (mW cm-2)
Vapp-Vbi-Va (V)
Fig. 5 Plots illustrating J1/2-V relationship of the hole-only devices (a) and electron-only devices (b) for
PM6:ITTBC and PM6:ITThBC.

(a)
(b) 0.88
ITTBC
ITTBC
ITThBC
ITThBC
10
1
0.84
0.80
0.76
0.72
0.68
0.1
1
10
Light Intensity (mW cm-2)
100
1
10
100
Light Intensity (mW cm-2)
(c)
ITTBC
ITThBC
10
1
0.1
0.01
0.1
Veff (V)
1
Fig. 6 Plots illustrating Jsc-Plight (a), Voc-Plight (b) and Jph-Veff (c) relationships of the PM6:ITTBC and
PM6:ITThBC devices.

Fig. 7 GIWAXS patterns of ITTBC (a), PM6: ITTBC blend films (b), ITThBC (c), PM6: ITThBC blend
films (d), and the corresponding intensity profiles (e) along the in-plane (dashed line) and out-of-plane
(solid line) directions.

Fig. 8 AFM height images (a,b) and phase images (c,d) of the PM6:ITTBC and PM6:ITThBC blend
films.

Table 1 Optical and electrochemical properties of the NF-SMAs.
a
b
opte
CVh
NF-SMA
λmax
λmax
εc
εd
Eg
HOMOf LUMOg Eg
(nm)
(nm)
(M-1 cm-1)
(cm-1)
(eV)
(eV)
(eV)
(eV)
ITTBC
711
676
719
685
b
10.78×104
10.99×104
6.15×104
5.98×104
1.53
1.58
-5.61
-5.71
-4.13
-4.15
1.48
1.56
ITThBC
aAbsorption maximum in solution. Absorption maximum in thin film. Molar extinction coefficient at λmax in solution.
c
dExtinction coefficient at λmax in film. eOptical bandgap calculated from the absorption edge of thin film. fHOMO energy
g
level estimated from the onset oxidation potential. LUMO energy level estimated from the onset reduction potential.
hHOMO-LUMO gap estimated from CV.
Table 2 Photovoltaic parameters of the optimized PSCs devices
Active layer
PM6:ITTBC
Voc (V)
Jsc (mA cm-2) JEQE (mA cm-2)a
FF (%)
PCE (%)
0.86
12.52
12.33
13.10
63.40
6.83
(0.85±0.01)b
(12.23±0.31)
(63.1±0.30)
(6.49±0.27)
PM6:ITThBC
0.87
13.36
65.30
7.59
(0.86±0.1)
(13.11±0.26)
(65.2±0.20)
(7.25±0.25)
b
aThe calculated current density (JEQE) was determined from EQE curve. Average values (in parentheses) are obtained
from 20 devices.