Alignment of linear polymeric grains for highly stable N-type thin-film transistors

Abstract

•Fast deposition of polymer thin films with aligned grains and molecules•The polyacrylonitrile can tune the size of the pre-aggregates in polymer solution•Microscopic structures of polymers affected the thermal stability of transistors•The electron mobilities of transistors were >3.5 cm2V–1s–1 from 200 to 460 K For polymeric thin-film transistors, the ordered arrangements of polymer backbones, the flat face-on crystallites, and long linear grains can simultaneously improve the carrier transport efficiency. These strategies reduce pinholes, grain boundaries, and barriers in the charge transport paths. The aligned films have smaller extent of microscopic structural disorders, fewer localized states, and lower structural energies, thereby improving the thermal stability of devices. Temperature-insensitive property is very important for transistors. Based on the aligned polymeric thin films, we prepared the transistors with great thermal stability. The electron mobilities based on top-gate transistors were more than 3.5 cm2V–1s–1 at temperatures between 200 and 460 K. Temperature-insensitive properties are attractive for most electronics, including polymeric semiconducting devices. Especially, polymeric field-effect transistors (FETs) with high mobility have been important research targets due to their broad applications. However, polymeric FETs with stable charge transport operating at extremely cold or hot zones are faced with enormous challenges. In this study, the polyacrylonitrile was found to significantly tune the sizes of pre-aggregates of polymers in solutions and the crystallinity of the polymeric films. The orientation of 5–25 μm linear grains in the films were prepared through the bar-coating process with polyacrylonitrile as an additive, which stabilized the electron mobility over a wide range of temperatures. The linear-grain morphology of the film contributed to reducing the holes and grain boundaries in the transport paths of carriers. Typically, the top-gate FETs based on P(NDI2OD-T2) displayed a stable electron transporting behavior from 200 to 460 K, with mobility greater than 3.5 cm2V−1s−1. Temperature-insensitive properties are attractive for most electronics, including polymeric semiconducting devices. Especially, polymeric field-effect transistors (FETs) with high mobility have been important research targets due to their broad applications. However, polymeric FETs with stable charge transport operating at extremely cold or hot zones are faced with enormous challenges. In this study, the polyacrylonitrile was found to significantly tune the sizes of pre-aggregates of polymers in solutions and the crystallinity of the polymeric films. The orientation of 5–25 μm linear grains in the films were prepared through the bar-coating process with polyacrylonitrile as an additive, which stabilized the electron mobility over a wide range of temperatures. The linear-grain morphology of the film contributed to reducing the holes and grain boundaries in the transport paths of carriers. Typically, the top-gate FETs based on P(NDI2OD-T2) displayed a stable electron transporting behavior from 200 to 460 K, with mobility greater than 3.5 cm2V−1s−1. The performance of electronic equipment can be affected in many extreme operating environments, such as in the South Pole with a minimum temperature of 191–290 K1Ruhl J.E. Ade P.A.R. Carlstrom J.E. Cho H.M. Crawford T. Dobbs M. Greer C.H. Halverson N.W. Holzapfel W.L. Lanting T.M. et al.The south pole telescope.Proc. SPIE. 2004; 5498: 11-29Crossref Scopus (241) Google Scholar and the Lut desert with a maximum temperature of 253–344 K.2Mildrexler D.J. Zhao M.S. Running S.W. 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Macroscopic and high-throughput printing of aligned nanostructured polymer semiconductors for MHz large-area electronics.Nat. Commun. 2015; 6: 8394Crossref PubMed Scopus (237) Google Scholar In this work, PAN was added in poly{[N,N9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} (P(NDI2OD-T2)) semiconductor solution to prepare highly crystalline linear-grain polymer films through the bar-coating approach (Figure 1). We found that PAN remarkably increased the sizes of the pre-aggregates in the solution, thereby increasing the sizes of the grains in the solid films and improving the crystallinity of the polymer molecules. Furthermore, the bar-coating method controlled the arrangement of P(NDI2OD-T2) molecular backbones and the stacking grain direction. The aligning backbone and grain arrangements contributed to reduce the grain boundaries and defects in the transport paths of the carriers,11Wang C.L. Dong H.L. Hu W.P. Liu Y.Q. Zhu D.B. 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The tapping mode atomic force microscopy (AFM) images show that the spin-coated P(NDI2OD-T2)/PAN films had longer and more ordered grains (Figure 1F) than those of the P(NDI2OD-T2) films (Figure 1D). Moreover, the bar-coating method was employed to prepare the aligned films on 40°C glass substrates in air, at a coating speed of 120 mm/s, and all bars moved in the direction indicated by the blue arrow in Figure 1E. After drying, the film was annealed at 190°C for 30 min under nitrogen atmosphere. The grains in the aligned P(NDI2OD-T2) film were observed to be small and closely connected with each other (Figure 1E), whereas the aligned P(NDI2OD-T2)/PAN film had long independently linear grains (Figure 1G). Most of the grains in the aligned P(NDI2OD-T2)/PAN film were 5–25 μm long and 150–350 nm wide (Figures S2 and S3). Moreover, the examination of the film morphologies revealed that the aligned P(NDI2OD-T2)/PAN films were anisotropic, and there were few grain boundaries in the parallel direction of the bar movement, whereas many grain boundaries in perpendicular direction. It is noteworthy to state that linearly aligned grains limit carrier transport paths. To verify the universality of PAN, PAN was added to PCII2T and DPPT-TT, and it was observed that PAN improved both the crystallinity of the polymer semiconductor films and the grain sizes. Basically, the success rate of the bar-coating method for the preparation of the aligned films was significantly improved by the presence of PAN. Root-mean-square (RMS) analysis of image height was used to investigate the roughness of the films, and the results show that the spin-coated P(NDI2OD-T2) film, aligned P(NDI2OD-T2) film, spin-coated P(NDI2OD-T2)/PAN film, and aligned P(NDI2OD-T2)/PAN film exhibited RMS surface roughness values of 1.10, 0.672, 2.57, and 3.92 nm, respectively. Additionally, the AFM micrographs of PCII2T monolayer films, 20 nm PCII2T/PAN films, and 20 nm DPPT-TT/PAN films, prepared by the bar-coating method, showed that the films contained long linearly aligned grains (Figure S4). Since GIWAXS is a powerful way to explain the correlation between molecular packing and the performance of transistors, 2D-GIWAXS was utilized in the analysis of the aligned bar-coated P(NDI2OD-T2)/PAN films (Figures 2A and 2 B), spin-coated P(NDI2OD-T2)/PAN films (Figure 2C), bar-coated P(NDI2OD-T2) films (Figures 2D and 2E), and spin-coated P(NDI2OD-T2) films (Figure 2F). The direction of the GIWAXS light source was parallel (Figures 2A and 2D) and perpendicular (Figures 2B and 2E) to the bar-coating direction. The line cuts of the P(NDI2OD-T2) and P(NDI2OD-T2)/PAN films are shown in Figure S5. The detailed crystallographic parameters were calculated and presented in Tables S1 and S2. Also, the 2D-GIWAXS diagrams and line cuts of PCII2T, DPPT-TT, and PAN films are shown in Figures S6–S11, while their corresponding detailed crystallographic parameters are listed in Tables S3–S6. According to the 2D-GIWAXS, the (010) peaks for all the films can be seen in the out-of-plane direction (Figure 2), and the weak in-plane (010) peak appeared in the aligned P(NDI2OD-T2)/PAN (parallel) and aligned P(NDI2OD-T2) films (parallel) (Figures 2A and 2D). The result also shows that in the spin-coated P(NDI2OD-T2)/PAN and spin-coated P(NDI2OD-T2) films, neat P(NDI2OD-T2) molecules adopted face-on π-stacking crystallites arrangements, as shown in Figure S12. Most of the P(NDI2OD-T2) molecules in the aligned P(NDI2OD-T2)/PAN and aligned P(NDI2OD-T2) films mainly adopted a face-on π-stacking crystallites arrangement, while a few adopted an edge-on crystallites arrangement. Furthermore, the intensities of the (002) signals were stronger than those of the (001) signals (Figures 2B, 2C, and 2E), suggesting that for two adjacent P(NDI2OD-T2) molecules, the NDI units of one molecule tend to stack on the T2 units of the other molecule.31Brinkmann M. Gonthier E. Bogen S. Tremel K. Ludwigs S. Hufnagel M. Sommer M. Segregated versus mixed interchain stacking in highly oriented films of naphthalene diimidebithiophene copolymers.ACS Nano. 2012; 6: 10319-10326Crossref PubMed Scopus (126) Google Scholar Additionally, the signal intensity and quantity of P(NDI2OD-T2)/PAN films were obviously better than those of P(NDI2OD-T2), which means the crystallinity of the P(NDI2OD-T2)/PAN films was significantly improved. For the parallel direction of P(NDI2OD-T2)/PAN film, the (010) signals in the out-of-plane direction showed two symmetrical peaks (Figure 2A), and the planes of the conjugated backbone of P(NDI2OD-T2), calculated from the signal positions, formed an angle of 14°–15° with the substrate, as shown in the inset of Figure 1A. According to the differences in the (010) signals for the parallel and perpendicular directions of the aligned P(NDI2OD-T2)/PAN film (Figures 2A and 2B), it was observed that the direction of the P(NDI2OD-T2) backbones was parallel to the bar-coating direction. The same phenomenon was observed for the (001) and (002) peaks in the perpendicular direction of P(NDI2OD-T2)/PAN film (Figure 2B). Alternatively, the (010) peak in the P(NDI2OD-T2) films was not divided into two symmetrical peaks (Figures 2D–2F). This may be due to the fact that the planes of the conjugated backbone of P(NDI2OD-T2) in the aligned P(NDI2OD-T2) films were parallel to the substrate. Together with the results from the AFM analysis, the undivided (010) signal may also have resulted from the poor crystallinity of the aligned P(NDI2OD-T2) film. According to the detailed crystallographic parameters (Table S3), the in-plane lamellar stacking correlation lengths of the aligned P(NDI2OD-T2)/PAN films were 325 Å (parallel) and 270 Å (perpendicular), which were longer than the 251 Å (parallel) and 141 Å (perpendicular) of the aligned P(NDI2OD-T2) films. Meanwhile, the in-plane backbone stacking correlation length of the aligned P(NDI2OD-T2)/PAN film (181 Å) was similar to that of the aligned P(NDI2OD-T2) film (193 Å), indicating that the addition of PAN resulted in the formation of larger crystallites. The out-of-plane π-stacking correlation lengths of the aligned P(NDI2OD-T2)/PAN films were smaller than those of the spin-coated films, which indicates that the molecules in the aligned P(NDI2OD-T2)/PAN films prefer stacking in the lamellar direction to the π direction. According to GIWAXS analysis, the addition of PAN was observed to markedly improve the film crystallinity, and the polymer backbones from bar coating were positioned in the same direction as the linear grains. Meanwhile, the small out-of-plane π-stacking correlation lengths were favorable to the in-plane carrier transport along the linear grains. This can limit the out-of-plane transport and reduce the chances of lattice scattering. In addition to the effects of the processing methods, the polymer film morphology is also closely related to the pre-aggregates in solution.32Zheng Y.Q. Yao Z.F. Lei T. Dou J.H. Yang C.Y. Zou L. Meng X.Y. Ma W. Wang J.Y. Pei J. Unraveling the solution-state supramolecular structures of donor–acceptor polymers and their influence on solid-state morphology and charge-transport properties.Adv. Mater. 2017; 29: 1701072Crossref Scopus (78) Google Scholar,33Li M.M. Mangalore D.K. Zhao J.B. Carpenter J.H. Yan H.P. Ade H. Yan H. Müllen K. Blom P.W.M. Pisula W. et al.Integrated circuits based on conjugated polymer monolayer.Nat. Commun. 2018; 9: 451Crossref PubMed Scopus (50) Google Scholar UV-vis spectroscopy was used to analyze the P(NDI2OD-T2)/PAN and P(NDI2OD-T2) solutions (Figure 3A). The test concentration of P(NDI2OD-T2) was 0.02 mg/mL, while PAN was 0.004 mg/mL, and tetralin was used as the solvent. Obvious changes in absorption spectra were observed during the heating process. From 283 to 393 K, the absorbance of the 0–0 peak at 718 nm decreased continuously and then disappeared, while the 0–1 peak at 601 nm gradually appeared. These results demonstrate the presence of strong pre-aggregation of P(NDI2OD-T2) in the low-temperature solution. The pre-aggregates were broken up since polymer chains separate from each other under heating conditions.34Chen Z.H. Cai P. Chen J.W. Liu X.C. Zhang L.J. Lan L.F. Peng J.B. Ma Y.G. Cao Y. 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Mater. 2017; 16: 356-362Crossref PubMed Scopus (272) Google Scholar For comparison, temperature-dependent absorption spectra was used to analyze P(NDI2OD-T2)/PAN and P(NDI2OD-T2) in o-dichlorobenzene (Figure S13), and the film spectra are shown in Figure S14. To further understand the effect of PAN on the formation of the pre-aggregates, dynamic light-scattering (DLS) technique was utilized in the size analysis of the pre-aggregates in low concentration solutions, while small-angle neutron scattering (SANS) technique was used to analyze the pre-aggregates in high concentration solutions. Figure 3B displays the DLS-generated results of the polymer particle sizes of P(NDI2OD-T2)/PAN and P(NDI2OD-T2) in solutions where tetralin and o-dichlorobenzene were the employed solvents, respectively. For the P(NDI2OD-T2)/PAN solution, the concentrations of P(NDI2OD-T2) and PAN were 0.01 and 0.002 mg/mL, respectively, whereas the concentration of P(NDI2OD-T2) in the P(NDI2OD-T2) solution was 0.012 mg/mL. The diameters of the particles in the tetralin P(NDI2OD-T2) solution were 67–125 nm, which was larger than those in the o-dichlorobenzene P(NDI2OD-T2) solution (37–78 nm). This indicates that the P(NDI2OD-T2) chains formed larger pre-aggregates in tetralin. Correspondingly, the diameters of the particles in the tetralin solution containing PAN were in the range of 127–236 nm and were larger than the particles for the tetralin solution without PAN, indicating that PAN promoted the increase in particle size even in extremely dilute solutions. The results of SANS analysis for P(NDI2OD-T2)/PAN and P(NDI2OD-T2) solutions are displayed in Figures 3C and 3D. The concentrations of P(NDI2OD-T2) and PAN in the P(NDI2OD-T2)/PAN solution were 6 and 1.2 mg/mL, respectively, while the P(NDI2OD-T2) concentration in the P(NDI2OD-T2) solution was 6 mg/mL. To improve the signal-to-noise ratio, deuterated 1,2-dichlorobenzene-d4 (ODCB-d4) was used as the solvent to reduce incoherent scattering.35Le Cœur C.L. Combet S. Carrot G. Busch P. Teixeira J. Longeville S. Conformation of the poly(ethylene glycol) chains in DiPEGylated hemoglobin specifically probed by SANS: correlation with PEG length and in vivo efficiency.Langmuir. 2015; 31: 8402-8410Crossref PubMed Scopus (22) Google Scholar The power exponent in the P(NDI2OD-T2)/PAN solution was 1.93, while it was 1.82 in the P(NDI2OD-T2) solution (Figure 3D). These indicate that the pre-aggregates in the two solutions adopted large rod-like structures.32Zheng Y.Q. Yao Z.F. Lei T. Dou J.H. Yang C.Y. Zou L. Meng X.Y. Ma W. Wang J.Y. Pei J. Unraveling the solution-state supramolecular structures of donor–acceptor polymers and their influence on solid-state morphology and charge-transport properties.Adv. Mater. 2017; 29: 1701072Crossref Scopus (78) Google Scholar,35Le Cœur C.L. Combet S. Carrot G. Busch P. Teixeira J. Longeville S. Conformation of the poly(ethylene glycol) chains in DiPEGylated hemoglobin specifically probed by SANS: correlation with PEG length and in vivo efficiency.Langmuir. 2015; 31: 8402-8410Crossref PubMed Scopus (22) Google Scholar From the fitted line,36Chen W.R. Butler P.D. Magid L.J. Incorporating intermicellar interactions in the fitting of SANS data from cationic wormlike micelles.Langmuir. 2006; 22: 6539-6548Crossref PubMed Scopus (148) Google Scholar the radius of the pre-aggregates in the P(NDI2OD-T2) solution was 1.6 nm, and the Kuhn length was 26 nm, whereas the radius and Kuhn length of the pre-aggregates in the P(NDI2OD-T2)/PAN solution were 1.6 and 280 nm, respectively. The lamella direction length was calculated by density functional theory (DFT), and its vale for the P(NDI2OD-T2) molecule was 3.22 nm. According to the fitting results of the experimental data generated from the SANS analysis, it was observed that the addition of PAN increased the length and rigidity of the pre-aggregates.37Pedersen J.S. Schurtenberger P. Scattering functions of semiflexible polymers with and without excluded volume effects.Macromolecules. 1996; 29: 7602-7612Crossref Scopus (474) Google Scholar Long rod-like aggregates can facilitate the formation of long linear grains in solid films. Molecular dynamics (MD) simulation was used to gain understanding to the relationship between the addition of PAN and the size increase of pre-aggregates. MD simulations can only reflect intermolecular accumulation and conformation. The MD simulation was carried out with the Gromacs-4.6.7 package based on the general Amber force field (see Supplemental information for details).38Hess B. Kutzner C. van der Spoel D. Lindahl E. GROMACS 4: algorithms for highly efficient, load-balanced, and scalable molecular simulation.J. Chem. Theor. Comput. 2008; 4: 435-447Crossref PubMed Scopus (11893) Google Scholar,39Wang J.M. Wolf R.M. Caldwell J.W. Kollman P.A. Case D.A. Development and testing of a general amber force field.J. Comput. Chem. 2004; 25: 1157-1174Crossref PubMed Scopus (10866) Google Scholar To match the experimental mass ratio of 5:1 for P(NDI2OD-T2) to PAN during the solvent evaporation process (Figure S15), the root-mean-square end-to-end distance (RMSD), the backbone radius of gyration, and the number of backbone aggregation of P(NDI2OD-T2), all increased upon PAN addition (Figure S16), indicating that the addition of PAN can indeed enhance the backbone ductility and aggregation ability of P(NDI2OD-T2). To illustrate the role of PAN in the self-assembly of P(NDI2OD-T2) in solvents, snapshots were taken from the MD trajectory and presented in Figures 3E, 3F, and S17. Figure 3E shows that P(NDI2OD-T2) chains aggregated around PAN, and PAN acted as the nucleation center of P(NDI2OD-T2). At the same time, some PAN served as a bridge for P(NDI2OD-T2) and increased the cluster sizes (Figure 3F). Combined with the results from SANS and DFT calculations, MD simulations show that the diameter of the pre-aggregate (3.2 nm) was close to the length of the lamella direction of the P(NDI2OD-T2) molecule (3.22 nm), so in the actual P(NDI2OD-T2)/PAN solution, the arrangement of P(NDI2OD-T2) molecules may be as shown in Figure 3F; that is, P(NDI2OD-T2) molecules were twining round the PAN molecules and PAN molecules served as a bridge for P(NDI2OD-T2). These calculation results are consistent with the experimental observation that the aggregate size of P(NDI2OD-T2) increased upon the addition of a small amount of PAN. FETs with top-gate bottom-contact (TGBC) configuration were fabricated to characterize charge carrier transport in the P(NDI2OD-T2) and P(NDI2OD-T2)/PAN films (Figure 4A). The parallel gold source-drain electrodes were modified with cesium carbonate (Cs2CO3), and the RMS of the Cs2CO3 film prepared by bar coating on the glass substrate was 0.27 nm (Figure S18). The P(NDI2OD-T2) and P(NDI2OD-T2)/PAN semiconductor films were prepared by bar coating, and for comparison, P(NDI2OD-T2) and P(NDI2OD-T2)/PAN films were also prepared by spin coating. Parylene-C (200 nm) was deposited as an insulating layer, and it also exhibited a packaging effect. Aluminum was used as a gate electrode. In the following description, the test mode is denoted as “para” when the direction of the electric field from the source electrode to the drain electrode was parallel to the direction in which the bar moved, and it was denoted as “perp” when the two directions were perpendicular to each other. The electron mobilities in the parallel direction for the 36-transistor array based on the aligned P(NDI2OD-T2)/PAN films were counted and shown in Figure 4B. Table 1 shows the device performance tested in air and at room temperature (295 K), and Figure S19 shows the device performance tested in air as a function of time. The average electron mobility of the spin-coated P(NDI2OD-T2) films at room temperature was 0.23 ± 0.07 cm2V−1s−1; whereas, the parallel electron mobility (μelec,∥) of the aligned P(NDI2OD-T2) films was 1.6 ± 0.4 cm2V−1s−1, while its perpendicular electron mobility (μelec,⊥) was 0.25 ± 0.05 cm2V−1s−1, μelec,∥/μelec,⊥= 5–10. Comparatively, the electron mobility of spin-coated P(NDI2OD-T2)/PAN films was 0.45 ± 0.1 cm2V−1s−1, the parallel electron mobility of aligned P(NDI2OD-T2)/PAN films was 4.85 ± 0.3 cm2V−1s−1, and its perpendicular mobility was 0.02 ± 0.01 cm2V−1s−1, μelec,∥/μelec,⊥= 150–520. The results show the correlation between electron mobility and film morphology. The better the grains order, the larger the μelec,∥, the higher the ratio of μelec,∥ and μelec,⊥, and the greater the anisotropy of the carrier transport. In addition, the performance of the FETs is also related to the energy level of the semiconductor layers (Figure S20).Table 1OFET parameters calculated from the saturation regime (Vds = 10 V)Depositionμe (cm2V–1s–1)aData are represented as mean ± SD.Von (V)Ion:Ioff (Log10)Vt (V)P(NDI2OD-T2)spin-coat0.23 ± 0.07254–5bar-coat (para)1.6 ± 0.424–55–6bar-coat (perp)0.25 ± 0.05242–3P(NDI2OD-T2)+PANspin-coat0.45 ± 0.1–151–2bar-coat(para)4.85 ± 0.3–0.574–5bar-coat (perp)0.02 ± 0.01–0.540–1The FETs in this table are tested in air at room temperature (295 K).a Data are represented as mean ± SD. Open table in a new tab The FETs in this table are tested in air at room temperature (295 K). The relationships between the device performance and the operating temperatures in vacuum environment were evaluated and the results are shown in Figures 4C, S21, and S22. It should be emphasized that the dielectric constant of the insulating layer was affected by temperature, as shown in Figure S23. The electron mobility increased with increasing temperature (Figures 4D and S24), and after 360 K, the mobility of the transistors with different semiconductor layers decreased to different degrees. As temperature increased, the spin-coated P(NDI2OD-T2)/PAN FETs exhibited mobility degradation around 360 K. The mobility degradation may be related to the disorder and large pinholes of the semiconductor films. The relationship between the carrier mobility and temperature was analyzed by the generalized Einstein relation (GER) method,40Liu C. Huang K. Park W.T. Li M. Yang T. Liu X. Liang L. Minari T. Noh Y.Y. A unified understanding of charge transport in organic semiconductors: the importance of attenuated delocalization for the carriers.Mater. Horiz. 2017; 4: 608-618Crossref Google Scholar as shown in Figure 4D, which is generally applicable to describe charge transport of various microscopic mechanisms, such as band-like hopping, multiple-trapping and releasing, variable range hopping, etc. Generally, the GER method completely fits the mobility data, as shown in Figure 4D, except the data from the devices with spin-coated films above 360 K, due to the degraded performance. Two characteristics parameters (the density of states [DOS] width, ΔE, and the delocalization degree parameter, ΔD) were listed in the figure captions and, in general, a smaller value of ΔE signifies less dispersed energy distribution in the Gaussian-like DOS and a larger value of ΔD signifies ordered charge transport (the maximum is 1 corresponding to the classic band transport in single crystals). Importantly, the transistor with aligned P(NDI2OD-T2)/PAN exhibited the smallest ΔE (50 meV) and the largest ΔD (0.7), signifying a much smaller extent of microscopic structural disorders and fewer localized states as compared with that of the spin-coated P(NDI2OD-T2)/PAN film (ΔE = 90 meV and ΔD = 0.42). The results are highly consistent with those of the AFM and GIWAXS analysis, showing that the former film features a much smaller number of grain boundaries or pinholes and a higher extent of chain alignment as compared with the latter film. Notice that, in the low-temperature region (< 200 K), the addition of PAN in the bar-coating process, sufficiently eliminated disorders in charge transport and enhanced mobility, but this was not the case in spin-coating films. This may be attributed to the fact that the bar-coating process provided a longer timescale to lower structural energy and to reach alignment with minimal disorders. According to the transfer characteristics of transistors (Figure S22), when the operating temperature was 440 K, the hysteresis voltage of the spin-coated P(NDI2OD-T2)/PAN FETs was 5 V, and this may be related to the morphology of the films. Although PAN improved the crystallinity of the P(NDI2OD-T2) films, there were many large irregular gaps in the P(NDI2OD-T2)/PAN films according to the AFM micrographs. This observation illustrates that the presence of too many static physical defects, such as grain boundaries and pinholes, may cause thermal instability of the device performance at high temperatures. The electron mobilities of the aligned P(NDI2OD-T2)/PAN FETs had high thermal stability. The value measured at 300–460 K was 5.5 ± 0.5 cm2V−1s−1, and at 200 K, the electron mobility was still above 3.5 cm2V−1s−1. In addition, within the temperature range from 200 to 460 K, the hysteresis voltage was small (Figure S22A), which may indicate that the P(NDI2OD-T2)/PAN films had few defects and holes in the carrier transport paths, therefore the fewer localized states and low structural energies may be the keys to ensure the thermal stability of devices. When the operating temperature increased from 160 to 460 K, the threshold voltage of the aligned P(NDI2OD-T2)/PAN transistor showed the least change compared with other transistors (Figure 4E). Additionally, the turn-on voltage of the aligned P(NDI2OD-T2)/PAN FETs was –0.5 V, which is smaller than that of other FETs. Meanwhile, the Ioff of the aligned P(NDI2OD-T2)/PAN transistors exhibited the least variation compared with the other transistors. The OFET channel current (Vds = 10 V, Vgs = 20 and 0 V) versus temperature is shown in Figure S25. For the aligned P(NDI2OD-T2)/PAN FETs, the increase in dielectric constant (Figure S23) of the insulating layer with increasing temperature was an important factor that affected the Ioff (Figure 4F). The study showed that controlling the charge transport paths by multiple strategies can effectively improve the mobility and thermal stability of polymer FETs. Also, the ordered arrangements of polymer backbones, the flat face-on crystallites, and long linear grains can simultaneously limit the carrier transport paths. These strategies reduce pinholes, grain boundaries, and barriers in the charge transport paths, making films have smaller extent of microscopic structural disorders, fewer localized states, and lower structural energies, thereby improving the thermal stability of devices. Vapor-deposited insulating parylene-C layers can provide great encapsulation and further ensure device stability. In addition, we found that adding PAN to polymer semiconductors increased the size of the pre-aggregates in solution, the grain sizes, and the crystallinity of films. To sum up, highly crystalline polymer films with aligned linear grains were successfully prepared by the bar-coating method. The electron mobilities based on top-gate FETs were 3.5–6 cm2V−1s−1 at 200–460 K and 5–6 cm2V−1s−1 at 300–460 K.