Manganese Oxide Nanoparticle as a New p-Type Dopant for High

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Manganese Oxides Nanoparticle as New P-type Dopant for High Performance Polymer Field-Effect Transistors Dang Xuan Long, Eun-Young Choi, and Yong-Young Noh ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b04729 • Publication Date (Web): 03 Jul 2017 Downloaded from http://pubs.acs.org on July 4, 2017

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ACS Applied Materials & Interfaces

Manganese Oxides Nanoparticle as New P-type Dopant for High Performance Polymer Field-Effect Transistors Dang Xuan Longa, Eun-Young Choib,*, Yong-Young Noha,* a

Department of Energy and Materials Engineering, Dongguk University, 30 Pildong-ro, 1-gil,

Jung-gu, Seoul 04620, Republic of Korea b

Korea Atomic Energy Research Institute, Daedoek-daero 989-111, Yuseong-gu, Daejeon

34057, Republic of Korea Corresponding Author *

E-mail: [email protected] (EYC), [email protected] (YYN)

Keywords: organic field-effect transistors, molecular doping, hole transport, p-type, manganese oxides.

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ABSTRACT We report a new p-type dopant, manganese oxide (Mn3O4) nanoparticle, to enhance organic field-effect transistors (OFETs) performance with conjugated polymers including poly(3hexylthiophene-2,5-diyl);poly[[N,N

9-bis(2-octyldodecyl)-

bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)];and

naphthalene-1,4,5,8-

poly[[2,5-bis(2-octyldodecyl)-

2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2′-(2,5-thiophene)bisthieno(3,2b) thiophene] -5,5′-diyl]] (DPPT-TT). Incorporating a small amount of Mn3O4 nanoparticle in the semiconductor film significantly improved hole mobility and decreased threshold voltage for all OFETs, indicating efficient Mn3O4 nanoparticle p-type doping. The Mn3O4 nanoparticle showed better doping efficiency than the widely used FeCl3 dopant due to better mixability with host conjugated polymers. In particular, doped DPPT-TT OFETs showed significantly improved mobility up to 2.35 (± 0.4) cm2/V·s with enhanced air and operational stability at 0.1 wt% doping concentration from 1.2 cm2/V·s for pristine devices.

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INTRODUCTION Organic semiconductors (OSCs) have received increasing attention in recent years because of their promising applications in various electric and optoelectric devices, such as organic photovoltaic cells1-3, organic light emitting diodes,4-5 and organic field-effect transistors (OFETs).6-7 OFETs are core devices for lightweight, flexible integrated circuits produced by cost effective solution based manufacturing processes.8-10 The quality of the semiconductor film and OSC structure mainly determines field-effect motility (µFET) which is a key figure of merit for OFETs.11-12 Conjugated polymers have been intensively investigated as the active layer for OFETs due to their easy solution processability, high mechanical flexibility, better device uniformity than small molecules, and electrical property tunability by controlling the polymer backbone and side chain structure.13-15 However, limited charge carrier motility and unstable device operation in ambient environments are major hurdles applying these devices in commercial products.16-17 Therefore, various approaches have been attempted to improve the electrical properties and ambient stability, largely by development of conjugated polymers and optimization the film molecular ordering and microstructure.18-20 Controlling OFET charge carrier density is another promising method to improve electric properties and stability, but has been less studied.21-23 Doping is a well-known conventional method to increase semiconductor charge carrier density. Doping has been employed to change OSCs to organic conductors or improve the charge injection property of organic devices through controlling barrier heights for charge injection at metal-OSC interfaces.24-25 Various inorganic and organic dopants have been developed for OSCs over the last two decades.26-27 Not only the dopant energetic structure with respect to host molecules, but also doping efficiency and stability without dopant diffusion are key requirements to develop high performance dopants.28 In particular, for solution based doping, the dopant molecule should be dissolved in the same solvent or have good mixability with OSCs to achieve efficient charge transfer from host molecules.28 Doping is also used for OFETs to improve µFET by filling trap states through the generated charge carriers.26,29 However, high doping concentrations decrease µFET by disrupting the semiconducting film crystallinity

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and also increasing the OFET off state current.30 Therefore, development of high efficiency dopant at low doping concentration is absolutely necessary. This study reports on manganese oxide (Mn3O4) nanoparticle as a new p-type dopant for conjugated polymers to improve OFET performance. Mn3O4 nanoparticle is commonly mixed in state of the art p and n-type ambipolar conjugated polymers, including poly(3hexylthiophene-2,5-diyl) (P3HT); poly[[N,N 9-bis(2-octyldodecyl)- naphthalene-1,4,5,8bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)] (P(NDI2OD-T2)); and poly[[2,5bis(2-octyldodecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2′-(2,5thiophene)bis-thieno(3,2b) thiophene] -5,5′-diyl]] (DPPT-TT) as the solution state at various doping concentrations to study doping effects on OFET characteristics. Structural and spectroscopic studies were performed to understand morphological feature changes and the conjugated polymer energetic levels after introducing the nanoparticle dopant. All Mn3O4 doped OFETs showed highly improved µFET even at low doping concentrations (0.1–0.2 wt%) without increasing the off state current. In particular, µFET of 2.35 (± 0.4) cm2/V·s was achieved with enhanced air stability for 0.1 wt% Mn3O4 doped DPPT-TT OFETs.

EXPERIMENTAL Synthesis of Mn3O4nanoparticle solution Mn3O4 nanoparticles were prepared by thermal decomposition of manganese (II) acetate tetrahydrate in the presence of surfactant molecules, such as oleic acid and oleylamine. Manganese (II) acetate tetrahydrate (Sigma Aldrich) was dissolved in xylenes to obtain a 20 mg/mL solution. A mixture of surfactant oleic acid (Sigma Aldrich) with oleylamine (Sigma Aldrich) (1:8, respectively) was adding in manganese (II) acetate tetrahydrate solution as a volume ratio of surfactant : solvent =1:4 ratio. The solution was heated to 90ºC over 5 min, under vigorous stirring, then 1 mL of deionized water was quickly added. The solution was maintained at 90ºC for 3 h, to induce sufficient growth. Finally, the resulting solution was cooled to room temperature and absolute ethanol was slowly added, to precipitate Mn3O4 nanoparticles (Figure S1 in supporting information). The precipitate was separated by

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centrifugation at 8000 rpm for 10 min, and washed twice with absolute ethanol. The resulting product was re-dispersed in n-hexane.31-32 The O2 dissolved solution and deionized water acted as the main oxidant, transforming partial Mn(II) into Mn(III); and the coexistence of Mn(II) and Mn(III) and ambient environment preferred formation of hausmannite Mn3O4, CH3COO–+ H2O → CH3COOH + OH–(1) and 6Mn2++12OH–+O2 → 2Mn3O4+6H2O (2).33 Device fabrication Source and drain (S/D) electrodes of Au/Ni (12 nm/3 nm) were patterned on glass substrates (Corning Eagle 2000) using conventional lift-off photolithography techniques. After cleaning in an ultrasonic bath with sequentially de-ionized water, acetone, and isopropanol, the S/D patterned substrates were treated with oxygen plasma. Semiconductor DPPT-TT, P3HT, and P(NDI2OD-T2) was dissolved in chlorobenzene (CB) to obtain a 5mg/mL solution. Mn3O4 in n-hexane and FeCl3 (Sigma Aldrich) were used as the p dopant, dissolved in 2-ethoxyethanol at 0.1wt%. To make a doped OSC base solution, blended OSCs and dopant solutions (0.05, 0.1, 0.2, and 0.4 wt%) were prepared by mixing the two separate solutions, and then shaking to obtain a homogenously mixture, which was maintained at 80°C overnight. The pristine and doped semiconductor solutions were spin-coated onto a patterned glass substrate as active layers and then annealed at 120°C or 250°C (DPPT-TT film) for 20 min. For the polymer gate dielectric, poly(methyl methacrylate) (PMMA) was spin-coated (~480 nm), and baked at 80°C for 2h to remove any residual solvent. The top gate bottom contact (TG/BC) OFETs were completed by forming gate electrodes on the channel region by evaporation of a thin Al film (50 nm) using a metal shadow mask.

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Thin film and device characterization OFET electrical characteristics were measured using a Keithley 4200-SCS in a nitrogen filled glove box. The µFET and threshold voltage (VTh) were calculated in the saturation regime using a gradual channel approximation equation. UPS measurements were performed using a PHI 5000 Versa Probe II (ULVAC-PHI, Inc) with base pressure 4.2×10−9 Torr. Contact resistance (RC) was extracted using the Y-function method (YFM).

RESULTS AND DISCUSSION

Figure 1. Chemical structure of (a) DPPT-TT, P3HT, and P(NDI2OD-T2) semiconductors; (b) Mn3O4 and FeCl3 used as dopant, and PMMA as gate dielectrics, and schematic diagram for top gate/bottom contact OFET geometry. Figure 1 shows the chemical structures for the employed conjugated polymers (semiconductor) and Mn3O4 and FeCl3 (dopant). FeCl3 is a commonly used p-type dopant for various organic devices24, 34 and was used as the reference dopant. Various dopant concentrations were directly mixed with the conjugated polymers. For p-type doping, the dopant must donate electrons to the highest occupied molecular orbital (HOMO) of host molecules. Efficient p-type doping is expected from Mn3O4 and FeCl3to DPPT-TT, P3HT, and P(NDI2OD-T2),because the Fermi levels (EF) of Mn3O4 and FeCl3 (-5.4 to -5.6 eV) are above the OSC HOMO levels (-5.0 to 5.3eV).7, 35Ultraviolet photoelectron spectroscopy (UPS) was used to check doping formation

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for pristine, and Mn3O4 and FeCl3 doped DPPT-TT films by observing the shift in OSC EF (∆EF) after doping. With addition of 0.2 wt% Mn3O4 or FeCl3, DPPT-TT EF shifted from -4.6 to -4.82 and -4.77 eV (Mn3O4 and FeCl3. respectively), corresponding to ∆EF = 0.22 and 0.17 eV, respectively (Figure 2(a)). The large shift of EF toward the DPPT-TT HOMO level indicates increased hole density at this doping concentration. Larger ∆EF for Mn3O4 doped DPPT-TT film means better doping efficiency of Mn3O4 than FeCl3 which is presumably due to better mixability of Mn3O4 nanoparticles with the conjugated polymer providing efficient charge transfer from the dopant to the host and higher metal atom content in Mn3O4 than FeCl3.28, 36

Figure 2(b) shows the UPS of pristine and Mn3O4doped DPPT-TT film with doping

concentrations 0.05 – 0.4 wt%. The DPPT-TT EF gradually decreased with increasing doping concentration, toward the DPPT-TT HOMO level. This indicates that higher doping concentration produce more holes up to 0.4 wt%.

Figure 2. Ultraviolet photoelectron spectra of bare and doped DPPT-TT films with (a) Mn3O4 and FeCl3 at 0.2 wt% and (b) Mn3O4 from 0.1wt% to 0.4 wt% doping concentration on indium thin oxide film. (c) X-ray photoelectron spectroscopy (XPS) for various doping levels and (d) Mn2pXPS spectra of bare and Mn3O4doped DPPT-TT films.

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To check the chemical composition at the doped DPPT-TT film surface, X-ray photoelectron spectroscopy (XPS) spectra were measured for pristine and DPPT-TT film with doping concentrations 0.1 – 0.4 wt%. The full XPS spectra of pristine and doped DPPT-TT films showed clear carbon C1s, sulfur S1s, and oxygen O1s peaks (Figure 2(c)). Figure S2a (supporting information) shows the C1s region enlarged for a clearer view. All films showed clear C1s peaks near 283.5 eV, corresponding to the strong C-C bond from DPPT-TT polymer at the film surface. Peaks for O1s, Mn2p, and Mn3s were also observed at 0.2 and 0.4 wt% doped DPPT-TT film surface. The Mn2p region in the XPS spectra is enlarged in Figure 2(d). The Mn2p spectrum from 0.2 wt% doping concentration shows two Gaussian curves corresponding to Mn2p2/3 (641.4 eV) and Mn2p1/2 (653.3 eV). Splitting between the Mn2p3/2 and the Mn2p1/2 level was 11.74 eV, which correlated well with the spin-orbit splitting width 12.10 eV for the two peaks.32 The peak position and splitting width for Mn3s (5.6 eV) are consistent with the values for Mn3O4.32, 37 The Mn2p peak intensity and ∆EF in UPS data of doped DPPT-TT film gradually increased with increasing of dopant concentration from 0.2 – 0.4 wt%. This indicates that Mn3O4 nanoparticles are well mixed with DPPT-TT up to 0.4 wt% blend ratio for efficient charge transfer.

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Figure 3. Transfer characteristics of (a) pristine and (b) Mn3O4 doped DPPT-TT; (c) P3HT and (d) P(NDI2OD-T2) OFETs with different doping concentrations (0.05, 0.1 and 0.2wt%). The DPPT-TT film was annealed at (a) 120°C and (b) 250°C. We studied the effect of doping on OFET characteristics using three different polymers, P3HT (p-type), P(NDI2OD-T2) (n-type), and DPPT-TT (ambipolar). Figure 3 shows the transfer curves of pristine and 0.05, 0.1, and 0.2 wt% Mn3O4 doped DPPT-TT (annealed at 120°C and 250°C), P3HT, and P(NDI2OD-T2) OFETs. The basic transistor properties are summarized in Table 1 and S1. All Mn3O4 doped devices showed highly improved hole µFET. The high temperature annealed (250°C) DPPT-TTOFETs showed rapidly increasing µFET (1.2 to 2.35 cm2/V·s for pristine and 0.1 wt% doping concentration, respectively), and then gradually decreased to 1.36 cm2/V·s at 0.4 wt% doped device. Mn3O4 doped P3HT OFETs showed similar µFET trend as DPPT-TT OFETs. P3HT OFETs exhibited maximum µFET of 0.28 cm2/V·s at 0.1 wt% doping and then decreased to 0.12 cm2/V·s at 0.4 wt% doping. On the other hands, the highest µFET (0.002 cm2/V·s) was obtained at 0.2 wt% doping concentration for (P(NDI2ODT2) OFETs. The large increase in µFET is due to filling the traps in the generated charge carrier by doping, creating more mobile carriers in the transport band under the same applied bias.29 The reduction in µFET at the high doping concentration (0.4 wt%) is due to crystallinity deterioration (Fig. S3) and long range OSC ordering due to adding excess dopant.30 We measured UV-vis absorption spectra for pristine and Mn3O4 doped DPPT-TT film (Fig. S9). By increasing dopant concentration, a small red shift of peak was observed. This data indicates better ordering of conjugated polymer film and is consistent with XRD result.38-39 However, no new absorption peak was detected after doping. The change in VTh with doping also supports this explanation. VTh in DPPT-TT OFETs gradually decreased from -42.8 to -37.7 V from pristine by 0.1wt% doping, and then slightly increased at high doping concentration (0.4 wt%).VTh of P3HT and P(NDI2OD-T2) devices showed similar trends with increasing of doping concentration. the critical control for VTh is the number of trap states in the OSC film. Thus, the largest shift of VTh in 0.1 wt% doped P3HT and DPPT-TT device means that most traps were filled by charge carriers generated from doping. In (P(NDI2OD-T2) OFETs, the highest µFET and the largest VTh shift occurred at 0.2

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wt% (not 0.1 wt%) doping, because n-type P(NDI2OD-T2) has more traps for holes at the tail state near HOMO than does DPPT-TT or P3HT. The shift of VTh in doped DPPT-TT OFETs was more clearly observed for the low temperature annealed device (120°C, Table S1). Therefore, a larger number of traps existed for the low temperature annealed DPPT-TT OFETs than high temperature case. The shift of subthreshold swing (SS) also was observe by doping of DPPT-TT film (Fig. S8) and details are summarized in Table S2 of supporting information. The maximum interface trap density (Nss) was also calculated by the SS value and added in Table S2.40-41 The lower Nss of doped DPPT-TT film is correlated with improved device performance by Mn3O4 doping. The on-state current (Ion) in the p-type region increased significantly for all doped devices, indicating increased charge carrier density by Mn3O4 doping. Interestingly, the off-state current (Ioff) remained almost constant at low doping concentration up to 0.2 wt%. On the other hand, doping concentration increased over 0.2 wt%, and Ioff increased significantly, finally keeping them “on" at all times (Fig. S4). This is consistent with previous research on doped OFETs.27

Figure 4. (a) Transfer characteristics of pristine and FeCl3 doped DPPT-TT OFETs (annealing temperature=250ºC). (b) Transfer characteristics of pristine, and FeCl3 (0.2 wt%) and Mn3O4 (0.1wt%) doped DPPT-TT OFETs (annealing temperature=250ºC).

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To investigate Mn3O4 doping efficiency, we compared against well-known FeCl3 dopant in DPPT-TT OFETs. Figure 4(a) shows the transfer characteristics for FeCl3 doping concentration in DPPT-TT OFETs. µFET increased from 1.41 for pristine to 1.78 cm2/V·s for 0.2 wt% FeCl3 doped DPPT-TT OFETs, and then decreased to 0.9 cm2/V·s at 0.4 wt% doping. The µFET improvement for FeCl3 doped DPPT-TT OFETs was less than that of Mn3O4 doped devices. Figure 4(b) shows the superior µFET enhancement and larger VTh shift for Mn3O4 than FeCl3 doped DPPT-TT OFETs, indicating better Mn3O4 doping efficiency. Mn3O4 doped DPPT-TT OFETs also showed the highest µFET at lower doping concentration (0.1 wt%) than FeCl3 (0.2 wt%). To further clarify the effect of doping on µFET, we used the doping concentration as the dopant molar ratio (MR). MR was calculated by the ratio of the number of dopant molecules used per monomer of the organic semiconducting polymer. The Mn3O4 dopant showed the highest µFET at around MR ~ 0.009, indicating better doping efficiency compared to the FeCl3 dopant showing the highest µFET at MR ~ 0.024. The better device performance in Mn3O4 doped DPPT-TT OFETs is also due to very good mixability of Mn3O4 nanoparticles with the conjugated polymer. Scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) mapping (Figure S6 in supporting information) clearly showed well dispersed Mn3O4 nanoparticles in OSC film even at higher concentration (1wt%) than normal doping concentration (0.1~0.4 wt%). Whereas FeCl3 showed a slightly aggregated feature in OSC film at 0.4 wt% doping concentration. Another doping benefit was a significant contact resistance (Rc) reduction, as shown in Figure S5 (supplementary information). We investigated Rc for Mn3O4 doped OFETs by YFM.42 All Mn3O4 doped OFETs had significantly reduced Rc compared to FeCl3 doping, and the smallest Rc were 16.2, 41.4, and 0.7×103 kΩ·cm (DPPT-TT, P3HT, and P(NDI2OD-T2), respectively) for 0.1 wt% doping concentration. Output characteristics of pristine and doped device also show a high Rc improvement.

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Figure 5. Fifty cycle scanned transfer curves of (a) pristine, (b) Mn3O4 doped, and (c) FeCl3 doped DPPT-TT OFETs for the bias stress test. (d) Normalized hole mobility of pristine and 0.2 wt% doped DPPT-TT devices with Mn3O4 and FeCl3 for 12 days stored in air.

We checked OFET air and operational stability improvement with Mn3O4 and FeCl3 doping, as shown in Figure 5. All doped DPPT-TT OFETs showed improved operational stability over pristine OFETs, as shown in Figures5 (a)–(c). DPPT-TT OFETs doped with Mn3O4 and FeCl3 exhibit better bias stress stability, with only 15% and 20%, respectively, decrease of hole mobility compared to pristine DPPT-TT OFETs (60%) after 50 cycling scans. Highly air-stable p-type OFETs have been recently demonstrated by addition of specific additives to remove residual water molecules in the OSC film.43 We also observed improved air stability for Mn3O4 doped OFETs comparing with pristine and FeCl3 doping. Figure 5(d) shows that storage in air for24h had no significant effect on hole µFET for all DPPT-TT OFETs (of pristine, and Mn3O4 and FeCl3 doped). However, hole µFET of pristine OFETs rapidly degraded

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when stored in air for longer periods. FeCl3 doped DPPT-TT OFETs showed better stability than pristine OFETS when stored for 3 days, but when stored for longer, hole µFET degraded faster than pristine OFETs. This is presumably due to the hygroscopic nature of FeCl3.44 Mn3O4 doped OFET showed superior stability for 12 days storage in air. Mn3O4 doped DPPT-TT OFET hole µFET decreased to 50% of its original value, whereas that of pristine or FeCl3 doped OFETs decreased to only 10–20% after 12 days storage in air. The improved air stability in Mn3O4 doped DPPT-TT OFETs is a consequence of reducing traps and/or preventing water penetration by the dopant. These results confirm that water in air has a very important effect on OFET ambient stability. Thus, Mn3O4 nanoparticle doping can improve not only device performance but also OFET ambient stability. Table 1. Fundamental parameters of pristine and doped DPPT-TT, P3HT and (P(NDI2OD-T2) OFETs with different Mn3O4 and FeCl3 doping concentrations. OFET characteristics were measured with VD = -80 V. The average mobility of the OFETs were measured with channel length L = 20 µm and channel width W = 1000 µm.

Semiconductor (dopant)

DPPT-TT annealed at 250ºC (Mn3O4) DPPT-TT annealed at 250ºC (FeCl3)

Doping ratio (wt%/MR)

Hole mobility (cm2/V·s)

VTh [V]

Ion and Ioff

Pristine 0.05wt%/0.0042 0.1wt% / 0.009 0.2wt% / 0.017 0.4wt% / 0.035 0.1wt%/ 0.012 0.2wt%/ 0.024 0.4wt%/ 0.049

1.2 (± 0.2) 1.65 (± 0.3) 2.35 (± 0.4) 1.87 (± 0. 5) 1.36 (± 0. 5) 1.41 (± 0.3) 1.78 (± 0.5) 0.9 (± 0.4) 2.5×10-4(± 1.1×10-4) 0.001 (± 0.001) 0.0016 (± 0.0005) 0.002 (± 0.0005) 1.0×10-3 (± 1.1×10-4) 0.1 (± 0.03) 0.17 (± 0.06) 0.28 (± 0.05) 0.15 (± 0.04) 0.12 (± 0.03)

42.8 (±2.1) 39.5 (±2.8) 37.7 (±2.5) 38.3 (±2.3) 39.4 (±2.7) 41.6 (±2.8) 40.3 (±2.8) 41.8 (±2.8)

102 102 102 102 102 102 102 102

Contact resistance [kΩ·cm] 32.1 (±3.4) 26.7 (±2.5) 16.2 (±4.2) 27.2 (±3.7) 33.4(±3.3) 28.7 (±28.5) 25.4(±28.5) 42.7 (±28.5)

90.4 (±5.0)

101

1.4×103

87.4 (±5.0) 83.6 (±5.0) 78.1 (±5.0)

101 101 101

0.9×103 0.7 ×103 0.4× 103

86.7 (±5.0)

101

-

pristine P(NDI2OD-T2) annealed at 150ºC(Mn3O4)

0.05wt%/ 0.004 0.1wt%/ 0.009 0.2wt%/ 0.018 0.4wt%/ 0.036

P3HTannealed at 150ºC(Mn3O4)

pristine 0.05wt%/ 0.007 0.1wt%/ 0.014 0.2wt%/ 0.028 0.4wt%/ 0.057

9.8 (±2.0) 4.5 (±1.7) 3.2 (±0.4) 2.1 (±0.4) 5.6 (±2.0)

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10 104 104 103 102

55.8 (±5.2) 48.3 (±6.1) 41.4(±5.8) 49.6 (±4.6) 54.7(±5.5)


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CONCLUSIONS We have reported a new p-type dopant, Mn3O4 nanoparticle and investigated dopant effects on OFET characteristics with three conjugated polymers: DPPT-TT, P3HT, and P(NDI2OD-T2). Mn3O4 showed efficient p-type doping for OFETs with these polymers even at very low doping concentration (0.1wt%), with superior doping efficiency and stability than FeCl3 due to better intermixing and stability of Mn3O4 itself. Mn3O4 doped OFETs exhibited significantly improved hole µFET, and ambient and operational stability. These results validate a simple and effective method to achieve high performance and stability of p-type polymer OFETs.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (EYC), [email protected] (YYN) Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This work was supported by the Center for Advanced Soft-Electronics (2013M3A6A5073183) funded by the Ministry of Science, ICT & Future Planning and the National Research Foundation of Korea (NRF) funded by the Korean Government (MISP) [Grant No. 2017M2A8A5015077].

Supporting Information Figures showing SEM, C1s S1s XPS, XRD, transfer characteristics P3HT films formed by spin coating high concentration Mn3O4 doping, output characteristics of TG/BC OFETs, EDX mapping and UV-vis absorption. Tables showing electrical characteristics of top-gate OFETs at 120ºC annealing and fundamental parameters in linear region.

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