New strategy for enhancing performance of P3HT-based organic field-effect transistor viaregulating the precipitated speed of solute in volatile solvents

Han, Tao; Sun, Linshan; Guo, Yanxi; Ding, Shufang; Jin, Gui; Jiang, Chunzhi; Huang, Xiaoyi;Zhang, Xiaofeng; Chang, Fa

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Published: 01/10/2020

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Published version (DOI):10.1016/j.polymertesting.2020.106788

Publication details:Han, T., Sun, L., Guo, Y., Ding, S., Jin, G., Jiang, C., Huang, X., Zhang, X., & Chang, F. (2020). New strategy forenhancing performance of P3HT-based organic field-effect transistor via regulating the precipitated speed ofsolute in volatile solvents. Polymer Testing, 90, [106788]. https://doi.org/10.1016/j.polymertesting.2020.106788

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Polymer Testing 90 (2020) 106788

Available online 30 July 20200142-9418/© 2020 Elsevier Ltd. All rights reserved.

New strategy for enhancing performance of P3HT-based organic field-effect transistor via regulating the precipitated speed of solute in volatile solvents

Tao Han a,b,*, Linshan Sun b, Yanxi Guo b, Shufang Ding b, Gui Jin b, Chunzhi Jiang b, Xiaoyi Huang b, Xiaofeng Zhang c,d,**, Fa Chang a

a Fujian Provincial Key Laboratory of Advanced Materials Processing and Application, Fujian University of Technology, Fuzhou, 350118, PR China b Hunan Provincial Key Laboratory of Xiangnan Rare-Precious Metals Compounds Research and Application, School of Electronic Information and Electrical Engineering, Xiangnan University, Chenzhou, 423000, PR China c Department of Mechanical Engineering, City University of Hong Kong, 999077, Hong Kong, China d National Engineering Laboratory for Modern Materials Surface Engineering Technology & the Key Lab of Guangdong for Modern Surface Engineering Technology, Guangdong Institute of New Materials, Guangzhou, 510650, PR China

A B S T R A C T

In this work, a new strategy is proposed to improve the performance of poly (3-hexylthiophene-2,5-diyl) (P3HT) based organic field-effect transistor (OFET). The high orientation of P3HT chain is obtained via utilizing precipitation characteristics of P3HT in volatile CH2Cl2 with the temperature decrease of solution in the hot spin- coating process. Meanwhile, a small amount of 1,2-dichlorobenzene (ODCB) with high boiling point is introduced into CH2Cl2 to make the inner part of the film stay in liquid state for a long time, and prolong the self-organization time of P3HT chain. Compared with control device prepared in pure CH2Cl2, the mobility of optimized device obtained by using blended solvent increases about 20-fold, the on/off ratio enhances about three orders of magnitude, and the operation time window of spin-coating up to 30 min (control device < 30 s). With this new strategy, the film quality can be easily controlled, which provides a new method for preparation of high-performance polymer optoelectronic devices.

1. Introduction

Poly (3-hexylthiophene-2,5-diyl) (P3HT), a classical p-type conju-gated polymer, is widely applied in organic photo-electronic devices, such as polymer solar cell (PSC), organic field-effect transistor (OFET) and so on, for its small weights, low costs, flexibility, solution process-ability and high mobility [1–4]. Generally speaking, the 3-alkyl sub-stituents of P3HT can be incorporated into a polymer chain with two different regioregularities: head to tail (HT) and head to head (HH). And the large percentage of the HH regioregularity can bring high regior-egularity and enhance mobility [5]. P3HT is easy to be self-organized in solution, resulting in the formation of two different orientations (face-on and edge-on) due to the interaction stacking. The difference of hole mobility at these two orientations can reach up to 100-fold [6]. Changing the processing conditions, such as molecular weight, dielectric layer, solvent annealing, marginal solvent, can significantly vary the mobility of P3HT, which, in nature, is equivalent to the effects of reasonably regulating the orientation of P3HT chain [7–12]. R.J. Kline et al. reported that the mobility of P3HT depended on its molecular

weight, and varied 3–4 orders of magnitude (from 10− 6 to 10− 2

cm2/(V⋅s)) with the increase of molecular weight [13]. The residual disorder in the P3HT films reported by H. Sirringhaus et al. was related to temperature, and increased temperature promoted the orderly crys-tallization of P3HT, improving the mobility [6]. Z. Bao et al. stated that the mobility of P3HT immensely varied (from 6.2 × 10− 4 to 4.5 × 10− 2

cm2/(V⋅s)) when different solvents were used [14]. As high molecular polymers, P3HT devices are normally prepared by

solution processing. The selection of solvent is the key to obtaining high- performance P3HT device. The critical factors include solvent boiling point, solvent polarity, and the solute solubility in solvent [15–19]. Good solvents, such as chloroform (CHCl3), chlorobenzene (CB) and 1, 2-dichlorobenzene (ODCB), which can completely dissolve P3HT poly-mer, are all suitable for P3HT film preparation [20]. However, mainly face-on alignment, which hinders obtainment of high hole mobility, are observed in P3HT chain prepared by spin-coating with good solvents [21]. At present, a wide variety of the blended solvents are used to improve the photo-electric performance of device, such as mixture of high/low boiling point solvent, strong/weak polarity solvent, and

* Corresponding author. Hunan Provincial Key Laboratory of Xiangnan Rare-Precious Metals Compounds Research and Application, School of Electronic Infor-mation and Electrical Engineering, Xiangnan University, Chenzhou, 423000, PR China. ** Corresponding author. Department of Mechanical Engineering, City University of Hong Kong, 999077, Hong Kong, China.

E-mail addresses: than_xnu@hotmail.com, than@xnu.edu.cn (T. Han), zxf200808@126.com (X. Zhang).

Contents lists available at ScienceDirect

Polymer Testing

journal homepage: http://www.elsevier.com/locate/polytest

https://doi.org/10.1016/j.polymertesting.2020.106788 Received 30 May 2020; Received in revised form 17 July 2020; Accepted 28 July 2020

Polymer Testing 90 (2020) 106788

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good/poor solvent [11,17,22–25]. P. Morvillo et al. optimized inkjet-printed P3HT-based photoactive layer morphology by using co-solvent systems composed of higher boiling point (ODCB) and rela-tively lower boiling point (CB) solvent, thus obtaining high photo-electric conversion efficiency [24]. When mixing good and poor solvents, unfavorable interactions between the polymer and the poor solvent drive the aggregation of chains, leading to its transformation into nanostructures [26,27]. S. Sun et al. found that when using poor solutions to drive P3HT chain self-assembly in the preparation of nanofibers, adding a small amount of good solvent (CB) facilitated the control of the nanofiber morphology and the crystallization of the P3HT chain [11]. Based on the fact that the hexane is a good solution for alkyl side chains, but a poor solvent for polythiophene backbones, N. Kiriy et al. added hexane into the good solvent (CHCl3) to induce ordered main-chain collapses and one dimensional aggregation of regioregular

poly (3-alkylthiophene)s [25]. In particular, CH2Cl2 is a marginal solvent of P3HT, since the solu-

bility of P3HT polymer is strongly dependent on solution temperature. At high temperature, P3HT polymer dissolves completely (equivalent to good solvent), while at low temperature it precipitates (equivalent to poor solvent), and the main chain of P3HT in this solvent tends to be edge-on alignment. By using this characteristics of CH2Cl2, H. Yang et al. obtained P3HT device of high mobility through spin-coating and drop- coating hot solution of P3HT polymer [28]. However, the marginal solvent CH2Cl2 with low boiling point (~41 ◦C) volatilizes easily, resulting in the rapid drying of P3HT films and large film roughness. Hence, it is difficult to control the morphology of P3HT films, leading to low repeatability of device performance. To solve above-mentioned problems, a new strategy is proposed, where the main solvent of CH2Cl2 is used to provide a better orientation for P3HT chain, and the good solvent (ODCB) with high boiling point is doped into CH2Cl2 to control the precipitation speed of P3HT. In this way, the crystallization time of P3HT is prolonged and the surface roughness of the film is reduced, eventually leading to a higher mobility in the device.

2. Experimental section

The bottom-gate OFET device structure used in this work is shown in Fig. 1. OFETs were fabricated in a top contact geometry with a structure composed of Si/SiO2/OTS/P3HT/Ag electrodes. Octadecyltri-chlorosilane (OTS, 98%), CH2Cl2 (99.9%), CB (99.9%) and ODCB (99%) were purchased from J&K. Regioregular P3HT (average Mw ~ 50,000–100,000), CHCl3 (99.8%) and NH3⋅H2O (28% NH3 in H2O) were purchased from Sigma-Aldrich. All of the commercially available chemicals were used without further purification. Highly n-doped sili-con and thermally grown SiO2 (300 nm) were selected as the back-gate

Fig. 1. The device structure of P3HT-based OFET. The inset image are chemical structures of P3HT and OTS.

Fig. 2. UV–vis absorption spectra of P3HT films by hot spin-coating (70 ◦C): (a) different solvent doping, (b) different concentration of ODCB solvent doping into CH2Cl2. GIXRD patterns of P3HT films by hot spin-coating (70 ◦C): (c) different solvent doping, (d) different concentration of ODCB solvent doping into CH2Cl2. Here, the P3HT films is treated by solvent annealing with NH3⋅H2O (70 ◦C, 8 h).

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and first inorganic gate dielectrics respectively. After cleaning Si/SiO2 substrates with plasma for 5 min, the substrates as well as the OTS (30 μl) were placed in a petri dish covered by aluminum foil, and heated at 140 ◦C for 2 h in nitrogen glove box. The extra OTS on Si/SiO2 substrates were cleaned by spin-coating (6000 r.p.m, 60 s) with CHCl3 solution (100 μl), followed by the drying of substrates in the vacuum environ-ment. The blended solution was heated at 70 ◦C and stirred with 250 r.p. m until the light orange color of solution appeared. The P3HT (0.4 wt%, 1500 r.p.m, 60 s) in different solvents was hot spin-coated on OTS self- assembly monolayer. Then, all the samples were heated at 100 ◦C for 5 min to regulate the orientation of P3HT chain. The P3HT films were further annealed with NH3⋅H2O or CH2Cl2 solvent in the petri dish covered by aluminum foil at 70 ◦C (8 h). The Ag electrodes (100 nm) were deposited under vacuum as the source and drain electrodes. The initial deposition rate of Ag electrodes were 0.1 Å/s, and it was increased with the increase of film thickness. Before testing the parameters of P3HT devices, the prepared OFETs were placed in a nitrogen glove box and annealed at different temperatures for 30 min to eliminate the de-fects or traps formed due to the contact between the Ag electrode and the active layer.

The atomic force microscopy (AFM) images were obtained by a Dimension edge (Bruker). Absorption measurement (UV–vis) was per-formed on a Shimadzu UV-3100 spectrophotometer. The grazing inci-dence X-ray diffraction (GIXRD) was measured by a Smart Lab III instrument (Rigaku). The OFET characterizations were tested in air using a four semiconductor parameter analyzer (Keithley 2636 B) with Cascade probe station. The saturation region output curves of OFET are obtained by applying the following equation [29].

Id =W2L

⋅μCi(Vg − Vth0

)2 (1)

where Id, μ, W (1000 μm) and L (50 μm) are the drain-source current, the field effect mobility, channel width and length of OFET, respectively. Ci (11.5 nF/cm2) is the capacitance perunit area of the SiO2 dielectric, since the capacitance of OTS (self-assembly monolayer) is neglected. Vg and Vth0 are the gate voltage and threshold voltage of OFET, respectively.

3. Results and discussion

The CH2Cl2 solvent is a unique marginal solvent for P3HT. The addition of CH2Cl2 solvent can lead to the complete dissolution of P3HT (light orange color) at high temperature (70 ◦C) and the re-precipitation of P3HT (dark red color) once the temperature decreases (Fig. S1). The volatilization rate of the solution can be controlled by doping solvents with different boiling point to CH2Cl2. Fig. S1 shows that after adding ODCB (boiling point: 180 ◦C) [30], the color of hot blend solution (70 ◦C) remains unchanged (light orange color) after 30 min cooling. The UV–vis absorption spectrum of P3HT film is measured (Fig. 2). The film absorption spectrum is composed of two parts: at low energy, the dominant part of the film corresponds to the weakly interacting H-aggregate states in the crystalline regions; at high energy, the intra-chain states form due to the abundant disordered chains [31]. For the active layer formed in pure CH2Cl2, its absorption bands at 515, 550 and 600 nm exhibit obvious peaks (Fig. 2a), showing highly crystalline order of P3HT chain with π-π stacking and H-aggregate states [26,31, 32]. When the good solvent CHCl3 with low boiling point (boiling point: 62 ◦C) [28] is blended with CH2Cl2, owing to the fast volatilization speed of the blended solvent, the film absorption peak of P3HT is similar to that of pure CH2Cl2. However, when CB or ODCB with high boiling point is selected as the doping solvent, the absorption peak of P3HT film in the range of 300–515 nm (high energy part) narrows obviously (Fig. 2a), indicating that the states of the intra-chain of P3HT are more orderly [22,31]. In addition, for the film prepared with high boiling point blended solvent, due to the decrease of the conjugation length of the

P3HT chain segments, the absorption peak intensity at 600 nm decreases (Fig. 2a), suggesting that P3HT chains could partly dissolve in a good solvent [22]. Moreover, P3HT films prepared with mixture of CH2Cl2 and ODCB at different ratio are tested. It can be seen that, the absorption peak of P3HT films has a slight red shift with the change of ODCB concentration (Fig. 2b), which indicates that changing the ODCB doping ratio can further regulate the crystalline order of P3HT chain [33]. Furthermore, inset image of Fig. 2b shows that the absorption peak of P3HT film decreases at the wavelength of 600 nm when ODCB is doped in high proportion (CH2Cl2:ODCB, volume ratio = 4:6), suggesting conjugation length of the P3HT chain, strongly influenced by the addi-tion of ODCB, also decreases.

Fig. 2c–d present the grazing incidence X-ray diffraction (GIXRD) of P3HT films. As shown in Fig. 2c, the strongest peak of P3HT film at 5.4◦

corresponds to (100) reflections [14]. The (h00) reflections are confined in a vertical narrow region (edge-on), while the (010) reflection is

Fig. 3. AFM topography images (2 μ m × 2 μ m) and phase images of P3HT film by hot spin-coating (70 ◦C) with different blended solvents: (a) pure CH2Cl2, (b) CH2Cl2:CHCl3 (volume ratio = 8:2), (c) CH2Cl2:CB (volume ratio = 8:2) and (d) CH2Cl2:ODCB (volume ratio = 8:2). Here, the P3HT films is treated by solvent annealing with NH3⋅H2O (70 ◦C, 8 h).

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present in the lateral horizontal one (face-on) [6,34]. Hence, the P3HT chain in pure CH2Cl2 or CH2Cl2:ODCB solvent tends to be edge-on alignment (Fig. 2c). In addition, the (100) reflection intensity of P3HT decreases after adding ODCB (Fig. 2c), which further indicates that pure CH2Cl2 is beneficial to the crystallization of P3HT chain. Besides, compared with the different concentration of ODCB solvent doping into CH2Cl2, it can be seen that the (100) reflection intensity at 8:2 (CH2Cl2: ODCB) is highest, showing the best crystallinity, which is consistent with the result of Fig. 2b.

Fig. 3 and Fig. S2 present the AFM topography images and phase

images of P3HT film doped with different types of blended solvents, where the effects of the changes of the CH2Cl2:ODCB ratio are also illustrated. It can be observed in the AFM topography images that the P3HT film doped in pure CH2Cl2 solvent has nanofibrillar structures (Fig. 3a). Since CH2Cl2 is the marginal solvent of P3HT, the use of this solvent can cause the hexyl side chains of P3HT to orient with an edge- on structure on the substrate easily via spin-coating (Fig. 2c), and π-π stacking planes of inter P3HT backbones form parallel to the substrate [28]. However, pure CH2Cl2 is highly volatile so that the surface of spin-coating film dries easily, and the mean-square surface roughness

Fig. 4. The dependence of the morphology of the P3HT films via hot drop-coating (70 ◦C) with different blended solvents on cooling time.

Fig. 5. The image of the P3HT films via hot spin-coating (70 ◦C) with doping different solvents.

Scheme 1. The solution state, solution cross section and morphology change of P3HT film by hot spin-coating with solution at low (a), middle (b) and high (c) boiling point.

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(Rq) is large (Rq: 8.92 nm, Fig. S3). After adding the volatile CHCl3 solvent into CH2Cl2 (Fig. 3b), the nanofibrillar structures of P3HT films disappear, and the roughness of P3HT films decreases significantly (Rq: 4.69 nm, Fig. S3). Besides, after doping high boiling point CB or ODCB, the roughness of P3HT film decreases more (Fig. 3c–d, and Figs. S2–S3). The phase images of P3HT film also show that the domain sizes of P3HT are large and presents in irregular shapes in pure CH2Cl2 solvent (Fig. 3a). While introducing high boiling point solvent into CH2Cl2 or changing ODCB doping concentration with CH2Cl2, domain sizes of P3HT decreases to different level (Fig. 2c–d, Fig. 3c–d, and Fig. S2), indicating that ordered chain alignment can be achieved by this method [35].

Fig. 4 shows that after the hot CH2Cl2 mixed with different boiling point solvent is dripped onto Si/SiO2 substrate, the drying time of the film increases with the rising boiling point of the doping solvent. For instance, pure CH2Cl2 solvent turns dark red and dries gradually within 30 s, while CH2Cl2:ODCB (volume ratio = 8:2) solvent remains un-changed for 30 min after hot drip-coating. This means that longer self- organization time in the P3HT chain is attained, which in turn allows the polymer chains to rearrange and brings high amount of π-π-stacking [36]. Besides, the hot spin-coating films with different morphologies can be controlled via mixing different solvents (Fig. 5). The higher the boiling point of the blend solvent, the smoother the spin-coating film, which is consistent with the film roughness as shown in Fig. 3 and Fig. S2. The above results indicate that doping high boiling point solvent induces the larger spin-coating operation time window is beneficial to the subsequent solution processing (Figs. 4–5).

According to the solution state, film absorption peak, AFM of different active layers from Figs. 2–3, images of hot drop-coating and spin-coating films (Figs. 4–5), and Figs. S1–S3, a model is established to analyze the change of solution in the spin-coating process (Scheme 1). Since the surface of solution (mainly based on CH2Cl2 solvent) is exposed to the external environment in the glove box, the solution surface cools and volatilizes first. Besides, the unique temperature characteristics of P3HT in CH2Cl2 solvent makes enormous P3HT pre-cipitate on the outermost surface, and the precipitated concentration gradually decreases from outside to inside (Scheme 1a). The analysis of the solution flow on the substrate during the spin-coating process reveals that the linear velocity of the solution near the substrate is larger than the upper part [37,38], leading to the solution spinning out through the bottom boundary from the top to the bottom (Scheme 1a). Meantime, the large surface tension and viscosity of precipitated P3HT in the outermost surface gradually lead the surface to collapse from top to bottom and spread into a plane. Scheme 1a and Figs. 4–5 illustrate that the P3HT precipitated from the surface basically covers the whole so-lution and remains complete during the hot spin-coating process. In addition, for pure CH2Cl2 solvent with low boiling point, large number of P3HT precipitates formed near the surface easily results in an increase

of the film roughness (Scheme 1a, Figs. 3a and 5). When a small amount of high boiling point good solvent (e.g. ODCB) add into CH2Cl2, there is no co-boiling point of blended solvents. During the hot spin-coating process, the CH2Cl2 solvent volatilizes first, leading to the precipita-tion of P3HT, and afterwards the P3HT precipitated far from the surface of the solution partially re-dissolves in ODCB solvent. Finally, the pre-cipitation of P3HT on the outer surface and a slowdown in the volatil-ization of the internal solvent can be obtained simultaneously, extending the self-organization time of P3HT chain and lowering film roughness (Scheme 1b, Figs. 2a and 3d). For the solution with high concentration of ODCB solvent, although low surface roughness can be obtained, the boiling point of the blended solvent is relatively high, which in turn hinders the precipitation of P3HT, and finally limits the crystallization of the film (Scheme 1c, Fig. 2b–d and Fig. S2b).

In order to further clarify the role of precipitated P3HT in the active layer, OFET is prepared to characterize the electrical properties (Fig. 6 and Figs. S4–S6). Taking CH2Cl2:ODCB (volume ratio = 8:2) blended solvent as an example, the effects of different vapor solution treatment, annealing temperature of electrode and active layer thickness on the device performance are optimized. The results show that the best device performance can be obtained by vapor solution treatment with NH3⋅H2O (70 ◦C) to active layer (60 nm thickness) and annealing (70 ◦C) again after thermal evaporating electrode (Figs. S7–S11). It can be seen from Fig. 6a and Figs. S4–S6 that P3HT devices exhibit typical p-type OFET performance. The on-state current (6.4 × 10− 7 A) of P3HT film prepared from pure CH2Cl2 solvent is significantly higher than that from pure CHCl3 solvent (3.2 × 10− 7 A, Fig. S5b) and pure ODCB solvent (2.8 ×10− 7 A, Fig. S6b). P3HT chain in CH2Cl2 tends to be edge-on alignment (Fig. 2c), benefiting carriers transfer in OFET, while P3HT in CHCl3 or ODCB tends to be face-on alignment, weakening carriers transfer in the active layer [28]. According to Scheme 1a and Scheme 1c, the on-state current of P3HT in pure CH2Cl2 solvent is larger than that in pure ODCB solvent possibly due to the abundant precipitated P3HT, and the precipitated P3HT may be more inclined to edge-on alignment (Fig. 2c). In addition, the P3HT devices prepared with pure CH2Cl2 solvent cannot be turn-off normally, resulting in high threshold voltage (Vth0 ~ 39 V), low hole mobility (~0.002 cm2/(V⋅s)) and on/off ratio (~200) as shown in Fig. 6. This is attributed to the strong volatility of pure CH2Cl2 solvent, a major contributing factor to the rapid drying, rough surface and abundant defects/traps in the film (Figs. 2–3). After doping CHCl3 sol-vent into CH2Cl2, the roughness (Rq ~ 4.69 nm, Fig. S3a), the Vth0 (~13 V), on/off ratio (~2.1 × 104), and hole mobility (~0.008 cm2/(V⋅s)) of the P3HT film improves significantly (Fig. 6b). It can be seen from Scheme 1b that CHCl3 is a good solvent for P3HT, enabling the surface of hot blended solution on the substrate to contain the precipitated P3HT during the spin-coating process. Meanwhile, the evaporation speed of the internal solution slows down, prolonging the self-organization time of P3HT chain. The results show that the on-state current of the device

Fig. 6. The electrical properties of P3HT devices by hot spin-coating (70 ◦C) with doping different solvents into CH2Cl2: (a) transfer curve, (b) on/off ratio, Vth0 and hole mobility. Here, the P3HT films is treated by solvent annealing with NH3⋅H2O (70 ◦C, 8 h) and further electrodes annealing with 70 ◦C (30 min).

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increases by using the precipitated P3HT, while the on/off ratio and threshold voltage decrease via slowing down the solution volatilization. After adding higher boiling point CB or ODCB solvent into CH2Cl2, the concentration of precipitated P3HT and volatilization speed of the blended solution further changed, improving the device performance. For instance, the on/off ratio of P3HT device from CH2Cl2:ODCB (vol-ume ratio = 8:2) solvent is as high as 2.4 × 105, and the mobility in-creases to 0.04 cm2/(V⋅s) (Fig. 6b). To sum up, the electrical properties of P3HT devices at different levels can be obtained by changing the solution boiling point to reasonably control the amount of precipitated P3HT.

In order to verify combined action between the precipitated P3HT and high boiling point solvent in regulating the electrical behavior of P3HT devices, the performance of P3HT devices with different CH2Cl2: ODCB ratios are further compared. According to Fig. S3b, the roughness of P3HT layer decreases with the increase of ODCB concentration in CH2Cl2. The high concentration of ODCB in blended solution means decreasing the proportion of CH2Cl2 solvent correspondingly, specif-ically speaking, the boiling point of the blended solution getting closer to that of ODCB solvent. Hence, the solution state during spin-coating process gradually changes from Scheme 1a to Scheme 1c, decreasing the amount of precipitated P3HT. Fig. 7a–b show that the on/off ratio and mobility of the device increase first, then decrease with the increase of doping ODCB concentration, and ultimately reach the optimum per-formance when volume ratio of CH2Cl2:ODCB is 8:2. Therefore, the P3HT devices with low roughness and high mobility can be easily ob-tained by blending high boiling point solvent with marginal solvent. This provides a simple and effective method for the preparation of high- efficiency P3HT organic solar cells, OLED and other devices, showing a broad application prospect.

4. Conclusions

In conclusion, the high performance of P3HT-based OFET is obtained via utilizing the volatile CH2Cl2 marginal solvent mixed with slight high boiling point good solvent (ODCB). With this new strategy, the precip-itation speed of P3HT is controlled in volatile solvent, improving the film quality effectively. Compared with P3HT device from pure CH2Cl2 solvent, the mobility of the device with blended solvent increased about 20-fold (μ: from 0.002 to 0.038 cm2/(V⋅s)), the on/off ratio increased about three orders of magnitude (on/off ratio: from 200 to 2.4 × 105), and the roughness decreased significantly (Rq: from 8.92 to 2.01 nm).

CRediT authorship contribution statement

T. H. conceived the research. L. S., Y. G. and G. J. fabricated the OFET device. S. D., C. J., F. C. and X. H. contributed to the electrical analysis of

OFET device. T. H. and X. Z. interpreted the results and wrote the manuscript.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors acknowledge the financial support by the Hunan Pro-vincial Natural Science Foundation of China (2019JJ50565), Open Fund Project of Fujian Provincial Key Laboratory of Advanced Materials Processing and Application of Fujian University of Technology (KF–C18004). We gratefully thank a Project Supported by Scientific Research Fund of Hunan Provincial Education Department (18A461, 16A199, 14C1060), Scientific Research Fund of Chenzhou (zdyf201908), Fund of Xiangnan University (2019XJ29), the Scientific Research Start-up Fund for High-level Talents in Xiangnan University.

Appendix B. Supplementary data

Supplementary data to this article can be found online at https://doi. org/10.1016/j.polymertesting.2020.106788.

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