Organohalide lead perovskite based photodetectors with much enhanced performance

Article abstract of DOI:10.1039/c4cc05960c

CH₃NH₃PbI₃ based photodetectors were fabricated by a facile low-cost process with much enhanced performance. The rise time changed from 2.7 s to 0.02 s, the decay time from 0.5 s to 0.02 s, and the ON/OFF ratio tripled with improved stability. The results indicate that perovskites are promising light-harvesting materials for photodetectors. This journal is

Full text of DOI:10.1039/c4cc05960c

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Organohalide lead perovskite based photodetectors
with much enhanced performance†
Cite this:DOI: 10.1039/c4cc05960c
ab
ac
ab
abc
Hua-Rong Xia, Jia Li, Wen-Tao Sun* and Lian-Mao Peng*
Received 31st July 2014,
Accepted 15th September 2014
DOI: 10.1039/c4cc05960c
www.rsc.org/chemcomm
3 3 3
CH NH PbI based photodetectors were fabricated by a facile low-
cost process with much enhanced performance. The rise time
changed from 2.7 s to 0.02 s, the decay time from 0.5 s to 0.02 s,
and the ON/OFF ratio tripled with improved stability. The results
indicate that perovskites are promising light-harvesting materials
for photodetectors.
Organic–inorganic perovskites such as CH
Br, I) have attracted much attention as light-harvesting materials
for mesoscopic solar cells with enhanced performance, since
the pioneering work by Tsutomu Miyasaka et al. Photodetectors
3 3 3
NH PbX (X = Cl,
Fig. 1 Scheme of the fabrication of organic–inorganic perovskite based
photodetectors.
1
–7
8
have important applications in many fields and light-harvesting the fabrication of perovskite based photodetectors includes
material is the key part of it. However, little work has been done three steps as shown in Fig. 1. First, the electrodes for photo-
on the research of perovskite based photodetectors. In this detectors were made as the following process: the FTO area
work, CH
3
NH
3
PbI
3
/TiO
2
photodetectors were fabricated by a used as electrodes was protected by tapes with others exposed;
then the tape-protected FTO was coated with a layer of zinc
facile and low-cost process. Compared with the plain TiO
2
photodetector, the performance was significantly improved. powder and immersed into 1 M hydrochloride solution to etch
The response speed is much faster with the rise time of the FTO without tape protection (details in ESI†). Second, TiO2
time response constants changing from 2.7 s to 0.02 s and the paste was coated onto the etched area to link the two electrodes
decay time from 0.5 s to 0.02 s. At the same time, the ON/OFF by a screen printing process and then annealed at 400 1C for
ratio is about three times that without CH
stability of the photodetector was also improved. The results In this way, a TiO
indicate that perovskites are promising light-harvesting materials the as-synthesized CH
for photodetectors. mesoscopic thin film and then dried at 115 1C for 15 min. Thus
Organohalide lead perovskite (CH NH PbI ) was prepared perovskite based photodetectors were successfully made. The
3
NH
3
PbI
3
, and the 1 hour to form a mesoscopic film with a thickness of about 2 mm.
-based photodetector was made indeed. Finally,
NH PbI solution was spun onto the TiO
2
3
3
3
2
3
3
3
9
according to the procedure reported by Kim et al. (details in performance of the photodetectors was measured using a CHI
ESI†). And TiO paste was made from P25 powder (TiO nano- 660C electrochemical workstation under a solar simulator
2
2
particles with a diameter of about 20 nm) with a procedure with AM 1.5 light. SEM (scanning electron microscope), XRD
1
0
similar to the report of Gratzel’s group. In a typical process, (X-ray diffraction spectrometer) and UV-Vis (ultraviolet-visible
spectrometer) were also used to characterize the morphologies,
a
structures and absorptions respectively.
Key Laboratory for the Physics and Chemistry of Nanodevices, Peking University,
Beijing 100871, China. E-mail: wtaosun@pku.edu.cn, lmpeng@pku.edu.cn
Department of Electronics, Peking Uniersity, Beijing 100871, China
Academy for Advanced Interdisciplinary Studies, Peking University,
Beijing 100871, China
The morphologies of the photodetectors were characterized
by SEM with typical images shown in Fig. 2a–c. Fig. 2a shows an
image of the conducting side of FTO glass, which is composed
of large numbers of close-packed particles with diameters from
b
c
†
Electronic supplementary information (ESI) available: Experimental details
10 to 100 nm. As seen from Fig. 2b, the mesoscopic TiO
2
thin
of CH
electrodes on glass, photographs of the CH
FTO electrodes. See DOI: 10.1039/c4cc05960c
3
NH
3
PbI
3
synthesis, preparation of TiO
2
paste, and fabrication of FTO
PbI solution, TiO paste and
film is made up of many interconnected TiO nanoparticles with
the diameter of about 20 nm. As there are a lot of nanopores in
2
3
NH
3
3
2
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Fig. 2 (a–c) SEM images of FTO glass, TiO
2
mesoscopic thin film, and
NH PbI
3
on a glass substrate (blue line).
CH
TiO
3
NH
3
PbI
3
/TiO
2
thin film respectively. (d) XRD patterns of CH
NH PbI
3
3
3
/
2
film (red line) and pure CH
3
3
the mesoscopic TiO
solution can penetrate into them and form perovskite/TiO
heterojunctions. Fig. 2c shows the images of CH NH PbI /TiO
2
2
film, the organohalide lead perovskite Fig. 3 (a) Crystal structures of organohalide lead perovskite compounds.
b) Transmission spectra of etched FTO (black line), mesoscopic TiO thin
film (red line) and CH NH PbI /TiO thin film (blue line) with the corre-
sponding photograph inset. (c, d) I–V cures of the photodetectors without/
with CH NH PbI . (e, f) Time response behaviors of the photodetectors
with (red line)/without (black line) CH NH PbI
(
2
2
3
3
3
2
3
3
3
film, with many perovskite particles penetrated into the film and
others forming large flakes onto the film which is similar to the
3
3
3
3
3
3
.
4
reference. The XRD patterns at 19.941, 28.421, 31.781, 40.481
and 43.041 correspond to the reflections from (110), (112),
(220), (310), (224) and (314) crystal planes respectively, indi- that the introduction of CH
3 3 3 2
NH PbI into the TiO mesoscopic
cating a tetragonal perovskite structure with a = 8.855 Å and photodetector improved the ON/OFF ratio (or gain) by about
1
1
c = 12.659 Å (Fig. 3a). No impurity peaks other than the ones three times. The improvement can be attributed to the much
attributed to CH NH PbI and TiO /FTO are observed, suggest- enhanced light harvesting capability resulting from the addition of
3
3
3
2
ing that CH NH PbI grown on the mesoporous TiO thin film CH NH PbI (shown in Fig. 3b). The corresponding photocurrent
3
3
3
2
3
3
3
is phase pure.
time response was measured at 3 V bias under solar simulator
Typical transmission spectra of the etched FTO glass (black ON/OFF switching irradiation with the light intensity of
À2
line), TiO
2
on etched FTO glass (red line) and CH
3
NH
3
PbI
3
/TiO
2
100 mW cm and an ON/OFF interval of 20 s. Ten cycle curves
on etched FTO glass (blue line) are shown in Fig. 3b, with the under ON/OFF illumination are shown in Fig. 3e. It can be seen
corresponding photograph inset. The sharp absorption edge of that the photocurrent of the CH NH PbI /TiO photodetector
the TiO -coated etched FTO glass has a red shift compared to that (red line) is consistent and repeatable while that of the TiO
of the etched FTO glass, which may result from the smaller band photodetector (black line) decays significantly, which is consistent
3
3
3
2
2
2
12
gap of TiO (3.2 eV) compared to SnO (3.6 eV). And the significant with the report. An enlarged typical ON/OFF cycle is shown in
2
2
enhanced absorption of CH NH PbI /TiO mesoscopic thin film Fig. 3f, from which it can be seen that the CH NH PbI /TiO
2
3
3
3
2
3
3
3
6
is ascribed to the large absorption coefficient of CH
Typical I–V curves of the TiO photodetector and CH
TiO
Clearly, I–V curves present linear dependence on the applied bias, stable photocurrent, and the decay time is the time to reach 1/e
3
NH
NH
3
PbI
PbI
3
.
photodetector switches much faster. To quantitatively extract the
time response constant, the well accepted quantitative criterion is
2
3
3
3
/
2
photodetector are shown in Fig. 3c and d respectively. introduced. That is, the rise time is the time to reach 90% of the
13
indicating the formation of ohmic contact between TiO
FTO electrode, which is crucial to photoconductive photodetec- the rise time and decay time of the TiO
tors. The dark currents at 3 V of the TiO photodetector (1.34 Â 2.7 s and 0.5 s respectively, which is comparable with the best
14,15
2
and the (37%) of the original photocurrent. According to this criterion,
2
photodetector are about
2
À10
À10
1
0
A) and the CH NH PbI /TiO photodetector (1.36 Â 10
A) performance of TiO2 photodetectors reported elsewhere.
/TiO While the rise time and decay time of the CH NH PbI /TiO
2
3
3
3
2
are similar, while the photocurrent at 3 V of the CH
3
NH
PbI
3 3
2
3
3
3
À9
6,16,17
photodetector (9.75 Â 10
A, corresponding responsivity photodetector are about 0.02 s and 0.02 s respectively.
À1
À9
0
(
.49 mA W ) is much larger than that of the TiO
2
photodetector
The mechanism of the significantly shortened rise and decay
NH PbI /TiO based photodetectors compared
À1
3.27 Â 10 A, corresponding responsivity 0.16 mA W ) showing time of the CH
3
3
3
2
Chem. Commun.
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with the TiO
2
based ones may be described as follows. For a the National Science Foundation of China (Grant No. 61306079,
2
pure TiO photodetector, it is generally accepted that the oxygen 61171023).
adsorption–desorption at the TiO surface plays an important
2
Notes and references
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1
6–18
rate of oxygen adsorption–desorption.
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heterojunction photodetector, band-bending at the interface
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2
3
illumination, large numbers of electrons are injected into TiO
rapidly, which increase the photoconductivity of the TiO film.
2
2
4, 2242.
While when the light is switched off, the sudden absence of
electron injection results in the decrease of the conductivity
rapidly. Since the light-induced carrier concentration modulation
is much faster than the one controlled by the oxygen adsorption–
4
5
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2
2
detector (Fig. 3f ). Besides, as the oxygen adsorption–desorption
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8
9
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2 2
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3
3
3
2
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This work was supported by the Ministry of Science and
Technology (Grant No. 2011CB933002 and 2012CB932702) and
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Chem. Commun.