Improved Performance of Printable Perovskite Solar Cells with Bifunctional Conjugated Organic Molecule

Article abstract of DOI:10.1002/adma.201705786

A bifunctional conjugated organic molecule 4-(aminomethyl) benzoic acid hydroiodide (AB) is designed and employed as an organic cation in organic–inorganic halide perovskite materials. Compared with the monofunctional cation benzylamine hydroiodide (BA) and the nonconjugated bifunctional organic molecule 5-ammonium valeric acid, devices based on AB-MAPbI₃ show a good stability and a superior power conversion efficiency of 15.6% with a short-circuit current of 23.4 mA cm^?2, an open-circuit voltage of 0.94 V, and a fill factor of 0.71. The bifunctional conjugated cation not only benefits the growth of perovskite crystals in the mesoporous network, but also facilitates the charge transport. This investigation helps explore new approaches to rational design of novel organic cations for perovskite materials.

Full text of DOI:10.1002/adma.201705786

CommuniCation
Perovskite Solar Cells
www.advmat.de
Improved Performance of Printable Perovskite Solar Cells
with Bifunctional Conjugated Organic Molecule
Yue Hu, Zhihui Zhang, Anyi Mei, Youyu Jiang, Xiaomeng Hou, Qifei Wang, Kai Du,
Yaoguang Rong, Yinhua Zhou, Gengzhao Xu, and Hongwei Han*
been tried to improve the device stabili-
A bifunctional conjugated organic molecule 4-(aminomethyl) benzoic acid
hydroiodide (AB) is designed and employed as an organic cation in organic–
inorganic halide perovskite materials. Compared with the monofunctional
cation benzylamine hydroiodide (BA) and the nonconjugated bifunctional
organic molecule 5-ammonium valeric acid, devices based on AB-MAPbI3
show a good stability and a superior power conversion efficiency of 15.6%
with a short-circuit current of 23.4 mA cm−2, an open-circuit voltage of
0.94 V, and a fill factor of 0.71. The bifunctional conjugated cation not only
benefits the growth of perovskite crystals in the mesoporous network,
but also facilitates the charge transport. This investigation helps explore
new approaches to rational design of novel organic cations for perovskite
materials.
ties. Among them, the 2D perovskites that
are crafted using bulkier alkylammonium
cations in place of methylammonium
exhibit appealing environmental stability.
However, the insulating alkylammonium
spacer cations hinder charge transport
and limit the efficiencies of the devices
based on such perovskites. As a conse-
quence, Ruddlesden–Popper 2D perov-
skites have been explored as fashionable
alternatives to pure 2D or 3D perovskite
with the aim to balance the PCE of these
PSCs and their long-term stability.[7] The
general formula of such 2D/3D perov-
skites is A2(MA)n−1PbnI3n+1, where A is a
primary aliphatic or aromatic alkylammo-
The past few years have witnessed a rapid evolution of hybrid
organic–inorganic perovskite solar cells (PSCs) with both low
cost and boosted high power conversion efficiency (PCE) over
22%.[1] The rapid growth of PCE attributed to many research
efforts on the evolution of device architectures as well as pro-
cessing techniques and material compositions.[2] In particular,
methylammonium lead iodide (MAPbI3) possess an appro-
priate bandgap, high absorption coefficient,[3] long-range bal-
anced ambipolar photocarrier diffusion lengths,[4] and high
defect tolerance.[5]
Despite the achievements, MAPbI3 suffers from inherent
instability over ambient operation conditions due to the low
formation energy of the material itself and the high hydrophi-
licity of the organic cations.[6] Efforts such as developing novel
device architectures as well as exploring novel materials have
nium cation and n represents the number of octahedra layers
within each quantum well. It consists a network of inorganic
layers of corner sharing [PbI6]4− octahedra confined between
interdigitating bilayers of intercalated bulky spacer cations.
In this respect, Cao et al. synthesized (n-BAM)2(MA)2Pb3I10
(BAM = n-butylammonium), yielding a PCE of 4.02%.[8]
Smith et al. reported the application of (PEA)2(MA)2Pb3I10
(PEA = 2-phenylethylammonium) with a PCE of 4.73%.[9]
Enhanced moisture stability was reported for both studies. Later
on, an advance in deposition technique using “hot-casting”
(HC) method induced preferential out-of-plane alignment of
(n-BAM)2 (MA)3Pb4I13 and increased the PCE to 12.52%.[10]
[7]
Tuning the dimensionality to give (PEA)2 (MA)59Pb60I181 or
replacing n-BAM with a shorter branched-chain butylamine
[11]
(iso-BAM) to give (iso-BAM)2 (MA)2Pb3I10 improved the effi-
ciency to 15.30% and 8.82%, respectively. The enhanced PCE
mainly comes from an enhanced charge transport between the
inorganic layers. On the other hand, recent work suggested that
the degradation of perovskite films starts from grain bounda-
ries.[12] By adding BAM into the FA0.83Cs0.17Pb(IyBr1−y)3 perov-
skites, Snaith and co-workers illustrated a model of 2D perov-
skite platelets interspersing between 3D perovskite grains that
improved the stability of perovskite without sacrificing the
efficiency.[13] Other molecules, such as phenyl-C61-butyric acid
methyl ester,[14] thiophene, pyridine,[15] urea,[16] or quaternary
ammonium halide[17] have also been proven to effectively pro-
tected the perovskites boundaries and prolonged the lifetime.
The perovskite material instability was controlled to a cer-
tain extent by using these quasi-3D or boundary protected
perovskites. However, the solar cell degradation is not only
due to the decomposition of perovskite layer, but can also be
Dr. Y. Hu, Z. H. Zhang, A. Y. Mei, Dr. Y. Y. Jiang, X. M. Hou, Q. F. Wang,
Dr. Y. G. Rong, Prof. Y. H. Zhou, Prof. H. W. Han
Michael Grätzel Center for Mesoscopic Solar Cells
Wuhan National Laboratory for Optoelectronics
Huazhong University of Science and Technology
Wuhan 430074, Hubei, P. R. China
E-mail: hongwei.han@mail.hust.edu.cn
K. Du, Prof. G. Z. Xu
Suzhou Institute of Nano-Tech and Nano-Bionics
CAS
Suzhou 215123, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.201705786.
DOI: 10.1002/adma.201705786
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accelerated by the lattice mismatch between perovskite and
TiO2 and the defects at the interfaces. Our group first intro-
duced a bifunctional 5-ammonium valeric acid hydroiodide
(AVAI) as a primary aliphatic alkylammonium cation into the
perovskites.[18] The perovskites were employed in the printable
HTM-free carbon-based PSC. By infiltrating the perovskite pre-
cursor solution into a mesoscopic TiO2/ZrO2/carbon scaffold
using a simple one-step dropping strategy followed by a slow
drying process, the components in the film reorganized and
self assembled the desired perovskites.[19] The small-area cell
based on this material gave a PCE of 12.8% and larger module
gave a PCE of 10.4%.[20] In addition, the cells exhibited high sta-
bility under AM 1.5G illumination over 10 000 h[21] and under
a range of harsh tests outdoor in Jeddah, Saudi Arabia.[22] The
high stability is a synergy consequence of both the protection
of boundaries and the protection of perovskite/TiO2 interface,
showing the advantages of bifunctional molecular. However,
the problem of such perovskites is that the
HOMO of AB and BA locates mainly on the iodide atom and the
LUMO lies over the whole molecule. On the contrary, the LUMO
of AVA only locates on the acid group while extends toward the
nearest CH2. The long distance between the HOMO and LUMO
of AVA certainly hinders charge transport through the molecule.
In addition, AB showed a conjugation-induced rigidity in the
molecule. The benzene part and the acid part of AB are on the
same platform as evidenced from the ≈0.2° dihedral angle.
Then the perovskites were prepared by mixing BA, AB,
AVA, methylammonium iodide (MAI), and PbI2 at judiciously
chosen stoichiometry to give (BA)2 (MA)49Pb50I151, (AB)2
(MA)49Pb50I151, (AVA)2 (MA)49Pb50I151, and MAPbI3. For con-
venience, we denote (BA)2 (MA)49Pb50I151 as BA-MAPbI3, (AB)2
(MA)49Pb50I151 as AB-MAPbI3, and (AVA)2 (MA)49Pb50I151 as
AVA-MAPbI3. The perovskite films were prepared by one-step
drop-casting method on 500 nm/2 µm mesoporous TiO2/ZrO2
substrates. As shown by X-ray diffraction (XRD) in Figure 1b,
insulating aliphatic alkylammonium cation
organic spacer cations hinder charge trans-
port thus limits the fill factor (FF) of PSCs.
In this scenario, an exploration of alterna-
tive yet effective organic spacer cations that
increase the charge transfer is imperative to
enhance the efficiency.
Herein, we designed such an alterna-
tive bifunctional conjugated organic cation
4-(aminomethyl) benzoic acid hydroiodide
(AB) and synthesized a novel perovskite AB-
MAPbI3. By applying this perovskite in HTM-
free printable PSCs, we obtained a best PCE
of 15.6% with a short-circuit current (JSC) of
23.4 mA cm−2, an open-circuit voltage (VOC
)
of 0.94 V, and an FF of 0.71. In addition,
the devices based on AB-MAPbI3 showed
improved stability compared with MAPbI3.
The bifunctional molecule 4-(aminomethyl)
benzoic acid hydroiodide (structure in Figure
1
1a) was synthesized and characterized by H
NMR (Figure S1, Supporting Information).
The nonconjugated cation, 5-aminovaleric
acid hydroiodide (AVA; structure in Figure 1a)
and the monofunctional cation, benzylamine
hydroiodide (BA) were also synthesized from
the according starting materials for com-
parison. Density functional theory (DFT) cal-
culations were carried out to investigate the
influence of conjugated bridge to the molec-
ular structure and electron distributions. The
calculations were performed by Gaussian 09
program[23] at B3LYP/6-31G* level in vacuum.
Through DFT calculation, we found that AB
and AVA have similar chain length (10.206 Å
for 5-AVA and 10.163 Å for AB) while BA is
shorter (7.063 Å). The highest occupied molec-
ular orbitals (HOMOs) of the molecule are
shown in red and green while the lowest unoc-
cupied molecular orbitals (LUMOs) are shown
in blue and yellow. It can be observed that the
Figure 1. a) The structures of AB, AVA, and BA together with their calculated properties, such
as the molecular length and the dihedral angles. The HOMOs of the molecule are shown in red
and green while the LUMOs are shown in blue and yellow. b) The XRD spectra of MAPbI3, BA-
MAPbI3, AVA-MAPbI3, and AB-MAPbI3 on 500 nm/2 µm mesoporous TiO2/ZrO2 substrates.
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Figure 2. The top view scanning electron microscopy (SEM) images for a) MAPbI3, c) BA- MAPbI3, e) AVA-MAPbI3, and g) AB-MAPbI3 on 500 nm TiO2/
2 µm ZrO2 and their cross-sectional SEM images of the cells filled with b) MAPbI3, d) BA- MAPbI3, f) AVA-MAPbI3, and h) AB-MAPbI3.
BA-MAPbI3, AB-MAPbI3, and AVA-MAPbI3 showed similar
crystal structure of MAPbI3. No peak at 12.6° was detected in
all samples, indicating a quantitative transformation of PbI2
into the perovskite material.[24] In addition, we found that the
(202) plane is highly preferred in the pristine MAPbI3 perov-
skite while (110) became the main preferred direction for BA-
MAPbI3, AB-MAPbI3, and AVA-MAPbI3.
AB-MAPbI3 and AVA-MAPbI3 showed a superior pore-filling
ability. The –COOH groups anchor a monolayer of AB or AVA
to the surface of the mesoporous TiO2 and ZrO2 by coordinative
binding to the exposed Ti(IV) or Zr(IV) ions, attaching the per-
ovskites close to the metal oxides and serve as nucleation sites
from perovskite growth.
The excellent loading and desired morphology of the perov-
skite is also evident from the UV–vis spectra as shown in
Figure 3a. The identical absorption onsets of all perovskites on
TiO2 indicate the same bandgap. The perovskites containing
larger cations exhibited enhanced light absorption through
the whole absorption profile due to the improved surface cov-
erage while the ones with bifunctional cations showed even
higher absorbance. The time-resolved photoluminescence
(TRPL) decay measurements can be used to investigate the
carrier lifetimes of the perovskite films and the charge-carrier
extraction at the interface between charge collection layer and
the perovskite layer.[26] Figure 3b shows the TRPL spectra and
the fitting curves of the perovskites on TiO2 and Figure 3c
shows the TRPL spectra and the fitting curves of those on
TiO2. The TRPL decay was fitted to a biexponential equation:
y = A1exp(−t/τ1) + A2exp(−t/τ2)[27] in which the shorter PL life-
time can be attributed to the defect-induced nonradiative recom-
bination and the longer PL lifetime can be attributed to the
radiative recombination.[4b,28] The fitted parameters are summa-
rized in Table S1 in the Supporting Information. On ZrO2, the
MAPbI3, BA-MAPbI3, AVA-MAPbI3, and AB-MAPbI3 perovskite
gave carrier lifetimes of 10.83, 18.38, 24.03, and 29.48 ns, respec-
tively. The longer charge-carrier lifetime observed with the per-
ovskites containing bifunctional cations may be attributed to a
lower defect concentration and an increase in crystallinity.[1a]
With the TiO2, the MAPbI3, BA-MAPbI3, AVA-MAPbI3, and
AB-MAPbI3 perovskite gave carrier lifetimes of 3.30, 2.48,
2.07, and 1.70 ns, respectively, indicating the charge carrier
extraction speed at the perovskite/TiO2 interface orders by
The top view scanning electron microscopy (SEM) images
gave a more intuitive view of the perovskite morphologies
(Figure 2a,c,e,g). The simple drop-casting method usually
resulted in a poor morphology. The huge discontinued crystals
gave a poor coverage of the surface and resulted in many bound-
aries. On the contrary, perovskites with larger cations showed
much denser morphology with less voids. The same behavior is
also observed by other researchers that use one-step spin-coating
method to prepare perovskite films.[8] The perovskites con-
taining bifunctional cation showed better morphology than the
one using monofunctional cation, due to strong adherence of the
acid group.[25] We then infiltrated these solutions in the print-
able carbon-based HTM-free PSCs. As shown in the cross-sec-
tional SEM images in Figure 2b,d,f,h, the solar cell architecture
used is a stack of glass/fluorine-doped tin oxide (FTO)/compact
TiO2/mesoporous TiO2/mesoporous ZrO2/mesoporous C and
perovskite solution is filled in the triple mesoporous scaffold fol-
lowed by annealing.[18] The mesoporous materials are prepared
by screen-printing technique followed by sintering. Then the
perovskite precursors are infiltrated into the scaffold by a simple
one-step dropping strategy. However, the morphology control of
the perovskite film in such triple-layer structures remains a crit-
ical challenge because dropping the perovskite precursor directly
into the scaffold usually causes an incomplete perovskite crystal
growth and a deficient interface contact. As shown in Figure 2b,
MAPbI3 does not go into the TiO2 mesopores. Clear particles
of TiO2 and ZrO2 can be observed from SEM. BA-MAPbI3 did
not infiltrate in TiO2 mesopores either. On the contrary, both
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Figure 3. a) The UV–vis absorption spectra on TiO2, b) the time-resolved photoluminescence spectra on ZrO2, and c) the time-resolved photolumi-
nescence spectra on TiO2 of MAPbI3, BA-MAPbI3, AB-MAPbI3, and AVA-MAPbI3 perovskite. d) The J–V curves for the champion devices using MAPbI3,
BA-MAPbI3, AB-MAPbI3, and AVA-MAPbI3 measured under AM 1.5G irradiation. e) The IPCE and corresponding integrated current for the champion
devices measured with a 10% bias light.
MAPbI3 < BA-MAPbI3 < AVA-MAPbI3 < AB-MAPbI3. The
anchoring group attaches the perovskite more intimately with
the TiO2 while at the same time the conjugated cation facilitates
charge transfer.
of such devices. Thanks to a better morphology of the perov-
skites, the BA-MAPbI3 cell gives a PCE of 12.0 %, with a VOC
of 0.9 V, a JSC of 20.3 mA cm−2, and an FF of 0.65. When the
monofunctional cation is replaced by a bifunctional cation, the
PCE increased further. The AVA-MAPbI3 cell gives a PCE of
14.1%, with a VOC of 0.92 V, a JSC of 22.8 mA cm−2, and an
FF of 0.67 while the AB-MAPbI3 cell gives a PCE of 15.6 %,
with a VOC of 0.94 V, a JSC of 23.4 mA cm−2, and an FF of 0.71.
Device hysteresis is checked and shown in Figure S3 in the
Supporting Information. The largely enhanced JSC, not only
comes from the better crystallinity of the perovskite, but also
from a more intimate contact of perovskite with TiO2 and a
down-shifted TiO2 work function (as evidenced by ultraviolet
photoelectron spectroscopy measurement. As shown in Figure
S4 in the Supporting Information, the work function of bare
TiO2 is ≈4.04 eV. With AVA and AB, the work function of the
TiO2 shifted to ≈4.16 and ≈4.14 eV, respectively). The –COOH
group from the bifunctional cations can attach with TiO2 layer
by chemical bonding as we learnt from dye-sensitized solar
cells.[30] This adds a surface dipole moment on TiO2 and thus
varied the energy level. The positively shifted
Figure 3d shows J–V curves for the champion cell using AB-
MAPbI3, AVA-MAPbI3, BA-MAPbI3, and MAPbI3. The device
photovoltaic statistics (VOC, JSC, FF, and PCE) measured under
a simulated air mass (AM) 1.5 irradiance of 100 mW cm−2 are
summarized in Table 1. The control device fabricated with pris-
tine MAPbI3 exhibits a poor performance of 6.47 %, with a VOC
of 0.88 V, a JSC of 13.1 mA cm−2, and a FF of 0.56, which is
comparable with the state-of-art device prepared with the same
perovskite composition and device architecture.[29] This poor
performance is a result of the incomplete perovskite crystal
growth and deficient interface contact in tens of micrometers
thick mesoporous layers. The electrons from the perovskite
have to travel the entire thickness of ZrO2, which can some-
times exceed hundreds of nanometers or even micrometers.
Most electrons recombine with the holes before they reach and
inject into TiO2, thus resulting in an extremely low photocurrent
Table 1. The characterization of TiO2 films modified with different functional molecular and
their devices performances.
TiO2 allows a larger driving force with an
increased density of acceptor states avail-
able in the TiO2 film for interfacial electron
injection from the Fermi level of perovskite,
thus facilitates the charge transport. Both
cells based on perovskites with bifunctional
cations show extremely high photocurrent
around 23 mA cm−2, and the enhanced JSC of
AB-MAPbI3 than AVA-MAPbI3 is revealed by
J
SC [mA cm−2
]
Additive
None
BA
Ef [eV]
4.04
4.04
4.14
4.16
VOC [V]
0.88
PCE [%]
6.47
FF
13.1
0.56
0.65
0.67
0.71
20.3
0.90
12.0
5-AVAI
AB
22.8
0.92
14.1
23.4
0.94
15.6
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Figure 4. Morphology AFM images of a) AVA-MAPbI3, c) AB-MAPbI3, and e) BA-MAPbI3 film and their corresponding current mappings b) AVA-MAPbI3,
d) AB-MAPbI3, and f) BA-MAPbI3 measured by cAFM with 1.0 V bias. g) The I–V plots of different films measured by c-AFM.
incident photon-to-current efficiency (IPCE) spectra. (Figure 3e)
The IPCE of AVA-MAPbI3 cell started to drop from 500 nm, as
we observed before in such cells.[18] AB-MAPbI3 cell showed an
ideal square shape IPCE, where the IPCE value is fairly con-
stant across the whole 400–800 nm. IPCE measures the per-
centage of photons that are converted to electric current as a
function of wavelength when the cell is operated under short
circuit conditions.[31] The value corresponds to the photocurrent
density produced in the external circuit under monochromatic
illumination of the cell divided by the photon flux that strikes
the solar cell. It can be affected by the light-harvesting effi-
ciency for photons at a certain wavelength λ, the quantum yield
for electron injection, and the electron collection efficiency.[32]
At longer wavelength, the photons have lower energy and thus
have more possibilities to be trapped and recombined.[33] The
higher IPCE of AB-MAPbI3 at the long wavelength region can
either be attributed to a lower trap states or a better electron
injection and electron collection efficiency of AB-MAPbI3.
We also noticed that the AVA-MAPbI3 cell showed a slower
response than the AB-MAPbI3 cell from the stabilized power
output under maximum power point tracking (Figure S5, Sup-
porting Information). In addition, we have noticed that the inte-
grated JSC from IPCE measurement is always tiny smaller than
the one measured from J–V curve. For the AVA-MAPbI3 cell we
certified before, the integrated current is 18 mA cm−2 but the
certified current density is 22.8 mA cm−2.[18] We found that the
integrated current agrees closely with the JSC of 18.4 mA cm−2
which was measured at the beginning of device testing. The
value then rose to 21.1 mA cm−2 after 3 min of light soaking.
Some initial stability tests have been performed on the devices
using AB-MAPbI3 as shown in Figure S7 in the Supporting
Information. Under 1 sun illumination, the cells were held at
their maximum power point. The device based on AB-MAPbI3
shows a much better stability trend with respect to MAPbI3
cell. Using AB-MAPbI3, the efficiency remained around 90%
of the initial value after 100 h continuous illumination, much
more stable than MAPbI3 perovskite. Importantly, the stability
test was performed without encapsulation. Upon encapsula-
tion and optimization, the stability and efficiency can be further
improved. In addition, the cells showed improved shelf-life sta-
bility in the dark within 1 month.
To directly investigate the charge-transport behavior of the
different perovskites, topography and photocurrent mappings
were performed using conductive-AFM (c-AFM) in contact
mode. To gain a surface flat enough for c-AFM measurement,
the films were prepared by toluene dripping on stoichiometric
precursors. As shown in Figure 4a,c,e, the root-mean-square
roughness of the perovskite film surfaces did not vary much
when we used different perovskites containing conjugated or
nonconjugated cations. However, an obvious difference in the
conductivity was observed. The current mappings of different
films were measured with a bias of 1.0 V. The results show that
the conductivities of the perovskite films using BA-MAPbI3
(Figure 4f) and AB-MAPbI3 (Figure 4d) are larger (by four times
over the conductive parts) than that of AVA-MAPbI3 (Figure 4b).
Photocurrent–voltage (I–V) curves were also measured, as
shown in Figure 4g. Higher current response was found for
the perovskites with conjugated cations. This indicates that
using conjugated cations is an efficient and rational method to
increase the conductivity of perovskites.
In summary, we report the first time the incorporation of a
bifunctional conjugated cation in perovskites and its implemen-
tation on solar cells. The use of bifunctional conjugated cations
enhances significantly the performance of the cells, reaching a
highest PCE of 15.6% with improved stability. By comparing
this cation with a monofunctional cation and a bifunctional
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a scan rate of 20 mV s−1. The active area of the device is about 0.8 cm2
and a black mask with a circular aperture (0.126 cm2) was applied for
J–V measurements. Incident photo-to-current conversion efficiency was
performed using a 150 W xenon lamp (Oriel) fitted with a monochromator
(Cornerstone 74004) as a monochromatic light source.
nonconjugated cation with similar structure, we found that the
bifunctional conjugated cation not only benefits the growth of
perovskite crystals in the mesoporous network, but also facili-
tates the charge transport. Our approach helps explore new
rational designs of cations in perovskites.
Supporting Information
Experimental Section
Supporting Information is available from the Wiley Online Library or
from the author.
Materials: 4-(Chloromethyl) benzoic acid, NaN3, tetra-n-
butylammonium azide, benzylamine (BA, 99%), ethyl acetate (EtOAc),
hydroiodic acid (HI, 57 wt% in H2O), acetonitrile (MeCN), and N,N-
dimethylformamide (DMF, anhydrous) were purchased from Sigma- Acknowledgements
Aldrich. All materials were used as received without further purification.
Y.H., Z.H.Z. and A.Y.M. contributed equally to this work. The authors
Synthesis of 4-(Aminomethyl) benzoic acid hydroiodide (AB):
4-(Chloromethyl) benzoic acid (2 g, 0.012 mol), NaN3 (1.5 g, 0.023 mol),
and tetra-n-butylammonium azide were dissolved in CH3CN/DMF
(80 mL) and heated at 130 °C for 8 h. The mixture was cooled down to
room temperature. Distilled water (100 mL) and EtOAc (200 mL) were
added in. The organic layer was washed with water, brine and dried over
Na2SO4. Then Na2SO4 was filtered off and the solvent was removed by
evaporation to give 2.3 g yellow solid product. The product was used
without further purification. Tetrahydrofuran (THF) (40 mL) and DMF
(15 mL) were added to dissolve the yellow solid and triphenylphosphine
(3.8 g, 0.015 mol) was added. The mixture was stirred for 10 min before
0.5 mL H2O was added and the resultant mixture was stirred for another
5 h at ambient temperature. 2 m HI (5 mL) was added and the solution
was refluxed for 1 h. Concentrated hydroiodic acid (3.5 mL, 0.014 mol)
was added and the mixture was refluxed for 2 h. The solvent was then
rotavaporated off and the crude product was washed with diethyl ether
to give a white powder (2.5 g, 67.6% yield). 1H NMR (500 MHz, CDCl3)
δH: 13.12 (s, 1H), 8.21 (s, 3H), 8.00 (d, J = 8.2 Hz, 2H), 7.59 (d, J = 8.2
Hz, 2H), 4.15 (s, 1H).
acknowledge financial support from the National Natural Science
Foundation of China (Grant Nos. 91733301, 91433203, 21702069,
61474049, and 51502141), the Ministry of Science and Technology
of China (Grant No. 2015AA034601), the Science and Technology
Department of Hubei Province (No. 2017AAA190), the 111 Project
(Grant No. B07038), and the China Postdoctoral Science Foundation
(Grant No. 2016M600588). The authors thank the Analytical and Testing
Center of Huazhong University of Science and Technology (HUST) for
performing various characterization and measurements.
Conflict of Interest
The authors declare no conflict of interest.
Keywords
Synthesis of Other Amino Iodides: 5-Ammonium valeric acid (AVA)
and methylamine (MA) were mixed with hydroiodic acid (HI, 57 wt% in
water) with a molar ratio of 1:1.1. The mixture was stirred for 4 h before
the solvent was removed. The crude product was then washed with
diethyl ether to give white powder and dried in a vacuum drying oven.
Precursor Preparation and Device Fabrication: The perovskite precursor
solution was obtained by mixing amines and PbI2 in a mixture of
γ-butyrolactone/ethanol (4:1). The pristine MAPbI3 solution contains
1 m MAI and 1 m PbI2. FTO glasses were laser-etched to give the desired
patterns. They were cleaned by ultrasonicating the glasses in soap water,
distilled water, and ethanol. A compact TiO2 layer was then deposited
on the FTO glass by spray pyrolysis at 450 °C with 20 × 10−3 m titanium
diisopropoxide bis(acetylacetonate) in ethanol (Aldrich). A 500 nm
nanoporous TiO2 (NR18) layer was screen-printed onto the compact
layer followed by a 2 µm ZrO2 space layer. Both layers were sintered at
500 °C in air for 30 min. After that, a 15 µm graphite/carbon black back
electrode was screen printed and sintered at 400 °C for 30 min. After
cooling down, the perovskite solution was drop casted on the carbon
layer to fill the triple layer structure and dried at 50 °C for 4 h.
Characterizations: The XRD spectra were measured with an X'pert PRO
X-ray Diffractometer using Cu Kα radiation under operation conditions of
40 kV and 40 mA from 5° to 70°, with a scanning speed of 5° per min.
Scanning electron micrographs (SEM) were obtained by a Nova NanoSEM
450 field emission SEM. The UV–vis spectra of perovskite-sensitized
TiO2 film were measure by a PerkinElmer Lambda950 spectrophometer.
Fourier Transform infrared spectroscopy (FTIR) spectra were recorded
by a VERTEX 70 Infrared Fourier transform microscopy. Ultraviolet
photoelectron spectroscopy (UPS) was performed on a Kratos Axis Ultra
DLD system with He I (hν = 21.22 eV) excitation. Device performance
were characterized by a Keithley 2400 source/meter and a Newport
solar simulator (model 91192) which offered the simulated AM 1.5G
illumination of 100 mW cm−2, calibration was done using a NIST-certified
monocrystalline Si solar cell (Newport 532 ISO1599). The J–V curves were
measured both reverse (1.2 to −0.2 V) and forward (−0.2 to 1.2 V) with
bifunctional, conjugated molecules, perovskites, printable, solar cells
Received: October 4, 2017
Revised: November 24, 2017
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