Controlling the Microstructure of Conjugated Polymers in High‐Mobility Monolayer Transistors via the Dissolution Temperature

Abstract

It remains a challenge to precisely tailor the morphology of polymer monolayers to control charge transport. Herein, the effect of the dissolution temperature (T _dis) is investigated as a powerful strategy for morphology control. Low T _dis values cause extended polymer aggregation in solution and induce larger nanofibrils in a monolayer network with more pronounced π–π stacking. The field‐effect mobility of the corresponding monolayer transistors is significantly enhanced by a factor of four compared to devices obtained from high T _dis with a value approaching 1 cm² V⁻¹ s⁻¹. Besides that, the solution kinetics reveal a higher growth rate of aggregates at low T _dis, and filtration experiments further confirm that the dependence of the fibril width in monolayers on T _dis is consistent with the aggregate size in solution. The generalizability of the T _dis effect on polymer aggregation is demonstrated using three other conjugated polymer systems. These results open new avenues for the precise control of polymer aggregation for high‐mobility monolayer transistors.

Cool down! The dissolution temperature is an efficient parameter to control the aggregation of conjugated polymers in solution and to influence their microstructure in monolayers. A lower dissolution temperature induces stronger π–π stacking interactions and larger fibrillar domains, resulting in high‐performance monolayer transistors with a mobility approaching 1 cm² V⁻¹ s⁻¹.

Introduction

In organic field‐effect transistors (OFETs), the few first monolayers of the organic semiconductor, either small molecules or conjugated polymers, at the interface with the insulator are of vital importance to the device performance due to their dominant role in transporting charges.1 Therefore, downscaling organic semiconductors to a single molecular layer (monolayer) provides an ideal platform to investigate the intrinsic mechanism of charge transport. Considerable efforts have been made to realize high‐performance organic‐monolayer transistors from small molecules. For instance, field‐effect mobilites of pentacene,2 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT),3 dicyanomethylene‐substituted fused tetrathienoquinoid,4 and 1,4‐bis((5′‐hexyl‐2,2′‐bithiophen‐5‐yl)ethynyl)benzene5 have reached values on the order of 1–10 cm² V⁻¹ s⁻¹ in monolayer transistors. In sharp contrast, monolayer transistors based on conjugated polymers generally exhibit mobilities that are orders of magnitude lower than their small‐molecule counterparts, apart from few exceptions,6 largely due to their lower crystallinity and associated challenges in controlling the morphology of the monolayer.

The aggregation behavior of conjugated polymers critically affects their film microstructure and subsequent performance in electronic devices. The microstructure can be affected via rational design of the chemical structure and control of the molecular weight or regioregularity.7 It was found that planar conjugated backbones and high molecular weights are able to enhance intermolecular π–π stacking, contributing to stronger aggregation and longer conjugation lengths of the polymer chains. Another efficient strategy for tuning polymer aggregation is to tune the solvent quality.8 For P(NDI2OD‐T2), tolerably poor solvents resulted in elongated rod‐like 300‐nm aggregates in solution and enhanced field‐effect mobility in thin films by a factor of 2.7.8b However, solvents with different qualities typically lead to a large variation of boiling points and vapor pressures, greatly limiting solution processing. For instance, the dip‐coating technique, which allows the alignment of organic semiconductors with monolayer precision (2–3 nm), generally prefers solvents with lower boiling points, such as chloroform and dichloromethane.9

The degree of polymer aggregation can also be modulated by controlling the temperature of the solution from which films are cast. For conjugated polymers with extremely strong aggregation, a warm or even hot solution is required to achieve a homogeneous morphology.7b, 10 Although a modified dip‐coating method operating at elevated temperatures was reported to tune the degree of polymer aggregation, the precision of thickness control is significantly reduced from 2–3 nm (one monolayer) to tens of nanometers due to the change of the solution viscosity and evaporation rate.11

In this contribution, a donor–acceptor‐conjugated polymer with strong aggregation behavior, PffBT4T‐2DT (Figure 1 a), is dissolved at various temperatures. It is found that at room temperature (RT), the peak in the UV/Vis–NIR absorption spectrum that corresponds to polymer aggregates is stronger and more pronounced when the polymer solution is prepared at a low dissolution temperature (T _dis). Furthermore, T _dis plays a critical role for the morphology of polymer monolayers obtained by dip‐coating at RT. With decreasing T _dis, the fibril width in the polymer monolayer is almost doubled, resulting in a significant increase in field‐effect mobility by a factor of 4. Particularly, at T _dis=55 °C, the saturated mobility of polymer‐monolayer transistors approaches 1 cm² V⁻¹ s⁻¹, which is among the best performances for polymer‐monolayer transistors.6a The improved performance can be ascribed to the stronger π–π stacking interaction indicated by grazing‐incidence wide‐angle X‐ray scattering (GIWAXS). The origin of the T _dis effect on polymer aggregation is explored by investigating the kinetics of aggregate growth and the dimension distribution of aggregates. It is demonstrated that a low T _dis leads to a higher growth rate and larger size of aggregates, facilitating the molecular order and subsequent charge transport. Importantly, the effect of T _dis on polymer aggregation appears to be a general phenomenon, as evidenced by studying three other conjugated polymers. As a result, T _dis provides a new, versatile parameter to precisely control polymer self‐assembly and, consequently, to realize high‐performance electronic devices.

Figure 1.

a) Structure of PffBT4T‐2DT. b), c) UV/Vis–NIR absorption spectra of chloroform solutions (b) and polymer monolayers (c) recorded at RT. PffBT4T‐2DT was dissolved at various temperatures (55, 65, 75, 90, and 100 °C). The polymer concentration in solution was 0.5 μm, and monolayers were dip‐coated from a 0.5 mg mL⁻¹ chloroform solution with a speed of 100 μm s⁻¹. d), e) Corresponding absorbance ratio of the 0–0 to the 0–1 peak as a function of T _dis, fitted by red dashed lines, for (b) and (c), respectively.

Results and Discussion

In spite of its strong tendency to aggregate, PffBT4T‐2DT can still be dissolved in chloroform with a polymer concentration of no less than 1 mg mL⁻¹ even at high molecular weight.6a It has to be emphasized that dissolved polymers will often exist in the form of solution‐state supramolecular polymer aggregates.12 The growth of these dissolved aggregates from a fully molecularly dissolved state has been explained by the disorder–order transition model13 and multi‐level self‐assembly processes.14 For conjugated polymers, the molecularly dissolved state is characterized by a single broad absorption peak in the UV/Vis–NIR absorption spectrum, while upon aggregation, a red‐shift is observed due to planarization of the polymer backbone, accompanied by the appearance of vibronic peaks or shoulders.13 Figure 1 b shows the RT UV/Vis–NIR absorption spectra of PffBT4T‐2DT (M _n=48 kg mol⁻¹) solutions in chloroform, dissolved at various temperatures ranging from 55 to 100 °C. It is clearly visible that T _dis critically affects the aggregation behavior of PffBT4T‐2DT in solution. For T _dis=55 °C, the absorption spectrum at RT is nearly identical to that in the solid state, where the intensity of 0–0 peak at 698 nm is larger than that of the 0–1 peak at 642 nm, which is indicative of J‐aggregation.15 In comparison, an increase in T _dis gradually reduces the intensity ratio of 0–0 to 0–1 peaks (A _0–0/A _0–1). At T _dis>65 °C, the A _0–0/A _0–1 ratio drops below 1. When the polymer is dissolved at 100 °C, A _0–0/A _0–1 is only 0.89 (Figure 1 d). It must be emphasized that the steady‐state photoluminescence of the PffBT4T‐2DT solution remains almost independent of T _dis, and time‐resolved photoluminescence reveals similar lifetimes of around 1.4 ns (Figures S1 and S2 in the Supporting Information). Additionally, the impact of the cooling rate on polymer aggregation in solution is not discernible (Figures S3 and S4).

The optical properties of the polymer monolayers were also studied. The dip‐coating technique that allows precise control of the film microstructure6a, 16 was employed to fabricate PffBT4T‐2DT monolayers at RT from 0.5 mg mL⁻¹ chloroform solutions that were prepared at different T _dis. The optimized dip‐coating speed is 100 μm s⁻¹. It is evident from Figure 1 c that at all T _dis values, the monolayers show strong J‐aggregation with A _0–0/A _0–1 up to 1.4. In comparison to the solution‐absorption spectra, the film spectra are red‐shifted by about 2 nm, suggesting a higher degree of molecular order and stronger π–π stacking interactions. Interestingly, T _dis has negligible influence on the UV/Vis–NIR spectra of the resulting polymer monolayers, as indicated by the red dashed line in Figure 1 e. Note that the change of A _0–0/A _0–1 in solution induced by T _dis is about 20 % (Figure 1 d). The polymer aggregation/conjugation length is notably promoted during film formation due to solvent evaporation. Apparently, strong π–π stacking interactions between PffBT4T‐2DT backbones in the solid films are capable of largely compensating the T _dis effect on polymer aggregation observed in solution.

To elucidate the impact of T _dis on the polymer monolayers in more detail, atomic force microscopy (AFM) in tapping mode was employed, and the corresponding surface topographies are shown in Figure 2. Heavily doped silicon wafers with 300 nm thermally grown SiO₂ were used as substrates. Figure 2 a shows that the thickness of the fibrillar ultrathin film is about 2.4 nm, which is defined as a single molecular layer because of its equivalence to the interlayer spacing of edge‐on oriented multilayers,6a as will be discussed. Dip‐coated at RT from solutions prepared at T _dis=55 °C, the fibril width of the resultant polymer monolayer is 74±30 nm, in agreement with literature,6a and the corresponding height profile is presented in Figure 2 e. A small fraction of bright domains exists in the AFM height image (Figure 2 a), indicative of the starting growth of a second monolayer. When T _dis is increased, similar fibrillar microstructures are observed, but the second monolayer becomes less apparent (Figures 2 b,c,d and S5). However, more detailed analysis reveals the remarkable impact of T _dis on the fibril width. At T _dis=75 °C, the fibril width decreases by 35 % with a value of 48±14 nm, but further increase of T _dis to 90 or 100 °C only has minor effect on the fibril width (Figure 2 f). This trend of the fibril width as a function of T _dis is in excellent agreement with the solution‐absorption spectra at various T _dis values (Figure 1 b,d). Therefore, it is concluded that the thinner nanofibers originate from decreased aggregation in solution at elevated T _dis.

Figure 2.

a)–d) AFM height images of PffBT4T‐2DT monolayers dip‐coated from solutions with different T _dis values. All AFM images have the same scale in x, y, and z direction. e) Corresponding height profiles of the white lines in (a)–(d). f) Fibril width as a function of T _dis. The average values and standard deviation for each sample are analyzed from over 100 fibers. g), h) GIWAXS in‐plane profiles of a monolayer (g) and multilayer (h) with different T _dis values.

The in‐plane organization and qualitative orientational texture of the PffBT4T‐2DT monolayer were probed by GIWAXS measurements. For the monolayers at T _dis=55 °C (black curve in Figure 2 g), a distinct (010) π–π stacking peak is visible at q=1.74 Å⁻¹ in the in‐plane profile, suggesting that the polymer chains are oriented in a pronounced edge‐on fashion within the monolayer, with a π–π stacking distance of 0.36 nm. Note that the direct observation of a π–π stacking peak for a polymer monolayer has been rarely reported.6b Our results demonstrate that the PffBT4T‐2DT monolayer prepared from a T _dis=55 °C solution possesses a high degree of molecular order, which is attributed to the stronger aggregation in solution because of a lower T _dis. In sharp contrast, the reduced aggregation at a higher T _dis not only decreases the dimension of semi‐crystalline fibrillar domains, that is, thinner nanofibers, but also noticeably influences the molecular order inside the nanofibers. It is evident that the (010) π–π stacking peak vanishes for the monolayer at T _dis=100 °C (red curve in Figure 2 g and Figure S6), indicating that π–π interactions between polymer chains are significantly less pronounced.

The impact of T _dis on the polymer packing is further supported by PffBT4T‐2DT drop‐cast multilayers. In the out‐of‐plane GIWAXS profiles, strong lamellar (100), (200), (300), and even (400) peaks are visible for multilayers at T _dis=55 and 90 °C (Figure S7), and a quantitative analysis reveals the same lamellar spacing of around 2.34 nm, in excellent agreement with the thickness of the PffBT4T‐2DT monolayer (Figure 2 a–e). This result demonstrates the negligible impact of T _dis on the out‐of‐plane molecular organization for multilayers. On the contrary, the pronounced (010) peak is present in the in‐plane profiles for both films, but the π‐stacking distance decreases from 0.36 nm at T _dis=90 °C to 0.35 nm at T _dis=55 °C (Figure 2 h). This closer polymer packing is consistent with the enhanced aggregation in solution at low T _dis.

To explore the relation between microstructure and charge transport for these polymer monolayers, field‐effect transistors were fabricated with a bottom‐gate bottom‐contact configuration and SiO₂ as the dielectric. The same processing conditions were applied as for AFM. Prior to the polymer monolayer deposition, Au electrodes were patterned onto the Si/SiO₂ substrate, acting as source and drain electrodes, which were further modified by a 2,3,4,5,6‐pentafluorothiophenol (PFBT) self‐assembled monolayer (SAM) to minimize the contact resistance and to decrease the surface tension of the Au electrodes.6a, 17

The transfer and output characteristics of the resultant polymer‐monolayer transistors exhibit a typical linear/saturation behavior, and minor hysteresis is observed, as shown in Figure 3 a,b. More importantly, the improvement of the device performance is achieved by applying a low T _dis. Starting from a gate voltage (V _GS) of 0 V, the drain current of the transistor obtained from T _dis=55 °C becomes higher than that obtained from T _dis=100 °C. When increasing V _GS to −30 V, the drain‐current difference roughly reaches one order of magnitude (Figure 3 a). Extracted from the transfer curves, the saturated hole‐mobilities (μ _h) are 0.87±0.04 cm² V⁻¹ s⁻¹ for T _dis=55 °C and 0.22±0.01 cm² V⁻¹ s⁻¹ for T _dis=100 °C. The dependence of the saturated mobility on T _dis is plotted in Figure 3 c. It seems that T _dis=65 °C is a threshold value after which the mobility significantly drops by 66 % (from 0.87±0.04 cm² V⁻¹ s⁻¹ to 0.30±0.01 cm² V⁻¹ s⁻¹). Above this T _dis, only a slight decrease in mobility is observed, with an average mobility of 0.22–0.30 cm² V⁻¹ s⁻¹. It is worth noting that this trend is similar with the fibril‐width dependence on T _dis, and the relation between mobility and fibril width is plotted in Figure 3 d. It is widely reported that a larger domain size is beneficial to the charge transport in OFET devices,16 therefore, it is reasonable that thicker fibrillar domains contribute to higher mobility. Apparently, the fibril width over 60 nm is crucial for high‐performance polymer monolayer transistors (Figure 3 d). Additionally, the improvement of the device performance due to a low T _dis is also reflected in the threshold voltage (V _T) and on–off ratio (I _on/I _off): V _T gradually increases with T _dis (Figure S8) and I _on/I _off of the device obtained from T _dis=55 °C reaches 10⁷, almost three orders of magnitude higher than that obtained from T _dis=100 °C (Figure 3 a).

Figure 3.

a) Transfer characteristics of PffBT4T‐2DT monolayer transistors dip‐coated from chloroform solutions with dissolution temperatures of 55 (red) and 100 °C (black). The drain voltage (V _DS) is −30 V. On‐current (I _on) is defined as I _DS at V _GS=−30 V, and off‐current (I _off) as I _DS at V _GS=4 V. b) Output characteristics of the PffBT4T‐2DT monolayer transistor with a dissolution temperature of 55 °C. c), d) Saturated field‐effect mobility (μ _h) as a function of dissolution temperature (c) and fibril width (d). The average value and error bar (standard deviation) for each condition are obtained from 10 devices.

The mechanism of polymer aggregation in solution has been extensively investigated, and the disorder–order transition is one of the most accepted models.13 In this model, starting from disordered polymer chains at high temperatures, polymer chains first planarize and then start to aggregate when the temperature of the solution is lowered. PffBT4T‐2DT follows the expected trend with a more red‐shifted and increasing aggregation peak in the UV/Vis–NIR absorption when the temperature of the solution decreases, as shown in Figure S9. To investigate the origin of the T _dis effect on the temperature‐dependent aggregation of PffBT4T‐2DT in more detail, UV/Vis–NIR absorption spectra were recorded for PffBT4T‐2DT solutions prepared at different T _dis values (Figure S10). At the stage of planarization of the amorphous phase (≈60 °C, Figure S10 a), a lower T _dis results in a small red‐shift (≈5 nm) of the main absorption peak at around 600 nm, indicative of a more planar polymer backbone. When solutions are cooled to 55 °C (formation of the aggregated phase, Figure S10 b), the T _dis effect on polymer aggregation is more pronounced, and larger red‐shifts (≈15 nm) of the main absorption peak at 600 nm as well as an enhanced intensity of the aggregate peak at 696 nm can be seen for lower T _dis. These observations suggest that the lower T _dis not only facilitates the planarization of the polymer backbone but also generates more aggregates. For solutions at 40 °C (Figure S10 c), further improvement of planarization or molecular order is obtained at low T _dis.

The polymer aggregation in solution can also be understood through a nucleation and growth process.18 Therefore, the evolution of solution‐absorption spectra with various T _dis values was studied, and the absorbance at 696 nm as a function of time is shown in Figure 4 a. Quantitative analysis is conducted using the Avrami equation:19

$${\displaystyle \varphi =1-\exp (-kt{}^n)}$$ (1)

Figure 4.

a) Evolution of absorbance at 696 nm with various T _dis values. PffBT4T‐2DT is dissolved in chloroform (0.5 μm) on a hotplate at a certain temperature, and then cooled at RT starting at t=0 s. For each T _dis, the first absorption spectrum is recorded at t=180 s, at which time the solution is considered to have reached RT. b) Relation between the fraction of the transformed aggregation (φ) and evolution time (t) at various T _dis values. c) Dependence of the half‐life (t _1/2) of the aggregation‐growth procedure on T _dis. d), e) Absorption spectra after multiple filtration with T _dis=55 and 100 °C. f) Size distribution of dissolved aggregates as a function of T _dis.

where φ is the fraction of transformed aggregation at time t, n is the Avrami index, and k is the growth rate of the aggregation. Equation (1) can also be written in its logarithmic form:

$${\displaystyle \ln [-\ln (1-\varphi \left)\right]=\ln k+n\ln t}$$ (2)

Here, the value of φ can be estimated by A/A _max, where A is the absorbance at 696 nm at time t, and A _max the absorbance at 696 nm when the aggregation growth is complete. It is evident from Figure 4 b that the Avrami equation describes the aggregation growth of PffBT4T‐2DT very well. The corresponding parameters are listed in Table 1. T _dis=55 °C results in an almost threefold higher growth rate of aggregation compared to T _dis=100 °C, implying the generation of aggregated species with larger dimension.18 Moreover, the half‐life of this hypothetical aggregation growth process can be obtained from t _1/2=[ln(2)/k]^1/n. It is interesting that the relation between t _1/2 and T _dis can be fitted by an Arrhenius equation:

$${\displaystyle t{}_{1/2}=t{}_0\exp (-E/k{}_{\mathrm{B}}T{}_{\mathrm{dis}})}$$ (3)

Table 1.

Avrami parameters of the polymer‐aggregation growth at various T _dis values.

T dis [°C]	55	65	75	90	100
k	1.43	1.11	0.90	0.55	0.46
n	0.16	0.19	0.19	0.24	0.27

where k _B is the Boltzmann constant and E is an apparent activation energy. E=1.41 eV is extracted from Figure 4 c, further confirming that T _dis has a significant effect on the rate of polymer aggregation.

To test the effect of T _dis on the dimension of polymer aggregates that are in solution, attempted dynamic light scattering was employed but not successful due to absorption of PffBT4T‐2DT in the range from 300 to 750 nm. Instead, the size of the aggregates is quantified by a three‐cycle filtration experiment. To this end, chloroform solutions of PffBT4T‐2DT were filtered sequentially using filters with pore sizes of 450, 200, and 100 nm, after which the corresponding UV/Vis–NIR absorption spectrum was recorded, as shown in Figures 4 d,e and S11. The spectra reveal that after the three‐cycle filtration, more aggregates are removed from solution at lower T _dis (purple spectra in Figure 4 d,e). Quantitative analysis was carried out through spectrum integration in order to evaluate the size distribution of the aggregates (Figure 4 f). With T _dis=55 °C, the aggregate fractions for <100 nm (purple diamonds), 100–200 nm (green triangles), 200–450 nm (red circles), and >450 nm (black squares) are 22.7 %, 34.4 %, 27.4 %, and 15.5 %, respectively. With increasing T _dis, the amount of aggregates over 100 nm gradually decreases, but more aggregates below 100 nm appear. Especially, when T _dis reaches up to 100 °C, the majority of polymer aggregates have a size of less than 100 nm. In all cases, the average size of the aggregates is roughly on the order of a few hundred nanometers, which seems larger than the value of the PffBT4T‐2DT derivative PffBT4T‐2OD, characterized by small‐angle neutron scattering (≈40 nm).20 It must be emphasized that the polymer aggregates tend to be reformed spontaneously after each filtration.21 Therefore, care must be taken when using these fraction values extracted from filtration experiments. Nevertheless, the results demonstrate in a semi‐quantitative way that a low T _dis is capable of sufficiently enhancing the polymer aggregation in solution, which is not only in excellent agreement with the solution absorption (Figure 1 b) but also strongly supports the variations in fibril width, π–π stacking interactions, and field‐effect mobility (Figures 2 and 3).

Several studies have emphasized that polymer aggregation and packing are largely dependent on the molecular weight.7a, 22 Therefore, two other batches of PffBT4T‐2DT with lower molecular weights (M _n=11 and 18 kg mol⁻¹) were synthesized. Figure 5 a reveals that the T _dis effect on the aggregation of the polymer decreases when lowering the molecular weight from 48 to 18 and then to 11 kg mol⁻¹. The concentration dependence was also investigated (Figure S12). The T _dis effect remains for polymer concentrations in the range of 0.5 to 50 μg mL⁻¹. From the data it is not possible to establish a quantitative relation between T _dis and the concentration of the polymer, but it is evident that at a fixed T _dis, the aggregation decreases for lower concentrations. The molecular weight and concentration‐dependent results demonstrate that the intermolecular interaction between polymers plays a dominant role on polymer aggregation and modulate the T _dis effect.

Figure 5.

a) T _dis effect on polymer aggregation of PffBT4T‐2DT as a function of molecular weight. b) Generalizability of the T _dis effect on polymer aggregation by characterizing three other conjugated polymers in chloroform. A _0/1=A _0–0/A _0–1, and ΔA _0/1=A _0/1(T)/A _0/1(100 °C), where A _0/1(T) and A _0/1(100 °C) are the A _0/1 values for solutions prepared at a certain temperature T and 100 °C, respectively. For PffBT4T‐2OD, ΔA _0/1=A _0/1(T)/A _0/1(120 °C).

To explore the generality of the T _dis effect, three other conjugated polymers P(NDI2OD‐2T),23 D‐DPP3T‐EH,10c and PffBT4T‐2OD,10b all of which exhibit temperature‐dependent aggregation behavior in chloroform, were studied (Figures 5 b and S13). For P(NDI2OD‐2T) and D‐DPP3T‐EH, the polymer aggregation is enhanced using lower T _dis, although the enhancement is smaller than for PffBT4T‐2DT. Due to the lower solubility of PffBT4T‐2OD compared to PffBT4T‐2DT, a higher T _dis with a minimum value of 80 °C is required to dissolve PffBT4T‐2OD, but the T _dis effect is otherwise identical to that of PffBT4T‐2DT.

Conclusion

In conclusion, a new strategy for the precise morphology control of polymer monolayers is proposed through tuning T _dis. It is confirmed by UV/Vis–NIR absorption that low T _dis values result in stronger polymer aggregation in solution, with more extended π–π stacking interactions and longer conjugation length. The T _dis effect on polymer aggregation is also observed for dip‐coated polymer monolayers. With decreasing T _dis, the width of monolayer fibrils in the monolayer network is significantly increased, leading to improved polymer packing, as evidenced by AFM and GIWAXS. Importantly, the improved molecular order due to low T _dis boosts the charge transport with the mobility approaching 1 cm² V⁻¹ s⁻¹. The origin of this T _dis effect on polymer aggregation was explored. The growth rate of aggregates at low T _dis values is almost threefold higher compared to high T _dis, and the relation between the half‐life of aggregation growth and T _dis can be well fitted by the Arrhenius equation. The generalizability of the T _dis effect is confirmed by investigating three other conjugated polymers. The results demonstrate that controlling the dissolution temperature of aggregated conjugated polymers is a new and interesting way to control polymer microstructures and enables to achieve high‐performance electronic devices, as shown here for polymer‐monolayer transistors.

Conflict of interest

The authors declare no conflict of interest.

Supporting information

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Supplementary

M. Li, H. Bin, X. Jiao, M. M. Wienk, H. Yan, R. A. J. Janssen, Angew. Chem. Int. Ed. 2020, 59, 846.