A Highly Sensitive Single Crystal Perovskite–Graphene Hybrid Vertical Photodetector

Article abstract of DOI:10.1002/smll.202000733

Organolead trihalide perovskites have attracted significant attention for optoelectronic applications due to their excellent physical properties in the past decade. Generally, both grain boundaries in perovskite films and the device structure play key roles in determining the device performance, especially for horizontal-structured device. Here, the first optimized vertical-structured photodetector with the perovskite single crystal MAPbBr₃ as the light absorber and graphene as the transport layer is shown. The hybrid device combines strong photoabsorption characteristics of perovskite and high carrier mobility of flexible graphene, exhibits excellent photoresponse performance with high photoresponsivity (≈1017.1 A W^?1) and high photodetectivity (≈2.02 × 10¹³ Jones) in a low light intensity (0.66 mW cm^?2) under the actuations of 3 V bias and laser irradiation at 532 nm. In particular, an ultrahigh photoconductive gain of ≈2.37 × 10³ is attained because of fast charge transfer in the graphene and large recombination lifetime in the perovskite single crystal. The vertical architecture combining perovskite crystal with highly conductive graphene offers opportunities to fulfill the synergistic effect of perovskite and 2D materials, is thus promising for developing high-performance electronic and optoelectronic devices.

Full text of DOI:10.1002/smll.202000733

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A Highly Sensitive Single Crystal Perovskite–Graphene
Hybrid Vertical Photodetector
Yuting Zou, Tingting Zou, Chen Zhao, Bin Wang, Jun Xing, Zhi Yu, Jinluo Cheng,
Wei Xin, Jianjun Yang, Weili Yu,* Huanli Dong, and Chunlei Guo*
wide application in optical communica-
Organolead trihalide perovskites have attracted significant attention for opto-
electronic applications due to their excellent physical properties in the past
decade. Generally, both grain boundaries in perovskite films and the device
structure play key roles in determining the device performance, especially
for horizontal-structured device. Here, the first optimized vertical-structured
photodetector with the perovskite single crystal MAPbBr3 as the light absorber
and graphene as the transport layer is shown. The hybrid device combines
strong photoabsorption characteristics of perovskite and high carrier mobility
of flexible graphene, exhibits excellent photoresponse performance with high
photoresponsivity (≈1017.1 A W−1) and high photodetectivity (≈2.02 × 1013 Jones)
in a low light intensity (0.66 mW cm−2) under the actuations of 3 V bias and
laser irradiation at 532 nm. In particular, an ultrahigh photoconductive gain of
≈2.37 × 103 is attained because of fast charge transfer in the graphene and large
recombination lifetime in the perovskite single crystal. The vertical architecture
combining perovskite crystal with highly conductive graphene offers opportuni-
ties to fulfill the synergistic effect of perovskite and 2D materials, is thus prom-
ising for developing high-performance electronic and optoelectronic devices.
tion, environmental monitoring, biological
detection, image sensing, space explora-
tion and other fields.[1–5] Recently, meth-
ylammonium lead halide (CH3NH3PbX3,
X = halogen) perovskites have become
promising candidate materials as building
blocks for light harvesting in photodetec-
tors due to their excellent photoelectric
properties, including direct bandgap, wide
spectral response (UV-NIR), large absorp-
tion coefficient (≈105 cm−1), high power
conversion (22.7%), high carrier mobility
(≈100 cm2 V−1 s−1), long carrier diffusion
length (≈0.1–10 µm) and small exciton-
binding energy (≈20 meV).[6–12] As a result,
this class of material has been widely
applied in photoelectric devices such as solar
cells,[13–15] light-emitting diodes (LED),[16–18]
lasers,[19–21] and field-effect transistor.[22–24]
To date, some groups have reported the
excellent performance of perovskite photo-
detectors with high gains, ultra-sensitivity,
ultra-fast response speed or wavelength selection.[25–28] Although
solution-processed perovskite thin film photodetectors have
made great achievements in recent years, their performance
is adversely affected by mass defects in the surface and grain
boundaries of the polycrystalline film.[29,30] The grain bounda-
ries of polycrystalline film will hinder the charge transport in
the horizontal direction and weaken the charge coupling, thus
lead to poor charge transport properties and low charge car-
rier mobility. Due to the adverse effects of defects in perovskite
polycrystalline films, it is necessary to passivation the defects or
traps to obtain devices with better performance. So many studies
have combined perovskite with high mobility 2D materials to
increase responsivity, with the perovskite as the photosensitive
layer and the 2D materials as the transport layer. In 2015, Cho
and co-workers[31] and others prepared a new type of hybrid pho-
todetector consisting of graphene and solution-based MAPbI3
perovskite, which showed a wide spectral response from 400 to
800 nm; and in the same year, Bao and co-workers[32] reported
a wide-spectrum heterojunction photodetector with monolayer
graphene covered with a thin layer of dispersive organolead
halide perovskite (CH3NH3PbBr2I) islands. Thereafter, Lee and
co-workers[33] demonstrated a highly sensitive hybrid photode-
tector based on graphene-CsPbBr3−xIx perovskite nanocrystals.
Zeng’s group fabricated a broad absorption spectrum photode-
tectors with 2D MoS2 layer and all-inorganic CsPbBr3 perovskite
1. Introduction
Photodetectors have attracted extensive attention in the field
of academic and industrial in recent decades owing to their
Y. Zou, T. Zou, C. Zhao, B. Wang, J. Xing, Dr. Z. Yu, Prof. J. Cheng,
Dr. W. Xin, Prof. J. Yang, Prof. W. Yu, Prof. C. Guo
The Guo Photonics Laboratory, State Key Laboratory of Applied Optics
Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP)
Chinese Academy of Sciences (CAS)
Changchun 130033, P. R. China
E-mail: weili.yu@ciomp.ac.cn
Y. Zou, T. Zou, C. Zhao, B. Wang, J. Xing
University of Chinese Academy of Sciences
Beijing 100049, P. R. China
Prof. H. Dong
Beijing National Laboratory for Molecular Science
Key Laboratory of Organic Solids
Beijing 100190, P. R. China
Prof. C. Guo
The Institute of Optics
University of Rochester
Rochester, NY 14627, USA
E-mail: chunlei.guo@rochester.edu
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.202000733.
DOI: 10.1002/smll.202000733
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Figure 1. a) Optical image of MAPbBr3 single crystal grown by ITC method (scale bar: 100 µm). b) 3D pseudo color plot of MAPbBr3 single crystal
thickness, the thickness is 2.25 microns. c) TEM photograph and d) SAED pattern of MAPbBr3 single crystal.
nanosheets.[34] In 2019, Wei Lin Leong attained an ultrahigh
photoconductive gain CsPbBrxI3−x nanocrystal-graphene hybrid
photodetector.[35] Although the performance of perovskite-2D
materials hybrid photodetector has been greatly improved, the
negative effects of grain boundary have not been resolved.
Herein, we report the first vertical-structured photodetector,
which combines monolayer graphene with a perovskite single
crystal MAPbBr3 as light collection material together. Taking the
advantages of graphene’s ultrahigh carrier mobility and single
crystal perovskite with low defects and high absorption coef-
ficient, the graphene–perovskite hybrid vertical photodetector
exhibits excellent photoresponse, i.e., an approximately order of
magnitude enhancement of photoresponsivity (≈1017.1 A W−1),
photodetectivity (≈2.02 × 1013 Jones) and photoconductive gain
(≈2.37 × 103) at 532 nm. The enhanced performance of vertical
photodetector can be attributed to the effective extraction of free
charges by graphene and the high carrier mobility of graphene
with high flexibility.[31,32] Our work shows that the hybrid gra-
phene–perovskite vertical photodetector has broad application
prospects in high-performance optoelectronic devices.
shows the optical image of the MAPbBr3 single crystal, from
which we can see that the surface of this single crystal is
smooth and the edge is regular. In Figure S1a (Supporting
Information), a scanning electron microscope (SEM) image of
MAPbBr3 single crystal shows the surface is flat and smooth
without grain boundary. The Energy dispersive X-ray spectrom-
etry (EDS) of the selected area was measured (Figure S1b, Sup-
porting Information) and the four elements including carbon
(C), nitrogen (N), lead (Pb), and bromine (Br) are evenly dis-
tributed, which demonstrated its high crystalline quality. This
high crystallinity facilitates the efficient transport of carriers,
resulting in excellent device performance. By controlling the
concentration of the precursor solution and crystallization
speed, a centimeter-size single crystal with the thickness of sev-
eral micrometers can be obtained on the silicon substrate. As
shown in Figure 1b, the thickness of the single crystal is about
2.3 µm measured by laser confocal microscope. Figure 1c,d
display the transmission electron microscope (TEM) image
and selected area electron diffraction (SAED) pattern of the
perovskite single crystal, from which the MAPbBr3 single
crystal shows regular crystal structure and evenly distributed
reflection matrix, implying the high quality of MAPbBr3 single
crystal synthesized. The high quality single crystal with smooth
surface ensures that MAPbBr3 single crystal can minimize the
contact resistance with Au electrodes and the charge can be
effectively transported in the channel.
2. Discussion
We synthesized the high-quality MAPbBr3 single crystal by the
inverse temperature crystallization (ITC) method.[36] Figure 1a
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Figure 2. a) The UV–vis pattern of MAPbBr3 single crystal; Inset: Tauc plot from UV–vis analysis of MAPbBr3 single crystal to calculate bandgap energy.
b) Photoluminescence spectra of MAPbBr3 single crystal with the excitation of 473 nm laser. c) The experimental and calculated powder X-ray diffraction
(XRD) patterns of MAPbBr3 single crystal. d) Raman spectra of MABr, PbBr2 and MAPbBr3 single crystal with the excitation of 785 nm laser.
In order to further characterize the crystallinity of the
MAPbBr3 single crystal, we measured the electrical proper-
ties of the perovskite single crystal by absorption, steady-state
fluorescence, X-ray diffraction and Raman spectrum, respec-
tively. Figure 2a shows the UV–vis spectrum of MAPbBr3 single
crystal. According to the absorption spectra, the bandgap energy
(Eg) is calculated to be 2.19 eV by the Tauc Plots method.[37]
Figure 2b presents the PL spectrum which was excited by
473 nm laser and displays a narrow peak at 535 nm. The power
X-ray diffraction (XRD) spectrum of MAPbBr3 single crystal is
shown in Figure 2c, it indicates that MAPbBr3 single crystal is
cubic structure which is in well agreement with the theoretical
calculation.[38] Figure 2d displays the Raman spectra of MABr,
PbBr2, and MAPbBr3 single crystal, from the spectra we can
conclude that the MABr and PbBr2 reacted completely and pure
MAPbBr3 single crystal formed.
monolayer graphene is used as the charge transport layer and
perovskite single crystal as the photoabsorption layer. The typ-
ical metal-semiconductor-mental (MSM) model, being the so-
called photoconductor type, was fabricated, which also helps to
analyze the process of photoresponse. The detailed process of
device preparation can be found in Section S3 in the Supporting
Information. Monolayer graphene synthesized on the surface
of copper foil by chemical vapor deposition (CVD) method[39]
was transferred to a pretreated Si/SiO2 (250 nm) substrate
with the aid of polymethyl methacrylate (PMMA) polymer
(Figure S2a, Supporting Information).[40] We characterized the
Raman spectra of the monolayer graphene transferred onto a
Si/SiO2 substrate. As shown in Figure S2b (Supporting Infor-
mation), the Raman spectrum has two distinct peaks, which are
located at 1585.3 cm−1 for G peak and 2701.06 cm−1 for 2D peak,
respectively. And the ratio of 2D peak and G peak is 2.438,[41]
which proved that the transferred graphene has good quality
and smooth surface. So it can be well contacted with MAPbBr3
single crystal. Then the gold electrodes were evaporated on the
prepared graphene. Subsequently, the MAPbBr3 single crystal
Based on the silicon substrate covered by a monolayer gra-
phene with high carrier mobility, hybrid graphene–perov-
skite single crystal vertical photodetector is prepared, as
shown in Figure 3a. In this hybrid vertical photodetector, the
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Figure 3. a) Schematic of the graphene–perovskite vertical photodetector. b) Cross-sectional SEM diagram of the device. c) I–V characteristics of the
device under 532 nm light illumination with various light intensities. d) Photocurrent as a function of the incident light intensity at 3 V. e) Gain, and
f) responsivity and detectivity as a function of incident light intensity.
were grown on the monolayer graphene by ITC. Finally, the
soft contact gold electrode was transferred on the top of the
perovskite single crystal by the probe method[42] to complete
the fabrication of the entire device. The mechanical-transfer-
gold-electrode technology provides an efficient method for fab-
ricating vertical electronic and optoelectronic devices, solving
the difficulty of preparing top-contact metal electrodes and pre-
venting Au electrodes from penetrating into the active layer.[43]
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Figure 4. a) Time–dependent photoresponse under 532 nm light illumination with reverse bias voltages (200.63 mW cm−2). b,c) The photoswitch of
the graphene – perovskite vertical photodetector.
Figure 3b shows the cross-sectional SEM image of the structure
of the device, i.e., graphene–perovskite single crystal-metal ver-
tical heterostructure. The interface between each layer is dis-
tinct and has no penetration, especially the interface between
gold electrode and MAPbBr3 single crystal, which indicates the
high interface quality of this device. The electrical properties
of the hybrid graphene–perovskite vertical photodetector were
measured at room temperature under atmospheric conditions.
We characterized the photoresponse of the hybrid vertical
photodetector. As plotted in Figure 3c, the nearly linear cur-
rent-voltage performance indicates that there is a good ohmic
contact between gold electrode and the graphene–perovskite. By
carefully studying the I–V characteristics of the device with dif-
ferent light intensities at 532 nm (Figure 3c), one can observe
a phenomenon that the photocurrent increases gradually with
increasing light intensity. This phenomenon can be attributed
to the increase in the number of photogenerated carriers as
the light intensity increasing. The dependence of photocurrent
on light intensity can be understood by a power law, Iph ∝ Pθ,
where Iph is the photocurrent, P is the light intensity and θ is
the index, which determines the recombination of the photo-
carriers. As shown in Figure 3d, the fitting curve in a wide light
intensity range shows that θ = 0.76, indicating that the com-
posite loss is relatively low in this range.[44]
And to characterize the sensitivity of the device, when the
dark current is dominated by the shot noise,[46] determine the
detectivity (D*) value was determined using the equation below
R
D* =
(3)
2q Jdark
where R is the photoresponsivity and Jdark is the dark current
density of the photodetector. According to the above formula,
when the bias was given as 3 V, R, D* and G were estimated to
be as high as ≈1017.1 A W−1, ≈2.02 × 1013 Jones, and ≈2.37 × 103
electrons per photon at light intensity of ≈0.66 mW cm−2.
The R, D* and G value is higher than that of photodetector
based on pure perovskite, which the details are shown in
Figure S4 (Supporting Information). And the relationship
between photoresponsivity and light intensity can be fitted with
a power function, as shown in Figure 3f. This relationship can
be analyzed using a model of carrier recombination in photo-
voltaic devices. As the carrier density increases, the probability
of carrier recombination increases, which is one of the reasons
for the decrease in the response rate of light intensity.
In addition, photoresponse is another crucial performance
parameter of a photodetector. As shown in Figure 4a, the time-
dependent photoresponse demonstrates that the sensitivity to
the incident light is highly repeatable and stable. In addition,
as the bias voltage increasing, the photocurrent monotonically
increases, which is understandable because a large electric field
can promote the effective transport of photocarriers and reduce
their composite activity. And Figure 4b presents the rising and
falling edges are very steep, indicating a fast response. The rise
time and decay time are 50.9 and 26 ms, respectively, which are
comparable to previous reports,[32,47] as shown in Figure 4c.
For comparison, the photodetectors based on pure MAPbBr3
single crystal were studied (the detailed information can be
found in Section S4 in the Supporting Information). Figure 5a
compares the I–V characteristics of pure perovskite and gra-
phene–perovskite heterostructures under illumination with
the laser irradiation (532 nm, 200.63 mW cm−2), respectively.
In order to further assess the performance of the hybrid gra-
phene–perovskite device, we compared the photoresponsivity,
detectivity and photoconductive gain, being three critical
parameters at 532 nm laser irradiation. Figure 5b–d respectively
show the photoresponsivity (R), detectivity (D*) and photocon-
ductive gain (G) comparison of the as-fabricated vertical photo-
detector at 532 nm laser with the bias of 3 V. It can be seen
Next, we calculated three important parameters of a photo-
detector, which are photoresponsivity (R), photodetectivity (D*),
and photoconductive gain (G). The parameter R refers to the
photocurrent generated by the unit power of the incident light on
the effective area and is expressed by the following equation[45]
Ilight − Idark
P ⋅ A
R =
(1)
where Ilight, Idark, P, and A are the photocurrent, dark current,
incident light power, and effective illumination area of the
device, respectively. The parameter G represents the number
of charge carrier detected relative to the number of photo-
generated electron–hole pairs, which is usually given by[45]
hc
G = R
(2)
eλ
where R is photoresponsivity, h is Planck’s constant, c is the
light velocity, e is the elementary charge, and λ is wavelength
of incident light.
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Figure 5. a) I–V characteristics of the perovskite and graphene–perovskite vertical photodetectors under 532 nm illumination. b–d) The responsivity,
detectivity, and gain of the perovskite and graphene – perovskite vertical photodetectors under 532 nm illumination at 3 V bias.
that the above parameters are increased by an order for hybrid
graphene–perovskite photodetector. The device performance is
greatly enhanced due to the effective charge transfer from the
graphene to perovskite. When graphene and perovskite are in
contact, their Fermi energy levels are not consistent. In order
to make the Fermi energy levels of the system consistent and
reach the thermal equilibrium state, the holes in graphene will
diffuse into the perovskite energy levels, leaving electrons in the
graphene and causing electron doping.[32,35] Due to the charge
transfer, the built–in electric field is formed, which makes
the perovskite band bend upward and provides the driving force
for the separation and transfer of photogenerated electron–hole
pairs.[32,48,49,50] As shown in Figure 6a, under light illumination,
perovskite absorbs light and excites electron–hole pairs. Due to
the mismatch of work functions of graphene and perovskite,
electron–hole pairs were separated by the internal electric field.
Figure 6. a) Energy band diagram of graphene–perovskite vertical device under illumination. b) PL spectra of MAPbBr3 single crystal and MAPbBr3
single crystal on graphene. c) PL lifetime of MAPbBr3 single crystal and MAPbBr3 single crystal on graphene.
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Table 1. Performance comparison of perovskite-based photodetectors.
R [mA W−1
]
Material structure
Light wavelength
(nm)/power
D* [Jones]
Gain
Ref.
MAPbI3/Graphene (G)
109
–
–
–
–
–
[31]
[54]
[55]
[56]
[35]
520/1 × 10−3 mW
532/1.4 × 10−2 mW cm−2
633/3.3 pW
1.8 × 105
2.1 × 106
2841
MAPbI3 island/G/Au NPs
MAPbI3 nanowire/graphene
MAPbI3/rGO
2.6 × 109
520/3.2 mW cm−2
525/80 µW cm−2
405/921.5 nW
−
73.9
CsPbBrxI3−x nanocrystal/Graphene
MAPbBr2I/Graphene
1.13 × 107
6.0 × 108
2.2
1.17 × 1011
–
9.32 × 1010
≈109
[32]
[57]
520/13.5 mW cm−2
650/25.1 mW cm−2
532/1.6 mW cm−2
450/46 nW cm−2
532/0.66 mW cm−2
1.78 × 105
4.2 × 1012
4.0 × 1010
1.04 × 1013
2.02 × 1013
MAPbI3 microwires/Graphene
FA0.85Cs0.15PbI3/Graphene
2D perovskite/MoS2
–
4.8 × 103
≈107
–
[58]
–
[59]
7.78 × 105
1.07 × 106
2.1 × 103
2.37 × 103
FA0.85Cs0.15PbI3/DNTT
[60]
MAPbBr3 single crystal/Graphene
Our work
And the holes are transferred to graphene because of the inter-
facial electric field, while the electrons are bound to perovskite
and act as an additional light tunable gate. The electric field
generated by these electrons causes holes in the graphene to
be induced, lowering the Fermi energy level of graphene and
further increasing the photocurrent.[12,51] And Figure 6b showed
the steady-state PL spectra of the perovskite and hybrid gra-
phene–perovskite samples, which were prepared on Si sub-
strates with 250 nm SiO2.
There are several strategies to improve the performance of
perovskite optoelectronic devices. The commonly used ones
include interface modification, multicomponent doping and
crystal morphology transformation. A detailed comparison
of these methods is summarized in Table 1. By comparison,
we believe that the method presented here is competitive in
enhancing the performance of perovskite vertical photode-
tectors. In addition, owing to the relatively mature graphene
transfer technology and single crystal growth technology, our
method is compatible with other optimization methods, and
has unique advantages in the actual industrial integration.
Under the same experimental conditions, PL peaks of
perovskite and hybrid graphene perovskite appeared at around
535 nm. However, the PL quantum yield of hybrid graphene–
perovskite is much lower than that of the original perovskite
single crystal. The dramatic PL quenching is caused by the
effective charge carrier transfer caused by π–π interaction
between the perovskite and the sp2 hybridized graphene
layer.[31] Generally, in the absence of graphene, photoinduced
electron–hole pairs in perovskite tend to recombine within the
lifetime; however, electrons in the graphene layer were trans-
ferred to the proximal perovskite layer to fill the vacancy in the
perovskite valence band due to photon absorption. Therefore,
the recombination of the photoexcited electron–hole pairs in
the perovskite was limited, and therefore, the photoexcited
electrons in the perovskite remained in the conduction band
without decaying. The process of trapping photoexcited elec-
trons is the main mechanism of the observation of a dramatic
quenching of the PL intensity in the hybrid graphene–perov-
skite system.[52] It is worth mentioning that in this unique
device geometry, the recombination of photoexcited electrons
and holes was greatly suppressed, because electrons can be
effectively extracted from the perovskite layer, which increases
the photocurrent. A time-resolved photoluminescence (TRPL)
dynamics were also performed to obtain a quantitative anal-
ysis of charge injection and separation (see Figure 6c). When
excited at 532 nm, the hybrid graphene–perovskite shows
much shorter lifetime, with an average lifetime of 4.50 ns, as
compared to that of the original perovskite (9.21 ns). The result
demonstrates a substantial charge extraction and transfer from
MAPbBr3 single crystal to graphene and therefore facilitating
an efficient photoresponse.
3. Conclusion
In conclusion, we demonstrated a novel hybrid vertical pho-
todetector consisting of monolayer graphene and MAPbBr3
single crystal. Comparing to photodetector based on pure perov-
skite single crystal, the hybrid vertical photodetector showed
an order of magnitude enhancement in the photoresponsivity
(≈1017.1 A W−1), photodetectivity (≈2.02 × 1013 Jones), photocon-
ductive gain (≈2.37 × 103) at 3 V bias under 200 mW cm−2 laser
actuation (532 nm). The enhanced performance can be attributed
to the effective charge transfer from the graphene to perovskite
and heterojunction formed between graphene and perovskite.
Graphene photodetectors based on organic-inorganic hybrid lead
halide can be further developed by introducing alternative organic
bonds or halide groups to meet the requirements of some spe-
cific applications.[53] The hybrid photodetectors described herein
are expected to facilitate the development of imaging sensors
for low light photography, UV detectors with high response, and
smart skin sensors that combine with other functions.
4. Experimental Section
Chemicals: Methylamine solution (40% aqueous solution, Aladdin),
lead bromide (PbBr2) (99%, Aladdin), N,N-dimethylformamide (DMF)
(99.5%,Aladdin), hydrobromic acid (HBr) (40% aqueous solution),
ethanol absolute, and diethyl ether were all purchased from Sinopharm
Chemical Reagent Co., Ltd. without further purification.
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Synthesis Methylammonium Bromide (MABr): The MABr was
synthesized by the reaction of HBr with methylamine solution, and then
recrystallized from absolute ethanol and diethyl ether. First, CH3NH3
(61 mL) was poured into a round bottom flask and hydrobromic acid
(56 mL) in a constant pressure funnel was slowly dropped into CH3NH3.
After all the hydrobromic acid was added, the mixed solution was placed
in an ice water bath for 2 h. Then the mixture was poured into a rotary
flask for rotary evaporation at 60 °C, when the clear liquid became white
power, it was washed with absolute ethanol for three times. Finally the
MABr was placed in a vacuum drying box and dried at 60 °C for 24 h.
Synthesis MAPbBr3 Single Crystal: The substrate (Si/SiO2) and the covering
glass were washed successively with deionized water, ethanol, acetone, and
isopropanol. After being dried in a drying box at 100 °C, the substrate and
the covering glass were placed in UV–O3 for hydrophilic treatment. The
covered glass was immersed in a mixed solution of hexane and OTS (600:1)
to obtain a hydrophobic surface, and then the glass was rinsed with acetone
for 30 s and then dried with nitrogen. A small amount (5 µL) of MAPbBr3
precursor solution was dropped onto the silicon substrate and then covered
it with covering glass. Then the sandwich structure sheet was put on a
hotplate, which slowly heated from 40 to 100 °C.
Characterization: The UV–vis absorption spectra of MAPbBr3 single
crystal was measured with a Cary 5000 spectrophotometer from Agilent
Company. Raman spectra of MABr, PbBr2 and MAPbBr3 single crystal
were measured by using a HORIBA Scientific Raman spectrometer
with a 785 nm laser. PL spectra were measured by a HORIBA Scientific
Raman spectrometer with 2.55 mW cm−2 laser intensity at 473 nm in air
at room temperature. Optical image of the perovskite single crystal was
performed on a Nikon SMZ25 stereomicroscope. The thickness of the
single crystal was performed on a Keyence laser confocal microscope
(VK-X1000). The SEM image of cross-sectional was obtained from
a Hitachi S-4800. The crystal structure was characterized by X-ray
diffraction with Bruker D8 Focus.
Keywords
graphene, perovskites, photoconductive gain, single crystal, vertical
photodetectors
Received: February 5, 2020
Revised: March 26, 2020
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Conflict of Interest
The authors declare no conflict of interest.
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