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Unique Energy Alignments of a Ternary Material System toward High‐Performance Organic Photovoltaics

1801501 (1 of 8) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Unique Energy Alignments of a Ternary Material System
toward High-Performance Organic Photovoltaics
Pei Cheng, Jiayu Wang, Qianqian Zhang, Wenchao Huang, Jingshuai Zhu, Rui Wang,
Sheng-Yung Chang, Pengyu Sun, Lei Meng, Hongxiang Zhao, Hao-Wen Cheng,
Tianyi Huang, Yuqiang Liu, Chaochen Wang, Chenhui Zhu, Wei You,* Xiaowei Zhan,*
and Yang Yang*
DOI: 10.1002/adma.201801501
Research on OPV has begun in as early
as 1950s, when the active layer consisted
of only a single organic semiconductor
(p-type or n-type).[8] Considering the large
binding energy of an organic semicon-
ductor (0.3–1 eV),[9] the single component
OPV yielded a very low PCE (1–3%) due to
the insufficient exciton dissociation by the
electric field. To overcome this problem,
the active layer consisted of donor/acceptor
binary blend (bulk heterojunction (BHJ)
structure) was reported in 1995.[10,11] In
this binary blend OPV, the exciton dissocia-
tion became much more efficient than that
in the single component solar cells due to
the increased donor/acceptor interfaces
in the active layer. In recent five years, a
new type of active layer with ternary blend
(donor, acceptor, and third component)
was developed to further enhance the performance of binary
blend OPV.[12–15] These ternary blend OPV presented some
advantages via various design strategies: broader and stronger
absorption,[16–25] more efficient charge transfer,[26–29] more effi-
cient charge transport pathways,[30–33] better charge extraction at
the electrodes,[34–37] and improved stability.[38–42]
Among the design strategies for ternary blend
OPV, employing a near-infrared (NIR) absorber as the third
component is the most successful one to boost the PCE of
Incorporating narrow-bandgap near-infrared absorbers as the third component
in a donor/acceptor binary blend is a new strategy to improve the power conver-
sion efficiency (PCE) of organic photovoltaics (OPV). However, there are two
main restrictions: potential charge recombination in the narrow-gap material
and miscompatibility between each component. The optimized design is to
employ a third component (structurally similar to the donor or acceptor) with a
lowest unoccupied molecular orbital (LUMO) energy level similar to the acceptor
and a highest occupied molecular orbital (HOMO) energy level similar to the
donor. In this design, enhanced absorption of the active layer and enhanced
charge transfer can be realized without breaking the optimized morphology of
the active layer. Herein, in order to realize this design, two new narrow-bandgap
nonfullerene acceptors with suitable energy levels and chemi cal structures are
designed, synthesized, and employed as the third component in the donor/
acceptor binary blend, which boosts the PCE of OPV to 11.6%.
Organic Solar Cells
Photovoltaic (PV) technology is one of the promising renew-
able energy technologies for the human future. Especially,
the solution-processable organic photovoltaics (OPV) have
attracted considerable attention in the last decade due to some
potential advantages, such as light-weight, flexibility, possible
semitransparence, low energy consumption, and fast and
large-area fabrication.[1–6] To date, OPV have shown the best
performance with certified power conversion efficiency (PCE)
exceeding 11%.[7]
The ORCID identification number(s) for the author(s) of this article
can be found under
Dr. P. Cheng, Dr. W. Huang, R. Wang, S.-Y. Chang, P. Sun, Dr. L. Meng,
H. Zhao, H.-W. Cheng, T. Huang, Y. Liu, C. Wang, Prof. Y. Yang
Department of Materials Science and Engineering
University of California
Los Angeles, CA 90095, USA
J. Wang, J. Zhu, Prof. X. Zhan
Department of Materials Science and Engineering
College of Engineering
Key Laboratory of Polymer Chemistry and Physics of Ministry of Education
Peking University
Beijing 100871, P. R. China
Q. Zhang, Prof. W. You
Department of Chemistry
University of North Carolina at Chapel Hill
Chapel Hill, NC 27599, USA
Dr. W. Huang, H. Zhao, H.-W. Cheng, Y. Liu, Prof. Y. Yang
California NanoSystems Institute
University of California
Los Angeles, CA 90095, USA
Dr. C. Zhu
Advanced Light Source
Lawrence Berkeley National Laboratory
Berkeley, CA 94720, USA
Adv. Mater. 2018, 30, 1801501
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1801501 (2 of 8)
OPV. These NIR absorbers, including donors[16–22,26] and accep-
tors,[23,43–46] can utilize photons in the NIR region, which will
potentially contribute to the short circuit current density (JSC)
of solar cells. On the other hand, the highest occupied mole-
cular orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) energy levels of NIR absorbers can be designed to be
positioned between the HOMOs and LUMOs of the donor and
acceptor, which can provide more routes for charge transfer
by forming a cascade energy heterojunction (Figure 1a).[47]
However, there are two main restrictions for the application
Adv. Mater. 2018, 30, 1801501
Figure 1. a) Schematic diagrams of different models for charge transfer. b) Molecular structures of donor (FTAZ), acceptor (IDIC), and third compo-
nents (ITIC-Th, ITIC-Th-S, ITIC-Th-O). c) Energy levels and optical bandgaps of FTAZ, IDIC, ITIC-Th, ITIC-Th-S, and ITIC-Th-O.
Figure 2. The synthetic routes of ITIC-Th-S and ITIC-Th-O.
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1801501 (3 of 8)
of NIR absorbers as the third component: potential charge
recombination in the narrow gap material and miscompatibility
between each component.[12,14,15] The charge recombination
traps can be formed if the bandgap of the third component
is too narrow (Figure 1a). The miscompatibility occurs if the
chemical structures of donor/acceptor and the third compo-
nent are mainly different, which will break the optimized mor-
phology of the donor/acceptor binary blend active layer.[48] Thus,
the optimized design is to employ a third component (structur-
ally similar to donor or acceptor) with a LUMO energy level
similar to the acceptor and a HOMO energy level similar to the
donor (Figure 1a). In this design, enhanced absorption of active
layer and enhanced charge transfer can be realized without the
breaking of the optimized morphology of active layer.
Herein, in order to realize this optimized design of ternary
blend OPV, we employed the third component in the active
layer with a similar chemical structure to the acceptor and
suitable energy levels. On the basis that 2,7-bis(3-dicyanometh-
b] thiophene) (ITIC-Th)[49,50] shows a similar backbone and
bandgap (1.60 eV), but up-shifted LUMO and HOMO energy
levels to 2,7-bis(3-dicyanomethylene-2Z-methylene-indan-
dithiophene (IDIC), ITIC-Th was chosen as the third com-
ponent in the blend of donor FTAZ[51]/acceptor IDIC.[52,53]
In order to achieve optimized energy level alignments of
ITIC-Th-based third component with the donor FTAZ/acceptor
IDIC, 2,7-bis(5-(3-dicyanomethylene-2Z-methylene-indan-1-
b] thiophene) (ITIC-Th-S), and 2,7-bis(5-(3-dicyanomethylene-
b]di(thieno[3,2-b]thiophene) (ITIC-Th-O) (Figure 1b) were
designed and synthesized through the incorporation of thio-
phene with alkylthio/alkoxy side chains as pi-bridge. This
approach could down-shift the LUMO energy level and up-shift
the HOMO energy level of the ITIC-Th counterpart and, there-
fore, redshift the absorption into the NIR region (bandgaps:
1.45 eV for ITIC-Th-S and 1.40 eV for ITIC-Th-O, as shown
in Figure 1c). Through this chemical modification, the HOMO
Adv. Mater. 2018, 30, 1801501
Figure 3. a) Cyclic voltammograms for ITIC-Th, ITIC-Th-S, and ITIC-Th-
O. b) Absorption spectra of pure FTAZ, IDIC, ITIC-Th, ITIC-Th-S, and
ITIC-Th-O films.
Figure 4. a) J–V curves and b) EQE spectra of devices based on FTAZ/
IDIC without or with different third components under illumination of an
AM 1.5G solar simulator, 100 mW cm2.
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1801501 (4 of 8)
and the LUMO energy levels of ITIC-Th-O were respectively
similar to the HOMO energy level of donor FTAZ (5.35 eV)
and the LUMO energy level of acceptor IDIC (3.91 eV). After
the device optimization, the best PCE of FTAZ/ITIC-Th-O/
IDIC ternary blend OPV was measured to be 11.6%, which
is higher than that of the controlled FTAZ/IDIC binary blend
OPV (10.4%).
The synthetic routes of ITIC-Th-S and ITIC-Th-O
are shown in Figure 2. The intermediate compounds
indaceno[1,2-b:5,6-b] di(thieno[3,2-b]thiophene)-2,7-diyl)bis(4-
(hexylthio)thiophene-2-carbaldehyde) (ITS-CHO)/5,5-(4,4,9,9-
b] di(thieno[3,2-b]thiophene)-2,7-diyl)bis(4-(hexyloxy)thiophene-
2-carbaldehyde) (ITO-CHO) were synthesized in 83%/71%
yield through the Stille coupling reaction using Pd(PPh3)4 as a
catalyst. A straightforward reaction of ITS-CHO/ITO-CHO with
1,1-dicyanomethylene-3-indanone afforded ITIC-Th-S/ITIC-Th-
O in 76%/95% yield. The compounds ITS-CHO/ITO-CHO and
ITIC-Th-S/ITIC-Th-O were fully characterized by MALDI-TOF
MS, 1H NMR, 13C NMR, and elemental analysis. ITIC-Th-S and
ITIC-Th-O were readily soluble in common organic solvents
such as chloroform and o-dichlorobenzene at room tempera-
ture. The details of synthesis and related characterization are
shown in the Supporting Information.
The cyclic voltammetry (CV) method was used to investi-
gate the electrochemical properties of ITIC-Th, ITIC-Th-S,
and ITIC-Th-O films and further estimate their energy levels
(Figure 3a). The HOMO/LUMO energy levels of ITIC-Th-S
and ITIC-Th-O were estimated to be 5.41 eV/3.86 eV and
5.36 eV/3.91 eV, respectively (calculation details were shown
in the Supporting Information). Due to electron-donating
nature of alkylthio/alkoxy side chains and high electronega-
tivity of sulfur (2.58) and oxygen atoms (3.44), ITIC-Th-S and
ITIC-Th-O exhibited an up-shifted HOMO energy levels and
down-shifted LUMO energy levels compared with ITIC-Th
(5.61 eV/3.81 eV). Through this simple chemical modifica-
tion, the LUMO energy level of the third component can be
down-shifted from 3.81 to 3.91 eV, which is similar to that of
the acceptor IDIC (3.91 eV[49]); and the HOMO energy level of
the third component can be up-shifted from 5.61 to 5.36 eV,
which is similar to that of the donor FTAZ (5.35 eV, Figure S1,
Supporting Information). Meanwhile, the down-shifted LUMO
energy level and up-shifted HOMO energy level of the third
component can narrow the bandgap and broaden the absorp-
tion of active layer into the NIR region. The absorption spectra
of FTAZ, IDIC, ITIC-Th, ITIC-Th-S, and ITIC-Th-O films are
shown in Figure 3b. Compared with ITIC-Th, ITIC-Th-S, and
ITIC-Th-O exhibit redshifted absorptions (855 and 885 nm) and
reduced bandgaps (1.45 and 1.40 eV). The redshifted absorption
of the third component can potentially benefit the absorption of
the ternary blend active layer, which is only cut-off at 775 nm
for the FTAZ/IDIC binary blend (1.60 eV).
The J–V curves and external quantum efficiency (EQE)
spectra of devices based on FTAZ/IDIC without or with dif-
ferent third components (ITIC-Th, ITIC-Th-S, and ITIC-Th-O)
under the illumination of an AM 1.5 G solar simulator
(100 mW cm2) are shown in Figure 4. The average (calculated
from 20 individual devices) and best device characteristics are
summarized in Table 1. The device characteristics of FTAZ/
ITIC-Th, FTAZ/ITIC-Th-S, and FTAZ/ITIC-Th-O binary
blend solar cells are also summarized in Table S1 (Supporting
Information). After addition of third component (10% of the
donor and acceptor by weight), the ternary blend OPV exhibited
an enhanced JSC with maintaining an open circuit voltage (VOC)
(0.85 V) and fill factor (FF) (0.71) comparable to controlled
FTAZ/IDIC binary blend device. The average JSC of devices
increased from 16.6 to 17.8 and 18.5 mA cm2 by employing
ITIC-Th-S and ITIC-Th-O as the third component, respectively.
As a result, the best PCE of the devices increased from 10.4% to
11.1% and 11.6% by incorporation of ITIC-Th-S and ITIC-Th-
O as the third component, respectively. The best ternary blend
OPV was based on ITIC-Th-O as a third component, which
showed similar LUMO energy level to acceptor IDIC (3.91 eV)
and similar HOMO energy level to donor FTAZ (5.35 eV).
In addition, PCE (11%) and FF ( 70%) of ternary blend
device can be mainly maintained by continuous increasing the
Adv. Mater. 2018, 30, 1801501
Table 1. Average and best device data based on FTAZ/IDIC without or with different third components.
Active layer VOC [V] JSC [mA cm2] Calculated JSC [mA cm2]FF [%] PCE [%]
Average Best
FTAZ/IDIC 0.85 ± 0.01 16.6 ± 0.5 15.9 71.0 ± 0.4 10.0 ± 0.3 10.4
FTAZ/ITIC-Th/IDIC 0.85 ± 0.01 17.1 ± 0.4 16.5 70.9 ± 0.5 10.3 ± 0.2 10.6
FTAZ/ITIC-Th-S/IDIC 0.85 ± 0.01 17.8 ± 0.5 17.1 71.2 ± 0.4 10.8 ± 0.2 11.1
FTAZ/ITIC-Th-O/IDIC 0.85 ± 0.01 18.5 ± 0.4 18.0 71.9 ± 0.4 11.3 ± 0.2 11.6
Figure 5. PL spectra of FTAZ/IDIC blend films without or with different
third components.
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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amount of third component (up to 30%, Table S2, Supporting
As shown in Figure 4b and Figure 3b, the EQE in 400–
600 nm range is attributed mainly to FTAZ, and the EQE in
600–750 nm range is attributed mainly to IDIC. After the addi-
tion of ITIC-Th-S or ITIC-Th-O as the third component, the
EQE can be broadened to 850 or 880 nm, which is consistent
with the absorption spectra of blend films (Figure S2, Sup-
porting information). From integration of the EQE spectra
with the AM 1.5G reference spectrum, the calculated JSC was
obtained, which was similar to J–V measurement (the average
error is 3.6%, Table 1).
In order to study the charge or energy transfer
between different components, we carry out the same method
as literatures (investigating the J–V curves of solar cells based
on two acceptors as active layer (without donor).[20,54] J–V curves
of devices based on pure IDIC, pure ITIC-Th-O, and IDIC/
ITIC-Th-O blend under illumination of an AM 1.5G solar simu-
lator, 100 mW cm
2 are shown in Figure S3 (Supporting infor-
mation). The JSC of solar cells based on IDIC/ITIC-Th-O blend
Adv. Mater. 2018, 30, 1801501
Figure 6. a–d) 2D GIWAXS patterns of FTAZ/IDIC film (a), FTAZ/ITIC-Th/IDIC film (b), FTAZ/ITIC-Th-S/IDIC film (c), and FTAZ/ITIC-Th-O/IDIC film (d).
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Adv. Mater. 2018, 30, 1801501
(6:1, same as the value in the best FTAZ/ITIC-Th-O/IDIC ter-
nary device) is much larger than that of the pure IDIC or pure
ITIC-Th-O based cells, which should be attributed to the effec-
tive charge transfer between IDIC and ITIC-Th-O. The steady
state photoluminescence (PL) was carried out to investigate
the charge transfer in active layer. The PL intensities of FTAZ/
IDIC films without or with different third components (ITIC-
Th, ITIC-Th-S, and ITIC-Th-O) are shown in Figure 5 (excite
at 660 nm). Considering the absorption edge of FTAZ is at
630 nm, the PL peak at 760 nm of FTAZ/IDIC blend film is
assigned to IDIC. Compared with FTAZ/IDIC binary blend
film, the PL intensity of ternary blend films decreased by 70%
(the PL intensities of different films were compared at their
PL peaks). The stronger PL quenching of IDIC can mainly
be caused by extra photoinduced hole transfer from IDIC to
donor FTAZ or to third components, which suggests a more
efficient charge transfer in the active layer. The more efficient
charge transfer in ternary blend active layer is attributed to the
formation of the optimized energy level alignment, which con-
sequently enhances the JSC and PCE of OPV.
In order to compare the film morphology of FTAZ/IDIC
active layer without or with third component, grazing-incidence
wide-angle X-ray scattering (GIWAXS) and transmission
electron microscopy (TEM) measurements were carried out.
GIWAXS provides molecular-level structural information such
as lattice constant and orientation of molecular packing, while
TEM provides larger length-scale phase separation information
up to hundreds of nanometers. Figure 6 shows 2D GIWAXS
patterns of FTAZ/IDIC films without or with different third
components (ITIC-Th, ITIC-Th-S, and ITIC-Th-O). The out-
of-plane and in-plane line cuts are shown in Figure S4 (Sup-
porting information). The molecular packing behavior in binary
blend film and all ternary blend films was similar in terms of
molecular crystallite orientation and aggregation. At the same
time, these binary blend and ternary blend films exhibited
similar scale of phase separation, which is apparent in TEM
images (Figure S5, Supporting information). Thus, the film
morphology of FTAZ/IDIC active layer without or with these
ITIC-Th based third components was shown to be similar at
both molecular-level and hundreds of nanometers scale. This
suggests that the employment of third component with good
compatibility (structurally similar to acceptor) can maintain the
optimized film morphology of active layer.
The space charge limited current (SCLC)[55] method was
employed to measure the hole and electron mobility of binary
and ternary blend films. Hole-only and electron-only diodes
were fabricated using the architectures of indium tin oxide
(ITO)/poly(3,4-ethylenedioxythiophene): poly(styrene sul-
fonate) (PEDOT: PSS)/active layer/gold (Au) for holes and
aluminum (Al)/active layer/Al for electrons. The dark J–V
curves of the devices are plotted as ln[Jd3/(Vappl – Vbi)2] versus
[(VapplVbi)/d]0.5 in Figure 7. The average hole and electron
mobilities are calculated and listed in Table 2. Thanks to pre-
served optimized film morphology of active layer, the average
hole and electron mobilities of the binary blend and all ternary
blend films were shown to be similar (1.0–1.4 × 104 cm2 V1 s1
for hole; 2.6–3.4 × 105 cm2 V1 s1 for electron).
In summary, two new nonfullerene acceptors ITIC-Th-S
and ITIC-Th-O were designed, synthesized and employed as a
third component in the blend of donor FTAZ/acceptor IDIC.
Through chemical modification, the HOMO energy level of the
third component was up-shifted from 5.61 eV (ITIC-Th) to
5.41 eV (ITIC-Th-S)/ 5.36 eV (ITIC-Th-O), which is similar
to that of the donor FTAZ (5.35 eV); and the LUMO energy
level of the third component was down-shifted from 3.81 eV
(ITIC-Th) to 3.86 eV (ITIC-Th-S)/ 3.91 eV (ITIC-Th-O), which
is similar to that of the acceptor IDIC (3.91 eV). The up-shifted
HOMO energy level and down-shifted LUMO energy level of the
third component was able to narrow the bandgaps and broaden
the absorption of active layer into the NIR region. Meanwhile,
Figure 7. a) Hole-only and b) electron-only devices based on FTAZ/IDIC
blend films without or with different third components.
Table 2 . Hole and electron mobilities of FTAZ/IDIC blend films without
or with different third components (average by five devices).
Active layer
h [cm2 V1 s1]
e [cm2 V1 s1]
FTAZ/IDIC 1.2 ± 0.4 × 1043.4 ± 1.5 × 105
FTAZ/ITIC-Th/IDIC 1.0 ± 0.3 × 1043.4 ± 1.4 × 105
FTAZ/ITIC-Th-S/IDIC 1.4 ± 0.4 × 1042.6 ± 1.2 × 105
FTAZ/ITIC-Th-O/IDIC 1.2 ± 0.4 × 1042.9 ± 1.4 × 105
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1801501 (7 of 8)
Adv. Mater. 2018, 30, 1801501
the optimized energy level alignment induces a more efficient
charge transfer. In addition, due to similar chemical structure
of these third components to the acceptor, these materials exhib-
ited a good compatibility which can maintain the optimized
film morphology of active layer at both molecular-level and hun-
dreds of nanometers-scale. As a result, the broadened absorp-
tion and enhanced charge transfer can contribute to JSC which
are the reasons for the higher performance of FTAZ/ITIC-Th-O/
IDIC ternary system compared with that of FTAZ/IDIC binary
system. The best PCE of FTAZ/ITIC-Th-O/IDIC ternary blend
OPV was measured to be 11.6%, which is higher than that of the
controlled FTAZ/IDIC binary blend OPV (10.4%).
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
P.C. and J.W. contributed equally to this work. Y.Y. acknowledges the Air
Force Office of Scientific Research (AFOSR) (Nos. FA2386-15-1-4108,
FA9550e15-1e0610, and FA9550-15-1-0333), Office of Naval Research
(ONR) (Nos. N00014-14-181-0648 and N00014-04-1-0434), National
Science Foundation (NSF) (No. ECCS-1509955), and UC-Solar Program
(No. MRPI 328368) for their financial support. Part of this research
was performed in beamline 7.3.3 in Advanced Light Source Lawrence
Berkeley National Laboratory. X.Z. acknowledges the National Science
Foundation China (NSFC) (Nos. 21734001 and 51761165023) for
financial support. W.Y. acknowledges NSF Grant (No. DMR-1507249)
and CBET-1639429 for financial support. The authors also thank Selbi
Nuryyeva for her insights on the manuscript.
Conflict of Interest
The authors declare no conflict of interest.
energy level alignments, fullerene-free, nonfullerene, organic solar cells,
ternary blends
Received: March 6, 2018
Revised: April 3, 2018
Published online: May 21, 2018
[1] C. J. Brabec, M. Heeney, I. McCulloch, J. Nelson, Chem. Soc. Rev.
2011, 40, 1185.
[2] P. Cheng, G. Li, X. Zhan, Y. Yang, Nat. Photonics 2018, 12, 131.
[3] G. Li, R. Zhu, Y. Yang, Nat. Photonics 2012, 6, 153.
[4] M. Graetzel, R. A. J. Janssen, D. B. Mitzi, E. H. Sargent, Nature
2012, 488, 304.
[5] Y. F. Li, Acc. Chem. Res. 2012, 45, 723.
[6] J. Peet, A. J. Heeger, G. C. Bazan, Acc. Chem. Res. 2009, 42,
[7] J. Zhao, Y. Li, G. Yang, K. Jiang, H. Lin, H. Ade, W. Ma, H. Yan,
Nat. Energy 2016, 1, 15027.
[8] G. A. Chamberlain, Solar Cells 1983, 8, 47.
[9] S. R. Forrest, Nature 2004, 428, 911.
[10] J. J. M. Halls, C. A. Walsh, N. C. Greenham, E. A. Marseglia,
R. H. Friend, S. C. Moratti, A. B. Holmes, Nature 1995, 376, 498.
[11] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science 1995,
270, 1789.
[12] T. Ameri, P. Khoram, J. Min, C. J. Brabec, Adv. Mater. 2013, 25, 4245.
[13] L. Lu, M. A. Kelly, W. You, L. Yu, Nat. Photonics 2015, 9, 491.
[14] B. M. Savoie, S. Dunaisky, T. J. Marks, M. A. Ratner, Adv. Energy
Mater. 2015, 5, 1400891.
[15] W. Huang, P. Cheng, Y. Yang, G. Li, Y. Yang, Adv. Mater. 2018, 30,
[16] H. Xu, H. Ohkita, Y. Tamai, H. Benten, S. Ito, Adv. Mater. 2015, 27,
[17] J.-S. Huang, T. Goh, X. Li, M. Y. Sfeir, E. A. Bielinski, S. Tomasulo,
M. L. Lee, N. Hazari, A. D. Taylor, Nat. Photonics 2013, 7, 479.
[18] P. P. Khlyabich, B. Burkhart, B. C. Thompson, J. Am. Chem. Soc.
2012, 134, 9074.
[19] L. Yang, H. Zhou, S. C. Price, W. You, J. Am. Chem. Soc. 2012, 134,
[20] L. Lu, T. Xu, W. Chen, E. S. Landry, L. Yu, Nat. Photonics 2014, 8,
[21] Y. Yang, W. Chen, L. Dou, W.-H. Chang, H.-S. Duan, B. Bob, G. Li,
Y. Yang, Nat. Photonics 2015, 9, 190.
[22] N. Gasparini, X. Jiao, T. Heumueller, D. Baran, G. J. Matt,
S. Fladischer, E. Spiecker, H. Ade, C. J. Brabec, T. Ameri, Nat. Energy
2016, 1, 16118.
[23] R. Yu, S. Zhang, H. Yao, B. Guo, S. Li, H. Zhang, M. Zhang, J. Hou,
Adv. Mater. 2017, 29, 1700437.
[24] G. Chen, H. Sasabe, X.-F. Wang, Z. Hong, J. Kido, Synth. Met. 2014,
192, 10.
[25] Z. Li, X. Xu, W. Zhang, X. Meng, Z. Genene, W. Ma, W. Mammo,
A. Yartsev, M. R. Andersson, R. A. J. Janssen, E. Wang, Energy
Environ. Sci. 2017, 10, 2212.
[26] X. Xu, Z. Bi, W. Ma, Z. Wang, W. C. H. Choy, W. Wu, G. Zhang, Y. Li,
Q. Peng, Adv. Mater. 2017, 29, 1704271.
[27] P. P. Khlyabich, B. Burkhart, B. C. Thompson, J. Am. Chem. Soc.
2011, 133, 14534.
[28] T. M. Grant, T. Gorisse, O. J. Dautel, G. Wantz, B. H. Lessard,
J. Mater. Chem. A 2017, 5, 1581.
[29] P. Cheng, M. Zhang, T.-K. Lau, Y. Wu, B. Jia, J. Wang, C. Yan,
M. Qin, X. Lu, X. Zhan, Adv. Mater. 2017, 29, 1605216.
[30] J. M. Lee, B.-H. Kwon, H. I. Park, H. Kim, M. G. Kim, J. S. Park,
E. S. Kim, S. Yoo, D. Y. Jeon, S. O. Kim, Adv. Mater. 2013, 25, 2011.
[31] M. Han, H. Kim, H. Seo, B. Ma, J.-W. Park, Adv. Mater. 2012, 24,
[32] S. Liu, P. You, J. Li, J. Li, C.-S. Lee, B. S. Ong, C. Surya, F. Yan,
Energy Environ. Sci. 2015, 8, 1463.
[33] Y. Huang, W. Wen, S. Mukherjee, H. Ade, E. J. Kramer, G. C. Bazan,
Adv. Mater. 2014, 26, 4168.
[34] Q. Wei, T. Nishizawa, K. Tajima, K. Hashimoto, Adv. Mater. 2008,
20, 2211.
[35] J. W. Jung, J. W. Jo, W. H. Jo, Adv. Mater. 2011, 23, 1782.
[36] Z. Xiao, Q. Dong, P. Sharma, Y. Yuan, B. Mao, W. Tian,
A. Gruverman, J. Huang, Adv. Energy Mater. 2013, 3, 1581.
[37] P. Cheng, R. Wang, J. Zhu, W. Huang, S.-Y. Chang, L. Meng, P. Sun,
H.-W. Cheng, M. Qin, C. Zhu, X. Zhan, Y. Yang, Adv. Mater. 2018,
30, 1705243.
[38] P. Cheng, C. Yan, Y. Wu, J. Wang, M. Qin, Q. An, J. Cao, L. Huo,
F. Zhang, L. Ding, Y. Sun, W. Ma, X. Zhan, Adv. Mater. 2016, 28,
[39] P. Cheng, C. Yan, T.-K. Lau, J. Mai, X. Lu, X. Zhan, Adv. Mater. 2016,
28, 5822.
[40] D. Baran, R. S. Ashraf, D. A. Hanifi, M. Abdelsamie, N. Gasparini,
J. A. Rohr, S. Holliday, A. Wadsworth, S. Lockett, M. Neophytou,
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1801501 (8 of 8)
Adv. Mater. 2018, 30, 1801501
C. J. M. Emmott, J. Nelson, C. J. Brabec, A. Amassian, A. Salleo,
T. Kirchartz, J. R. Durrant, I. McCulloch, Nat. Mater. 2017,
16, 363.
[41] B. C. Schroeder, Z. Li, M. A. Brady, G. C. Faria, R. S. Ashraf,
C. J. Takacs, J. S. Cowart, D. T. Duong, K. H. Chiu, C.-H. Tan,
J. T. Cabral, A. Salleo, M. L. Chabinyc, J. R. Durrant, I. McCulloch,
Angew. Chem., Int. Ed. 2014, 53, 12870.
[42] L. Derue, O. Dautel, A. Tournebize, M. Drees, H. Pan,
S. Berthumeyrie, B. Pavageau, E. Cloutet, S. Chambon, L. Hirsch,
A. Rivaton, P. Hudhomme, A. Facchetti, G. Wantz, Adv. Mater.
2014, 26, 5831.
[43] B. Fan, W. Zhong, X.-F. Jiang, Q. Yin, L. Ying, F. Huang, Y. Cao, Adv.
Energy Mater. 2017, 7, 1602127.
[44] T. Liu, Y. Guo, Y. Yi, L. Huo, X. Xue, X. Sun, H. Fu, W. Xiong,
D. Meng, Z. Wang, F. Liu, T. P. Russell, Y. Sun, Adv. Mater. 2016, 28,
[45] H. Lu, J. Zhang, J. Chen, Q. Liu, X. Gong, S. Feng, X. Xu, W. Ma,
Z. Bo, Adv. Mater. 2016, 28, 9559.
[46] X. Xu, Z. Li, J. Wang, B. Lin, W. Ma, Y. Xia, M. R. Andersson,
R. A. J. Janssen, E. Wang, Nano Energy 2018, 45, 368.
[47] C. Groves, Energy Environ. Sci. 2013, 6, 1546.
[48] F. Machui, S. Rathgeber, N. Li, T. Ameri, C. J. Brabec, J. Mater.
Chem. 2012, 22, 15570.
[49] Y. Lin, F. Zhao, Q. He, L. Huo, Y. Wu, T. C. Parker, W. Ma, Y. Sun,
C. Wang, D. Zhu, A. J. Heeger, S. R. Marder, X. Zhan, J. Am. Chem.
Soc. 2016, 138, 4955.
[50] F. Zhao, S. Dai, Y. Wu, Q. Zhang, J. Wang, L. Jiang, Q. Ling, Z. Wei,
W. Ma, W. You, C. Wang, X. Zhan, Adv. Mater. 2017, 29, 1700144.
[51] S. C. Price, A. C. Stuart, L. Yang, H. Zhou, W. You, J. Am. Chem. Soc.
2011, 133, 4625.
[52] Y. Lin, Q. He, F. Zhao, L. Huo, J. Mai, X. Lu, C.-J. Su, T. Li, J. Wang,
J. Zhu, Y. Sun, C. Wang, X. Zhan, J. Am. Chem. Soc. 2016, 138, 2973.
[53] Y. Lin, F. Zhao, Y. Wu, K. Chen, Y. Xia, G. Li, S. K. K. Prasad, J. Zhu,
L. Huo, H. Bin, Z.-G. Zhang, X. Guo, M. Zhang, Y. Sun, F. Gao,
Z. Wei, W. Ma, C. Wang, J. Hodgkiss, Z. Bo, O. Inganäs, Y. Li,
X. Zhan, Adv. Mater. 2017, 29, 1604155.
[54] Q. An, F. Zhang, J. Zhang, W. Tang, Z. Deng, B. Hu, Energy Environ.
Sci. 2016, 9, 281.
[55] G. G. Malliaras, J. R. Salem, P. J. Brock, C. Scott, Phys. Rev. B 1998,
58, 13411.
... [170] mitigated the FF loss against J sc while keeping V oc constant. They used energy levels modulation in ITIC-Th by introducing an adjoining thiophene ring, with an extra S atom or O atom into its side chain, between the central core of ITIC-Th and each of the outer dangling units, to form ITIC-Th-S and ITIC-Th-O. ...
Incorporating a third element in the active layer of organic photovoltaic (OPV) devices is a promising strategy towards improving the efficiency and stability of this technology while maintaining relatively low costs. While ternary organic solar cells (TOSCs) have been widely studied during the last decade, there has been a meteoric rise in TOSC research after a breakthrough efficiency of 14.1% was reported in 2017. Such values of efficiency make TOSCs promising third-generation solar technologies, prompting worldwide research efforts into the inclusion of a third element for high-performance TOSCs. These efforts have further boosted their efficiency, which is currently approaching 19%, and improved the stability of OPVs. This review discusses the role of the third component in improving efficiency and stability, emphasizing the period after 2016, which witnessed huge increases in efficiency and the boom that ensued. Since their introduction in 2008 for applications in photovoltaics and optoelectronics, colloidal quantum dot solar cells (CQDSCs), among other third-generation technologies, have recently experienced a level of success comparable to TOSCs. Finally, we compare the performance of TOSCs to CQDSCs, a complementary third-generation solar technology.
Organic photodetectors (OPDs) detecting light in the near‐infrared (NIR) range from 900 to 1200 nm offer numerous applications in biomedical imaging and health monitoring. However, an ultra‐low bandgap of the electron donor compound required to achieve NIR detection poses a unique challenge in selecting a complementary acceptor material with a suitable energy‐level offset. To tackle this, a solution‐processed, fullerene‐dominated, ternary device is engineered by adding an ultra‐low bandgap (0.6–0.8 eV) ambipolar polymer, polybenzobisthiadiazole‐dithienocyclopentane (PBBTCD), into the active layer of visible‐light‐responsive OPDs (bandgap of 1.8 eV) to form a ternary blend. The resulting OPD benefits from the extended absorption beyond 1000 nm. The cascaded energy level alignment within the ternary blend and the applied reverse bias both improve the overall NIR photocurrent responsivity by 2 orders of magnitude, reaching 0.4 mA W ⁻¹ at 1050 nm and −2 V for ternary devices. Furthermore, a photovoltage responsivity of 0.3 mV m ² W ⁻¹ along with significant open‐circuit voltage ( V oc ) of 0.12 V allow NIR detection in the V oc mode. Prominently, this ability is accomplished with a minimal presence of PBBTCD. Taken together, this work indicates potential strategies for extending the spectral activity of conventional OPDs through introduction of an ambipolar ultra‐low bandgap polymer as a minor element.
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This article presents recent advances in the ternary organic solar cell (TOSC), such as technological interventions from the material design to the device performance, which led to more than 19% of power conversion efficiency. The research and developments in TOSCs reported in the past decade have been inspiring and promising in terms of molecular processing to device properties for low‐power devices and building integrated photovoltaics applications. Many of these are still in the early phase, enabling researchers to explore more and flourish. The research community has made numerous efforts to address the different aspects to enhance the efficiency and stability of the TOSCs. Therefore, the objective of this paper is to review the recent advances in TOSCs and present a comprehensive discussion in this regard. This review also identifies and suggests the possible outlooks for the critical issues associated with TOSCs, along with future perspectives. This article is protected by copyright. All rights reserved.
Fused-ring electron acceptors (FREAs) have a donor–acceptor–donor structure comprising an electron-donating fused-ring core, electron-accepting end groups, π-bridges and side chains. FREAs possess beneficial features, such as feasibility to tailor their structures, high property tunability, strong visible and near-infrared light absorption and excellent n-type semiconducting characteristics. FREAs have initiated a revolution to the field of organic solar cells in recent years. FREA-based organic solar cells have achieved unprecedented efficiencies, over 20%, which breaks the theoretical efficiency limit of traditional fullerene acceptors (~13%), and boast potential operational lifetimes approaching 10 years. Based on the original studies of FREAs, a variety of new structures, mechanisms and applications have flourished. In this Review, we introduce the fundamental principles of FREAs, including their structures and inherent electronic and physical properties. Next, we discuss the way in which the properties of FREAs can be modulated through variations to the electronic structure or molecular packing. We then present the current applications and consider the future areas that may benefit from developments in FREAs. Finally, we conclude with the position of FREA chemistry, reflecting on the challenges and opportunities that may arise in the future of this burgeoning field. Fused-ring electron acceptors are excellent n-type organic semiconductors with outstanding optoelectronic conversion and electron transport abilities. This Review highlights the fundamental principles, design strategies and versatile applications of fused-ring electron acceptors in photovoltaics, electronics and photonics. As part of the Springer Nature Content Sharing Initiative, a view-only version of this paper can be accessed and publicly shared through the following SharedIt link:
Due to the complicated synthesis routes of ladder-typed fused ring small molecule acceptors (SMAs), simple non-fused-ring SMAs have been received attention. However, their photovoltaic properties have not made great progress due to the subtle crystallinity and intramolecular interaction. In this work, in order to advance photovoltaic properties, a type of non-fused-ring asymmetrical SMAs with an A-D-D'-A framework, named as IOMe-4Cl and IOEH-4Cl, was primarily designed and synthesized with a multifunctional alkoxy indenothiophene (INT) unit assembled with a classic dithienocyclopentadiene (DTC) unit as an electron-donating D-D' central build. The influence of asymmetric structure, non-covalent bond and alkoxy chain from the alkoxy INT unit on optical, electrochemical and photovoltaic properties was systemic studied. It was found that both SMAs exhibited strong near infrared absorption at about 900 nm. In comparison to the IOMe-4Cl with methoxy, the IOEH-4Cl with 2-ethyl-hexyloxy exhibited better regular film morphology and more suitable frontier orbital energy level with polymer PM6. As a result, IOEH-4Cl exhibited better photovoltaic properties than IOMe-4Cl in the solution-processing binary OSCs using polymer PM6 as donor material. A compelling PCE of 13.67% with high Jsc of 23.00 mA cm⁻², Voc of 0.85 V and FF of 70.19% was obtained for the PM6:IOEH-4Cl based binary cells. This work clearly states that the multifunctional alkoxy INT is an appealing unit to construct high-performance non-fused-ring asymmetric SMAs by asymmetric unit, non-covalent bond and alkoxy chain effect.
Comprehensive Summary Fullerene derivatives are classic electron acceptor materials for organic solar cells (OSCs) but possess some intrinsic drawbacks such as weak visible light absorption, limited optoelectronic property tunability, difficult purification and photochemical/morphological instability. Fullerene acceptors are a bottleneck restricting further development of this field. Our group pioneered the exploration of novel nonfullerene acceptors in China in 2006, and initiated the research of two representative acceptor systems, rylene diimide polymer and fused‐ring electron acceptor (FREA). FREA breaks the theoretical efficiency limit of fullerene‐based OSCs (~13%) and promotes the whole field to an unprecedented prosperity with efficiency of 20%, heralding a nonfullerene era for OSCs. In this review, we revisit 15‐year nonfullerene exploration journey, summarize the design principles, molecular engineering strategies, physical mechanisms and device applications of these two nonfullerene acceptor systems, and propose some possible research topics in the near future. What is the most favorite and original chemistry developed in your research group? Fused‐ring electron acceptor for photovoltaics. How do you get into this specific field? Could you please share some experiences with our readers? In 2006 when I came back to ICCAS from USA and started my independent academic career, I was interested in organic photovoltaics (OPV) which I had never touched before since I believed it is useful and should have a bright future. OPV converts renewable solar energy to clean electricity through photovoltaic effect. The active layer in OPV device consists of electron donor and electron acceptor. Although fullerenes were prevailing acceptor materials in OPV at that time, I doubted if this choice is correct considering their fatal flaws such as weak absorption. I was curious about why no research groups in China explored fullerene alternatives before 2006. In 2006 our group initiated the nonfullerene OPV research of China. In 2015 we invented the milestone molecule ITIC and pioneered fused‐ring electron acceptor (FREA). Around 300 research groups in >20 countries have utilized the FREA to fabricate high‐efficiency OPV devices with champion efficiency of >20%. The FREA has subverted previously predominant fullerenes, and is inaugurating a new era of the OPV field. How do you supervise your students? I expect that my students should have some essential personalities such as curiosity, creativity, devotion, persistence and diligence. I encourage them to do original, unique and leading research. I endow them with cheerful academic atmosphere such as self‐motivation, open‐mindedness and cross‐cooperation. I would like to provide them with warm human solicitude when they need help or suffer from bitterness. What is the most important personality for scientific research? Curiosity; uniqueness; persistence.
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High‐performance solar‐blind photodetectors are widely studied due to their unique significance in military and industrial applications. Yet the rational molecular design for materials to possess strong absorption in solar‐blind region is rarely addressed. Here, an organic solar‐blind photodetector is reported by designing a novel asymmetric molecule integrated strong solar‐blind absorption with high charge transport property. Such alkyl substituted [1]benzothieno[3,2‐b][1]‐benzothiophene (BTBT) derivatives Cn‐BTBTN (n = 6, 8, and 10) can be easily assembled into 2D molecular crystals and perform high mobility up to 3.28 cm2 V−1s−1, which is two orders of magnitude higher than the non‐substituted core BTBTN. Cn‐BTBTNs also exhibit dramatically higher thermal stability than the symmetric alkyl substituted C8‐BTBT. Moreover, C10‐BTBTN films with the highest mobility and strongest solar‐blind absorption among the Cn‐BTBTNs are applied for solar‐blind photodetectors, which reveal record‐high photosensitivity and detectivity up to 1.60 × 107 and 7.70 × 1014 Jones. Photodetector arrays and flexible devices are also successfully fabricated. The design strategy can provide guidelines for developing materials featuring high thermal stability and stimulating such materials in solar‐blind photodetector application. Asymmetric [1]benzothieno[3,2‐b][1]‐benzothiophene (BTBT) derivatives of Cn‐BTBTNs that integrate strong solar‐blind absorption with high mobility are designed and synthesized. C10‐BTBTN‐based solar‐blind photodetectors demonstrate preeminent performance with the P, R, and D* up to 1.60 × 107, 8.40 × 103 A W−1, and 7.70 × 1014 Jones, respectively, which exhibit a broad prospect in optoelectronic device applications.
The multifunction of molecule-based devices is always achieved by improving their charge transport characteristics. These characteristics depend strongly on the energy levels of molecular semiconductors, which fundamentally govern the working principle and device performance. Therefore, an accurate measurement of these energy levels is crucial for evaluating the availability of the prepared materials and thus optimizing the device performance. Here, an easy-to-operate three-terminal hot electron transistor has been developed, which comprises a molecular optoelectronic device that records the charge transport. It achieves exceptional properties including the lowest unoccupied molecular orbit level, highest occupied molecular orbit level, higher energy states, and higher electronic bandgap. When compared with existing techniques such as cyclic voltammetry, inverse photoemission spectroscopy, and ultraviolet photoemission spectroscopy, the hot electron transistor provides in-situ characterization and categorizes the measured energy information as intrinsic properties of the molecular semiconductor. Furthermore, we provide an in-depth understanding of the fundamental device-physics, which provides promising guidance for performance optimization.
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Multi-component organic photovoltaics (OPVs), e.g., ternary blends, are effective for high performance, while the fundamental understanding from the molecular to device level is less-known. To address this issue, we here...
Solar energy offers an alternative solution to the global community's growing energy demands. Semitransparent organic photovoltaics (ST-OPVs) have received tremendous attention due to their tunable energy levels and rising power conversion efficiency (PCE). Because of its transparency, ST-OPVs are able to serve as the power-generating roof of the greenhouse, and color-tunable walls/windows for modern buildings or façades. With the rapid development of narrow-bandgap semiconductors to absorb near-infrared photons, the performances of ST-OPVs has progressed with PCEs over 12% with average visible transmittances over 20%. Here, recent developments in ST-OPVs based on narrow-bandgap donors and non-fullerene acceptors are reviewed. Several strategies for chemical structures design have been reported to lower bandgaps semiconductor materials. The recent developments of non-fullerene acceptor structures for ST-OPVs are categorized into A-D-A, A-π-D-π-A, and A-DAD-A by the structure alignment. From device perspectives, the strategies such as ternary blend, distributions of donors and acceptors in active layers, tandem and transparent conductive electrodes for high-performance ST-OPVs are summarized. To conclude, some insightful guidelines for future developments in ST-OPVs from both materials and device points of views are provided.
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Over the past three years, a particularly exciting and active area of research within the field of organic photovoltaics has been the use of non-fullerene acceptors (NFAs). Compared with fullerene acceptors, NFAs possess significant advantages including tunability of bandgaps, energy levels, planarity and crystallinity. To date, NFA solar cells have not only achieved impressive power conversion efficiencies of ~13–14%, but have also shown excellent stability compared with traditional fullerene acceptor solar cells. This Review highlights recent progress on single-junction and tandem NFA solar cells and research directions to achieve even higher efficiencies of 15–20% using NFA-based organic photovoltaics are also proposed. This Review describes how non-fullerene electron acceptor materials are bringing improvements in the power conversion efficiency and stability of organic solar cells.
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Organic solar cells (OSCs) based on bulk heterojunction structures are promising candidates for next-generation solar cells. However, the narrow absorption bandwidth of organic semiconductors is a critical issue resulting in insufficient usage of the energy from the solar spectrum, and as a result, it hinders performance. Devices based on multiple-donor or multiple-acceptor components with complementary absorption spectra provide a solution to address this issue. OSCs based on multiple-donor or multiple-acceptor systems have achieved power conversion efficiencies over 12%. Moreover, the introduction of an additional component can further facilitate charge transfer and reduce charge recombination through cascade energy structure and optimized morphology. This progress report provides an overview of the recent progress in OSCs based on multiple-donor (polymer/polymer, polymer/dye, and polymer/small molecule) or multiple-acceptor (fullerene/fullerene, fullerene/nonfullerene, and nonfullerene/nonfullerene) components.
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Recently, a new type of active layer with a ternary system has been developed to further enhance the performance of binary system organic photovoltaics (OPV). In the ternary OPV, almost all active layers are formed by simple ternary blend in solution, which eventually leads to the disordered bulk heterojunction (BHJ) structure after a spin-coating process. There are two main restrictions in this disordered BHJ structure to obtain higher performance OPV. One is the isolated second donor or acceptor domains. The other is the invalid metal–semiconductor contact. Herein, the concept and design of donor/acceptor/acceptor ternary OPV with more controlled structure (C-ternary) is reported. The C-ternary OPV is fabricated by a sequential solution process, in which the second acceptor and donor/acceptor binary blend are sequentially spin-coated. After the device optimization, the power conversion efficiencies (PCEs) of all OPV with C-ternary are enhanced by 14–21% relative to those with the simple ternary blend; the best PCEs are 10.7 and 11.0% for fullerene-based and fullerene-free solar cells, respectively. Moreover, the averaged PCE value of 10.4% for fullerene-free solar cell measured in this study is in great agreement with the certified one of 10.32% obtained from Newport Corporation.
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Integration of a third component into a single-junction polymer solar cell (PSC) is regarded as an attractive strategy to enhance the performance of PSCs. Although binary all-polymer solar cells (all-PSCs) have recently emerged with compelling power conversion efficiencies (PCEs), the PCEs of ternary all-PSCs still lag behind those of the state-of-the-art binary all-PSCs, and the advantages of ternary systems are not fully exploited. In this work, we realize high-performance ternary all-PSCs with record-breaking PCEs of 9% and high fill factors (FF) of over 0.7 for both conventional and inverted devices. The improved photovoltaic performance benefits from the synergistic effects of extended absorption, more efficient charge generation, optimal polymer orientations and suppressed recombination losses compared to the binary all-PSCs, as evidenced by a set of experimental techniques. The results provide new insights for developing high-performance ternary all-PSCs by choosing appropriate donor and acceptor polymers to overcome limitations in absorption, by affording good miscibility, and by benefiting from charge and energy transfer mechanisms for efficient charge generation.
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A new fluorinated nonfullerene acceptor, ITIC-Th1, has been designed and synthesized by introducing fluorine (F) atoms onto the end-capping group 1,1-dicyanomethylene-3-indanone (IC). On the one hand, incorporation of F would improve intramolecular interaction, enhance the push–pull effect between the donor unit indacenodithieno[3,2-b]thiophene and the acceptor unit IC due to electron-withdrawing effect of F, and finally adjust energy levels and reduce bandgap, which is beneficial to light harvesting and enhancing short-circuit current density (JSC). On the other hand, incorporation of F would improve intermolecular interactions through CF···S, CF···H, and CF···π noncovalent interactions and enhance electron mobility, which is beneficial to enhancing JSC and fill factor. Indeed, the results show that fluorinated ITIC-Th1 exhibits redshifted absorption, smaller optical bandgap, and higher electron mobility than the nonfluorinated ITIC-Th. Furthermore, nonfullerene organic solar cells (OSCs) based on fluorinated ITIC-Th1 electron acceptor and a wide-bandgap polymer donor FTAZ based on benzodithiophene and benzotriazole exhibit power conversion efficiency (PCE) as high as 12.1%, significantly higher than that of nonfluorinated ITIC-Th (8.88%). The PCE of 12.1% is the highest in fullerene and nonfullerene-based single-junction binary-blend OSCs. Moreover, the OSCs based on FTAZ:ITIC-Th1 show much better efficiency and better stability than the control devices based on FTAZ:PC71BM (PCE = 5.22%).
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A new, easy, and efficient approach is reported to enhance the driving force for charge transfer, break tradeoff between open-circuit voltage and short-circuit current, and simultaneously achieve very small energy loss (0.55 eV), very high open-circuit voltage (>1 V), and very high efficiency (>10%) in fullerene-free organic solar cells via an energy driver.
Growing interests have been devoted to the synthesis of polymer acceptors as alternatives to fullerene derivatives to realize high-performance and stable all-polymer solar cells (all-PSCs). So far, one of the key factors that limit the performance of all-PSCs is low photocurrent density (normally < 14 mA/cm²). One potential solution is to improve the dielectric constants (εr) of polymer:polymer blends, which tend to reduce the binding energy of excitons, thus boosting the exciton dissociation efficiencies. Nevertheless, the correlation between εr and photovoltaic performance has been rarely investigated for all-PSCs. In this work, five fluorinated naphthalene diimide (NDI)-based acceptor polymers, with different content of fluorine were synthesized. The incorporation of fluorine increased the εr of the acceptor polymers and blend films, which improved the charge generation and overall photocurrent of the all-PSCs. As a result, the PTB7-Th:PNDI-FT10 all-PSC attained a high power conversion efficiency (PCE) of 7.3% with a photocurrent density of 14.7 mA/cm², which surpassed the values reported for the all-PSC based on the non-fluorinated acceptor PNDI-T10. Interestingly, similarly high photovoltaic performance was maintained regardless of a large variation of donor:acceptor ratios, which revealed the good morphological tolerance and the potential for robust production capability of all-PSCs.
In this work, highly efficient ternary-blend organic solar cells (TB-OSCs) are reported based on a low-bandgap copolymer of PTB7-Th, a medium-bandgap copolymer of PBDB-T, and a wide-bandgap small molecule of SFBRCN. The ternary-blend layer exhibits a good complementary absorption in the range of 300-800 nm, in which PTB7-Th and PBDB-T have excellent miscibility with each other and a desirable phase separation with SFBRCN. In such devices, there exist multiple energy transfer pathways from PBDB-T to PTB7-Th, and from SFBRCN to the above two polymer donors. The hole-back transfer from PTB7-Th to PBDB-T and multiple electron transfers between the acceptor and the donor materials are also observed for elevating the whole device performance. After systematically optimizing the weight ratio of PBDB-T:PTB7-Th:SFBRCN, a champion power conversion efficiency (PCE) of 12.27% is finally achieved with an open-circuit voltage (Voc ) of 0.93 V, a short-circuit current density (Jsc ) of 17.86 mA cm(-2) , and a fill factor of 73.9%, which is the highest value for the ternary OSCs reported so far. Importantly, the TB-OSCs exhibit a broad composition tolerance with a high PCE over 10% throughout the whole blend ratios.
Efficient ternary polymer solar cells are constructed by incorporating an electron-deficient chromophore (5Z,5′Z)-5,5′-((7,7′-(4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(6-fluorobenzo[c][1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) (IFBR) as an additional component into the bulk-heterojunction film that consists of a wide-bandgap conjugated benzodithiophene-alt-difluorobenzo[1,2,3]triazole based copolymer and a fullerene acceptor. With respect to the binary blend films, the incorporation of a certain amount of IFBR leads to simultaneously enhanced absorption coefficient, obviously extended absorption band, and improved open-circuit voltage. Of particular interest is that devices based on ternary blend film exhibit much higher short-circuit current densities than the binary counterparts, which can be attributed to the extended absorption profiles, enhanced absorption coefficient, favorable film morphology, as well as formation of cascade energy level alignment that is favorable for charge transfer. Further investigation indicates that the ternary blend device exhibits much shorter charge carrier extraction time, obviously reduced trap density and suppressed trap-assisted recombination, which is favorable for achieving high short-circuit current. The combination of these beneficial aspects leads to a significantly improved power conversion efficiency of 8.11% for the ternary device, which is much higher than those obtained from the binary counterparts. These findings demonstrate that IFBR can be a promising electron-accepting material for the construction of ternary blend films toward high-performance polymer solar cells.