Bilayer p-n heterojunctions are promising structures to construct ambipolar organic field-effect transistors (aOFETs) for organic integrated circuits. However, due to the lack of effective strategies for high-quality p-n heterojunctions with clear interfaces, the performance of aOFETs is commonly and substantially lower than that of their unipolar counterparts, which hinders the development of aOFETs toward practical applications. Herein, a one-step solution crystallization strategy was proposed for the preparation of high-quality bilayer p-n heterojunctions. A mixed solution of a p- and an n-type organic semiconductor was dropped on a liquid substrate, and vertical phase separation occurred spontaneously during crystallization to produce bilayer p-n heterojunctions composed of molecularly thin two-dimensional molecular crystals. Due to the clear interface of the bilayer p-n heterojunctions, the maximum mobility (average mobility) reached 1.96 cm2 V−1 s−1 (1.12 cm2 V−1 s−1) for holes and 1.27 cm2 V−1 s−1 (0.61 cm2 V−1 s−1) for electrons in ambient air. So far as we know, these values were the highest among double-channel aOFETs measured in ambient air. This work provides a simple yet efficient strategy to construct high-quality bilayer p-n heterojunctions, which lays a foundation for their application in high-performance optoelectronic devices.

Organic p-n heterojunctions have gained considerable attention in organic electronics1–4 because they are the basic elements of various organic optoelectronic devices,5,6 such as organic light-emitting diodes (OLEDs),7,8 organic photovoltaics (OPVs),9–11 and complementary integrated circuits (CICs).12,13

Ambipolar organic field-effect transistors (aOFETs),14,15 in which both electrons and holes can be transported, are essential for building organic integrated circuits (ICs) with high noise margin, low power consumption, and high integration density.16,17 The simplest strategy to construct an aOFET is to use a single-component organic semiconductor as the active layer to transport both holes and electrons. However, this strategy poses a huge challenge for both material design and device fabrication. On the one hand, most organic semiconductors are unipolar,18 and ambipolar materials are scarce.19 On the other hand, there is an injection barrier for either electrons or holes in devices with symmetric electrodes.20 Thus, new strategies are urgently needed for high-performance aOFETs. To date, both p- and n-type organic semiconductors have been developed rapidly and have demonstrated high mobility exceeding 10 cm2 V−1 s−1,21–23 which laid a solid foundation for the development of double-channel aOFETs. Actually, researchers have already made various attempts to fabricate high-performance double-channel aOFETs. In the early days, bilayer p-n heterojunctions were obtained by evaporating two different materials sequentially on the substrate using a two-step process.24,25 However, the mobilities of these aOFET devices were typically less than 10−2 cm2 V−1 s−1.26,27 The reason for the poor performance is that bilayer p-n heterojunctions are composed of polycrystalline thin films with rough surfaces and high density of defects, which are not conducive to the transport of charge carriers. With the continuous development of crystal engineering, the successful preparation of organic single-crystalline p-n heterojunctions has significantly improved the mobility of aOFETs. In 2013, Fan et al.28 prepared organic single-crystalline bilayer p-n heterojunctions from a mixed solution using the droplet pinned crystallization method. Both the p-channel and n-channel of the aOFETs were composed of aligned ribbon-like crystals. The maximum mobility was 0.16 cm2 V−1 s−1 for holes and 0.17 cm2 V−1 s−1 for electrons in ambient air. The achievement of high-performance aOFETs was ascribed to the high quality of the single crystals. The improvement in device performance indicated that single-crystalline bilayer p-n heterojunctions could be an important structure to realize high-performance aOFETs. Regrettably, the small effective area of the heterojunctions based on the ribbon crystals hindered their practical application.9,14,28,29

Two-dimensional molecular crystals (2DMCs) are monolayer or few-layered organic single crystals.30,31 They are compatible with thin-film technology for large-area applications. Compared with commonly used polycrystalline films, 2DMCs exhibited many advantages, including atomically flat surface, long-range order, low density of defects, and molecular scale thickness. Thus, bilayer p-n heterojunctions composed of 2DMCs will surely showcase their brilliance in high-performance aOFETs. Several strategies including solution-epitaxy32 and space-confined strategy31 to grow 2DMCs have been reported, which laid a foundation for the fabrication of bilayer p-n heterojunctions composed of 2DMCs. In 2019, Zhu et al.33 constructed bilayer p-n heterojunctions composed of 2DMCs of 2,6-bis(4-hexylphenyl)anthracene (C6-DPA) and a furan-thiophene quinoidal compound (TFT-CN) by stacking the 2DMCs layer by layer (LBL) manually. Well-balanced aOFETs were achieved with a hole mobility of 0.87 cm2 V−1 s−1 and an electron mobility of 0.82 cm2 V−1 s−1 in ambient air.33 However, both the hole and electron mobilities of the bilayer p-n heterojunctions decreased substantially compared with the single-component materials (the maximum hole mobility was 2.74 cm2 V−1 s−1 for C6-DPA,30 and the maximum electron mobility was 1.36 cm2 V−1 s−1 for TFT-CN34). The reason was that the multiple transfer processes introduced contaminants to the interface of the heterojunctions, which was detrimental for devices.35,36 Thus, it was imperative to develop alternative strategies to fully exploit the high performance of bilayer p-n heterojunctions composed of 2DMCs.

Herein, a one-step solution crystallization strategy was developed for the preparation of high-quality bilayer p-n heterojunctions composed of 2DMCs. A mixed solution of a p- and an n-type semiconductor was dropped on a liquid substrate. Vertical phase separation occurred spontaneously during the crystallization, and bilayer p-n heterojunctions composed of 2DMCs were formed on the liquid surface. The detrimental manual transfer procedure was totally eliminated by the one-step solution crystallization strategy; thus, the contamination problem of the LBL process was avoided. Due to the clear interface of the bilayer p-n heterojunctions, the maximum mobility (average mobility) reached 1.96 cm2 V−1 s−1 (1.12 cm2 V−1 s−1) for holes and 1.27 cm2 V−1 s−1 (0.61 cm2 V−1 s−1) for electrons in ambient air, which was the highest values among double-channel aOFETs measured in ambient air.

C6-DPA and TFT-CN were purchased from Luminescence Technology Corp. Sodium perfluorooctanoate was purchased from J&K Scientific Ltd.

Optical and cross-polarized optical microscope images were obtained using a Nikon ECLIPSE Ci-POL polarized optical microscope. Tapping mode atomic force microscopy (AFM) was carried out using a Bruker Dimension Icon. X-ray diffraction (XRD) was measured using a Rigaku Smartlab diffractometer at 45 kV and 200 mA with monochromatic Cu Kα radiation. The UV–Vis absorption spectrum was measured using a SHIMADZU UV-3600 Plus spectrophotometer. Photoluminescence (PL) spectroscopy was carried out using a confocal smart Raman system with 405 nm laser excitation. The electrical properties of the OFETs were obtained using a Keithley 4200 SCS in ambient air at room temperature.

OFETs were fabricated with bottom-gate/top-contact configurations. Octadecyltrichlorosilane (OTS) modified SiO2 (300 nm) was used as the gate dielectric layer. Ag (80 nm) electrodes were fabricated by a “gold-layer sticking” technique.37 The mobility was calculated in the saturation regime according to the formula IDS = (W/2L)μCi(VGSVth)2, where IDS stands for the source–drain current, μ stands for the field-effect mobility, Vth stands for the threshold voltage, VGS stands for the applied gate voltage, L stands for the channel length, W stands for the channel width, and Ci stands for the specific capacitance (10 nF cm−2).

Both C6-DPA31,32 and TFT-CN34,38 [see Fig. 1(a) for their chemical structures] are high-performance organic semiconductors with high mobility and high ambient stability (see Fig. S1 in the supplementary material for unipolar OFETs), and they were used as the p- and n-type semiconductors, respectively, in this study. The details of producing their pristine 2DMCs were given in the supplementary material.

FIG. 1.

Schematic illustration of the one-step solution crystallization strategy to produce bilayer p-n heterojunctions composed of 2DMCs.

FIG. 1.

Schematic illustration of the one-step solution crystallization strategy to produce bilayer p-n heterojunctions composed of 2DMCs.

Close modal

The procedures to construct the bilayer p-n heterojunctions by the one-step solution crystallization strategy are shown in Fig. 1. First, both C6-DPA and TFT-CN were dissolved in chlorobenzene, and the concentrations were 0.2 mg ml−1 for C6-DPA and 0.5 mg ml−1 for TFT-CN [Fig. 1(a) and Fig. S2 in the supplementary material]. Sodium perfluorooctanoate with a concentration of ∼0.001 mg ml−1 was added to the solution to increase the spreading of the solution.30 The mixed solution was dropped on the liquid substrate of glycerol [Fig. 1(b)]. Vertical phase separation occurred spontaneously during crystallization.39 After the solvent evaporated completely, bilayer p-n heterojunctions composed of 2DMCs of C6-DPA and TFT-CN floating on the glycerol surface were produced [Fig. 1(c)]. Then, the bilayer p-n heterojunctions were transferred to OTS-modified SiO2/Si substrates by stamping [Fig. 1(d)]. Finally, the substrate carrying the bilayer p-n heterojunctions was rinsed using deionized water and dried.

Figures 2(a)2(c) show the optical microscope (OM) images of 2DMCs of C6-DPA, TFT-CN, and their bilayer p-n heterojunctions, respectively. There was a distinct boundary between the 2DMCs and the substrate, and no notable cracks were present on the films. The OM images of the two pristine 2DMCs showed different colors [Figs. 2(a) and 2(b)], indicating that they had different thicknesses. Judging from the AFM measurements, the thicknesses of 2DMCs of C6-DPA and TFT-CN were 9.3 and 3.4 nm, respectively, corresponding to three and two molecule layers (see the supplementary material for calculating the layer number of 2DMCs). The root mean square (rms) roughness was 0.17 and 0.19 nm, respectively [Figs. 2(d) and 2(e)]. Figure 2(f) showed the AFM image of a bilayer p-n heterojunction. Clear boundaries between the two pristine 2DMCs and the bilayer p-n heterojunction were observed. The thickness of the bilayer p-n heterojunction was 12.6 nm, which was consistent with the sum of the thicknesses of 2DMCs of C6-DPA (9.5 nm) and TFT-CN (3.1 nm). The surface of the bilayer p-n heterojunction was smooth (rms = 0.43 nm) without notable cracks, indicating the high quality of the prepared bilayer p-n heterojunction [Fig. 2(f)].

FIG. 2.

OM images of 2DMCs of (a) C6-DPA, (b) TFT-CN, and (c) their bilayer p-n heterojunctions. (d)–(f) The corresponding AFM images of the grown crystals.

FIG. 2.

OM images of 2DMCs of (a) C6-DPA, (b) TFT-CN, and (c) their bilayer p-n heterojunctions. (d)–(f) The corresponding AFM images of the grown crystals.

Close modal

To identify the layer sequence of the bilayer p-n heterojunctions (whether 2DMCs of TFT-CN or C6-DPA were on top), the rectification behavior of the heterojunction was probed. According to the energy level diagram of C6-DPA and TFT-CN,33 spontaneous charge transfer from TFT-CN to C6-DPA occurred when they were brought together to form the bilayer p-n heterojunctions (Fig. S3 in the supplementary material). Therefore, the direction of the built-in electric field was from TFT-CN to C6-DPA. The current–voltage (IV) curves of the bilayer p-n heterojunction showed an obvious rectification behavior (Fig. S4 in the supplementary material). The source–drain current (IDS) was able to pass through the device only under forward bias (VDS > 0). Judging by the direction of rectification, the built-in electric field was from the top layer to the bottom layer of the bilayer p-n heterojunction. Based on the IV analysis and the energy level diagram of C6-DPA/TFT-CN, the layer sequence of the bilayer p-n heterojunctions was that 2DMCs of TFT-CN were on top of 2DMCs of C6-DPA (denoted as TFT-CN on C6-DPA hereafter) after transferring to the SiO2/Si substrates.

The OM image of a bilayer p-n heterojunction is shown in Fig. 3(a). The area of the bilayer p-n heterojunction was larger than 5 × 104µm2. Under a polarized optical microscope (POM), when the sample was rotated by 45°, the color of the bilayer p-n heterojunction changed uniformly, confirming the single-crystalline nature of the bilayer p-n heterojunction [Figs. 3(b) and 3(c)]. We further checked the structures of the bilayer p-n heterojunctions by out-of-plane XRD [Fig. 3(d)]. In the XRD patterns of C6-DPA, three sharp diffraction peaks at 2θ = 2.8°, 5.5°, and 13.7° were observed. XRD patterns of TFT-CN showed two sharp peaks at 2θ = 5.5° and 11.0°, which corresponded to the (001) and (002) planes based on the single crystal structure of TFT-CN (TFT-CN belonged to the triclinic crystal system with a = 10.396 Å, b = 11.133 Å, c = 16.325 Å, α = 79.71°, β = 86.14°, and γ = 63.27°).34 All characteristic peaks of C6-DPA and TFT-CN appeared in the XRD patterns of the bilayer p-n heterojunctions, indicating the successful production of the bilayer p-n heterojunctions. Furthermore, the optical properties of the p-n heterojunctions were investigated by UV–Vis absorption spectroscopy and PL spectroscopy [Figs. 3(e) and 3(f)]. Both the absorption and emission spectra of the p-n heterojunctions were composed of characteristic peaks of C6-DPA and TFT-CN. No new peak appeared, and no peaks of C6-DPA or TFT-CN disappeared. We did not observe the charge transfer absorption or emission bands at longer wavelengths than the optical gap of the pristine 2DMCs.40,41 All these pieces of evidence confirmed the successful production of bilayer p-n heterojunctions composed of 2DMCs.

FIG. 3.

(a) An OM image and (b) and (c) POM images of a 2DMC bilayer p-n heterojunction. (d) XRD patterns, (e) UV–Vis absorption spectroscopy and (f) PL spectroscopy of 2DMCs of C6-DPA, TFT-CN, and their p-n heterojunctions.

FIG. 3.

(a) An OM image and (b) and (c) POM images of a 2DMC bilayer p-n heterojunction. (d) XRD patterns, (e) UV–Vis absorption spectroscopy and (f) PL spectroscopy of 2DMCs of C6-DPA, TFT-CN, and their p-n heterojunctions.

Close modal

Encouraged by the highly ordered structure of the bilayer p-n heterojunctions, aOFETs were constructed to investigate their electrical properties. All aOFETs were fabricated and measured in ambient air (see Fig. S5 in the supplementary material for the device configurations). Figures 4(a) and 4(d) show the transfer characteristics of the bilayer aOFETs, where typical V-shaped curves were obtained. The two arms represent electron and hole transport. In the output curves of both the p-channel and the n-channel mode, the aOFETs exhibited a sharp increase in IDS at low gate voltages (VGS) and high drain voltages (VDS) due to the transport of both electrons and holes15,29,33 [Figs. 4(b) and 4(e)]. In addition, the linear relationship between IDS and VDS at low VDS in the output curves demonstrated that the contact resistance between the electrodes and semiconductors was small. Due to the clear interface of the bilayer p-n heterojunctions, the maximum mobility (average mobility) reached 1.96 cm2 V−1 s−1 (1.12 cm2 V−1 s−1) for holes and 1.27 cm2 V−1 s−1 (0.61 cm2 V−1 s−1) for electrons [Figs. 4(c) and 4(f)]. Table I summarizes the performances of organic single-crystalline double-channel aOFETs. As can be seen from Table I, the mobilities in this work were the highest among those measured in ambient air.

FIG. 4.

OFET characteristics of bilayer p-n heterojunctions composed of 2DMCs: (a) Typical transfer curves, (b) output curves, and (c) the mobility distribution in the p-channel operation mode. (d) Typical transfer curves, (e) output curves, and (f) the mobility distribution in the n-channel operation mode.

FIG. 4.

OFET characteristics of bilayer p-n heterojunctions composed of 2DMCs: (a) Typical transfer curves, (b) output curves, and (c) the mobility distribution in the p-channel operation mode. (d) Typical transfer curves, (e) output curves, and (f) the mobility distribution in the n-channel operation mode.

Close modal
TABLE I.

Performance comparison of double-channel aOFETs based on organic single crystals.

p-type materialsMorphologiesn-type materialsMorphologiesMax μh (cm2 V−1 s−1)Max μe (cm2 V−1 s−1)AtmosphereReferences
TIPS-pentacene Microcrystals PTCDI-C13 Thin film 8.8 × 10−3 3.8 × 10−2 Air 1  
CuPc Nanoribbons F16CuPc Nanoribbons 0.07 0.05 N2 45  
C8-BTBT Ribbons C60 Ribbons 0.16 0.17 Air 28  
Tips-pentacene Wire PTCDI-C8 Wire 0.23 0.13 Air 14  
C8-BTBT 2DMC TFT-CN 2DMC 0.43 0.11 Air 44  
C6-DPA 2DMC TFT-CN 2DMC 0.87 0.82 Air 33  
C8-BTBT 2DMC NDI-C6 2DMC 1.40 0.65 Vacuum 46  
diF-TES-ADT Ribbons C60 Ribbons 0.60 1.55 N2 29  
C8-BTBT Ribbons TIPS-TAP Ribbons 1.84 0.27 N2 29  
TIPS-BP Ribbons TIPS-TAP Ribbons 1.02 1.90 N2 29  
C6-DPA 2DMC TFT-CN 2DMC 1.96 1.27 Air This work 
p-type materialsMorphologiesn-type materialsMorphologiesMax μh (cm2 V−1 s−1)Max μe (cm2 V−1 s−1)AtmosphereReferences
TIPS-pentacene Microcrystals PTCDI-C13 Thin film 8.8 × 10−3 3.8 × 10−2 Air 1  
CuPc Nanoribbons F16CuPc Nanoribbons 0.07 0.05 N2 45  
C8-BTBT Ribbons C60 Ribbons 0.16 0.17 Air 28  
Tips-pentacene Wire PTCDI-C8 Wire 0.23 0.13 Air 14  
C8-BTBT 2DMC TFT-CN 2DMC 0.43 0.11 Air 44  
C6-DPA 2DMC TFT-CN 2DMC 0.87 0.82 Air 33  
C8-BTBT 2DMC NDI-C6 2DMC 1.40 0.65 Vacuum 46  
diF-TES-ADT Ribbons C60 Ribbons 0.60 1.55 N2 29  
C8-BTBT Ribbons TIPS-TAP Ribbons 1.84 0.27 N2 29  
TIPS-BP Ribbons TIPS-TAP Ribbons 1.02 1.90 N2 29  
C6-DPA 2DMC TFT-CN 2DMC 1.96 1.27 Air This work 

There are four main reasons for achieving high performance: (i) The molecular thin thickness of the 2DMCs can effectively reduce the contact resistance, thereby ensuring high injection efficiency.42 (ii) The high-quality single-crystalline nature of the 2DMCs is conducive to charge transport in aOFETs.43 (iii) The atomically flat surface and long-range order of the 2DMCs provide a smooth and clean interface.21 (iv) More importantly, the problem of interface contamination of the manual transfer procedure is totally eliminated by the one-step solution crystallization strategy.33,44

In conclusion, a simple yet efficient one-step solution crystallization strategy was developed to produce bilayer p-n heterojunctions composed of 2DMCs. By dropping a mixed solution on a liquid substrate, vertical phase separation occurred spontaneously during crystallization, and bilayer p-n heterojunctions composed of 2DMCs were formed on the liquid surface. Benefiting from the small contact resistance, clean interface, and single-crystalline nature of the 2DMCs, aOFETs exhibited superior performance, with a maximum mobility of up to 1.96 cm2 V−1 s−1 for holes and 1.27 cm2 V−1 s−1 for electrons. So far as we know, these values were the highest among double-channel aOFETs measured in ambient air. The one-step solution crystallization strategy provided an effective route for producing bilayer p-n heterojunctions composed of 2DMCs, which opened a new door for fabricating high-performance and well-balanced aOFETs.

See the supplementary material for detailed descriptions of substrate modification, growth and transfer of pristine 2DMCs, calculation of the layer number of 2DMCs, unipolar OFETs based on C6-DPA and TFT-CN, the influence of concentrations on the morphologies of p-n heterojunctions, the energy level diagram of C6-DPA and TFT-CN, IV characteristics, and the schematic diagram of the aOFETs.

This study was supported by the National Natural Science Foundation of China (Grant Nos. 51873148, 51903186, 52073206, and 51633006) and the Natural Science Foundation of Tianjin City (Grant No. 18JCYBJC18400).

J.Y. and X.T. contributed equally to this work.

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

1.
U.
Jeong
,
G.
Tarsoly
,
J.
Lee
,
Y.
Eun
,
J.
Do
, and
S.
Pyo
,
Adv. Electron. Mater.
5
,
1800652
(
2019
).
2.
J.
Wu
,
Q.
Li
,
G.
Xue
,
H.
Chen
, and
H.
Li
,
Adv. Mater.
29
,
1606101
(
2017
).
3.
Y.
Wu
,
P.
Ma
,
N.
Wu
,
X.
Kong
,
M.
Bouvet
,
X.
Li
,
Y.
Chen
, and
J.
Jiang
,
Adv. Mater. Interfaces
3
,
1600253
(
2016
).
4.
Q.
Li
,
S.
Ding
,
W.
Zhu
,
L.
Feng
,
H.
Dong
, and
W.
Hu
,
J. Mater. Chem. C
4
,
9388
9398
(
2016
).
5.
Q.
Tang
,
G.
Zhang
,
B.
Jiang
,
D.
Ji
,
H.
Kong
,
K.
Riehemann
,
Q.
Ji
, and
H.
Fuchs
,
SmartMat
2
,
109
118
(
2021
).
6.
Y.
Yao
,
Y.
Chen
,
H.
Wang
, and
P.
Samorì
,
SmartMat
1
,
e1009
(
2020
).
7.
X.
Wang
,
C.
Shi
,
Q.
Guo
,
Z.
Wu
,
D.
Yang
,
X.
Qiao
,
T.
Ahamad
,
S. M.
Alshehri
,
J.
Chen
, and
D.
Ma
,
J. Mater. Chem. C
4
,
8731
8737
(
2016
).
8.
Q.
Zhang
,
J.
Li
,
K.
Shizu
,
S.
Huang
,
S.
Hirata
,
H.
Miyazaki
, and
C.
Adachi
,
J. Am. Chem. Soc.
134
,
14706
14709
(
2012
).
9.
X.
Zhao
,
T.
Liu
,
Y.
Zhang
,
S.
Wang
,
X.
Li
,
Y.
Xiao
,
X.
Hou
,
Z.
Liu
,
W.
Shi
, and
T. J. S.
Dennis
,
Adv. Mater. Interfaces
5
,
1800336
(
2018
).
10.
J. W.
Mok
,
Z.
Hu
,
C.
Sun
,
I.
Barth
,
R.
Muñoz
,
J.
Jackson
,
T.
Terlier
,
K. G.
Yager
, and
R.
Verduzco
,
Chem. Mater.
30
,
8314
8321
(
2018
).
11.
A.
Tada
,
Y.
Geng
,
Q.
Wei
,
K.
Hashimoto
, and
K.
Tajima
,
Nat. Mater.
10
,
450
455
(
2011
).
12.
K.-J.
Baeg
,
J.
Kim
,
D.
Khim
,
M.
Caironi
,
D.-Y.
Kim
,
I.-K.
You
,
J. R.
Quinn
,
A.
Facchetti
, and
Y.-Y.
Noh
,
ACS Appl. Mater. Interfaces
3
,
3205
3214
(
2011
).
13.
Y.
Sakamoto
,
T.
Suzuki
,
M.
Kobayashi
,
Y.
Gao
,
Y.
Fukai
,
Y.
Inoue
,
F.
Sato
, and
S.
Tokito
,
J. Am. Chem. Soc.
126
,
8138
8140
(
2004
).
14.
H.
Shim
,
A.
Kumar
,
H.
Cho
,
D.
Yang
,
A. K.
Palai
, and
S.
Pyo
,
ACS Appl. Mater. Interfaces
6
,
17804
17814
(
2014
).
15.
H.
Wang
,
J.
Wang
,
X.
Yan
,
J.
Shi
,
H.
Tian
,
Y.
Geng
, and
D.
Yan
,
Appl. Phys. Lett.
88
,
133508
(
2006
).
16.
E. J.
Meijer
,
D. M.
De Leeuw
,
Setayesh
,
E.
van Veenendaal
,
B. H.
Huisman
,
P. W. M.
Blom
,
J. C.
Hummelen
,
U.
Scherf
, and
T. M.
Klapwijk
,
Nat. Mater.
2
,
678
682
(
2003
).
17.
B.
Crone
,
A.
Dodabalapur
,
Y.-Y.
Lin
,
R. W.
Filas
,
Z.
Bao
,
A.
LaDuca
,
R.
Sarpeshkar
,
H. E.
Katz
, and
W.
Li
,
Nature
403
,
521
523
(
2000
).
18.
H.
Dong
,
X.
Fu
,
J.
Liu
,
Z.
Wang
, and
W.
Hu
,
Adv. Mater.
25
,
6158
6183
(
2013
).
19.
R.
Ozdemir
,
D.
Choi
,
M.
Ozdemir
,
G.
Kwon
,
H.
Kim
,
U.
Sen
,
C.
Kim
, and
H.
Usta
,
J. Mater. Chem. C
5
,
2368
2379
(
2017
).
20.
J.
Zaumseil
and
H.
Sirringhaus
,
Chem. Rev.
107
,
1296
1323
(
2007
).
21.
D.
He
,
J.
Qiao
,
L.
Zhang
,
J.
Wang
,
T.
Lan
,
J.
Qian
,
Y.
Li
,
Y.
Shi
,
Y.
Chai
,
W.
Lan
,
L. K.
Ono
,
Y.
Qi
,
J.-B.
Xu
,
W.
Ji
, and
X.
Wang
,
Sci. Adv.
3
,
e1701186
(
2017
).
22.
Y.
Yuan
,
G.
Giri
,
A. L.
Ayzner
,
A. P.
Zoombelt
,
S. C.
Mannsfeld
,
J.
Chen
,
D.
Nordlund
,
M. F.
Toney
,
J.
Huang
, and
Z.
Bao
,
Nat. Commun.
5
,
3005
(
2014
).
23.
C.
Liu
,
T.
Minari
,
X.
Lu
,
A.
Kumatani
,
K.
Takimiya
, and
K.
Tsukagoshi
,
Adv. Mater.
23
,
523
526
(
2011
).
24.
J.
Wang
,
H.
Wang
,
X.
Yan
,
H.
Huang
,
D.
Jin
,
J.
Shi
,
Y.
Tang
, and
D.
Yan
,
Adv. Funct. Mater.
16
,
824
830
(
2006
).
25.
J.
Wang
,
H.
Wang
,
X.
Yan
,
H.
Huang
, and
D.
Yan
,
Chem. Phys. Lett.
407
,
87
90
(
2005
).
26.
K.
Eguchi
,
M. M.
Matsushita
, and
K.
Awaga
,
J. Phys. Chem. C
122
,
26054
26060
(
2018
).
27.
C.
Rost
,
D. J.
Gundlach
,
S.
Karg
, and
W.
Rieß
,
J. Appl. Phys.
95
,
5782
5787
(
2004
).
28.
C.
Fan
,
A. P.
Zoombelt
,
H.
Jiang
,
W.
Fu
,
J.
Wu
,
W.
Yuan
,
Y.
Wang
,
H.
Li
,
H.
Chen
, and
Z.
Bao
,
Adv. Mater.
25
,
5762
5766
(
2013
).
29.
H.
Li
,
J.
Wu
,
K.
Takahashi
,
J.
Ren
,
R.
Wu
,
H.
Cai
,
J.
Wang
,
H. L.
Xin
,
Q.
Miao
,
H.
Yamada
,
H.
Chen
, and
H.
Li
,
J. Am. Chem. Soc.
141
,
10007
10015
(
2019
).
30.
J.
Yao
,
Y.
Zhang
,
X.
Tian
,
X.
Zhang
,
H.
Zhao
,
X.
Zhang
,
J.
Jie
,
X.
Wang
,
R.
Li
, and
W.
Hu
,
Angew. Chem., Int. Ed.
58
,
16082
16086
(
2019
).
31.
Q.
Wang
,
F.
Yang
,
Y.
Zhang
,
M.
Chen
,
X.
Zhang
,
S.
Lei
,
R.
Li
, and
W.
Hu
,
J. Am. Chem. Soc.
140
,
5339
5342
(
2018
).
32.
C.
Xu
,
P.
He
,
J.
Liu
,
A.
Cui
,
H.
Dong
,
Y.
Zhen
,
W.
Chen
, and
W.
Hu
,
Angew. Chem., Int. Ed.
55
,
9519
9523
(
2016
).
33.
X.
Zhu
,
Y.
Zhang
,
X.
Ren
,
J.
Yao
,
S.
Guo
,
L.
Zhang
,
D.
Wang
,
G.
Wang
,
X.
Zhang
,
R.
Li
, and
W.
Hu
,
Small
15
,
1902187
(
2019
).
34.
C.
Wang
,
X.
Ren
,
C.
Xu
,
B.
Fu
,
R.
Wang
,
X.
Zhang
,
R.
Li
,
H.
Li
,
H.
Dong
,
Y.
Zhen
,
S.
Lei
,
L.
Jiang
, and
W.
Hu
,
Adv. Mater.
30
,
1706260
(
2018
).
35.
F.
Liu
,
W.
Wu
,
Y.
Bai
,
S. H.
Chae
,
Q.
Li
,
J.
Wang
,
J.
Hone
, and
X.-Y.
Zhu
,
Science
367
,
903
(
2020
).
36.
K. S.
Novoselov
,
D.
Jiang
,
F.
Schedin
,
T. J.
Booth
,
V. V.
Khotkevich
,
S. V.
Morozov
, and
A. K.
Geim
,
Proc. Natl. Acad. Sci. U. S. A.
102
,
10451
10453
(
2005
).
37.
Q.
Tang
,
Y.
Tong
,
H.
Li
,
Z.
Ji
,
L.
Li
,
W.
Hu
,
Y.
Liu
, and
D.
Zhu
,
Adv. Mater.
20
,
1511
1515
(
2008
).
38.
Y.
Xiong
,
J.
Tao
,
R.
Wang
,
X.
Qiao
,
X.
Yang
,
D.
Wang
,
H.
Wu
, and
H.
Li
,
Adv. Mater.
28
,
5949
5953
(
2016
).
39.
M.
Kang
,
H.
Hwang
,
W.-T.
Park
,
D.
Khim
,
J.-S.
Yeo
,
Y.
Kim
,
Y.-J.
Kim
,
Y.-Y.
Noh
, and
D.-Y.
Kim
,
ACS Appl. Mater. Interfaces
9
,
2686
2692
(
2017
).
40.
Y.
Zhang
,
S.
Yang
,
X.
Zhu
,
F.
Zhai
,
Y.
Feng
,
W.
Feng
,
X.
Zhang
,
R.
Li
, and
W.
Hu
,
Sci. China-Chem.
63
,
973
979
(
2020
).
41.
Y.
Wang
,
Y.
Li
,
W.
Zhu
,
J.
Liu
,
X.
Zhang
,
R.
Li
,
Y.
Zhen
,
H.
Dong
, and
W.
Hu
,
Nanoscale
8
,
14920
14924
(
2016
).
42.
A.
De Sanctis
,
G. F.
Jones
,
D. J.
Wehenkel
,
F.
Bezares
,
F. H. L.
Koppens
,
M. F.
Craciun
, and
S.
Russo
,
Sci. Adv.
3
,
e1602617
(
2017
).
43.
B.
Peng
,
S.
Huang
,
Z.
Zhou
, and
P. K. L.
Chan
,
Adv. Funct. Mater.
27
,
1700999
(
2017
).
44.
L.
Wang
,
C.
Wang
,
X.
Yu
,
L.
Zheng
,
X.
Zhang
, and
W.
Hu
,
Sci. China-Mater.
63
,
122
127
(
2019
).
45.
Y.
Zhang
,
H.
Dong
,
Q.
Tang
,
S.
Ferdous
,
F.
Liu
,
S. C. B.
Mannsfeld
,
W.
Hu
, and
A. L.
Briseno
,
J. Am. Chem. Soc.
132
,
11580
11584
(
2010
).
46.
J.
Guo
,
S.
Jiang
,
M.
Pei
,
Y.
Xiao
,
B.
Zhang
,
Q.
Wang
,
Y.
Zhu
,
H.
Wang
,
J.
Jie
,
X.
Wang
,
Y.
Shi
, and
Y.
Li
,
Adv. Electron. Mater.
6
,
2000062
(
2020
).

Supplementary Material