Transformative Evolution of Organolead Triiodide Perovskite Thin Films from Strong Room-Temperature Solid-Gas Interaction between HPbI3-CH3NH2 Precursor Pair

Article abstract of DOI:10.1021/jacs.5b11824

We demonstrate the feasibility of a nonsalt-based precursor pair - inorganic HPbI₃ solid and organic CH₃NH₂ gas - for the deposition of uniform CH₃NH₃PbI₃ perovskite thin films. The strong room-temperature solid-gas interaction between HPbI₃ and CH₃NH₂ induces transformative evolution of ultrasmooth, full-coverage perovskite thin films at a rapid rate (in seconds) from nominally processed rough, partial-coverage HPbI₃ thin films. The chemical origin of this behavior is elucidated via in situ experiments. Perovskite solar cells, fabricated using MAPbI₃ thin films thus deposited, deliver power conversion efficiencies up to 18.2%, attesting to the high quality of the perovskite thin films deposited using this transformative process.

Full text of DOI:10.1021/jacs.5b11824

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Communication
Transformative Evolution of Organolead Triiodide Perovskite
Thin Films from Strong Room-Temperature Solid-
Gas Interaction between HPbI3-CH3NH2 Precursor Pair
Shuping Pang, Yuanyuan Zhou, Zaiwei Wang, Mengjin Yang, Amanda
R Krause, Zhongmin Zhou, Kai Zhu, Nitin P Padture, and Guanglei Cui
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b11824 • Publication Date (Web): 05 Jan 2016
Downloaded from http://pubs.acs.org on January 6, 2016
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Transformative Evolution of Organolead Triiodide Perovskite
Thin Films from Strong Room-Temperature Solid-Gas Interac-
tion between HPbI -CH NH Precursor Pair
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Shuping Pang , Yuanyuan Zhou , Zaiwei Wang , Mengjin Yang , Amanda R. Krause , Zhongmin Zhou , Kai Zhu ,
‡,*
†,*
Nitin P. Padture , Guanglei Cui
†
Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P.R. China
School of Engineering, Brown University, Providence, RI 02912, United States
Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, CO 80401, United States
‡
¶
Supporting Information Placeholder
ABSTRACT: We demonstrate here the feasibility of a non-salt-
based precursor pair — inorganic HPbI3 solid and organic
CH NH gas — for the deposition of uniform CH NH PbI perov-
3
2
3
3
3
skite thin films. The strong room-temperature solid-gas interac-
tion between HPbI and CH NH induces transformative evolution
3
3
2
of ultrasmooth, full-coverage perovskite thin films at a rapid rate
(in seconds) from nominally-processed rough, partial-coverage
HPbI thin films. The chemical origin of this behavior is elucidat-
3
ed via in situ experiments. Perovskite solar cells fabricated using
MAPbI thin films thus deposited deliver power conversion effi-
3
ciencies up to 18.2%, attesting to the high quality of the perov-
skite thin films deposited using this transformative process.
Since the use of methylammonium lead triiodide (CH NH PbI
3
3
3
or MAPbI ) perovskite as the light absorber material in solar cells
3
1
by Miyasaka and co-workers in 2009, the power conversion effi-
ciency (PCE) of perovskite solar cells (PSCs) has shot up rapidly
2
within a short period of time. The rapid advances in PSCs are
enabled by enhanced control over the formation of uniform MAP-
3,4
bI absorber films via myriad processing methods. In particular,
3
the sequential deposition method, where the formation of the
MAPbI occurs by reaction between the organic precursor with
3
the pre-deposited inorganic precursor counterpart, has gained
4
wide popularity. Unprecedented amount of effort has been devot-
ed to developing this method, and its variations, for improving the
quality of resultant MAPbI films, but it has yielded mixed re-
3
4-6
sults. All this effort invariably involves precursor pairs consist-
ing of an inorganic lead salt and an organic methylammonium
4-6
Figure 1. (A) XRD pattern from HPbI3 powder and the Pawley fit. (B) HR-
TEM image of HPbI deposited on the TEM grid directly. (C) XRD pattern
from MAPbI powder converted from the HPbI powder after CH NH -gas
treatment and the Pawley fit. (D) HR-TEM image of MAPbI converted from
salt, with the PbI -MAI pair being the most typical example.
2
3
The reaction, PbI + MAI → MAPbI , involves the formation of
2
3
3
3
3
2
new Pb-I bonds towards the construction of the 3D perovskite
3
structure, and it is regarded as a neutralization reaction of the
the HPbI
of crystallographic conversion from HPbI
CH NH
3
from Fig. 1B after CH
3
NH
2
-gas treatment. (E) Schematic illustration
7
to MAPbI upon reaction with
3
electrophile (acid) PbI with the nucleophile (base) MAI, but the
3
2
3
2
.
acidity/basicity of these two salts are low. Thus, the mutual inter-
action between salts-based precursors is expected to be relatively
weak. Also, the insertion kinetics of MAI species into 2D layered
These considerations provide the motivation for discovering
new precursor pairs that: (i) exhibit strong mutual interaction, (ii)
enhance perovskite-crystallization kinetics, and (iii) avoid the use
of liquid solvents. In this context, inspection of the stoichiometry
4-
PbI6 octahedral arrays of PbI , especially in its bulk form, is
2
sluggish considering the long diffusion pathways and the recon-
structive nature of the 2D → 3D structural transformation. Fur-
thermore, the use of certain solvents (e.g. isopropanol) usually
associated with this process have a detrimental effect on the mor-
of MAPbI
hydrogen lead triiodide (HPbI
methylamine gas (CH NH ) as the organic component. The syn-
thesis of HPbI was first reported by Zhao et al., but in this study
suggests a new possible precursor pair consisting of
3
) as the inorganic component and
3
3
2
4,5
8
phology of the final perovskite films.
3
1
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we have used an antisolvent-crystallization method (described in
gas at room temperature, the liquid drop gradually crystallizes
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the Supporting Information (SI)) based on stoichiometric PbI /HI
into MAPbI perovskite (30 min), as confirmed by XRD in Fig.
2
3
precursors for obtaining excellent quality HPbI crystals. Pawley
1C. Since HPbI , the intermediate liquid phase, and MAPbI per-
3
3
3
fitting of the X-ray diffraction (XRD) pattern of these HPbI crys-
ovskite have obviously distinct PL responses, in situ PL micros-
copy is an ideal tool for following the evolution of these phases
3
tals (powder) in Fig. 1A shows an orthorhombic (space group
P6 mc) structure with lattice parameters a=b=8.765(1) Å,
during the reaction in thin films. Here, HPbI dissolved in DMF
3
3
c=8.177(2) Å. This is further supported by the high-resolution
transmission electron microscopy (HR-TEM) image of HPbI3,
solution-deposited onto a TEM grid directly, shown in Fig. 1B.
The lattice fringes with interplanar distance of 0.62 nm can be
solvent is spin-coated (60 wt%, 6000 rpm, 20 s) onto a glass sub-
strate, and heated (150 ˚C, 2 min) to form a HPbI thin film. In
3
Fig. 2B (left), which is an optical image with superimposed PL
map, the initial as-synthesized HPbI film shows highly heteroge-
3
assigned to (110) planes of the orthorhombic HPbI crystal. (Note
neous morphology and incomplete coverage, and as expected no
PL emission is observed within the detection limit. Upon expo-
sure to CH NH gas at room temperature for 2 s (Fig. 2B center)
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that the H atom that is intercalated into the orthorhombic crystal is
not considered for the symmetry here; more detailed characteriza-
tion is underway for further elucidation of the complete crystal
structure of HPbI .) The other precursor in the new pair, CH NH ,
3
2
the HPbI grains have disappeared showing null optical contrast
3
and PL signal that of a non-luminescent liquid. Upon degassing
3
3
2
has a boiling point of -6.8 ˚C and is a gas at room temperature.
for 2 s (Fig. 2B right) a strongly luminescent MAPbI film readily
3
Thus, to demonstrate the feasibility of MAPbI perovskite for-
appears with uniform coverage on the substrate. The MAPbI3
perovskite phase in that film is confirmed by XRD (Fig. S2),
which shows strong absorption in the UV-vis spectrum (Fig. S3).
The intermediate liquid phase is clearly the result of the strong
interaction between HPbI solid and CH NH gas, and its amor-
3
mation using this new precursor pair, the solid HPbI powder is
3
simply exposed to the CH NH gas, and is then removed from the
3
2
gas. The light yellow HPbI powder is converted into a black
3
phase when this process is complete. The Pawley fit of the XRD
pattern (Fig. 1C) of the resultant black phase confirms tetragonal
MAPbI3 perovskite (space group I4/mcm; lattice parameters
a=b=8.873(1) Å, c=12.662(1) Å). The HR-TEM images in Fig.
3
3
2
phous structure and transparent nature are revealed by XRD and
UV-vis in Fig. S4, respectively. Through careful weighing of the
initial HPbI powder and the liquid (Fig. S5A) it is determined
3
1
D shows lattice fringes with interplanar distance of 0.44 nm,
that the liquid contains ~4.5 CH NH per HPbI . From stoichiom-
3
2
3
corresponding to (112) or (020) planes in MAPbI perovskite.
etry considerations, this is reminiscent of the MAPbI •xCH NH
3
3 3 2
These results clearly show the conversion of HPbI crystalline
(x~3.5) intermediate liquid phase that forms when MAPbI solid
3
3
phase to MAPbI perovskite with CH NH -gas treatment.
uptakes CH NH gas molecules via “metastable” interaction in
3
3
2
3
2
10
our previous report. It is observed (Fig. S6) that such CH NH -
The possible crystallographic conversion mechanism from
HPbI to MAPbI is shown schematically in Fig. 1E. The pseudo-
3
2
uptake behavior does not occur when the MAPbI is heated to an
3
3
3
elevated temperature (150 ˚C), indicating that ‘metastable’ inter-
action observed at room temperature is unfavorable at 150 ˚C.
Therefore, a set of control in situ optical and PL microscopy ex-
periments were conducted at 150 ˚C to gain insight into the origin
of the ~4.5 CH NH uptake per HPbI at room temperature.
3D crystal structure of HPbI consists of arrays of 1D face-shared
3
4-
+
PbI6 octahedra with intercalated protons (H ) for charge balance.
Upon exposure to CH NH gas, the CH NH molecules readily
react with H via the reaction, CH NH + H → CH NH , with
enhanced affinity toward the 1D face-shared PbI octahedra
3
2
3
2
+
+
+
3
2
3
3
4
-
3
2
3
6
4
-
chains. Once the adjacent 1D PbI6 octahedra chain come close
2+
-
enough to each other, the Pb cation from each array share an I
+
anion to form a linear Pb-I-Pb bond. As a result, the H -
intercalated 1D structure with face-shared PbI6 octahedra transi-
tions into 3D perovskite structure with corner-shared PbI6 octa-
hedra. It is obvious that H plays an important role in the stoichi-
4
-
4-
+
ometric formation of MAPbI perovskite, which is further sup-
3
ported by the fact that stable perovskite phase could not be formed
using a KI-PbI system instead of HPbI (see Fig. S1).
2
3
The new HPbI -CH NH precursor pair for the formation of
3
3
2
MAPbI perovskite has the following unique characteristics, as
3
compared with the conventional PbI -MAI precursor pair. First,
2
the perovskite formation is driven by the strong acid-base interac-
+
tion between H with the CH NH . Second, the gaseous nature of
3
2
CH NH allows highest contact area with the HPbI solid precur-
3
2
3
4
sor and facilitates the reaction, precluding the need for solvents
or thermally-induced ionization that are typically needed for
making the MAI phase more reactive in salt-based precursor
6
pairs. Finally, in the HPbI structure, Pb-I bonds are fully formed,
3
whereas the intercalation reaction of PbI with MAI entails the
2
formation of new Pb-I bonds in the conventional precursor pair
10
case. Thus, a near-topotactic conversion of the HPbI crystal
3
Figure 2. In situ optical microscopic observation of the morphological
evolution of a HPbI crystal during interaction with CH NH gas: (A) at
room temperature (RT) and (C) at 150 ˚C. In situ PL maps (superimposed
on optical microscopic images) of HPbI thin film during interaction with
CH NH gas: (B) at RT and (D) at 150 ˚C. The elapsed time is indicated.
structure to MAPbI perovskite occurs, as illustrated in Fig. 1E.
3
3
3
2
In order to gain insight into the details of the HPbI -to-MAPbI3
3
phase conversion process and the associated morphological evolu-
tion, a combination of in situ optical and photoluminescence (PL)
microscopies is used. Figure 2A shows the evolution of a rod-like
HPbI crystal (typical morphology for solution-grown HPbI ) into
3
3
2
Figure 2C shows the morphological evolution of a HPbI crys-
3
3
3
tal upon treatment of CH NH at 150 ˚C using optical microscopy.
3
2
a MAPbI particle using optical microscopy. Upon exposure to
It can be seen the HPbI crystal darkens progressively upon expo-
3
3
CH NH gas at room temperature for 5 min, the HPbI crystal
sure to CH NH , (Fig. 2C), but even after 30-min exposure there
3
2
3
3
2
gradually turns into a liquid phase. Upon removal of the CH NH2
is no formation of liquid or change in the morphology of the crys-
3
2
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tal. The corresponding results from the HPbI thin film are pre-
3
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sented in Fig. 2D. Upon exposure to CH NH gas at 150 ˚C for 5 s
3 2
(Fig. 2D, center) some PL signal is observed. After 20 s (Fig. 2D,
3
right) all the HPbI grains in the film have transformed to MAPbI3
without significant change in the film morphology — the PL map
mirrors the heterogeneity and the partial coverage of the initial
HPbI thin film. The XRD pattern (Fig. S7) and UV-vis absorp-
3
tion spectrum (Fig. S3) of the resultant film confirm MAPbI3
5
perovskite phase. The striking contrast between the homogenous,
full-coverage morphology of the final MAPbI thin films obtained
3
by room-temperature CH NH -gas treatment (Fig. 2B, right) and
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the heterogeneous, partial-coverage morphology obtained at 150
C (Fig. 2D, right) indicates that the MAPbI perovskite recon-
˚
3
struction via the MAPbI -CH NH ‘metastable’ interaction does
3
3
2
not occur in the latter. This is also supported by the distinct crys-
tallographic characteristics (texture, etc.) of the two MAPbI films
3
as revealed by the XRD patterns (Figs. S2 and S7). Thus, at ele-
vated temperature, only 1 CH NH is uptaken per HPbI , resulting
3
2
3
in the formation of a stoichiometric MAPbI perovskite via stable
3
ionic/covalent interaction (Rxn. 1). This is further supported by
careful weighing experiments (Fig. S5B). Therefore, the 4.5
CH NH uptaken by HPbI at the CH NH -exposure stage at room
Figure 4. SEM images of the starting rough, partial-coverage HPbI
film (A, B) and the corresponding converted smooth, full-coverage MAP-
bI thin film after CH NH treatment at RT (D, E). AFM images of the
starting rough, partial-coverage HPbI thin film (C) and the corresponding
converted smooth, full-coverage MAPbI thin film after CH NH treat-
ment at RT (E).
3
thin
3
2
3
3
2
temperature includes two parts: 1 CH NH that is responsible for
3
2
3
3
2
the stoichiometric formation of MAPbI nuclei and 3.5 CH NH
3
3
2
3
that rapidly ‘melts’ the as-nucleated MAPbI perovskite. As the
3
3
3
2
CH NH -uptake behavior occurs at the molecular scale, these two
3
2
parts appear to occur simultaneously (Fig. 2A-B), resulting in the
formation of the intermediate MAPbI3 3.5CH NH liquid phase,
where the excess 3.5 CH NH is subsequently released upon de-
Figures 4A-4B are scanning electron microscope (SEM) imag-
es showing the top-surface morphology of the as-deposited HPbI3
film at low and high magnifications, respectively. The poor quali-
•
3
2
3
2
gassing due to the ‘metastable’ nature of the original 3.5 CH NH2
3
ty of the HPbI film with only ~50% coverage is clearly evident in
3
uptake (Rxn. 2).
Figs. 4A-4B. (The underlying substrate is visible in Fig. 4B top-
left corner. The atomic force microscope (AFM) 3D image in Fig.
HPbI
HPbI
→ MAPbI
3
(s)+CH
(s) + (1+x) CH
(s)+ xCH
2
NH
2
(g) → MAPbI
NH (g) → MAPbI
NH (g)
3
(s)
(1)
3
3
2
3
•xCH
3
NH
2
(l)
4
C confirms the rough surface, with a high root-mean-square
(RMS) roughness of ~180 nm. After CH NH -gas exposure for 2
3
3
2
(2
)
3
2
s at room temperature followed by degassing for 2 s, the convert-
ed MAPbI perovskite film appears remarkably uniform and full-
3
coverage in the top-surface SEM image in Fig. 4D. The higher
magnification SEM image in Fig. 4E shows uniform microstruc-
ture of MAPbI grains. The inset in Fig. 4E is an AFM top-view
3
image of a local area confirming the smoothness of the film. The
AFM 3D image in Fig. 4F further demonstrates the uniform mor-
phology and the smoothness (RMS roughness ~6 nm) of the
2
MAPbI perovskite film over a 20×20 µm area. This confirms
3
that the morphology of the resulting MAPbI perovskite is nearly
3
independent of the morphology of the nominally-processed HPbI3
solid precursor film, which is the direct result of the underlying
transformative film-evolution mechanism illustrated in Fig. 3.
PSCs were then fabricated using the MAPbI perovskite thin
Figure 3. Schematic representation of the room-temperature formation of
ultrasmooth, full-coverage MAPbI perovskite film from the interaction of
rough, partial-coverage HPbI thin film with CH NH gas
3
films deposited using the method described above. Cross-
sectional SEM image of a typical PSC (fractured) is shown in Fig.
3
3
3
2
.
5
A. The various layers are visible in that micrograph, and are
The room-temperature interaction between the nanoscale film
of HPbI and the CH NH gas occurs within seconds (Rxn. 2),
labeled as such: glass/FTO, c-TiO , meso-TiO /MAPbI perov-
2
2
3
3
3
2
skite, MAPbI perovskite (capping layer), hole-transporting mate-
3
which opens up a remarkable opportunity to form ultrasmooth
rial (HTM), and Ag top contact. The mesoporous TiO layer is
2
MAPbI perovskite thin films using this facile chemical route, as
3
tightly infiltrated with the fully-converted phase-pure perovskite
shown schematically in Fig. 3. First, upon simple exposure to
CH NH gas, the nominally solution-deposited HPbI film (rough,
(Fig. S8) forming a bi-continuous structure with a dense perov-
3
2
3
skite capping layer, as shown in Fig. S9. Current density (J) -
voltage (V) responses in Fig. 5B from the champion PSC (cell
partial coverage) uptakes (1+x) CH NH , converting it into a
3
2
smooth ‘liquid’ film of MAPbI •xCH NH that spreads over the
3
3
2
2
area 0.12 cm ) shows PCE of 16.4% and 18.2% in forward and
whole substrate. This step is the result of the ‘shape-preserved’
perovskite formation with 1 CH NH uptake, followed rapidly by
reverse scan, respectively, under one sun illumination (AM 1.5G,
3
2
-2
1
00 mW.cm ). Since the typical J-V hysteresis is observed, stabi-
perovskite ‘melting’ process with excess x CH NH uptake (indi-
3
2
lized PCE and J output at maximum power point (MPP) were
measured over a period of 100 s under continuous one sun illumi-
nation, and are plotted in Fig. 5C; a stable PCE of ~17.1% and J
cated by dashed arrows in Fig. 3). Upon the removal of CH NH2
3
atmosphere, supersaturation occurs rapidly with the release of x
CH NH , resulting in the crystallization of the ultrasmooth stoi-
3
2
-2
1
2
of 19.5 mA.cm are reported. The external quantum efficiency
chiometric MAPbI perovskite thin film.
3
measurement (Fig. S10) shows an integrated current density con-
3
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sistent with the J . The PCE of small-area (0.12 cm ) PSCs
age technology; Y.Z., A.R.K. and N.P.P acknowledge the support
SC
1
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shows a tight distribution (Table S1). Figure 5D shows J-V re-
sponse for a large-area PSC (1.17 cm ) with a PCE of 14.5% (see
from the National Science Foundation (award nos. DMR-1305913
and OIA-1538893) for the work performed at Brown University;
and M.Y. and K. Z. acknowledge the support from the U.S. De-
partment of Energy SunShot Initiative under the Next Generation
Photovoltaics 3 program (DE-FOA-0000990) for the work per-
formed at the National Renewable Energy Laboratory (contract
no. DE-AC36-08-GO28308)
2
Fig. S11 for the MPP stabilized J and PCE output), which is close
1
3
to the-state-of-the-art square-centimeter area PSCs, attesting to
scalability of this MAPbI perovskite thin films deposition meth-
3
od based on HPbI -CH NH precursor pair.
3
3
2
REFERENCE
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3) (a) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu,
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Phys. Chem. Lett. 2014, 5, 4175; (e) Xiao, M.; Huang, F.;
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A.; Bach, U.; Cheng, Y.-B.; Spiccia, L. Angew. Chem. Intl.
Ed. 2014, 53, 9898;
Figure 5. (A) Cross-sectional SEM of a typical PSC (fractured) fabricat-
ed using the HPbI -CH NH precursor-pair based deposition method. (B)
3
3
2
J-V responses under forward and reverse scans and (C) maximum-power-
point stabilized PCE and JSC. (D) J-V response and photovoltaic parame-
2
ters of large-area ‘champion’ PSC (1.17 cm cell area)
.
(
4) Burschka, J.; Pellet, N.; Moon, S.-J.; Humphrey-Baker, R.;
Gao, P.; Nazeeruddin, M. K.; Grätzel, M. Nature 2013, 499,
316;
In closing, we have observed a strong room-temperature solid-
gas interaction behavior between the HPbI -CH NH precursor
3
3
2
pair, which shows promise for the deposition of high-quality
(5) (a) Xiao, Z.; Bi, C.; Shao, Y.; Dong, Q.; Yuan, Y.; Wang,
C.; Gao, Y.; Huang, J. Energy Environ. Sci. 2014, 7, 2619.
(b) Zhou, Y.; Yang, M.; Vasiliev, A. L.; Garces, H. F.;
Zhao, Y.; Wang, D.; Pang, S.; Zhu, K.; Padture, N. P. J.
Mater. Chem. A 2015, 3, 9249; (c) Kutes, Y.; Ye, L.; Zhou,
Y.; Pang, S.; Huey, B. D.; Padture, N. P. J. Phys. Chem.
Lett. 2014, 5, 3335;
(6) (a) Chen, Q.; Zhou, H.; Hong, Z.; Luo, S.; Duan, H.-S.;
Wang, H.-H.; Liu, Y.; Li G.; Yang, Y. J. Am. Chem. Soc.
2014, 136, 622. (b) H. Hu, D. Wang, Y. Zhou, J. Zhang, S.
Lv, S. Pang, X. Chen, Z. Liu, N. P. Padture, G. Cui, RSC
Adv. 2014, 4, 28964.
(7) (a) Ahn, N.; Son, D.-Y.; Jang, I.-H.; Kang, S. M.; Choi, M.;
Park, N.-G. J. Am. Chem. Soc. 2015, 137, 8696; (b) Wang,
Z.; Zhou, Y.; Pang, S.; Xiao, Z.; Zhang, J.; Chai, W.; Xu,
H.; Liu, Z.; Padture, N. P.; Cui, G. Chem. Mater. 2015, 27,
7149.
MAPbI perovskite thin films for high-PCE PSCs. This strong
3
precursor interaction results in ultrasmooth, full coverage MAPbI3
perovskite thin films, which is virtually independent of the poor
morphology of the starting HPbI precursor films, making this
3
deposition process highly robust. The chemical origins responsi-
ble for the transformative evolution of MAPbI perovskite thin
3
films are elucidated. This study highlights the significance of
precursor-interaction chemistry in the formation of high-quality
hybrid perovskite thin films, which is playing a central role in the
scalable production of high-PCE PSCs of the future.
ASSOCIATED CONTENT
Supporting Information
Experimental procedures and additional results are included in SI.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(8) Wang, F.; Yu, H.; Xu, H.; Zhao, N. Adv. Funct. Mater.
2
015, 25, 1120.
AUTHOR INFORMATION
Corresponding Authors
(9) Shi, D.; Adinofi, V.; Comin, R.; Yuan, M.; Alarousu, E.;
Buin, A.; Chen, Y.; Hoogland, S.; Rosenberger, A.; Katsiev,
K.; Losovyj, Y.; Zhang, X.; Dowben, P. A.; Mohammed, O.
F.; Sargent, E. H.; Bakr, O. M. Science 2015, 347, 519.
kai.zhu@nrel.gov (K.Z.); nitin_padture@brown.edu (N.P.P.);
cuigl@qibebt.ac.cn (G.C.).
(
10) Clarke, J. B.; Hastie, J. W.; Kihlborg, L. H. E.; Metselaar,
R.; Thackeray, M. M. Pure &Appl. Chem. 1994, 66, 577.
11) Zhou, Z.; Wang, Z.; Zhou, Y.; Pang, S.; Wang, D.; Xu, H.;
Liu, Z.; Padture, N. P.; Cui, G. Angew. Chem. Int. Ed. 2015,
Author Contributions
(
#
These authors contributed equally
Notes
5
4, 9705.
The authors declare no competing financial interests.
(12) Zhou, Y.; O. S. Game; S. Pang; Padture, N. P. J. Phys.
Chem. Lett. 2015, 6, 4827.
ACKNOWLEDGMENT
(
13) (a) Yang, M.; Zhou, Y.; Zeng, Y.; Jiang, C.-S.; Padture, N.
P.; Zhu, K. Adv. Mater. 2015, 27, 6363; (b) Chen, W.; Wu,
Y.; Yue, Y.; Liu, J.; Zhang, W.; Yang, X.; Chen, H.; Bi, E.;
Ashraful, I.; Grätzel, M.; Han, L. Science, 2015, 350, 944.
S.P., Z.W, Z.Z. and G.C. acknowledge the support from the Inter-
national S&T Cooperation Program of China (2015DFG62670),
the Youth Innovation Promotion Association of CAS (2015167),
the Qingdao Key Lab of solar energy utilization and energy stor-
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Figure 1. (A) XRD pattern from HPbI3 powder and the Pawley fit. (B) HR-TEM image of HPbI3 deposited on
the TEM grid directly. (C) XRD pattern from MAPbI3 powder converted from the HPbI3 powder after
CH3NH2-gas treatment and the Pawley fit. (D) HR-TEM image of MAPbI3 converted from the HPbI3 from
Fig. 1B after CH3NH2-gas treatment. (E) Schematic illustration of crystallographic conversion from HPbI3 to
MAPbI3 upon reaction with CH3NH2.
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Figure 2. In situ optical microscopic observation of the morphological evolution of a HPbI3 crystal during
interaction with CH3NH2 gas: (A) at room temperature (RT) and (C) at 150 ˚C. In situ PL maps
superimposed on optical microscopic images) of HPbI3 thin film during interaction with CH3NH2 gas: (B) at
RT and (D) at 150 ˚C. The elapsed time is indicated.
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Figure 4. SEM images of the starting rough, partial-coverage HPbI3 thin film (A, B) and the corresponding
converted smooth, full-coverage MAP-bI3 thin film after CH3NH2 treatment at RT (D, E). AFM images of the
starting rough, partial-coverage HPbI3 thin film (C) and the corresponding converted smooth, full-coverage
MAPbI3 thin film after CH3NH2 treat-ment at RT (E).
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