Self-powered X-ray detector based on methylammonium lead tribromide single crystals

Article abstract of DOI:10.1016/j.jallcom.2020.157826

Low-cost, high sensitivity and self-powered radiation detectors are highly demanded for photon flux detection. Here the fabrication of a self-powered X-ray detector with schottky structure is reported. Organic-inorganic perovskite CH₃NH₃PbBr₃ single crystals have been grown on ITO glass with the solution-processed method at relatively low temperature. Low work function Ag has been deposited on the surface of the crystal to form schottky contact. The devices exhibit an obvious response to both the wavelength of 405 nm laser and X-ray photons without external bias. The achieved X-ray sensitivity is up to 2.35 × 10^?4 μC μGy^?1cm^?2 under 35 kV X-ray exposure without bias. The results demonstrated that this schottky diode based on perovskite enable for energy-saving X-ray detection.

Full text of DOI:10.1016/j.jallcom.2020.157826

Journal of Alloys and Compounds xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Self-powered X-ray detector based on methylammonium lead
tribromide single crystals
a
,
*
a
a
a
b
b
Qiang Xuc , Bohao Zhang , Jing Nie , Hang Zhang , Xiaoping Ouyang , Jun Liu ,
Yang Liu
a
Department of Nuclear Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing, 211106, China
Northwest Institute of Nuclear Technology, Xi’an, 710024, China
School of Nuclear Science and Engineering, North China Electric Power University, Beijing, 102206, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 May 2020
Received in revised form
Low-cost, high sensitivity and self-powered radiation detectors are highly demanded for photon flux
detection. Here the fabrication of a self-powered X-ray detector with schottky structure is reported.
Organic-inorganic perovskite CH NH PbBr single crystals have been grown on ITO glass with the
3 3 3
13 October 2020
solution-processed method at relatively low temperature. Low work function Ag has been deposited on
the surface of the crystal to form schottky contact. The devices exhibit an obvious response to both the
wavelength of 405 nm laser and X-ray photons without external bias. The achieved X-ray sensitivity is up
Accepted 2 November 2020
Available online xxx
ꢁ
4
ꢁ1 ꢁ2
mC mGy cm under 35 kV X-ray exposure without bias. The results demonstrated that
to 2.35 ꢀ 10
Keywords:
Self-power
X-ray detectors
Perovskite
this schottky diode based on perovskite enable for energy-saving X-ray detection.
©
2020 Elsevier B.V. All rights reserved.
Schottky diode
1. Introduction
[8,9]. To best of knowledge, so far, there is few work focusing on the
application of self-powered X-ray detectors.
Thanks to the unique properties such as high absorption coeffi-
cient, long carrier lifetimes, and diffusion lengths, hybrid organic-
inorganic perovskite-based devices have achieved great success in
optoelectronics and radiation detection field including X-ray [1],
gamma-ray and charged particles [2e5]. Wei and co-workers re-
ported a sensitive X-ray detector based on methylammonium lead
tribromide perovskite single crystals with sandwich photoconductor
structure. Theirresults demonstratedthatthe lowestdetectableX-ray
Recently, self-poweredsensors haveattractedmuch attention for
various applications including photodetector, biosensor, and energy
[10e15]. Typically, self-powered devices are operated without any
external bias, and with the structural such as pen junction, heter-
ojunction, or Schottky junctions which can immediately separate
the electron-hole pairs by the built-in electric field [16,17].
Herein, in this paper, we have synthesized high-quality MAPbBr
3
single crystals on the surface of ITO glass by using a solution growth
method. The schottky contact and ohmic contact have been formed
ꢁ1
dose rate of this X-ray detector is 0.5
m
Gy s with a sensitivity of
[6]. Furthermore, Yihui He et al. designed a
Schottky-type MAPbI device that achieved a gamma detector with
ꢁ1
ꢁ2
8
0
mC Gy
cm
at the interface of MAPbBr
a high sensitivity self-powered X-ray detector based on MAPbBr
SCs schottky diode has been achieved. The devices exhibit high
3 3
/Ag and MAPbBr /Au, respectively. Then
3
3
5
6
anenergyresolution of 6.8%for Co122keV atroomtemperature [7].
Conventionally, these semiconductor radiation detectors
require an external electrical field to force the ionized electron-hole
pairs to move both electrical contacts. In some specific applications
such as nuclear power and space exploration under high radiation
or energy limitation applications, a self-powered detector to detect
invisible radiation signals to avoid unexpected damage is necessary
ꢁ ꢁ2
1
sensitivity of 235
high performances of this self-powered detector are mainly attrib-
uted to the build-in barrier height between ITO and MAPbBr
mC Gy cm at the 35 keV incident X-ray. The
3
.
2. Material and methods
2.1. Materials growth and device fabrication
3
High-quality organic-inorganic MAPbBr SCs were synthesized by
*
Corresponding author.
E-mail address: xuqiangxmu@nuaa.edu.cn (Q. Xu).
using the inverse temperature crystallization. Firstly, a molar ratio of
https://doi.org/10.1016/j.jallcom.2020.157826
925-8388/© 2020 Elsevier B.V. All rights reserved.
0
Please cite this article as: Q. Xu, B. Zhang, J. Nie et al., Self-powered X-ray detector based on methylammonium lead tribromide single crystals,
Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2020.157826

Q. Xu, B. Zhang, J. Nie et al.
Journal of Alloys and Compounds xxx (xxxx) xxx
3 3 3
Fig. 1. Basic properties, (a) powder XRD pattern of MAPbBr ; (b) optical transmission spectra of MAPbBr , the inset is the calculated optical bandgap; (c) PL spectra of MAPbBr that
excited by a wavelength of 405 nm laser; (d), full XPS spectra of MAPbBr .
3
methylamine (CH
iodic acid (HBr) (57 wt% in water) were stirred at 0 C for 2 h to syn-
thesize methylammonium iodide (CH NH Br) powder. The residual
solvent was evaporated using a rotary evaporator. The raw CH NH Br
powder was washed three times with ethanol and diethyl. Then, the
3
NH
2
MA) (33 wt% in absolute ethanol) and hydro-
Fig. 1a. All peaks ascribed to the different crystal planes of MAPbBr
3
ꢂ
SCs have been observed, which reveals it is a cubic structure with
ꢁ
3
3
Pm3 m space group [18,19]. The optical properties of the MAPbBr
3
3
3
SCs are shown in Fig. 1b. The optical band gap can be estimated
from transmission spectra based on Tauc equation [20,21]. The
calculated optical band gap is about 2.21 eV. To measure the
luminescence properties, a high sensitivity spectrometer has been
employed to characterize the emission spectra. During the mea-
surement, the samples were placed in air at room temperature and
excited by a laser with a wavelength of 405 nm. As shown in Fig. 1c,
the PL peak of the sample is located at around 565 nm with narrow
full width at half maximum (FWHM) of 26 nm, which is ascribed to
precursor solution is prepared by a molar ratio of 1:1 MABr to PbBr
dissolved into N,N-dimethylformamide (DMF) solvent at 60 C. The
2
ꢂ
cleaned ITO substrate was placed in a glass container containing a
ꢂ
transparent precursor solution and keeping it in an 80 C oil bath.
After24h, thehigh-qualityMAPbBr
solution. The whole device was annealed in a drying oven at 80 C for
3
crystalswereharvestedfrom the
ꢂ
5
min to ensure good contact between perovskite and the ITO sub-
strate. A thickness of 50 nm Ag electrode was deposited onto the
surface of MAPbBr
SCs with a mask of 1.2 mm ꢀ 1.2 mm ꢀ 0.5 mm.
the bandgap emission of the MAPbBr
3
material [22,23]. The XPS
3
survey scan of the MAPbBr single crystal is shown in Fig. 1d. The
3
signal is ascribed to the elements of C, N, Pb, Br. The measured
elemental ratio of N:Pb:Br equals to 1.17:1:3.36, which is very close
2.2. Characterization
to the ideal stoichiometry of MAPbBr
3
. All the above characteriza-
Powder X-ray diffraction (XRD) was performed using a Rigaku
Ultimate IV Discover X-ray diffraction system. The photo-
luminescence (PL) spectra of MAPbBr single-crystal was excited a
wavelength of the 405 nm laser and collected by an Ideaoptics Nova
spectrometer. The optical transmission spectrum was measured by
a Shimadzu UV 2550 spectrophotometer at room temperature. The
surface composition and the electronic structure of perovskite
tion of MAPbBr perovskite material indicate it has high crystalline
quality with minimum defect [24].
We have designed sandwich structural devices with Ag and ITO
contact. The photograph of devices is shown in Fig. 2a. A Schottky
contact and ohmic contacts were obtained at the interface of
3
3
MAPbBr
schematic energy level diagram of the MAPbBr
powered X-ray detector with Ag/MAPbBr /ITO sandwich structure
3
/ITO and MAPbBr
3
/Ag, respectively (supplemental). The
3
single crystals self-
MAPbBr
3
SCs were measured by X-ray photoelectron spectrometer
3
(
XPS). XPS analyses were performed using a Thermo Scientific
is shown in Fig. 2b. Electron-holes have been generated after
absorbing high energy X-ray photons. The photogenerated hole
charge carriers can be drifted to Ag contact under the build-in
ESCALAB250Xi. The IeV characteristics were measured using a
Keithley 2450 source meter and excited by X-ray with Ag target X-
ray tube that operated at various voltages.
barrier. The energy band diagram of ITO-MAPbBr
shown in Fig. 2c fB0is the ideal barrier height produced by ITO-
MAPbBr contact. The built-in potential Vbi is calculated according
to the formula, Vbi ¼ f ꢁ f . Fig. 2d shows the energy band di-
3
contact is
3
. Results and discussion
3
B0
n
The structure of the MAPbBr
3
material was carried out by
3
agram of MAPbBr -Ag contact. In this case, the electrons could be
powder X-ray diffraction in air at room temperature, as shown in
easily crossed the barrier and collected by the Ag contact.
2

Q. Xu, B. Zhang, J. Nie et al.
Journal of Alloys and Compounds xxx (xxxx) xxx
3 3
Fig. 2. (a) Structural schematic of self-powered X-ray detector; (b) energy band diagram of MAPbBr SCs self-powered X-ray detector; (c) band gap diagram of ITO-MAPbBr
contact; (d) band gap diagram of MAPbBr -Ag contact.
3
Fig. 4. X-ray detection performances at zero bias: (a) Current response of devices On
and Off under X-ray (Ag target) that operated with various applied voltages; (b) cur-
rent density of devices at various dose rate with different operating voltages.
Fig. 3. Optical response: (a) Current-voltage (IeV) curve of the devices under dark
atmosphere and a wavelength of 405 nm laser. (b) Photoresponse of the device under
2
4
05 nm laser with the power density of 0.636 mW/cm at zero bias voltage. ON is the
device under the exposure of laser. OFF is the device under a dark atmosphere.
3

Q. Xu, B. Zhang, J. Nie et al.
Journal of Alloys and Compounds xxx (xxxx) xxx
Table 1
Performance comparisons of self-powered photodetector based on perovskites.
Responsivity(mA W 1
ꢁ
)
power density (mW cm2)
Wavelength (nm)
reference
devices
Au/MAPbBr3/FTO
FTO/ZnO micro sphere/MAPbI
11.5
48
0.11
11.5
22
~
2
~
~
450
380
405
405
405
[16]
[25]
[26]
[26]
3
3
/MoO /Au
Ag/CsPbBr
Ag/CsPbBr
3
/ITO
:ZnO/ITO
3
Ag/MAPbBr
3
/ITO
0.636
this work
A
high-quality MAPbBr
3
SCs with
a
diameter of about
photons enables supply energy to generate large numbers of pho-
togenerated electron-hole pairs. Therefore, a Schottky structure
high-performance self-powered X-ray detector expect to have a
high barrier height.
1
.2 mm ꢀ 1.2 mm ꢀ 0.5 mm was selected. Typical Schottky char-
acterizes the current-voltage (IeV) curve of the devices are shown
in Fig. 3a. The ratio of photocurrent to dark current is about 500
times at reverse 2 V, while the device under 405 nm laser with a
2
power density of 0.636 W/cm . Furthermore, we have investigated
4. Conclusion
the visible photon detection performances of the devices at zero
bias. A good self-powered photodetector has been achieved with
the 700 times high of photocurrent density to dark current density.
The photoresponsivity (R) is calculated according to the formula,
In conclusion, we have successfully fabricated an X-ray detector
based on MAPbBr3 SCs with the Schottky structure. The device
exhibited high performances for visible light (405 nm) and X-ray
R ¼ ðI
ꢁ I
Þ=Plight, where Plightis the photocurrent, Idark is the
detect under 0 bias. The MAPbBr absorbed incident X-ray energy
and generated electron-holes. In this Schottky device, photoexcited
light
dark
3
dark current, P
is the incident light intensity. The photo-
light
responsivity is as high as 22 mA/W. The comparable responsivity
of perovskites based self-powered photodetector is listed in Table 1.
As shown in Table 1, the optical response performance of the device
carriers in the depletion layer are collected in metal electrodes
under the build-in electric field. Here, photo responsivity (405 nm)
ꢁ
4
of 22 mA/W and X-ray sensitivity of as high as 2.35 ꢀ 10
mC
ꢁ
1
ꢁ2
with Ag/MAPbBr
the previously reported device based on MAPbBr
3
/ITO has been significantly improved compared to
. This is attributed
mGy cm for the incident X-ray energy of 35 kV have been ach-
3
ieved. Our results provide a strategy for energy-saved self-powered
radiation detection technology.
to the built-in electric field of the Schottky junction which helps
exciton dissociation. Photo-generated electron-hole pairs are
separated by a build-in barrier arising from the band bending at the
junction [27]. This high and stable On-Off IeV curve of the devices
reveals it is a high-performance self-powered photodetector with
good schottky-structure [16]. These self-powered visible photons
detection reveals it could be served as a good self-powered X-ray
detector [28,29].
CRediT authorship contribution statement
Qiang Xu: Writing - review & editing. Bohao Zhang: Materials
growth, device fabrication. Jing Nie: XRD and transmission mea-
surement. Hang Zhang: PL and XPS measurement. Xiaoping
Ouyang: Supervision. Jun Liu: optical response measurement. Yang
Liu: X-ray detection measurement.
Fig. 4a shows the current response of a device under various
incident X-ray energy with a bias of 0 V. The energy of incident X-
ray changed when the operated the X-ray tube voltage various from
Declaration of competing interest
3
5 kV to 50 kV. The results reveal the devices are with high stability.
Further, we have studied the sensitivity of the device under X-ray
with various energy. High X-ray generated current density has been
obtained at high incident dose, as shown in Fig. 4b. The sensitivity
of the device under the X-ray energy of 35, 40, 45, 50 kV are
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
ꢁ
4
ꢁ4
ꢁ4
ꢁ4
m
2
.35 ꢀ 10 , 2.02 ꢀ 10 , 1.66 ꢀ 10
and 1.15 ꢀ 10
C
Acknowledgment
ꢁ1
ꢁ2
m
Gy cm , respectively.
Energy absorption and charges drift are the two key physical
This work was funded by the National Natural Science Foun-
dation of China (Grants No. 11705090, 11875166, and 11435010).
This work also supported by the Fundamental Research Funds for
the Central Universities (No. NT2019018).
processes for self-powered X-ray detection. The X-ray attenuation
performances could be estimated with Beer-Lambert law
ꢁ
ux
relationship: I ¼ I e
[30], where I0 is the number of incident X-
0
ray photons, I is the number of transmitting X-ray photons, u is the
linear attenuation coefficient that is correlated with both effective
.
Appendix A. Supplementary data
atomic number (Zeff ) and X-ray photon energy (E) by Z4
,
AE3
eff
where A is the atomic mass, and x is the thickness of the medium
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jallcom.2020.157826.
[
31].
For a Schottky diode, the X-ray generated electron-holes in the
depletion layer could be collected by the metal electrode and the
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3
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