Research and development of science

1. Article
Modulation of vacancy-ordered double
perovskite Cs2SnI6 for air-stable thin-film
transistors
Liu et al. report the deposition of eco-friendly vacancy-ordered double perovskite
Cs2SnI6 thin films using a one-step solution process. Subsequently, an external
atomic doping is adopted to modulate the electrical property of the Cs2SnI6
perovskite. The resulting transistors exhibit appealing electrical performance with
highly stable characteristics.
Ao Liu, Huihui Zhu, Youjin
Reo, ..., Weihua Ning, Sai Bai,
Yong-Young Noh
sai.bai@liu.se (S.B.)
yynoh@postech.ac.kr (Y.-Y.N.)
Highlights
Precursor engineering for one-
step solution deposition of
Cs2SnI6 thin films
Electrical modulation of the
Cs2SnI6 perovskite for transistor
application
Integrated transistors exhibit
appealing electrical performance
with high stability
Liu et al., Cell Reports Physical Science 3,
100812
April 20, 2022 ª 2022 The Author(s).
https://doi.org/10.1016/j.xcrp.2022.100812
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2. Article
Modulation of vacancy-ordered double perovskite
Cs2SnI6 for air-stable thin-film transistors
Ao Liu,1 Huihui Zhu,1 Youjin Reo,1 Myung-Gil Kim,2 Hye Yong Chu,3 Jun Hyung Lim,3 Hyung-Jun Kim,3
Weihua Ning,4 Sai Bai,5,6,* and Yong-Young Noh1,7,*
SUMMARY
Vacancy-ordered halide double perovskites are promising non-toxic
and stable alternatives for their lead- and tin (II)-based counterparts
in electronic and optoelectronic applications. Despite extensive
theoretical studies on this emerging family of materials, efforts
devoted to the chemical modulation of their thin-film properties
and their potential application in electronic devices remain rare.
Here, we develop a facile one-step solution processing strategy to
tune the film quality of cesium tin (IV) iodide (Cs2SnI6) perovskite
and demonstrate its feasibility in thin-film transistor (TFT) applica-
tion. We reveal critical roles of precursor stoichiometric ratio and sol-
vent engineering in achieving uniform and highly crystalline Cs2SnI6
films with superior electron mobility. We further modulate the elec-
tronic properties by incorporating an external manganese (Mn2+
)
dopant, achieving high-performance air-stable n-channel TFTs and
all-perovskite complementary inverters. We anticipate that the pre-
sent study would pave the way for expanding the environmentally
friendly and stable perovskites toward widespread applications.
INTRODUCTION
Metal halide perovskites with a chemical formula of ABX3, in which A is an organic or
cesium cation, B is a divalent lead (Pb2+
) or tin (Sn2+
) cation, and X is a halide anion,
have achieved great success in a wide range of electronic and optoelectronic appli-
cations because of their superior optoelectronic property, low-cost processing
capability, and unique defect tolerance character.1–6
Unfortunately, practical appli-
cations of state-of-the-art devices using Pb2+
- and Sn2+
-based perovskites remain
concerning due to their toxicity and/or poor long-term stability, motivating intensive
efforts on searching non-toxic and environmentally stable alternatives to circumvent
the inherent problems of materials.7–15
By replacing two B2+
in the ABX3 perovskites
with a combination of B+
and B3+
or a combination of B4+
and a vacancy, halide dou-
ble perovskites with the chemical formula of A2B+
B3+
X6 or A2B4+
X6 (vacancy-or-
dered double perovskites) were recently demonstrated.16–20
Extensive theoretical
calculations have demonstrated rich structural and functional diversity of the halide
double perovskites and similarly promising material properties as their ABX3 coun-
terparts, suggesting their great potential to replace the dominant Pb2+
- and Sn2+
-
based perovskites in electronic and optoelectronic devices.
Cesium tin (IV) iodide (Cs2SnI6), as one of the most widely investigated vacancy-or-
dered halide double perovskites, can be illustrated as a defect variant of the three-
dimensional (3D) CsSnI3 perovskite, with half of the Sn atoms in the Sn-centered
octahedral missing (Figure 1A).21
Benefiting from the stable Sn tetravalent state
1Department of Chemical Engineering, Pohang
University of Science and Technology, 77
Cheongam-Ro, Nam-Gu, Pohang 37673,
Republic of Korea
2School of Advanced Materials Science and
Engineering, Sungkyunkwan University, Suwon
16419, Republic of Korea
3R&D Center, Samsung Display, Yongin 17113,
Republic of Korea
4Institute of Functional Nano & Soft Materials
(FUNSOM), Jiangsu Key Laboratory for
Carbon-Based Functional Materials & Devices,
Soochow University, Suzhou 215123, PR China
5Institute of Fundamental and Frontier Sciences,
University of Electronic Science and Technology
of China, Chengdu 611731, China
6Department of Physics, Chemistry and Biology
(IFM), Linköping University, 58183 Linköping,
Sweden
7Lead contact
*Correspondence: sai.bai@liu.se (S.B.),
yynoh@postech.ac.kr (Y.-Y.N.)
https://doi.org/10.1016/j.xcrp.2022.100812
Cell Reports Physical Science 3, 100812, April 20, 2022 ª 2022 The Author(s).
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1
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3. and the strong Sn-I covalent bonding, the Cs2SnI6 perovskite exhibits high stability
against oxidization.19,22
In addition, despite the isolated [SnI6]2
octahedra, the de-
localized spherical Sn 5s states and closely packed iodide sublattice still engage in
the orbital overlap between adjacent octahedra to produce dispersive conduction
band states.17
As a result, the Cs2SnI6 possesses a small electron effective mass
(0.25 m0, where m0 is the free electron mass) with a high calculated electron mobility
of approximately 100 cm2
V1
s1
.23–27
The non-toxic and air-stable nature of
Cs2SnI6 perovskite, coupled with the excellent electrical property and the suitable
band gap for light absorption, has led to quite a few studies to examine its applica-
bility as a functional material in diverse optoelectronic devices.21,27–31
However, sys-
tematic modulation strategies for thin-film properties of Cs2SnI6 perovskite, which
are critical for their device applications, remain rarely explored, resulting in unsatis-
factory device performance.
A B C
D
E F G
Figure 1. Cs2SnI6 perovskite films deposited from precursors with varied component ratios
(A) Crystal structure of the vacancy-ordered double perovskite of Cs2SnI6.
(B) Optical absorption spectra of Cs2SnI6 thin films as a function of the CsI:SnI4 feed ratio in the precursor solution.
(C) Corresponding film XRD patterns and the diffraction peak pattern of Cs2SnI6 JCPDS card (no. 51-0466).
(D) SEM images of Cs2SnI6 thin films with different CsI:SnI4 feed ratios.
(E) Cs:Sn element ratios in different Cs2SnI6 thin films.
(F) CsI and Cs2SnI6 component ratios calculated from XPS results.
(G) Hall mobility and electron concentration of Cs2SnI6 thin films processed from precursors with different CsI:SnI4 feed ratios. The error bars were
calculated from 6 samples.
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4. In this work, we develop a synergetic solution-based processing strategy to manipulate
the film quality of Cs2SnI6 perovskite and demonstrate its feasibility in thin-film tran-
sistor (TFT) application. We show that incorporating a slight excess of tin (IV) iodide
(SnI4) in a mixed N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)-
based precursor solution is favorable to enable one-step solution processing of Cs2SnI6
thin films with high crystallinity, uniform morphology, and high electron mobility. More-
over, we demonstrate that the electronic structure of the Cs2SnI6 film could be modu-
lated further by incorporating external metal dopants. With the optimized manganese
(Mn2+
)-doped Cs2SnI6 films, we achieve n-channel perovskite TFTs with good opera-
tional and air stability. By further integrating the devices with p-channel perovskite
TFTs, we realize the first all-perovskite complementary inverter with a high gain
voltage, suggesting their great potential in complex electronic applications.
RESULTS AND DISCUSSION
Precursor engineering enabling one-step fabrication of high-quality Cs2SnI6
thin films
The Cs2SnI6 precursor solutions were prepared by dissolving CsI and SnI4 powders
with varied molar ratios (CsI: SnI4 = 2:x) in a mixed solvent of DMSO/DMF (1:9, v/v).
The films were fabricated by one-step spin coating of the precursor solution fol-
lowed by a low-temperature annealing process at 100
C for 5 min in a nitrogen
(N2)-filled glove box. The optical absorption spectra of thin films deposited from
precursors with different CsI: SnI4 feed ratios show minor differences and a similar
optical band gap (Eg) of 1.64–1.66 eV (Figures 1B and S1). The X-ray diffraction
(XRD) pattern in Figure 1C for the film processed from the stoichiometric precursor
exhibited two main diffraction peaks at 2q angles of 15.2
and 30.7
, which corre-
spond to the (002) and (004) crystalline planes of Cs2SnI6 (Joint Committee on Pow-
der Diffraction Standards [JCPDS] card no. 51-0466), respectively. In addition, we
detected a diffraction peak at 39.5
, which can be indexed to the (200) plane of
the cubic CsI phase. Interestingly, as the SnI4 feed ratio (x) increased from 1 to
1.8, the peak intensity of CsI gradually decreased, while the formation of the Cs2SnI6
perovskite phase was promoted. Further increasing the SnI4 in the precursor (x = 2.2)
eliminated the CsI impurity phase, however, and negatively affected the formation
of the perovskite phase, as evidenced by the significantly reduced diffraction peak
intensities of Cs2SnI6 perovskite (Figure 1C). As revealed by the scanning electron
microscopy (SEM) images (Figure 1D), the film processed from the stoichiometric
precursor showed poor coverage, while more uniform films were obtained with
increased SnI4 contents until the perovskite formation was disturbed (x = 2.2).
Note that uniform Cs2SnI6 films are highly desired for realizing high-performance
electronic and optoelectronic devices with high reproducibility, yet they have not
been achieved using the one-step spin-coating approach.
To further understand the beneficial roles of the excess SnI4 on the Cs2SnI6 film
deposition, we characterized the components of the as-fabricated films. The energy
dispersive spectroscopy (EDS) element mapping results revealed a Cs+
:Sn4+
ratio of
2:0.7 for the film fabricated from the stoichiometric precursor (Figure 1E), indicating
the formation of a 30% Sn-deficient Cs2SnI6 in this case. This result was not surpris-
ing, considering the volatile nature of SnI4, which tends to be lost during the thermal
annealing process,21,31
which is consistent with the formation of low-crystalline films
with incomplete coverage and obvious CsI impurities from stoichiometric precur-
sors. The precursors with x values of 1.5 and 1.8 produced Cs2SnI6 films with a
nearly stoichiometric component ratio (2:0.95 and 2:1.02), while the use of excess
SnI4 (x = 2.2) resulted in Sn4+
-rich films with a Cs+
:Sn4+
ratio of approximately
2:1.08. We then analyzed the X-ray photoelectron spectroscopy (XPS) results by
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5. fitting the Cs 3d5/2 spectra to elucidate specific information regarding the CsI and
Cs2SnI6 components in the films (Figure S2).22
As presented in Figure 1F, the stoi-
chiometric precursor-derived Cs2SnI6 film exhibited a high amount of CsI residual
(28.5%), which gradually decreased to less than 10% for film processed from the pre-
cursor, with an x value of more than 1.8. Both the EDS and XPS results revealed
obvious component variations between the precursor and the as-deposited film of
Cs2SnI6, revealing an easy loss of SnI4 during film formation. We infer that the
component loss should have been properly compensated for by incorporating
excess SnI4 in the precursor, rationalizing the improved crystallinity and uniformity
of the ensuing Cs2SnI6 films.
We proceeded to investigate the electrical properties of the Cs2SnI6 films using Hall
measurements (Figure 1G). The Hall data were not available for the sample processed
from the stoichiometric precursor owing to its high resistivity, which was likely due to the
low film crystallinity and abundant CsI residuals in the film. We measured similar elec-
tron concentrations in a range of (0.8–1.5) 3 1016
cm3
for films deposited from precur-
sors with excess SnI4. Cs2SnI6 films fabricated from the precursor with x = 1.8 demon-
strated an average Hall mobility of 79 cm2
V1
s1
, which declined to approximately
50 and 30 cm2
V1
s1
for films deposited from precursors with x = 1.5 and 2.2, respec-
tively. The mobility of the optimized Cs2SnI6 films here is more than 25 times that of pre-
viously demonstrated two-step deposited thin films, with a Hall mobility of 3 cm2
V1
s1
.25
We emphasize that the high mobility slightly degraded to 75 cm2
V1
s1
after
a 1-week air storage (relative humidity [RH], 30%–40%), indicating excellent ambient
stability of the Cs2SnI6 films. We further note that the electrical properties of Cs2SnI6
films are superior to those of the widely investigated polycrystalline Pb-halide perov-
skites (8–35 cm2
V1
s1
),32
suggesting their great potential in electronic devices.
It is worth noting that a small amount of DMSO in the precursor solution was also
important to ensure the fabrication of high-quality Cs2SnI6 thin films. Thin films
deposited from the pure DMF-based precursor (x = 1.8) exhibited low crystallinity
and poor film coverage with a dendritic morphology (Figure 2A), which can be
ascribed to the formation of a few nucleation sites during the film-coating process
and the rapid crystallization. As a comparison, the precursor in mixed DMF-DMSO
(5–10 vol %) produced thin films with notably improved uniformity and coverage,
along with increased crystallinity. Previous studies have demonstrated that the Lewis
base solvent of DMSO could readily form an intermediate phase with SnI2 (i.e.,
SnI2$3DMSO),33
which promotes the homogeneous nucleation and retards the crys-
tallization rate of perovskite crystal, leading to improved film quality.34
Considering
the greater Lewis acidic strength of Sn4+
(higher ion charge) than that of Sn2+
, the
similar Lewis acid/base adduct theory would be applicable for the deposition of
high-quality Sn4+
-based perovskite films. The DMSO addition enables the clear pre-
cursor solution compared with the use of pure DMF solvent (Figure 2B). However,
owing to the high boiling point and low vapor pressure of DMSO, the excessive sol-
vent residuals in the precursor film would deteriorate the perovskite phase growth,
as evidenced by decreased XRD peak intensities (Figure 2C) and the aggregates
that appeared in the SEM image of the film processed from a precursor containing
20 vol % DMSO (Figure 2A).
Mn2+
doping enabling high-performance Cs2SnI6 TFTs
To assess the applicability of the Cs2SnI6 thin films in a transistor application, we
fabricated bottom-gate, top-contact TFTs on silicon dioxide (SiO2)/p+
-Si substrates
with gold (Au) source/drain electrodes. The device structure is illustrated in Figure 3A
with a cross-sectional transmission electron microscopy (TEM) image. The device
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6. measurements were performed at room temperature (20
C) under the continuous
bias mode in a dark N2-filled environment. Unfortunately, all TFTs based on Cs2SnI6
channels fabricated from precursors with x = 1.5–2.2 exhibited conductor-like trans-
fer curves, showing almost constant drain currents (IDS) and negligible gate modula-
tion behaviors (Figures 3B and S3). Among these, the channel film deposited from
the precursor with x = 1.8 delivered the highest current level, which is consistent
with the Hall measurement results (Figure 1G). We inferred that the electron concen-
trations of pristine Cs2SnI6 films may remain too high to enable effective IDS modu-
lation, considering that the carrier concentrations of approximately 1015
cm3
are
generally more desirable for efficient transistor operation.35,36
Inspired by the success of the external doping strategy in conventional metal oxides and
emergingmetal-halidesemiconductors,37–41
weattemptedtoexplorep-typedopantsto
further reduce the electron concentration of the Cs2SnI6 channel layer. To ensure a high
doping efficiency and free-hole generation after Sn4+
substitution, an ideal p-dopant
should possess an ionic radius similar to that of Sn4+
and a lower valence state. To this
end, we selected Mn2+
, which has been demonstrated to be effective in modulating
the film quality of various halide perovskites,42,43
as the dopant for Cs2SnI6. As expected,
the resultant TFTs based on Mn2+
-doped Cs2SnI6 channel films exhibited typical n-chan-
nel transistor behavior and a positively shifted threshold voltage (VTH), with the doping
ratio increasing from 1.5 to 5 mol % (Figure 3B). As we presented in Figures 3B and
3C,TFTsusing3mol%Mn2+
-dopedCs2SnI6 channelsdemonstratedthebestdeviceper-
formance, showing a field-effect electron mobility (me) of 1.2 cm2
V1
s1
, an Ion/Ioff of
104
, a VTH of 15.5 V, and a sub-threshold swing (SS) of 3 V dec1
, respectively. The
corresponding output curves exhibited excellent current linearity and saturation at low
and high source-drain voltages, respectively (Figure 3D), indicating ohmic contact be-
tween the perovskite channel and Au electrodes. The modulated Mn-doped Cs2SnI6
channels also enabled high device reproducibility, with the ensuing 50 TFTs showing
an average Ion/Ioff of 104
and an average me of 1.2 G 0.2 cm2
V1
s1
(Figures 3E and
3F). The mobility value here is notably improved in comparison with recently achieved
TFTs based on other Pb2+
/Sn2+
-free halide double perovskites (e.g., Ag+
/Bi3+
A B
C
Figure 2. Cs2SnI6 perovskite films deposited from precursors with different DMSO solvent mixing ratios
(A) SEM images of Cs2SnI6 (x = 1.8) thin films deposited with different DMSO volume ratios.
(B) Pictures of precursor solutions (x = 1.8) using pure DMF and DMF/DMSO (DMSO = 10 vol %) as solvents.
(C) Corresponding film XRD patterns.
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7. based).44,45
Similar to previously demonstrated perovskite TFTs, the obvious hysteresis
was observed in the transfer curves of our TFTs (Figure S4), which may originate from
non-negligible ion migration in the perovskite films or trap states in the polycrystalline
channel layer and/or at the channel-dielectric interface.46–50
To elucidate the critical roles of Mn2+
doping in ensuring the fabrication of operating
TFTs based on Cs2SnI6 perovskite films, a series of film characterizations were per-
formed. XRD patterns of films with 1.5–5 mol % Mn2+
doping revealed perovskite
features similar to that of the pristine Cs2SnI6 film, indicating that negligible struc-
tural changes were induced by the low-level Mn2+
doping (Figure 4A). We detected
a slight shift of the Cs2SnI6 diffraction peaks toward lower 2q angles upon Mn2+
doping (Figure S5), which can be attributed to the incorporation of the larger-size
Mn2+
ions that increased the lattice constant of the perovskite unit. Interestingly,
the CsI impurity phase was almost eliminated in all Mn2+
-doped Cs2SnI6 samples.
We speculated that the Mn2+
dopant would have induced changes to the activation
energy of the precursor components, leading to further modified film crystallization
processes, similar to the previous observation in the synthesis of Mn2+
-doped
Cs3Bi2I9 perovskite.42
We note that the excessive Mn2+
dopant (5 mol %) resulted
in low diffraction peak intensities in the XRD patterns and aggregates in the SEM
I
I
(
)
V
I
I
V
I
V V
I
V
A B C
F
E
D
Figure 3. TFT performance with different channels and reproducibility evaluation
(A) Transistor structure used in this study and the corresponding TEM cross-section image (x = 1.8).
(B) Transfer curves of Cs2SnI6 TFTs without and with Mn2+
doping at different ratios (Ig: gate leakage current).
(C) Summary of the me and Ion/Ioff of the TFTs. The error bars were calculated from 10 individual devices.
(D) Output curves of 3 mol % Mn2+
-doped Cs2SnI6 TFT.
(E) Transfer curves of 50 Mn2+
-doped Cs2SnI6 TFTs (3 mol % Mn2+
).
(F) me statistical data of the Mn2+
-doped Cs2SnI6 TFTs.
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8. images (Figure S6), similar to the case with 20 vol % DMSO, indicating the necessity
of careful control of the precursor components.
The corresponding Hall measurement results revealed that Mn2+
doping can effec-
tively reduce the electron concentrations (Figure 4B). The simultaneously reduced
Hall mobilities are possibly caused by the increased impurity scattering with the
Mn2+
doping in the Cs2SnI6 perovskite (Figure S6). It is worth noting that the
1.5 mol % Mn2+
addition showed greatly enhanced film crystallinity compared
with the pristine Cs2SnI6 perovskite; however, the resulting TFTs still delivered a rela-
tively high off-state current (Figure 3B), indicative of the necessity of further suppres-
sion of the electron concentration. As a comparison, the 3 mol % Mn2+
-doped
Cs2SnI6 film delivered an electron concentration of 1015
cm3
and a moderate
Hall mobility of 30 cm2
V1
s1
, leading to a satisfied transistor behavior. The results
suggested that the doping-induced electron suppression seems to be the dominant
factor over the crystallinity variation for the achievement of well-operating TFTs. UV
photoemission spectroscopy (UPS) tests provided more evidence for the variation in
the electronic band structure after Mn2+
doping. For pristine Cs2SnI6, the Fermi level
(EF) is very close to the conduction band (CB) edge (0.02 eV), indicating a strong n-
type characteristic with high conductivity. For comparison, the 3 mol % Mn2+
doping
led to an upshift in the band energy and drove the EF away from the CB (Figures 4C
and 4D). The results further confirmed that Mn2+
acts as an efficient p-dopant to
weaken the n-type conductivity of Cs2SnI6, rationalizing the modulated channel
properties and the device performance of the ensuing TFTs.
E
A B
D
C
Figure 4. Film characterizations of Cs2SnI6 thin films as a function of Mn2+
doping ratio
(A and B) XRD patterns and Hall measurement results of Cs2SnI6 (CsI:SnI4 = 2:1.8) thin films as a
function of the Mn2+
doping ratio.
(C and D) UPS spectra of pristine Cs2SnI6 (CsI:SnI4 feed ratio = 2:1.8) and the one with 3 mol % Mn2+
doping. The inset in (D) shows the corresponding energy level diagrams.
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9. Highly stable Cs2SnI6-based TFTs and high-performance all-perovskite
complementary inverter
We noted that the optimized Mn2+
-doped Cs2SnI6 TFTs exhibited excellent oper-
ational and ambient stabilities. The fast-switching test of the device revealed a
constant current response with clear on/off states, satisfying the requirement as
a switching unit (Figure 5A). Continuous transfer curve scanning also indicated reli-
able device operation with negligible variations after 100 scans (Figure 5B). A more
in-depth device stability evaluation was performed at constant positive bias volt-
ages (VGS = VDS = 40 V), which showed a VTH shift of 7 V after 1.5 h of the
bias stress test (Figure 5C). We further examined the ambient stability of the de-
vices by monitoring the transfer characteristics as a function of the air exposure
time. The ambient stability of an Sn2+
-based phenethylammonium tin iodide
((PEA)2SnI4) TFT was also examined as a reference. Although the large molecular
spacer of PEA+
cations can act as a protective barrier against air invasion,51
the de-
vice still experienced rapid degradation due to the inherent Sn2+
oxidation issue
(Figure S7). To date, the stabilization of Sn2+
-based perovskites remains a consid-
erable obstacle to their practical application. Impermeable encapsulation, which
undoubtedly increases the production difficulty and costs, is necessary to ensure
high ambient stability. The Cs2SnI6-based TFT, which benefits from the stable
Sn4+
state and the strong Sn-I bonds, exhibits impressive durability with more reli-
able operation under ambient conditions for more than 1 week (Figures 5D and
S7), suggesting the great promise as a replacement for Sn2+
-based perovskites
in device applications.
We finally evaluated the feasibility of the optimized Cs2SnI6 TFT for more complex
circuit applications. We implemented a complementary inverter composed of
n-channel TFTs based on Mn-doped Cs2SnI6 and p-channel (PEA)2SnI4 TFTs (Fig-
ure 5E). The voltage transfer characteristics, as shown in Figure 5F, exhibited full
swing characteristics and rapid voltage transitions with a switching voltage close
to the ideal half-supply voltage (i.e., VDD/2). This indicated the matched electron
and hole mobilities of the two types of devices, which enabled a high peak gain of
38 at a VDD of 40 V (Figure 5G). This demonstration represents the first complemen-
tary inverter using devices with both n- and p-type halide perovskite semiconductor
channels, highlighting the potential of emerging halide perovskites for logic circuits
in various electronic applications.
In summary, we developed facile strategies to modulate the film quality of Cs2SnI6
perovskite and demonstrated their application in electronic devices of TFTs and
complementary inverters. We emphasize the important roles of the precursor engi-
neering and the Mn2+
doping in simultaneously modulating the film quality and elec-
tronic property of Cs2SnI6 perovskite films, ensuring the achievement of TFTs with
excellent operational and air stability. We believe that further developments of
film optimization and doping strategies of the environmentally friendly and stable
vacancy-ordered halide double perovskites would promote their widespread appli-
cation in various electronic and optoelectronic devices.
EXPERIMENTAL PROCEDURES
Resource availability
Lead contact
Further information and requests for resources and reagents should be directed
to and will be fulfilled by the lead contact, Prof. Yong-Young Noh (yynoh@
postech.ac.kr).
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10. V
I
V
V
I
FE
V
V V
V
I
V
V
A
B C D
E F G
Figure 5. TFT stability evaluation and all-perovskite complementary inverter
(A) Continuous on/off switching test.
(B) Consecutive transfer curve measurement with 100 cycles (VDS = 40 V).
(C) Variation of transfer curves under positive-bias stress measurements at different durations (VGS = VDS = 40 V).
(D) Normalized field-effect mobilities for the Sn2+
-based (PEA)2SnI4 and Sn4+
-based doped Cs2SnI6 TFTs as a function of air exposure time. RH, relative
humidity. The error bars were calculated from 4 individual devices.
(E) Diagram of complementary metal-oxide semiconductor (CMOS) inverter with assembled p-channel (PEA)2SnI4 TFT and n-channel doped Cs2SnI6
TFT.
(F and G) Voltage transfer and gain voltage curves of the complementary inverter at different VDDs.
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Cell Reports Physical Science 3, 100812, April 20, 2022 9
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11. Materials availability
This study did not generate new unique reagents.
Data and code availability
The authors declare that the data supporting the findings of this study are available
within the article and the supplemental information. All other data are available from
the lead contact upon reasonable request.
Materials
CsI (99.999%, perovskite grade), SnI4 (anhydrous, 99.99% trace metals basis), MnI2
(anhydrous, 99.99% trace metals basis), DMF (anhydrous, 99.8%), and DMSO (anhy-
drous, R99.9%) were used. All of the materials were purchased from Sigma-Aldrich
and used as received without further purification.
Preparation of the precursor solution
The Cs2SnI6 (0.1 M) precursor solutions were prepared by dissolving CsI and SnI4
powders with varied molar ratios (CsI:SnI4 = 2:1, 2:1.5, 2:1.8, and 2:2.2) in DMF/
DMSO (DMSO = 0–20 vol %) followed by stirring on a hot plate at 50
C for 2 h.
The MnI2 solution was prepared by dissolving MnI2 in DMF with the same conditions
and then mixed it into the Cs2SnI6 solution with different molar ratios, followed by
the 50
C stirring for 30 min before use. The precursor preparation was carried out
in an N2-filled glove box.
Thin-film fabrication and characterization
The samples for film characterizations were prepared by spin coating the precursors
on different Ar plasma-treated substrates at 8,000 rpm, followed by thermal anneal-
ing at 100
C for 5 min. The whole process was carried out in an N2-filled glove box.
The crystal structures of the different films were analyzed using XRD with CuKa radi-
ation (Bruker D8 ADVANCE) based on samples on glass substrates. The SEM images
were recorded using JSM-7800F Prime based on samples on Si wafers. The optical
absorptions of the thin films on quartz were conducted by a UV-visible spectropho-
tometer (JASCO V-770). The XPS and UPS analysis was performed using PHI 5000
VersaProbe (Ulvac-PHI, Japan) on Au/Ni/Si substrates. The TEM image was recorded
using JEOL JEM 2200FS.
Device fabrication and characterization
We fabricated the TFTs based on a bottom-gate, top-contact device structure in an
N2-filled glove box. Heavily doped Si substrates (resistivity: 1–100 U cm) with 100-
nm thermally grown SiO2 were used as the gate electrode and dielectric layer,
respectively. The deposition of Cs2SnI6-based channel layers follows the above pro-
cedures. The transistor fabrication was completed by evaporating Au source and
drain electrodes (40 nm) with a shadow mask under a high vacuum (107
Torr) using
a thermal evaporator placed in an N2-filled glove box. The channel length/width of
the TFTs is 150/1,000 mm.
All perovskite TFTs were characterized at room temperature (RT) in a dark N2-filled
glove box using a Keithley 4200-SCS (Tektronix) at a continuous bias mode. The
Cs2SnI6-based channel layers were properly isolated channels using the probe
scratch approach for the low gate leakage current (Ig). The mobility values (me) of
the TFTs were calculated in the saturation region:
me =
2L
WCi
v
ffiffiffiffiffiffi
IDS
p
vVGS
2
ll
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10 Cell Reports Physical Science 3, 100812, April 20, 2022
Article

12. where the L, W, and Ci are the channel length and width and dielectric areal capac-
itance (34 nF/cm2
), respectively. The IDS and the VGS are the source-drain current and
gate-source voltage, respectively. VTH was estimated by linearly fitting IDS
1/2
with
respect to VGS. The SS is the inverse of the maximum slope of the IDS-VGS plot. Before
the air stability measurement, all of the samples were simply encapsulated with poly
(perfluorobutenylvinylether) (CYTOP, AGC, TCL-801M). The Hall measurements
were performed with the van der Pauw method, using a 0.51-T magnet and home-
made sample holder in an N2-filled glove box at RT. The electrical signal during
the Hall measurement was obtained with a Keithley 4200-SCS.
SUPPLEMENTAL INFORMATION
Supplemental information can be found online at https://doi.org/10.1016/j.xcrp.
2022.100812.
ACKNOWLEDGMENTS
This study was supported by the Ministry of Science and ICT through the National
Research Foundation funded by the Korean government (NRF-2021R1A2C3005401)
and the Samsung Display Corporation. S.B. is grateful for the financial support of the
Swedish Research Council (no. 2020-03564).
AUTHOR CONTRIBUTIONS
A.L. and Y.-Y.N. conceived the project. A.L. carried out the experiments and
analyzed the data. H.Z., Y.R., and W.N. assisted in the film characterization and anal-
ysis. S.B., M.-G.K., H.-J.K., J.H.L., and H.Y.C. contributed to the experimental design
and data analysis. A.L., S.B., and Y.-Y.N. wrote the manuscript. All of the authors
contributed to the final version of the manuscript.
DECLARATION OF INTERESTS
The authors declare no competing interests.
Received: January 4, 2022
Revised: January 27, 2022
Accepted: February 21, 2022
Published: March 14, 2022
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