Cocrystal Engineering: Toward Solution-Processed Near-Infrared 2D Organic Cocrystals for Broadband Photodetection

Article abstract of DOI:10.1002/anie.202015326

Large-area 2D cocrystals with strong near-infrared (NIR) absorption have been designed and prepared. Driven by the intermolecular charge-transfer (CT) interactions, zinc tetraphenylporphyrin (donor) and C₆₀ (acceptor) self-assemble into a NIR cocrystal with absorption wavelength up to 1080 nm. By tailoring the growth solvents and processes, the cocrystal morphologies can be tuned from 1D nanowires, 2D nanosheets to large-area 2D cocrystal films with length reaching several millimeters. Owing to the highly ordered donor–acceptor arrangement, the CT absorption in the 2D cocrystals is enhanced and is comparable to singlet absorption. The uniform 2D cocrystals, with enhanced CT absorption in the NIR region, displays a high responsivity of 2424 mA W^?1 to NIR light and a fast response time of 0.6 s. The excellent device performance is attributed to the generation of long-lived free charge carriers as revealed by transient absorption spectroscopy and optimization of device configuration.

Full text of DOI:10.1002/anie.202015326

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
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Accepted Article
Title: Cocrystal Engineering: toward Solution-Processed Near-Infrared
2D Organic Cocrystals for Broadband Photodetection
Authors: Wenping Hu, Yu Wang, Huang Wu, Weigang Zhu, Xiaotao
Zhang, Zheyuan Liu, Yishi Wu, Changfu Feng, Yanfeng Dang,
Huanli Dong, and Hongbing Fu
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202015326
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10.1002/anie.202015326
Angewandte Chemie International Edition
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Cocrystal Engineering: toward Solution-Processed Near-Infrared
2D Organic Cocrystals for Broadband Photodetection
Yu Wang+, Huang Wu+, Weigang Zhu+, Xiaotao Zhang, Zheyuan Liu, Yishi Wu, Changfu Feng,
Yanfeng Dang, Huanli Dong, Hongbing Fu, and Wenping Hu*
Abstract: Two-dimensional (2D) cocrystals open a new way to get
2D functional materials via crystal engineering instead of molecular
engineering. Here, large-area 2D cocrystals with length reaching
several millimeters with strong near-infrared (NIR) absorption have
been successfully designed and prepared. Driven by the
Organic photoresponse materials,[1] given their advantages of
tunable absorption, inherent flexibility, solution and low-
temperature processibility, hold great promise for next-
generation flexible and wearable photodetectors.[2] Developing
optoelectronic materials with broad spectral response from
ultraviolet-visible to the infrared region is a great challenge on
molecular engineering,[3] which has been an attractive objective
due to their potential applications involving image sensing,
optical communications, remote control and environmental
monitoring.[4] In order to achieve wide spectral detection, organic
intermolecular
charge-transfer
(CT)
interactions,
zinc
tetraphenylporphyrin (donor) and C60 (acceptor) self-assemble into a
NIR cocrystals with absorption wavelength up to 1080 nm. By
tailoring the growth solvents and processes, the cocrystal
morphologies can be tuned from 1D nanowires, 2D nanosheets to
large-area 2D cocrystal films with length reaching several millimeters. donor-acceptor (D-A) blends are widely employed as the
Impressively, due to the highly ordered donor-acceptor arrangement,
the CT absorption in the 2D cocrystals is significantly enhanced and
becomes comparable to singlet absorption. The uniform 2D
cocrystals, with enhanced CT absorption in the NIR region, displays
a high responsivity of 2424 mA/W to NIR light and a fast response
time of 0.6 s. The excellent device performance can be attributed to
the generation of long-lived free charge carriers as revealed by
transient absorption spectroscopy and the optimization of device
configuration. This work shows an example of controlled growth of
2D cocrystals for broadband photodetectors, which reveals the
brilliant future of cocrystal films for high-performance electronics and
paves their way towards large-scale, integrated, flexible, practical
applications.
photoactive layer in photoresponse devices.[5] On one hand, the
interface charge-transfer (CT) interaction between donors and
acceptors generates a new energy state with red-shifted
absorption, which enables to realize near-infrared (NIR)
absorption.[6] On the other hand, the efficient exciton dissociation
and carrier transport in D-A blends facilitate the improvement of
device performance.[7] However, CT absorption in organic D-A
blends is typically two orders of magnitude weaker than the
singlet absorption on account of its intermolecular nature.[8] This
weak absorption limits the photocurrent generation in NIR
region,[9] which engenders it challenging to construct high-
performance photodetectors with a wide spectra response.
Recently, cocrystal engineering has emerged as an effective
approach to construct functional materials.[10] By taking
advantages of the noncovalent interactions between donor and
acceptor molecules, cocrystals with highly ordered D-A
arrangement, can be easily fabricated in low-cost and facile
solution-processed methods.[11] Composed of multi-components,
cocrystals can not only retain the properties of their individual
molecules,[12] but also enable to exhibit innovative properties
arising from the intermolecular collaborative effects.[13] To date,
various unpredicted properties have been achieved in cocrystal
materials,[14] such as metallic electrical conductivity,[15] ambipolar
charge transport,[16] room-temperature ferroelectricity,[17] stimuli
response,[18] white-light emitting,[19] and room-temperature
phosphorescence[20]. CT cocrystals are emerging as excellent
candidates for advanced functional materials, on account of that
the electron delocalization natures from donor to acceptor
molecules, involving CT degree, charge generation, separation
and recombination dynamics, play a critical role to the resulting
photophyscial properties.[21] In particular, due to the orbital
hybridization between the highest occupied molecular orbital
(HOMO) of donor and the lowest unoccupied molecular orbital
(LUMO) of acceptor, the bandgap of CT cocrystals are narrowed,
allowing their CT absorption red-shifted to the NIR region.[22] In
comparison with D-A blends, the regular donor and acceptor
[*]
Dr. Y. Wang,[+] Dr. W. Zhu,[+] Dr. X. Zhang, Dr. Z. Liu, Dr. Y. Dang,
Prof. W. Hu
Tianjin Key Laboratory of Molecular Optoelectronic Science,
Department of Chemistry, School of Science, Tianjin University &
Collaborative Innovation Center of Chemical Science and
Engineering (Tianjin), Tianjin 300072, China
E-mail: huwp@tju.edu.cn
Prof. H. Dong
Laboratory of Organic Solids, Institute of Chemistry, Chinese
Academy of Science (ICCAS), Beijing 100190, China
Dr. H. Wu[+]
Department of Chemistry, Northwestern University, 2145 Sheridan
Road, Evanston, Illinois 60208, United States.
Dr. Y. Wu, Prof. H. Fu
Beijing Key Laboratory for Optical Materials and Photonic Devices,
Department of Chemistry, Capital Normal University, Beijing
100048, China
C. Feng
School of Chemical Engineering and Technology, Tianjin University,
Tianjin 300072, China
Prof. W. Hu
Joint School of National University of Singapore and Tianjin
University, International Campus of Tianjin University, Binhai New
City, Fuzhou 350207, China
arrangement in CT cocrystal forms
a
nanoscale D-A
interpenetrating network. The network may not only contribute to
the enhancement of CT absorption, promoting the formation of
photo-generated carrier, but also provide sufficient D-A interface
for exciton dissociation and continuous pathways for carrier
transport. Therefore, CT cocrystals may provide a fascinating
[+]
These authors contributed equally to this work
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.202015326
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prospect in broadband photoresponse devices. However,
current cocrystal optoelectronic devices are generally based on
micro/nano-sized crystals.[23] They generally grow or locate at
the substrates in a manner of random orientation and disordered
distribution, which nature hinders further applications of
cocrystals in large-area electronic devices.[24]
controlled growth of cocrystal morphology, which provide
guidelines for further regulation of cocrystal active layer in large-
area electronic devices and applications.
Meanwhile, two-dimensional (2D) organic semiconductor
crystals, with long-range ordered arrangement and minimal
defects, have received increasing interest in optoelectronic
field.[25] In particular, they possess unique morphological
features, involving (i) a high specific surface area, which ensures
efficient photo absorption; (ii) a smooth surface that reduces
interface defects, which would promote charge injection and
collection. These features engender them serve as outstanding
candidates for photodetectors.[26] Furthermore, large-area 2D
organic crystals may be under a bright future in large-scale
integrated devices.[27] And their small thickness increases their
mechanical flexibility, which also enhances their potential for
flexible applications.[28] In this regard, the exploration of 2D
cocrystal film constitutes a promising objective, which not only
displays great potential in the construction of high-performance
photoresponse devices, but also paves their way for developing
integrated and flexible practical applications.
In this work, a cocrystal with NIR absorption is designed and
synthesized (Figure 1a), wherein ZnTPP (5,10,15,20-
tetraphenyl-21H,23H-porphine Zinc, C44H28N4Zn) and fullerene
(C60) are selected as donor and acceptor, respectively (Figure
S1). The ZnTPP-C60 cocrystals (ZCCs), with
a 1:1 D-A
Figure 1. (a) Molecular structure and cocrystallization process of ZnTPP and
stoichiometry, crystallize in a triclinic P-1 space group (Table
S1). As revealed by single-crystal X-ray diffraction (XRD)
analysis, ZnTPP molecules and C60 molecules stack in a zigzag
manner with D-A distances of 2.796 and 2.821 Å (Figure 1e and
Figure S6). Such close contacts reveal the strong π–π
interactions between donor and acceptor molecules, which
support the D-A alternate arrangement and lay the foundation
for the intermolecular CT. Moreover, the D-A π–π interactions,
togher with the -CH…N- interactions between ZnTPP molecules,
the π–π interactions between C60 molecules and van der Waals
C60
. (b) Optical microscope image of ZCC 1D nanowires. (c) Optical
microscope image of ZCC 2D nanosheets. (d) TEM image of cocrystal ZCC
and its corresponding SAED pattern. (e) Single-crystal structure of cocrystal
ZCC.
As shown in Figure 2a, cocrystal ZCC exhibits a broad
absorption spectrum in the region of 200-1080 nm, which is
significantly red-shifted compared to that of ZnTPP and C60
crystals, indicating the strong CT interaction between donors
and acceptors. Notably, ZCC shows a strong CT absorption,
which intensity is comparable to the singlet absorption.
Meanwhile, ZnTPP-C60 blend film displays strong singlet
absorption, but negligible CT absorption. With the same
molecular composition, ZnTPP-C60 blend film and ZCC cocrystal
display a quite different D-A packing mode. While the donors
and acceptors disperse with a random manner in D-A blend film,
they stack face to face in cocrystal, forming a nanoscale D-A
interpenetrating network and providing a plenty of molecular-
scale D-A interfaces. These results imply that the highly ordered
D-A arrangement in cocrystal system could greatly promote the
enhancement of CT absorption. In addition, the calculated
absorption sepectra of ZCC (Figure S11) is in good agreement
with the experiments, which further supports that the CT
absorption can be enhanced by cocrystal engineering. Moreover,
in order to gain deep insights on the cocrystal system, further
photophysical characterizations were carried out. IR spectrum
(Figure 2b) of ZCC is almost the combination of individual
components. Its Raman spectrum (Figure S8) also involves the
peaks of individual component, indicating the formation of
cocrystal. The tiny peak shifts in both IR and Raman spectra
suggest the unchanged molecular structures in cocrystal system,
indicating the noncovalent assembly nature of cocrystallization
process. The thermal stability of ZCCs was studied by
forces (Figure S6), build
a
multi-dimensional D-A
interpenetrating network. The network provides sufficient D-A
interfaces, which would facilitate the exciton generation and
separation. The crystal morphology of ZCC was observed to
highly depend on the selection of solvents, which may arise from
the varation of crystal surface attachment energy in different
solvents.[29] When chlorobenzene was chosen as the solvent,
ZCC preferred to one-dimensional (1D) assembly and grows into
nanowires (Figure 1b). With the presence of 1,2-
dichlorobenzene solvent, ZCC favors two-dimensional (2D)
assembly and exhibits hexagonal morphology (Figure 1c). With
increasing concentration of ZnTPP and C60, larger cocrystals
can be obtained (Figure S2-3). Both the 1D nanowires and 2D
nanosheets exhibit the same crystal structure as discussed
above. According to powder X-ray diffraction (XRD) experiments,
these ZCC 1D nanowires and 2D nanosheets display similar
diffraction peaks that are consistent with the single-crystal XRD
data of ZCC (Figure S4-5). Moreover, the transmission electron
microscope (TEM) and selected area electron diffraction (SAED)
images of ZCC 1D nanowire (Figure 1d) and 2D nanosheet
(Figure S3d) can be indexed based on the lattice parameters of
a=14.189 Å, b=16.710 Å, c=16.902 Å, α=69.989°, β=86.220°,
γ=79.392° (Table S1), in agreement with the single-crystal and
powder XRD experiments. These results shed light on the
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thermogtavimeteric (TG) analysis (Figure S9). Similar to other
C60-based complexes,[30] the TG curve of ZCCs displays three
temperature ranges involving the removal of solvent (129 °C ),
the decomposition of donors (470 °C ) and fullerene sublimation
(727 °C ). Compared with ZnTPP (467 °C ) and C60 (709 °C ),
ZCC exhibits a higher thermal stability on account of the strong
D-A interactions. Moreover, according to solid-state 13C NMR
spectra (Figure 2c), after cocrystallization, the chemical shift of
C60 shows an obvious upfield shift from 144.9 to 142.8 ppm,
indicating the increase of electron density. Meanwhile, the
chemical shifts of ZnTPP at around 120-135 ppm exhibit
downfield shifts. These observations demonstrate the π electron
delocalization from ZnTPP to C60 molecules, implying the
existence of intermolecular CT interactions. The electron spin
resonance (ESR) spectrum of ZCCs exhibits a strong resonance
signal with g factor of 2.0037 (Figure 2d). This result suggests
the existence of unpaired electrons in ZCCs, which arises from
the CT process. Moreover, the molecular orbital diagrams
(Figure S10) reveal that the cocrystal HOMO is concentrated on
the electron-donor ZnTPP, while its LUMO is localized on the
acceptor C60, which further reveal the CT characteristics in ZCC
system.
various functional applications. A typical as-prepared ZCC
cocrystal film was shown by an optical microscope image in
Figure 3b. Its correponding polarized optical microscope (POM)
images (Figure 3c-d) reveal that the whole cocrystal film
exhibits a uniform color change from bright to dark with a sample
rotation angle of 45°, indicating that the ZCC film is free of grain
boundaries and exhibits single-crystal nature. As revealed by
atomic force microscopy (AFM) image (Figure 3e), the ZCC
cocrystal film shows small root mean square (RMS) roughness
of 0.591 nm. Such a smooth surface demonstrates the high
quality and crystallinity of ZCC film. The TEM image also reveals
the uniform morphology of ZCC film (Figure 3f). Its
corresponding SAED patterns can be indexed with the single-
crystal XRD data of ZCCs. The powder XRD experiments of
ZCC films (Figure S14) display similar diffraction peaks to that
of micro/nano crystals of ZCC. These experiments suggest that
this film exhibits the same crystal structure with bulk crystals of
ZCC, indicating the successful controlled growth of ZCC from 1D
nanowires, 2D nanosheets to cocrystal films. Impressively, the
as-grown ZCC film has a large area, wherein its length
approaches a centimeter and width is up to a millimeter (Figure
S14). These results imply that this simple, low-cost, solution
epitaxy method serves as an effective approach to fabricate
large-area cocrystal films, which paves the way for the practical
application of organic cocrystals.
Figure 2. (a) Absorption spectra of cocrystal ZCC and ZnTPP/C60 blend film.
The dash lines show the absorption spectra of ZnTPP and C60 crystals. (b) IR
spectra (c) Solid-state 13C NMR spectra of ZnTPP, ZCC and C60. (d) ESR
spectrum of cocrystal ZCC.
In order to fabricate large-area 2D cocrystal film, 1,2-
dichlorobenzene was selected as the solvent, which leads to the
2D assembly of ZCC as discussed above. High-quality ZCC
cocrystal films were prepared by a facile, low-cost, solution
epitaxy method[31] (Figure 3a and Figure S12). The growth
process and mechanism are described as follows. When D-A
mixed solution is dropped onto water surface, the solution
droplets would float on the water surface. The high surface
tension of water increases the spreading area of solution
droplets, which reduces the nucleation density and leads to the
growth of small-size cocrystals. By dropping the D-A solution
once more, these small cocrystals then serve as seed crystals
and contribute to the epitaxy growth of large-area cocrystal films.
The as-grown cocrystal film floats on the water surface and can
be easily transferred to any substrate by simply inserting the
substrate into the water (Figure S13), which is suitable for
Figure 3. (a) Schematic diagram of drop-casting onto water surface. (b)
Optical microscope image of a ZCC cocrystal film. (c, d) Polarized optical
microscope images of the ZCC cocrystal film. (e) AFM image of a typical ZCC
film. (f) TEM and its corresponding SAED images of a ZCC film.
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To explore the photoelectrical properties of ZCC,
photodetector devices were fabricated based on ZCC
micro/nano crystals and 2D cocrystal films. Due to the small size
of ZCC micro/nano crystal, a planar photoconductor device was
fabricated using an organic ribbon as mask. With strong photon
absorption and charge transport ability, ZCC micro/nano crystal
exhibits a fast photoresponse behavior with responsivity (R) of
11.7 mA/W under white light illumination (Figure S15). The
photocurrent degradation of ZCC micro/nano crystals-based
photodetector may be ascribed to the relatively poor stability of
ZCC crystals under ambient conditions.[32] Meanwhile, 2D
cocrystal films, with a large surface area, reduce the difficulty of
device preparation, which increases the possibilities for device
structure optimization and performance improvement. As shown
in Figure 4a, a vertical photodetector device was fabricated
based on cocrystal films, which consisted of an indium tin oxide
(ITO) substrate modified with Ag (120 nm) electrode as a
cathode, a layer of Au (30 nm) electrode as a anode, and the
photoactive layer of ZCC film was sandwiched between the
asymmetrical electrodes. The introduction of asymmetrical
electrodes suppresses the dark current, and the short
interelectrode spacing of vertical device greatly increases the
carrier collection efficiency. Moreover, the bottom Ag electrode
could also act as a reflecting layer, which enhances the photo
absorption efficiency of ZCC film. Consequently, the vertical
photodetector based on ZCC film displays a high responsivity of
1233 mA/W under white light illumination (Figure 4b), which
improves up to 105 times than the planar photoconductor device
based on ZCC micro/nano crystals. Moreover, the vertical
photodetector based on ZnTPP-C70 cocrystal film exhibits a
responsivity of 55 mA/W (Figure S16-S17), which are far less
than that of ZCC film. These results indicate the superior
photoresponse ability of ZCC film, demonstrating its great
potential for practical photoelectric applications.
mA/W at 800 nm, with detectivity of 3.77×1011 Jones and EQE of
376%, which performance is superior to other NIR
photodetectors based on organic D-A photoactive layers (Table
S2).[35] Moreover, by comprasion with other 2D organic and
inorganic materials,[36] the ZCC film photodetector not only
shows a wide spectra response,[37] but also achieving a high
responsivity[38] and fast response times[39], demonstrating the
great potential of cocrystal materials for high-performance
broadband photodetectors.
Benefitted from the strong absorption of ZCC, the vertical
photodetector of cocrystal film exhibits a broad spectra response
from 400 to 1000 nm (Figure 4c), which shows a maximum
responsivity of 6393 mA/W at 400 nm with corresponding
detectivity (D*) of 9.94×1011 Jones. Its external quantum
efficiency (EQE) profile is in agreement with the absorption
spectrum of ZCC (Figure 4d), suggesting that the generation of
photocurrent arises from the photon absorption of ZCC film. And
the high EQE may arise from the fast transit caused by short
interelectrode spacing and externally applied voltage, long
carrier lifetime as revealed by transient absorption, and the
injection of charge carrier.[33] The temporal response of ZCC film
photodetectors is characterized by a light pulse with an interval
of 5 s. As shown in Figure 4e, the photodetector exhibits a rapid
and reproducible photoswitching behavior, implying its excellent
photostability and cycling stability. Compared with ZCC
micro/nano sized cocrystals, the superior photostability of ZCC
film is owning to the protection of top Au electrode layer. The
rise and decay response times,[34] which are defined as the
times that current changes from 10 to 90% or vice versa, are 0.6
and 0.7 s, respectively. Such fast response times reveal the low
defect density of the photoactive layer and device interface
contacts. The current density under illumination shows a linear
relationship to the incident power intensity in a wide range, as
revealed by Figure 4f. It is worth to mention that the
photodetector of ZCC film displays a high sensitivity to the NIR
light. In the NIR region, it displays a high responsivity of 2424
Figure 4. (a) The device architecture diagram of a ZCC film photodetector. (b)
The current density-voltage (J-V) curves of a ZCC film photodetector under
dark and light illumination (L = 4.59 mW/cm2). (c) Device responsivity and
detectivity as a function of wavelength at voltage of -30 V. (d) The external
quantum efficiency of the ZCC film photodetector. (e) Temporal response of
ZCC film photodetector showing a rise time of 0.6 s and a decay time of 0.7 s.
(f) The light intensity-dependent current density of ZCC film photodetector.
Transient absorption (TA) spectra of ZCC cocrystal film were
employed, in order to shine deeper insight onto the exciton and
charge carrier dynamics. As shown in Figure 5a and Figure
S18, a ground state bleaching (GSB) signal is observed at 553
nm, which reflects the absorption of ZnTPP. The excited state
absorption (ESA) bands appear at 529, 579 and 643 nm, which
are assigned to the one-electron-oxidized ZnTPP radical cation
(ZnTPP•+) absorption.[40] Meanwhile, the one-electron-reduced
C60 radical anion (C60•−) absorption band is observed at 1046 nm
(Figure 5b), indicating the electron transfer takes from ZnTPP to
C60.[41] The charge carrier dynamics can be monitored by
following the kinetic features of the radical ion pair state, which
decays are well fitted with a multi-exponential function (Figure
S19 and Table S3). Consequently, the three lifetimes that
derived for the ZnTPP radical cation are 15 ps, 260 ps and >7 ns,
while the three lifetimes of 1.8 ps, 103 ps and >7 ns are
observed at the C60 radical anion absorption. In ZnTPP-C70
cocrystal, the radical ion pair state undergoes a faster decay
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10.1002/anie.202015326
Angewandte Chemie International Edition
COMMUNICATION
•−
process, wherein the C70 decays with two lifetimes of 9.7 ps
region, and the intermolecular CT interaction induced the
generation of long-lived free charge carriers, making the
cocrystal ZCC an excellent candidate for photoresponse
applications. Moreover, by successful fabrication of large-size
2D cocrystal film, the performance of photoresponse device has
been greatly improved, which displays a responsivity 105 times
higher than that based on micro/nano-sized cocrystal. In
particular, the cocrystal film-based photodetector exhibits a high
responsivity of 2424 mA/W in the NIR region, coupled with fast
response times and high EQE, which performance is superior to
other NIR photodetectors based on organic D-A photoactive
layers. This work provides a rare example of 2D cocrystal film for
high-sensitivity NIR light detection, which not only gains insights
for 2D cocrystal materials and their potential in high-
performance organic electronics, but also promotes their
development towards low-cost, large-area practical applications.
and 173 ps, and two time constants of 7.1 ps and 116 ps were
derived for ZnTPP•+ (Table S3).[40] These observations indicate
the slower recombination rates in ZCC film, and the long-lived
features (>7 ns) suggest the generation of long-lived free charge
carriers.[42] Since that the free carriers in ZCC film would
promote the carriers transport and collection in photoresponse
devices,[43] ZCC film display a higher responsivity in comparision
to ZnTPP-C70 cocrystal film. These observations provide deeper
insights on the high-performance photodetectors we fabricated
based on ZCC films, which further reveals their potential in
practical optoelectronic devices and applications. Overall, the
successful fabrication of
high-performance broadband
photodetectors based on ZCC cocrystal can be attributed to
following points: (1) the highly ordered D-A arrangement
enhances the CT absorption in the NIR region, which ensures
the efficient photon absorption; (2) the intermolecular CT
interaction facilitates the generation of long-lived free carriers,
which reduces the charge recombination rates; (3) the large-
area cocrystal film enables the device configuration optimization,
which improves the device performance more than 100 times.
Since that the cocrystal photoresponse materials and devices
still remain at an early stage, it is believed that, with further
exploring cocrystals with wider response spectra and higher
carrier mobility, as well as optimizing device structure, there
would be a great improvement to the overall performance of
cocrystal photodetectors in the near future.
Acknowledgements
The authors acknowledge financial support from the Ministry of
Science and Technology of China (Grants 2016YFB0401100
and 2017YFA0204503), the National Natural Science
Foundation of China (51702297, 51633006, 51725304,
51733004, and 51703159), and the Strategic Priority Research
Program of the Chinese Academy of Sciences (Grant No.
XDB12030300). W. Zhu thanks the Open Foundation of Key
Laboratory of Multi-spectral Absorbing Materials and Structures,
Ministry of Education (ZYGX2019K009-1, Metal Oxide-Organic
Hybrid Films and Devices) for partial financial support.
Keywords: 2D Cocrystal • Photodetector • Near-IR Absorption •
Charge Transfer • Large-area crystal
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COMMUNICATION
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This article is protected by copyright. All rights reserved.

10.1002/anie.202015326
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
A
large-area cocrystal film is
Yu Wang, Huang Wu, Weigang Zhu,
Xiaotao Zhang, Zheyuan Liu, Yishi
Wu, Changfu Feng, Yanfeng Dang,
Huanli Dong, Hongbing Fu and
Wenping Hu*
designed and fabricated in a low-
cost solution-processed method.
Attributed to the enhanced charge-
transfer absorption in the NIR
region, the generation of long-lived
free carriers, and the device
configuration optimization, the
cocrystal film-based photodetector
exhibits a high responsivity to a
wide spectra range, coupled with
fast response times and large
EQE. This work provides a rare
example of tailored growth of
cocrystal film, which reveals the
Page No. – Page No.
Cocrystal Engineering: toward
Solution-Processed Near-Infrared
2D
Organic
Cocrystals
for
Broadband Photodetection
possibilities
of
large-scale
fabrication of cocrystal materials
and their potential for practical
high-performance
photodetectors.
broadband
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