Chemical Pathways Connecting Lead(II) Iodide and Perovskite via Polymeric Plumbate(II) Fiber

Article abstract of DOI:10.1021/jacs.5b10599

Despite tremendous progress in optoelectronic devices using lead perovskite (CH₃NH₃⁺PbI₃^-), there has been a paucity of mechanistic information on how photoactive micron-sized crystals of lead perovskite grow from a mixture of a layered crystal of lead(II) iodide and methylammonium iodide mediated by a polar solvent, DMSO or DMF. We report here that the whole process of the lead perovskite synthesis consists of a series of equilibria driven by reversible solvent participation involving a polymeric strip of plumbate(II) oligomer as a key intermediate. A significant finding includes quick decomposition of perovskite crystal upon exposure to DMSO or DMF at room temperature, where the solvent molecules act as a base to remove acidic ammonium iodide from the perovskite crystal. This observation accounts for the difficulty in controlling perovskite solar cell fabrication. Overall, the polar solvent is indispensible first to degrade a 2-D sheet of crystals of lead(II) iodide into 1-D fibrous intermediates and then to promote Oswald ripening of perovskite crystals. The detailed chemical information provided here will help to rationalize the photovoltaic device studies that have so far remained empirical and to open a new venue to a developing field of microscale lead perovskite devices, as illustrated by fabrication of photovoltaic devices and photodetectors.

Full text of DOI:10.1021/jacs.5b10599

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Article
Chemical Pathways Connecting Lead(II) Iodide
and Perovskite via Polymeric Plumbate(II) Fiber
Yunlong Guo, Kazutaka Shoyama, Wataru Sato, Yutaka Matsuo, Kento
Inoue, Koji Harano, Chao Liu, Hideyuki Tanaka, and Eiichi Nakamura
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b10599 • Publication Date (Web): 29 Nov 2015
Downloaded from http://pubs.acs.org on December 3, 2015
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Chemical Pathways Connecting Lead(II) Iodide and Perovskite
via Polymeric Plumbate(II) Fiber
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‡
‡
Yunlong Guo, Kazutaka Shoyama, Wataru Sato, Yutaka Matsuo, Kento Inoue, Koji Harano, Chao
Liu, Hideyuki Tanaka and Eiichi Nakamura*
Department of Chemistry, The University of Tokyo 7ꢀ3ꢀ1 Hongo, Bunkyoꢀku, Tokyo 113ꢀ0033, Japan.
+
–
ABSTRACT: Despite tremendous progress in optoelectronic devices using lead perovskite (CH NH PbI ), there has been a
3
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3
paucity of mechanistic information on how photoactive ꢁmꢀsize crystals of lead perovskite grow from a mixture of a layered crystal
of lead(II) iodide and methylammonium iodide mediated by a polar solvent, DMSO or DMF. We report here that the whole process
of the lead perovskite synthesis consists of a series of equilibria driven by reversible solvent participation, involving a polymeric
strip of plumbate(II) oligomer as a key intermediate. A significant finding includes quick decomposition of perovskite crystal upon
exposure to DMSO or DMF at room temperature, where the solvent molecules act as a base to remove acidic ammonium iodide
from the perovskite crystal. This observation accounts for the difficulty of the control of perovskite solar cell fabrication. Overall,
the polar solvent is indispensible to first degrade a 2–D sheet crystals of lead(II) iodide into 1–D fibrous intermediates, and then to
promotes Oswald ripening of perovskite crystals. The detailed chemical information provided here will help rationalizing the
photovoltaic device studies that have so far remained empirical, and open a new venue to a developing field of microscale lead
perovskite devices, as illustrated by fabrication of photovoltaic devices and photodetectors.
INTRODUCTION
us to fabricate microscale photovoltaic devices and
photodetectors, which show performance comparable to that
Development of solar cell (SC) devices using lead perovskite
11,18
+
–
+
–
1, 2,3,4, 5,6,7, 8,9
revitalized the
10 11
of singleꢀblock crystal device.
The high performance of
(
CH NH PbI ; MA PbI ; PV)
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these devices attests to the value of the mechanistic insights
for the development of miniature devices and for the study of
the optoelectronic properties of PV materials.
research on materials morpho6l,o12g,1y3,,14 e.g., large crystals and
oneꢀ dimensional (1ꢀD) fibers,
both of which have been
observed during conversion of a mixture of (PbI ) (PI) and
2
n
+
–
15,16
CH NH I (MAI) to PV
mediated by DMSO or DMF.
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However, the chemical origin of this diversity of morphology
has been unknown unlike similar organic fiber materials on
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which some studies have been reported. We thus became
intrigued by the reaction pathway, where a twoꢀdimensional
(2ꢀD) crystal of PI is converted to a threeꢀdimensional (3–D)
cubic lattice of PV (Fig. 1). We have isolated some new
fibrous 1–D crystalline intermediates in the PIꢀtoꢀPV
conversion and determined their crystal structure. Here we
report that 1ꢀD fibrous intermediates lie in the middle of the
whole equilibrium and connect a PI sheet and a large PV
cubic crystal through reversible participation of the polar
solvent molecules (Fig. 2aꢀf). The equilibrium is mobile in
the presence of MAI and solvent at 30–100 °C, faster in DMF
than in DMSO, but stops at the PV stage when solvent is lost
while MAI is retained. For instance, a fibrous plumbate INT-3
synthesized in DMSO (Fig. 2g) loses solvent molecules at 100
°C to produce PV as a crystalline fiber (Fig. 2h), which is
stable if solventꢀfree. However, it goes back quickly to INT-3
at room temperature upon exposure to solvent vapor, because
the solvent molecules act as a base to remove MAI molecules
from the PV crystal. This process accounts for the growth of
Figure 1. PI to PV conversion mediated by DMSO or DMF
which accompanies significant dislocation of atoms.
Crystallographic structures of PI and PV (seen along two
orthogonal directions). The scale bars are 0.5 nm.
1
–D fibers to large crystals via Ostwald ripening (Fig. 2i and
j). It also accounts for the wellꢀknown difficulty of controlling
solar cell fabrication – an adverse effect. The single crystalline
PV nanofiber obtained by the use of DMSO (Fig. 2h) allowed
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Figure 2. Pathways of PI-to-PV conversion mediated by
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DMSO. Productive pathways in the solution processed SC
fabrication are shown in bold arrows. (a-f), Sheets of PI to
cubic crystals of PV in DMSO. (g) Lowꢀlanding voltage
scanning electron microscopic (SEM) image of INT-3. (h)
SEM image of PV obtained after heating INT-3 at 100 °C. (i)
SEM image of polycrystalline PV after one solvent annealing
cycle. (j) PV crystal network formed after Ostwald ripening.
RESULTS AND DISCUSSION
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Solvent effects on chemical pathways of perovskite
formation. We first synthesized and isolated the intermediates
INT-1, 2, 3, 6, and 7 (Fig. 3; all except INT-1 were obtained
as ꢁmꢀsized fibers), occurring under the conditions of the
standard SC device fabrication as described in the Methods
section (a 30–50 wt% PI and MAI solution in DMSO or DMF
heated at 60 °C). The compounds in red boxes were
characterized by single crystal Xꢀray crystallographic analysis
for the first time in this work (INT-2 and 3) or previously
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(
INT-1, 6, and 7 ), and those in blue boxes (INT-4 and 5)
were identified by in situ Xꢀray diffraction (XRD) in this work
Fig. S1ꢀS3). Fig. 3 summarizes their reactions as revealed by
in situ 2ꢀD XRD analysis of a sample held on a loop (cf. Fig.
b). Scanning electron microscopic (SEM) images
(
3
supplemented the XRD crystallographic information.
Figure 3. Chemical reactions between PI and PV mediated by DMSO or DMF studied for isolated crystalline intermediates.
Productive pathways in the solution processed SC fabrication are shown in bold arrows. (a), DMSOꢀmediated pathways as studied
for freeꢀstanding crystals, except for steps i–iii (also steps xv, xvi) performed in solution. Detailed conditions are shown in Figs.
S1–3. (b), Optical microscopic image of an INT-3 fiber on a loop for in situ Xꢀray diffraction (XRD) experiments. (c), DMFꢀ
mediated pathways. (d), SEM image of a brittle PV fiber obtained by heating INT-7.
+
–
The reaction mediated by DMF (Fig. 3c) is mechanistically
simpler than the DMSOꢀmediated reaction and described first.
A mixture of PI and MAI in hot DMF directly produces a key
as a crystalline fiber (INT-7, (MA ) (PbI ) •DMF , step xvi),
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+
–
which easily loses DMF to produce a PV fiber (MA PbI )
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under nitrogen at 20–100 °C (step xviii). This PV fiber is
brittle and fractured as seen by SEM (Fig. 3d). The formation
–
22,23
intermediate, a diꢀnuclear plumbate (i.e., Pb(II)I )
isolated
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of INT-7 from PI was found to occur in two steps: First,
Because INT-3 ((PbI ) PbI ) needs one additional MAI
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exfoliation and truncation of a 2ꢀD sheet of PI in hot DMF
give reversibly a polymer strip of neutral (PbI ) (INT-6,
molecule to make PV (3(PbI )), heating at 100 °C produces a
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1:2 mixture of PI and PV (step vi). When INT-3 fibers are
coated with MAI, intrusion of MAI into the fibers occurs to
produce INT-4, followed by loss of two DMSO molecules to
produce PV via INT-5 (steps vii–ix). INT-4 and INT-5 were
identified by 2ꢀD XRD analysis (vide infra). The PV fiber
produced in this way from INT-3 is highly crystalline, as
supported by SEM (Fig. 2h), XRD, selectedꢀarea electron
diffraction of the fiber (SAED, Fig. S5). The INT-3ꢀtoꢀPV
conversion accompanies mechanical stiffening of the fiber and
a color change from yellow to black with a ratio of Pb:I = 1:3
(Fig. S6 and Fig. S7). Like DMF, DMSO vapor quickly
extract MAI to convert PV fiber into INT-3 fiber at 25 °C
2
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crystalline fiber, steps xv and xxi). Second, supply of MAI by
surface coating of INT-6 results in rapid ligand exchange at
2
5 °C to give INT-7 (step xvii). The PV fiber is stable at 100
°
C under nitrogen, but regenerates PI at >130 °C by loss of
MAI (step xx). Notably, under DMF vapor, the PV fiber
spontaneously regenerates INT-7 at 25 °C within 0.5 h (step
xix); that is, the DMF molecules act as a base to extract acidic
–
–
MAI molecules out of the PbI3 crystal lattice, and PbI3 is
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converted to the diꢀnuclear cluster INT-7. This process will be
+
discussed later for Fig. 4, where MA •DMF hydrogen bonding
interaction is illustrated.
(
step x). The interꢀconversion between PV and INT-3 is so
The DMSO reaction is similar to the DMF reaction except
for a few important details (Fig. 3a). A mixture of PI and MAI
in hot DMSO produces a new class of triꢀnuclear plumbate as
fast that exposure of the crystalline PV fibers to DMSO vapor
at 25 °C causes quick degradation of the fiber to powder via
INT-3, followed by Ostwald ripening of crystals, as seen in
SEM images in Fig. 2g–j.
+
–
fibers (INT-3, (MA ) [(PbI ) PbI ]•DMSO , step iii). Very
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smooth surface of the fibers is notable (Fig. 2g). The structure
was determined by single crystal analysis (Fig. 4d, e). Dropꢀ
casting on ITO and slow evaporation of the same mixture of
PI and MAI in DMSO also produces the INT-3 fibers (Fig.
S4). An entity that shows the same XRD pattern as INT-3 was
Single crystal structure analysis of Intermediates. Fig. 4a–
e, j, k shows the crystal structures of PI, INT-1, 2, 3, 6,
and 7 as viewed approximately along the (PbI ) polymer
chains (only two sets of Pb atoms are shown for clarity). All of
these structures have in common a ꢀꢀiodoꢀbridged, square
bipyramidal (PbI ) polymer chain (Fig. 4a–e, j, k). The
(PbI ) PbI structure in INT-3 is stabilized by hydrogenꢀ
bonding network of MA •DMSO (Fig. 4e). INT-7 is similarly
25
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n
+
–
previously assigned to be MA PbI •DMSO based on
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elemental analysis. INT-3 also forms in two steps from PI:
INT-1 and INT-2 are synthesized under reaction conditions of
subtle difference (see the Methods section; steps i and ii as
well as xii and xiii). When coated with MAI, monoꢀnuclear
INT-1 gives triꢀnuclear INT-3 within 30 s at 25 °C (step iv),
while diꢀnuclear INT-2 gives it more slowly (step v).
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n
–
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arranged in the crystal (Fig. 4k).
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Figure 4. Crystal structures of intermediates and their inter-conversions. Only two Pb sequences are shown for clarity. Atomic
distances in Å in crystallographic structures. The structures of INT-2 and 3 were determined in this study. (Top panel) (a) PI (Ref.
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5). (b) INT-1. (c) INT-2. (d) INT-3 seen approximately along the aꢀaxis (= fiber axis). a = 4.6216(7) Å, b = 27.455(4) Å, c =
6.933(4) Å, = 90°. (e) INT-3. (Middle panel) (f) Topological illustration from PI to INT-1 to INT-3. (g) INT-3 in Fig.
d projected onto the cubic lattice of PV in Fig. 4h. The polymer chains extend along the aꢀaxis perpendicular to the plane of the
α
= β = γ
paper. Triꢀnuclear strips move along the red arrows to form PV. (h) PV crystal lattice correlated to INT-3 in Fig. 4g. Red arrows
illustrate conversion to INT-3. (i) Top view of Fig. 4h. The (110) normal = the aꢀaxis of INT-3 (= the fiber axis). (Bottom panel) (j)
INT-6 (Ref. 20). (k) INT-7 (Ref. 21). (l) INT-7 in Fig. 4k projected onto the crystal lattice of PV in Fig. 4m. (m) PV crystal lattice
correlated to INT-7 in Fig. 4l. (n) Top view of Fig. 4m. The (110) normal = the aꢀaxis of INT-7.
+
The very facile conversion of PV back to INT-3 (step x)
suggests their topological similarity, which we can identify by
superimposing the crystal structure of INT-3 on the cubic
lattice of PV (Fig. 4 middle panel). Here, we see that the
motion of each triꢀnuclear plumbate in a pair along the red
arrow directions converts INT-3 (Fig. 4g) to PV or vice versa
PV to form MA •DMSO hydrogenꢀbonded to the triꢀnuclear
–
(PbI ) PbI of INT-3. The same applies to the correlation
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between INT-7 and PV shown in Fig. 4l–n. These processes
accompany rotation of the crystal aꢀaxis lattice of INT-3 by
ca. 45°, which was experimentally verified by 2ꢀD XRD
analysis, as described next.
15
(
Fig. 4h, i; see Fig. 1 for the experimental crystal structure of
2
-D XRD analysis of interconversion between INT-3 and
PV on which Fig. 4h and 4i were drawn). In this way, the
polymer strips of INT-3 laid along the fiber axis are zipped
together to form a cubic PV crystal with minimum atomic
motions (Fig. 2a–f). In the reverse process that occurs quickly
PV. Experimental evidence for the 45° rotation was provided
by 2ꢀD XRD analysis of freeꢀstanding fibers (cf. Fig. 3b),
which also allowed us to in situ study the PV crystal annealing
process (Fig. 5a–d for DMSO and 5e–h for DMF). Fig. 5a
shows a 2ꢀD XRD image of several parallel fibers of the
–
at 25 °C, DMSO extracts MAI from the cubic PbI3 lattice of
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PV fibers with DMSO vapor at 25 °C and with heating at 100
plumbate INT-3, where (002), (021) and (022) diffractions are
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aligned linearly, indicating that the 1ꢀD polymer axis (crystal
aꢀaxis) is parallel to the fiber axis. The PV fiber obtained by
first heating INT-3 (DMSO) in Fig. 5b shows six spots on the
(100) circle, two on the horizontal line and four with 45°
inclination. Thus, as shown in the inset (Fig. 5b), the (110)
normal runs parallel to the fiber axis (Fig. 4i), leaving two of
the axes to make 45° and the other 90° angles to the fiber axis.
°C regenerated first partially oriented INT-3 (Fig. 5c) and then
PV that shows random crystal orientation (Fig. 5d). Fig. 2i
illustrates such randomness. Regenerated INT-3 shows an
interesting feature; the INT-3 crystals have grown mainly in a
direction orthogonal to the fiber axis (cf. Fig. 5c vs. 5a); that
is, the crystals grew from the surface towards the center, as
DMSO molecules diffused from the surface.
Crystal annealing was examined next. Heating at 100 °C
converted INT-3 to PV (Fig. 5b). Sequential treatment of the
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Figure 5. Fiber XRD analyses of sequential conversion of INT-3 or -7 to PV. The reaction of a bundle of several fibers coated
with MAI (inset: lattice orientation in the fiber and BFDH simulated crystal morphology in blue). (a) INT-3 at 20 °C. (b) PV at 100
°
C after heating INT-3 at 100 °C. (c) INT-3 at 20 °C obtained by exposure of PV to DMSO vapor. (d) PV at 100 °C after heating
INT-3 at 100 °C. (e–h) The reactions of a single fiber of INT-7. e, INT-7 at 20 °C. (f) 2ꢀD XRD image of PV at 100 °C after
heating INT-7 at 100 °C, (g) INT-7 at 20 °C by exposure of PV to DMF vapor. (h) PV at 100 °C after heating INT-7 at 100 °C. (i)
Change of XRD signal intensity (2
min). (j) Time lapse of XRD signal intensity for the data in Fig. 5i, revealing intermediacy of INT-4 (red line, 2
(black line, 2
in Fig. 5k.
θ
= 5–15°) during INT-3–PV conversion (measured every 10 °C, which was maintained for 5
= 5.7°) and INT-5
θ = 7.9°). (k) The same data as Fig. 5i for INT-7–PV conversion. (l) Time lapse of XRD signal intensity for the data
θ
Similarly to DMSO, in Fig. 5e for INT-7 from DMF, we see
that the 1ꢀD polymer axis (crystal aꢀaxis) is also parallel to the
fiber axis. However, Fig 5f shows two additional spots at
upper and bottom tangential positions, indicating that it is a
ca. 1:1 mixture of crystals (inset) whose (110) normal runs
both parallel and orthogonal to the fiber axis. As to the crystal
annealing, heating/DMFꢀannealing of INT-7 rapidly
randomize the crystal orientation (Fig. 5h), indicating that
DMF is an effective solvent for production of polycrystalline
PV powder.
We consider that the difference in the crystal volume change
during conversion of INT-3 or INT-7 into PV affects the
crystal quality of PV fibers. INT-3 takes one MAI and loses
two DMSO molecules to produce PV (steps vii–ix), resulting
3
in only 13% decrease of the crystal volume (285 Å to 247
3
Å /Pb at 20 °C). On the other hand, INT-7 loses two DMF
molecules to produce PV (step xviii), resulting in a 30%
3
3
decrease (354 Å to 247 Å /Pb at 20 °C).
Temperatureꢀdependent in situ 1ꢀD XRD analysis tells us the
timeꢀcourse of the DMSOꢀmediated reaction (Fig. 5i, j). As
the ambient nitrogen temperature was increased from 20 °C to
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30 °C, INT-3 coated with MAI changes to PV in three stages
via INT-4 (2 = 5.7°) and INT-5 (2 = 7.9°) (Fig. S8). The
decrease of the smallest 2 value of 6.6° in INT-3 to 5.7° in
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INT-4 (i.e., spacing increase of ca. 0.21 nm) suggests an MAI
uptake as the first step at >30 °C, followed by loss of one
DMSO molecule to form INT-5 and another to form PV. In
contrast, the diꢀnuclear plumbate INT-7 loses DMF molecules
at >50 °C and produces PV in a single step (Fig. 5k and 5l).
Photovoltaic device and photodetectors. We describe finally
that this oriented PV fiber made from INT-3 shows excellent
optoelectronic properties as examined for photovoltaic (Fig.
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a, and Fig. S9). Made entirely free from solvent, this fiber
exhibits a high chemical stability and ohmic contact with gold
electrodes, and optoelectronic properties comparable to a
singleꢀblock crystal. In contrast, the PV fiber annealed under
DMSO vapor exposure hardly maintains its structural integrity
for device applications (cf. Fig. 2i), indicating that quality
control of the PV fiber is a worthwhile future task for
realization of PVꢀbased microdevices. Fig. 6b indicates that
the photocurrent density of the fiber device (red) is
comparable with that of a 200ꢀꢀmꢀthick perovskite blockꢀ
Figure 7. Details of single fiber photodetector. (a),
Photodetector using a single PV fiber (the width of fiber is 0.5
m and fiber length in channel is 24 ꢀm). Inset: schematic
device structure. Before testing, the device was protected by
coating CYTOP. (b), The current response of photodetector
based on fiber perovskite under different irradiance. c,
Responsivity and photocurrent/dark current ratios versus
irradiance of the photodetectors.
ꢀ
11
crystal device reported recently (blue).
We describe the photovoltaic devices in some detail. We
transferred a single fiber of INT-3 onto the silicon wafer
covered with a SiO layer (470 nm), heated them at 130 °C for
2
1
0 min under nitrogen, and finally vacuum deposited Au (50
nm) and Ag (100 nm) on fibers separated from each other by
5 ꢀm. We stabilized the device by spin coating with CYTOP
We also fabricated a photodetector on silicon wafer
covered with a SiO layer (300 nm) by depositing two parallel
2
2
1
00 nm thick Au electrodes over a single PV nanofiber
27
followed by heating at 100 °C for 30 min in N . The
2
followed by coating with a film CYTOP
(details in
characteristics of these devices summarized under irradiation
with different light intensities. The PV fiber device shows a
power conversion efficiency (PCE) of 1.35% (average 1.27%)
experimental section). The observed linearity of the current–
voltage curve at different light powers indicated ohmic contact
between the nanofibers and gold electrodes (Fig. 7). The
devise was found to show respectable responsivities of 1.1
2
at a light power of 8.1 mW/cm with a shortꢀcircuit current
2
2
2
density (J ) of 0.567 mA/cm , an openꢀcircuit voltage (V ) of
sc
oc
A/W at 8.1 mW/cm and 0.23 A/W at 194.1 mW/cm .
0
(
.65 V and a fill factor (FF) of 29.7%. Since the fiber is thin
ca. 500 nm), its contact with the electrodes is limited and the
photocurrent gradually saturated under highꢀpower light
irradiance.
CONCLUSION
We have elucidated on the crystalꢀtoꢀcrystal basis various
pathways connecting PI and PV in the presence of MAI and
DMSO or DMF – polar solvents used widely for solution
processed PV SC devices. The reaction is driven by reversible
participation of the solvent molecules, and involves
conversion of a 2ꢀD sheet crystal of PI first to 1ꢀD polymeric
–
strips of PbI and PbI3 oligomers and then to a 3ꢀD cubic PV
2
crystal. Mobile equilibria among various chemical species are
established under 100 °C until the solvent is lost from the
system by evaporation. The extreme facility of reversion of
PV back to plumbate intermediates such as INT-3 and 7
occurring even at room temperature is
a particularly
Figure 6. Lateral device using submicron PV fiber and
device characteristics. (a), Optical microscopic image of a
photovoltaic device using a single PV fiber, which is protected
by a CYTOP film of 500 nm thickness (fiber width is 0.4 ꢀm
and channel width 25 ꢀm). Inset: schematic device structure.
problematic step from the context of device fabrication, and
probably accounts for irreproducibility of device fabrication
and device longevity. This reversibility between PV and the
plumbate intermediates, however, is indispensible for the
growth of the initially formed PV fibrous crystals into larger
of PV crystals required for highꢀperformance SC devices.
Temperature higher than 130 °C regenerates PI by loss of
MAI from PV, providing another pathway of SC device
degradation. DMSO and DMF play essentially the same role
(
b), Photocurrent density of the PV fiber device (red)
compared with a device using a 200 ꢀmꢀthick singleꢀblock
crystal of PV (blue, Ref. 11).
throughout the reaction: Conversion of 2ꢀD PbI sheet to 2ꢀD
2
strips (INT-1 and INT-6) and stabilization of plumbate
+
crystals through hydrogen bonding to the MA molecules
(e.g., Fig. 4e). Solvent choice is critical, however, because
different solvents cause different crystallographic conversions
(Fig. 5), and hence affect the morphology and stability of
intermediates. As a consequence, DMSO but not DMF
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Journal of the American Chemical Society
The fiber was kept under nitrogen atmosphere during
produces oriented crystalline PV fibers that serve as a stable
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and highꢀperformance active material for miniature
optoelectronic devices such as photovoltaic and
photodetecting devices.
measurement. A heater attached to the nitrogen generator
controlled the temperature. Image acquisition took 5 min (3
min for exposure, 2 min for IP reading).
For the fibers coated with MAI and DMSO, first, a bundle of
fibers was removed from the mother liquor by tweezers and
put on a glass slide. Then a sample loop was used to pick up
multiple fibers without removing liquid from their surface and
mounted on a goniometer.
EXPERIMENTAL SECTION
Materials. PbI (99.999% purity) was purchased from Strem
2
Chemicals, Inc. and used without further purification. MAI
was prepared by using the procedure reported in Ref. 2.
For fibers without MAI and DMSO, first, a sample loop was
used to pick up a single fiber. To remove liquid from the
surface, the fiber was dipped in a droplet of dichloromethane
and then mounted on a goniometer.
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Preparation of INT-1 (mono-nuclear strips of (PbI ) ,
2
n
PbI •DMSO ). A 30 wt% PbI solution was prepared by
2
2
2
adding PbI (448 mg) to DMSO/γꢀbutyrolactone (GBL) (1.0
2
mL, 3:7 vol/vol ratio) and stirred for 12 h at 60 °C. The
solution was then cooled to room temperature to obtain
crystals of INT-1.
The conversion from INT-3 to PV was performed in the
following manner. INT-2 fibers were put on a glass slide
without removing solvent surrounding them. The sample was
left under ambient conditions until most of the solvent
evaporated (for 2 h) to obtain INT-3 fibers covered with MAI.
A bundle of fibers aligned in the same direction was then
taken by a sample loop and mounted on a goniometer. INT-3
fibers were heated from 20 °C to 100 °C with an interval of 5
min for each 10 °C. Conversion to PV was completed around
Preparation of INT-2 (di-nuclear strips of (PbI ) ,
2
n
(
PbI ) •DMSO ). A 40 wt% PbI /MAI solution was prepared
2 2 2 2
by adding PbI (555 mg) and MAI (192 mg) in DMSO/GBL
2
(1.0 mL, 3:7 vol/vol ratio) and stirred for 12 h at 60 °C. The
solution was cooled to room temperature, and 10–20 vol% of
toluene added to obtain fibers of INT-2.
0
.5 h after the temperature reached 100 °C. The conversion
Preparation of INT-3 (tri-nuclear strips of (PbI ) coꢀ
2
n
quickly finished at 130 °C.
+
ordinated by two iodide ions, (MA ) [(PbI ) PbI ]•DMSO ). A
2
3 2
2
2
The conversion from INT-7 to PV was studied in a similar
manner as for INT-3–PV conversion. INT-7 fibers were
prepared directly from solution. A single INT-7 fiber was
heated from 20 °C to 100 °C with an interval of 5 min for each
50 wt% PbI /MAI solution was prepared by adding PbI2
2
(833 mg) and MAI (287 mg) in DMSO/GBL (1.0 mL, 3:7
vol/vol ratio) and stirred for 12 h at 60 °C. The solution was
cooled to room temperature to obtain fibers of INT-3.
1
0 °C. The conversion completed when the temperature
Preparation of INT-6 (di-nuclear strips of (PbI ) ,
2
n
reached 100 °C.
(
PbI ) •DMF ). A 30 wt% PbI solution was prepared by
2 2 2 2
For the vaporꢀtreatment experiment, the PV fiber sample was
prepared from INT-3 or INT-7 as described above. The PV
fiber sample was kept for 0.5 h under nitrogen saturated with
DMSO or DMF vapor. The fiber XRD measurement was
performed at 20 °C. Conversion to PV finished at 100 °C.
adding PbI (405 mg) to DMF (1.0 mL) and stirred for 12 h at
2
6
0 °C. The solution was then cooled to room temperature to
obtain fibers of INT-6.
Preparation of INT-7 (di-nuclear strips of (PbI ) co-
2
n
+
–
ordinated by two iodide ions, (MA ) (PbI ) •DMF ). A 50
2
3
2
2
Preparation of photovoltaic device and photodetector. A
lateral photovoltaic device or photodetector using PV fiber
wt% PbI /MAI solution was prepared by adding PbI (702 mg)
2
2
and MAI (242 mg) in DMF (1.0 mL) and stirred for 12 h at
0 °C. The solution was cooled to room temperature to obtain
was fabricated on a silicon wafer covered with a SiO layer
2
6
(470 nm). Two parallel asymmetric (Au and Ag) or symmetric
(Au only) metal electrodes were vacuum deposited on a single
PV fiber made from an INT-3 fiber (without washing) heating
at 130 °C/10 min. A MAXꢀ303 xenon lamp (VIS) light source
from ASAHI SPECTRA illuminated the photovoltaic device
and photo detector from the top of the device. The value of
photocurrent density in Figure 6 refers to the short circuit
current density of the device.
fibers of INT-7.
Crystallographic analysis of single crystals INT-1–3. The
diffraction images for Xꢀray crystallographic analysis were
collected on a Rigaku Rapid II diffractometer equipped with
an imaging plate (IP) using Cu Kα (λ = 1.5419 Å) radiation.
For crystallographic analysis, the sample was removed from
the mother liquor and put onto a glass slide. A crystal was
chosen and then it was put on and taken off from a glass slide
several times to remove liquid from its surface.
The photodetector showed respectable photoresponse
characteristics, working at a voltage below 2 V with dark
current of 0.04 nA. Responsivity (R) was calculated by
following equation:
R = (Ilight − Idark)/Plight
(1)
The Cambridge Crystallographic Data Centre (CCDC), nos.
where Ilight is photocurrent and Idark is the dark current in
1
063982, 1063983, 1064049, 1415480 and 1415481, contains
amperes, and the incident light power in watts Plight (Plight
=
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from CCDC via
www.ccdc.cam.ac.uk/data_request/cif.
Irradiance × S, S is the area of active materials. S=W×L, W is
width of the fiber and L is length between two electrodes.
Fiber XRD diffraction analyses. The diffraction images for
fiber Xꢀray analyses were collected on a Rigaku Rapid II
ASSOCIATED CONTENT
Supporting Information. Details of XRD analysis and device
fabrication are supplied as Supporting Information. This
material is available free of charge via the Internet at
http://pubs.acs.org.
diffractometer equipped with an IP using Cu Kα (
λ
= 1.5419 Å)
radiation. Diffraction images were taken under the following
conditions. Exposure time: 1 s/°, d : 180°. The fiber was
placed with its fiber axis perpendicular to the horizontal line.
ω
AUTHOR INFORMATION
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Journal of the American Chemical Society
Page 8 of 8
Corresponding Author
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*Email: nakamura@chem.s.uꢀtokyo.ac.jp.
(
20) Wakamiya, A.; Endo, M.; Sasamori, T.; Tokitoh, N.; Ogomi, Y.;
Hayase, S.; Murata, Y. Chem. Lett. 2014 43, 711–713.
,
Author Contributions
(
21) Hao, F.; Stoumpos, C. C.; Liu, Z.; Chang, R. P. H.; Kanatzidis, M.
‡
These authors contributed equally.
G. J. Am. Chem. Soc. 2014
,
136, 16411–16419.
(
(
22) Møller, C. K. Nature 1958
,
182 (4647), 1436–1436.
23) Chung, I.; Song, J.ꢀH.; Im, J.; Androulakis, J.; Malliakas, C. D.;
Notes
Li, H.; Freeman, A. J.; Kenney, J. T.; Kanatzidis, M. G. J. Am.
The authors declare no competing financial interests.
Chem. Soc. 2012
24) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S.
I. Nat Mater 2014 13 (9), 897–903.
25) Terpstra, P.; Westenbrink, H. G. Proceedings of the Koninklijke
Nederlandse Academie van Wetenschappen 1926 29, 431–442.
26) Beckmann, P. A. Cryst. Res. Technol. 2010 45, 455–460.
27) Guo, Y.; Liu, C.; Tanaka, H.; Nakamura, E. J. Phys. Chem. Lett.
2015 , 535–539.
, 134 (20), 8579–8587.
ACKNOWLEDGMENT
(
(
,
We thank MEXT for financial support [KAKENHI 15H05754
and CREST, JST to E.N., and “Nanotechnology Platform”
(No. 12024046)]. Y.G. thanks Strategic Promotion of
Innovative Research, JST, K.S. thanks the Japan Society for
the Promotion of Science for Leading Graduate Schools
(MERIT), and K.I. for Advanced Leading Graduate Course for
Photon Science (ALPS).
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