Planar heterojunction perovskite solar cells via vapor-assisted solution process

Article abstract of DOI:10.1021/ja411509g

Hybrid organic/inorganic perovskites (e.g., CH₃NH ₃PbI₃) as light absorbers are promising players in the field of third-generation photovoltaics. Here we demonstrate a low-temperature vapor-assisted solution process to construct polycrystalline perovskite thin films with full surface coverage, small surface roughness, and grain size up to microscale. Solar cells based on the as-prepared films achieve high power conversion efficiency of 12.1%, so far the highest efficiency based on CH ₃NH₃PbI₃ with the planar heterojunction configuration. This method provides a simple approach to perovskite film preparation and paves the way for high reproducibility of films and devices. The underlying kinetic and thermodynamic parameters regarding the perovskite film growth are discussed as well.

Full text of DOI:10.1021/ja411509g

Subscriber access provided by TAIPEI MEDICAL COLLEGE
Communication
Planar heterojunction perovskite solar
cells via vapor assisted solution process
Qi Chen, Huanping Zhou, Ziruo Hong, Song Luo, Hsin-Sheng
Duan, Hsin-Hua Wang, Yongsheng Liu, Gang Li, and Yang Yang
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 20 Dec 2013
Downloaded from http://pubs.acs.org on December 26, 2013
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 6
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Planar heterojunction perovskite solar cells via vapor assisted
solution process
Qi Chen1,2+, Huanping Zhou1,2+*, Ziruo Hong1, Song Luo1,2, Hsin-Sheng Duan1,2, Hsin-Hua Wang1,2, Yongsheng
Liu1,2, Gang Li1,2, Yang Yang1,2*
1) Department of Materials Science and Engineering, 2) California NanoSystems Institute, University of California, Los Angeles, California
90095, USA.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Supporting Information Placeholder
(e.g. α-Si, Cu(InGa)S2 and CdTe), vacuum evaporation is one of the
ABSTRACT: Hybrid organic-inorganic perovskites (e.g.,
most promising techniques to construct perovskite thin films for planar
junctions. The resulting perovskites prepared by co-evaporation of two
precursors (PbCl2 and CH3NH3I) exhibit satisfactory film coverage
and uniformity within expectations.4 However, this technique demands
high vacuum, which is too energy consuming and hinders mass
production. Alternatively, solution process techniques have been
proposed to fabricate thin films as well, where the mixture of two
precursors was used. Due to the lack of suitable solvents which can
dissolve both components and their high reaction rate however, this
process resulted in thin films with pinhole formation and moderate
surface coverage, which deteriorated the film quality and hampered the
device performance.23 The two-step approach has been demonstrated
to fabricate efficient PV devices by dipping the inorganic precursor
films into the solution of organic species.3 Unfortunately, this method
succeeds in films with nano-structured scaffolds,3 but has seldom been
reported to be applicable for fabricating planar heterojunctions in PV
devices. Constructing a CH3NH3PbI3 film with a thickness of several
hundred nanometers requires long reaction times due to the limited
reaction interface area. Often it results in films with strikingly enhanced
surface roughness, which ultimately peel off from the substrate.26 As
such, there is an urge to develop a facile solution approach to
perovskite materials with enhanced controllability of the film quality to
construct planar structured devices with competitive performance.
CH3NH3PbI3) as light absorbers are promising players in the field
of third-generation photovoltaics. Herein we demonstrate a low
temperature vapor assisted solution process to construct
polycrystalline perovskite thin films with full surface coverage,
small surface roughness, and grain size up to 1 micrometer. Based
on the as-prepared films, solar cells achieve high power
conversion efficiency of 12.1%, which is so far the highest
efficiency based on CH3NH3PbI3 with the planar heterojunction
configuration. This method provides a simple approach to
perovskite film preparation and paves the way for high
reproducibility of films and devices. The underlying kinetic and
thermodynamic parameters regarding the perovskite film growth
are discussed as well.
Recently, hybrid organic-inorganic perovskite materials (e.g.
CH3NH3PbI3) have been highlighted as one of the most competitive
candidates for absorber materials for thin film photovoltaic (PV)
applications.1,2 Perovskite solar cells have already been reported to
achieve the remarkably high efficiency of around 15% within the last 4
years.3,4 The reason for the rapid increase in power conversion
efficiency (PCE) of such devices is that perovskite materials possess
most of the properties that are required to be an excellent absorber:
appropriate direct bandgap, high absorption coefficient, excellent
carrier transport, and apparent tolerance of defects.2 Besides their
extremely low cost and ease of fabrication, perovskite materials provide
a wide tenability on composition and structure by adjusting the metal
halide framework and the intercalated organic species. Pioneering work
has suggested that these perovskite films exhibit composition/structure
dependent properties, which can be accessed by various processing
approaches.5,6 Thus, it is essential to achieve a fine controllability over
the reaction between the inorganic and organic species, resulting in
perovskites with desired properties and device performance.
Scheme 1: Schematic illustration of the perovskite film formation,
through vapor assisted solution process. Both the deposition of
inorganic film and the organic vapor treatment are carried out in N2
atmosphere.
In this manuscript, we demonstrate the vapor assisted solution process
(VASP) to fabricate perovskite thin films and PV devices with planar
geometry subsequently. The key step includes the film growth via the
as-deposited film of PbI2 in-situ reacting with CH3NH3I vapor
(Scheme 1). This method is conceptually different from either the
current solution process or vacuum deposition, by avoiding the co-
deposition of organic and inorganic species. It utilizes the kinetic
reactivity of CH3NH3I and thermodynamic stability of perovskite
Although first implemented in dye-sensitized solar cells based on
mesoporous structures,7-15 the perovskites have been gradually found to
assume all of the principal roles of PV operation,16-22 and PV devices
with planar architecture have been demonstrated.4,23-25 Planar
architecture potentially provides enhanced flexibility for device
optimization, multi-junction construction and investigation of the
underlying device physics, but it requires tremendous effort to fabricate
high quality perovskite films. Similar to other thin film PV technologies
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 6
1
2
3
4
5
6
7
8
during the in-situ growth process, and provides films with well-defined
formed perovskite film possesses the characteristics of full surface
grain structure with grain sizes up to micro-scale, full surface coverage,
and small surface roughness, which suits PV applications. Devices
based on films prepared via VASP have achieved a best PCE of 12.1%,
which is so far the highest efficiency of CH3NH3PbI3 with the planar
structure.
coverage on the substrates, with remarkable grain size up to micro-scale.
The surface roughness of the film was measured by AFM (Figure 1c),
and calculated to be 23.2 nm in the range of 5 μm × 5 μm. The
roughness of the film fabricated via VASP is relatively small compared
to other solution processed films,26 regardless of its micro-scale grain
size. Typical cross-sectional SEM image indicates the resulting film has
a thickness of ~350 nm with well-defined grains across the film
thickness. The as-prepared film with 100% surface coverage, micro-
scale grain size, and uniform grain structure suggest its promising
applicability for PV devices. These overwhelming characteristics could
be due to the combination of the relative smoothness of the pre-formed
PbI2 film and the effective intercalation of CH3NH3I vapor into the
inorganic framework and fast reaction, as will be discussed later.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Film formation is crucial to fabricate planar heterojunctions in most
thin film PV techniques, it is thus necessary to understand the
underlying kinetic and thermodynamic mechanism of perovskite thin
film fabrication via VASP. The investigation of perovskite thin film
evolution was carried out by annealing ~200 nm thick PbI2 films in the
presence of CH3NH3I at 150 °C in N2 atmosphere for different lengths
of time. Four representative samples with different annealing times
were prepared: the initial stage (0 h, Figure 2b), intermediate stage
(0.5 h, Figure 2c), complete stage (2 h, Figure 1b), and post stage (4 h,
Figure 2d). (SEM images of samples of 1 h and 3 h are included in
Figure S2 in the supporting information.) The XRD pattern (Figure 2a)
clearly shows that at the initial stage, the film is composed of PbI2 phase,
while in the intermediate stage, both phases, PbI2 and perovskite, co-
exist in the film as the appearance of their corresponding peaks,
respectively. With time evolution, the PbI2 phase disappears at the
complete stage, and no new peak is observed at the post stage.
Figure 1: The perovskite film on the FTO/c-TiO2 substrate, obtained
from the reaction of the PbI2 film and CH3NH3I vapor at 150 °C for 2h
in N2 atmosphere: (a) XRD pattern; (b) Top-view SEM image (inset
image with higher resolution, scale bar is 1 μm); (c) Tapping-mode
AFM height images (5 × 5 μm) (Inset: the corresponding 3D
topographic image); (d) Cross-sectional SEM image.
The vapor assisted solution process (VASP) was developed to fabricate
organic-inorganic hybrid perovskite film (e.g. CH3NH3PbX3, X=Cl, Br,
I), where the inorganic framework film is formed by depositing
precursor solution on the substrates, and subsequently treated with the
desired organic vapor (Scheme 1). As an illustration, PbI2 and
CH3NH3I are the corresponding precursor couple which forms
CH3NH3PbI3 in this work (see the experimental section for details).
PbI2 films were deposited on fluorine-doped tin oxide (FTO) glass
coated with a compact layer of TiO2 (c-TiO2), followed by annealing in
CH3NH3I vapor at 150 °C in N2 atmosphere for 2 hours to form the
perovskite films. Figure 1a shows the corresponding X-ray diffraction
(XRD) of the as-prepared CH3NH3PbI3 film on FTO/c-TiO2 substrate.
A set of strong peaks appeared at 14.08°, 28.41°, and 31.85°, 43.19°,
which are assigned to the (110), (220), (310) and (330) of
CH3NH3PbI3 crystal,7,27,28 indicate an orthorhombic crystal structure of
halide perovskite with high crystallinity. According to the literature,4
there is often a tiny signature peak at 12.65°, corresponding to a low-
level impurity of PbI2. The absence of the aforementioned peak in the
present perovskite film suggests a complete consumption of PbI2 via
VASP. The film quality of the perovskite is further evaluated by
scanning electron microscopy (SEM) images and atomic force
microscopy (AFM) characterization. As shown in Figure 1b, the as-
Figure 2: Time evolution characterization of the perovskite thin film,
by annealing ~200 nm PbI2 film in the presence of CH3NH3I at 150 °C
in N2 atmosphere: (a) XRD patterns of the film annealed at 0 h, 0.5 h,
and 4 h respectively; (b-d) Top-view SEM images of: (b) the initial
stage at 0 h; (c) the intermediate stage at 0.5 h ( inset: wider view, scale
bar 3 μm); (d) the post stage at 4 h.
ACS Paragon Plus Environment

Page 3 of 6
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
The grain structure of the corresponding deposited film changes
rearrangement of the aggregated structure of PbI2 driven by the
strikingly along with the intercalation reaction as well. The initial PbI2
film exhibits uniform polygon grains of a few hundred nanometers, as
well as scattered voids among adjacent grains. As the PbI2 film was
exposed to CH3NH3I vapor for 30 minutes, it exhibited two distinct
shapes with different contrast. The dark grains show similar
morphology to those in Figure 2b, which is considered to be un-reacted
PbI2. The relatively light grains appeared right on the top of the original
PbI2 film with larger grain size and different grain morphology. As the
coexistence of two phases in the film is confirmed by the XRD pattern,
they are speculated to be the newly formed perovskite. These species
on the top of PbI2 films significantly promote the film thickening, as
shown in Figure S1b in the supporting information, probably due to
the volume expansion from the intercalation of CH3NH3I,
accompanying with the transformation of PbI2 framework from the
originally edge sharing octahedral structure to the corner-sharing
octahedral structure in perovskite films.27 It is worth noting the
appearance of some dots with sizes of tens of nanometers on the
surface of un-reacted PbI2. It is highly suspected that these tiny dots are
reactive “nuclei” for the growth of grains, originating from the reaction
between PbI2 and CH3NH3I vapor. With the presence of the newly
formed perovskite crystals on top, accompanying with the “nuclei”
decorated around, we believe that the intercalation reaction took place
on top of the PbI2 film in this stage. As the reaction time increased to 2
h, perovskite films with grain size up to the micro-scale have been
observed. Compared to the original PbI2 film, the perovskite film
differs in both morphology and size, where the film thickness of
perovskite increases to ~350 nm from the original PbI2 film of ~200 nm
(Figure S1a). The in-plane grain size of perovskite is three times the
film thickness, which indicates the growth of perovskite polycrystalline
films follows normal grain growth mode.29 In addition, the voids
present in between the adjacent crystals in the original PbI2 film
vanished after the formation of perovskite crystals. Interestingly,
further prolonging the reaction time to 4 h does not affect the grain
structure (Figure 2d). There is no obvious observation of ripening, or
coarsening process at post stage, which often appears during
polycrystalline film growth.30 This indicates a thermodynamically
stable film is formed after the reaction is complete at the moderate
temperature. Further prolonging reaction time is outside of the current
research scope, though.
reduction of boundary length to minimize the grain boundary energy.30
Also, the absence of voids in the final film, which appeared in the
original PbI2 film, suggests that VASP promotes a re-arrangement of
PbI2 and/or re-organization of PbI2 and CH3NH3I via intensive
diffusion during the film growth.31,32 It should be noted that VASP is
especially applicable in fabricating the 3D structure thin films
compared to the conventional two-step solution process. Since there is
no kinetically favorable Van der Waal’s gap in the PbI2/CH3NH3PbI3
interface where the transformation can occur,26,33 a rather long reaction
time is required to transform inorganic precursors into perovskite
completely. Films often deteriorated upon extended dipping. In VASP
however, the absence of solvent media and a moderate processing
temperature, collectively contribute a complete reaction between PbI2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
and
CH3NH3I
without
impairing
the
film
quality.
The present VASP results in perovskite films with full surface coverage,
small surface roughness, and complete conversion of PbI2, which
addresses most crucial issues regarding perovskite thin film formation
for PV applications. Remarkably different from previously reported
solution processing approaches, the two-step VASP exhibits its
distinctiveness. In the first step, the inorganic precursors are spin-
coated to form a smooth and uniform PbI2 film with the surface
roughness of less than 20 nm (Figure S3). It avoids the extremely high
reaction rate of perovskite film that often happens in the co-deposition
process.26 This film acts not only as a superior framework for the
perovskite formation, but also as a reservoir of one of the reactants to
provide the kinetically favorable “nucleation” centers to allow further
perovskite formation. In addition, the voids in the PbI2 film facilitate
the subsequent reaction by providing more surface area. When exposed
to the CH3NH3I vapor in the second step, the intercalation reaction
occurs in situ with simultaneous polycrystalline film growth, where the
specific surface and interface energy minimizing crystallographic
orientations are favored. The enhanced grain size can be ascribed to
the volume expansion during the transformation from PbI2 to
perovskite by the intercalation of CH3NH3I, as well as the
Figure 3: (a) Current density-voltage (J–V) characteristics of the solar
cell based on the as-prepared perovskite films under AM 1.5G
illumination, and the cross-sectional SEM image of the device (Inset).
(b) EQE spectrum (black) and the integrated photocurrent (red) that
is expected to be generated under AM 1.5G irradiation of the device.
The as-formed perovskite films with complete conversion of PbI2,
experienced a proper post-annealing time, were subsequently used to
photovoltaic devices fabrication. The detailed device fabrication
process is described in the experimental section in the supporting
information. The cross-sectional SEM image of the device reveals its
planar architecture, where the absorber layer has been well
implemented into the device with intimate contact to adjacent layers:
the FTO substrate is coated with a compact layer of TiO2 (~70 nm),
followed by the CH3NH3PbI3 layer (~350 nm). 2,2’,7,7’-tetrakis(N,N-
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 6
1
2
3
4
5
6
7
8
di-p-methoxyphenylamine)-9,9’-spirobifluorene
(spiro-MeOTAD)
with the thickness of ~300 nm is employed as a hole-transporting layer
(HTL). A thermally evaporated silver layer (~100 nm) forms the back
contact of the device.
approach exhibits full surface coverage, uniform grain structure with
grain size up to micrometers, and 100% precursor transformation
completeness. A film evolution study on perovskite transformation
indicates an appropriate re-arrangement of PbI2 film during
intercalation of CH3NH3I driven by the reduction of grain boundary
energy. Facilitated by the excellent film quality, the CH3NH3PbI3
materials enable an impressive device PCE of 12.1% in a planar
The corresponding device performance characterization is conducted
by current density (J) - voltage (V) measurement under simulated AM
1.5G (100 mW/cm2) solar irradiation in the air. Without encapsulation,
the solar cells can last several hours in air with reproducible efficiency.
As shown in Figure 3a, the optimum device exhibits outstanding
performance with a JSC of 19.8 mA/cm2, VOC of 0.924 V, FF of 66.3%
and PCE of 12.1%, which is so far the highest efficiency based on
CH3NH3PbI3 with planar structure. In general, the devices exhibit
open circuit voltage in the range of 0.83 to 0.94 V, short circuit current
in the range of 17.3 to 20.8 mA/cm2, fill factor in the range of 56.0% to
68.2%, and the resulting PCE ranging from 9.3% to 12.1%. Figure 3b
shows external quantum efficiency (EQE) spectrum for the perovskite
cell. Generation of photocurrent starts at 780 nm, in agreement with
the bandgap of the CH3NH3PbI3,9 and reaches peak values of ~80% in
the visible spectrum. Integrating the overlap of the EQE spectrum with
the AM 1.5G solar photon flux yields a current density of 18.5 mA/cm2.
The slightly lower current density obtained from EQE measurement,
compared to that from J-V curve, is probably attributed to the surface
trap of TiO2 transporting layer.34 One of the important factors that
contribute to the high PCE is the high quality of the absorber film
fabricated via VASP. The full surface coverage of this film provides
more absorption to contribute to the high JSC. The large grains with
reduced grain boundaries, and the uniform nature in the vertical
direction over a range of length scale may help to alleviate surface
recombination when carriers are transported in the perovskite layer,
which leads to high VOC. The improvement of FF is largely attributed
to the decrease of parasitic loss currents and the parallel resistance of
the devices in this pin-hole free thin film. It is worthy noted that the
reported minority carrier diffusion length for CH3NH3PbI3 is quite
short, in a level of ~ 100 nm, which results in relatively low device
efficiencies (normally less than 10%) within the planar device
architecture.16,17 The remarkably high efficiency of 12.1% based on
present CH3NH3PbI3, may be resulted from the improved electrical
property of the high quality film. Further study on the understanding of
the relevance between the film property and device performance is
underway.
architecture. VASP presents a simple, controllable, and versatile
approach toward the pursuit of high quality perovskite film and the
resulting high performance PV devices. Incorporation of organic
species into the as-deposited inorganic framework through vapor,
effectively avoids the high reaction rate of perovskite during co-
deposition of precursors, and the possible film deterioration concern
when dipping an inorganic framework into an organic species solution.
Future work will be focused on property investigation within the
resulting films, e.g. charge transport behavior. More importantly,
continuous advancement of film engineering will enable high
performance perovskite solar cells and other organic-inorganic hybrid
optoelectronics.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ASSOCIATED CONTENT
Supporting Information
Detailed experimental procedures and Figures S1 to S5 are shown in
supplementary information. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
+ Both authors contributed equally to this work
Corresponding Author
* happyzhou@ucla.edu and yangy@ucla.edu
ACKNOWLEDGMENT
This work was financially supported by a grant from the National
Science Foundation (grant number: ECCS-1202231, Program
Director: Dr. George N. Maracas), Air Force Office of Scientific
Research (Grant number FA9550-12-1-0074, Program Manager Dr.
Charles Lee), and UCLA Internal Funds. The authors sincerely
acknowledge Prof. King-Ning Tu of UCLA and Dr. Su-Huai Wei of
NREL for the valuable discussion on the crystal growth mechanism
and the energy band structure of the perovskite crystal. Also, we
acknowledge Dr. Xiaolei Wang, Dr. Ge Li and Eric Richard for their
help on the electrode fabrication, the graphic drawing, and English
editing.
By utilizing a pre-formed solution processed PbI2 film and the effective
reaction between PbI2 and CH3NH3I at moderate temperature, VASP
provides the perovskite film with grain size significantly larger than that
based on vacuum deposition on a non-heated substrate. Through
carefully controlling the parameters of crystal growth, the grain size of
the continuous film is expected to be adjustable from 200-300 nm to
over 1 μm. Further study will be focused on optimizing solar cell
performance by controlling the grain size of perovskite thin films
toward enhanced optical and electrical properties and consequent high
performance. Besides current CH3NH3PbI3, other inorganic-organic
hybrid materials that contain low-melting point organic species, e.g.
Cl/Br containing materials, or their combinations, may also be
explored by simply switching the precursors. Additionally, the
fabrication of other optoelectronics, such as light-emitting diodes, field
effect transistors, and detectors may also benefit from VASP.
REFERENCES
(1) Park, N.-G. J. Phys. Chem. Lett. 2013, 4, 2423.
(2) Snaith, H. J. J. Phys. Chem. Lett. 2013, 4, 3623.
(3) Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao, P.;
Nazeeruddin, M. K.; Gratzel, M. Nature 2013, 499, 316.
(4) Liu, M.; Johnston, M. B.; Snaith, H. J. Nature 2013, 501, 395.
(5) Kagan, C.; Mitzi, D.; Dimitrakopoulos, C. Science 1999, 286, 945.
(6) Mitzi, D. B. Prog. Inorg. Chem. 2007, 48, 1.
(7) Im, J.-H.; Lee, C.-R.; Lee, J.-W.; Park, S.-W.; Park, N.-G. Nanoscale 2011, 3,
4088.
(8) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. J. Am. Chem. Soc. 2009,
131, 6050.
(9) Kim, H. S.; Lee, C. R.; Im, J. H.; Lee, K. B.; Moehl, T.; Marchioro, A.; Moon,
S. J.; Humphry-Baker, R.; Yum, J. H.; Moser, J. E.; Gratzel, M.; Park, N. G. Sci.
Rep. 2012, 2, 591.
In summary, we report VASP, a novel low temperature approach to
fabricate planar perovskite films and their corresponding PV devices. It
is based on the kinetically favorable reaction between the as-deposited
film of PbI2 and CH3NH3I vapor. The perovskite film derived from this
ACS Paragon Plus Environment

Page 5 of 6
Journal of the American Chemical Society
1
(10) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J.
2
3
4
5
6
7
8
Science 2012, 338, 643.
(11) Heo, J. H.; Im, S. H.; Noh, J. H.; Mandal, T. N.; Lim, C.-S.; Chang, J. A.;
Lee, Y. H.; Kim, H.-j.; Sarkar, A.; NazeeruddinMd, K.; Gratzel, M.; Seok, S. I.
Nat. Photon. 2013, 7, 486.
(12) Abrusci, A.; Stranks, S. D.; Docampo, P.; Yip, H.-L.; Jen, A. K. Y.; Snaith, H.
J. Nano Lett. 2013, 13, 3124.
(13) Kim, H.-S.; Lee, J.-W.; Yantara, N.; Boix, P. P.; Kulkarni, S. A.; Mhaisalkar,
S.; Grätzel, M.; Park, N.-G. Nano Lett. 2013, 13, 2412.
(14) Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I. Nano Lett. 2013,
13, 1764.
(15) Zhang, W.; Saliba, M.; Stranks, S. D.; Sun, Y.; Shi, X.; Wiesner, U.; Snaith,
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
H. J. Nano Lett. 2013, 13, 4505.
(16) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J. P.;
Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Science 2013, 342, 341.
(17) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Grätzel, M.;
Mhaisalkar, S.; Sum, T. C. Science 2013, 342, 344.
(18) Ball, J. M.; Lee, M. M.; Hey, A.; Snaith, H. J. Energ. Environ. Sci. 2013, 6,
1739.
(19) Laban, W. A.; Etgar, L. Energ. Environ. Sci. 2013, 6, 3249.
(20) Zhao, Y.; Zhu, K. J. Phys. Chem. Lett. 2013, 4, 2880.
(21) Etgar, L.; Gao, P.; Xue, Z.; Peng, Q.; Chandiran, A. K.; Liu, B.;
Nazeeruddin, M. K.; Grätzel, M. J. Am. Chem. Soc. 2012, 134, 17396.
(22) Kim, H.-S.; Mora-Sero, I.; Gonzalez-Pedro, V.; Fabregat-Santiago, F.;
Juarez-Perez, E. J.; Park, N.-G.; Bisquert, J. Nat. Commun. 2013, 4, 2242.
(23) Eperon, G. E.; Burlakov, V. M.; Docampo, P.; Goriely, A.; Snaith, H. J. Adv.
Func. Mater. 2013, (DOI: 10.1002/adfm.201302090).
(24) Jeng, J.-Y.; Chiang, Y.-F.; Lee, M.-H.; Peng, S.-R.; Guo, T.-F.; Chen, P.;
Wen, T.-C. Adv. Mater. 2013, 25, 3727.
(25) Sun, S.; Salim, T.; Mathews, N.; Duchamp, M.; Boothroyd, C.; Xing, G.;
Sum, T. C.; Lam, Y.-M. Energy Environ. Sci. 2013, 6,
(DOI:10.1039/C3EE43161D).
(26) Liang, K.; Mitzi, D. B.; Prikas, M. T. Chem. Mater. 1998, 10, 403.
(27) Baikie, T.; Fang, Y.; Kadro, J. M.; Schreyer, M.; Wei, F.; Mhaisalkar, S. G.;
Graetzel, M.; White, T. J. J. Mater. Chem. A 2013, 1, 5628.
(28) Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Inorg. Chem. 2013, 52,
9019.
(29) Thompson, C. Annu. Rev. Mater. Sci. 2000, 30, 159.
(30) Ohring, M. The materials science of thin films; Academic Press: Boston,
1992.
(31) Era, M.; Hattori, T.; Taira, T.; Tsutsui, T. Chem. Mater. 1997, 9, 8.
(32) Mitzi, D. B.; Prikas, M.; Chondroudis, K. Chem. Mater. 1999, 11, 542.
(33) Mitzi, D. B.; Dimitrakopoulos, C. D.; Rosner, J.; Medeiros, D. R.; Xu, Z.;
Noyan, C. Adv. Mater. 2002, 14, 1772.
(34) Boschloo, G. K.; Goossens, A. J. Phys. Chem. 1996, 100, 19489.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 6
1
2
3
4
5
TOC:
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment