A Three‐in‐One Hybrid Strategy for High‐Performance Semiconducting Polymers Processed from Anisole

Abstract The development of semiconducting polymers with good processability in green solvents and competitive electrical performance is essential for realizing sustainable large‐scale manufacturing and commercialization of organic electronics. A major obstacle is the processability‐performance dichotomy that is dictated by the lack of ideal building blocks with balanced polarity, solubility, electronic structures, and molecular conformation. Herein, through the integration of donor, quinoid and acceptor units, an unprecedented building block, namely TQBT, is introduced for constructing a serial of conjugated polymers. The TQBT, distinct in non‐symmetric structure and high dipole moment, imparts enhanced solubility in anisole—a green solvent—to the polymer TQBT‐T. Furthermore, PTQBT‐T possess a highly rigid and planar backbone owing to the nearly coplanar geometry and quinoidal nature of TQBT, resulting in strong aggregation in solution and localized aggregates in film. Remarkably, PTQBT‐T films spuncast from anisole exhibit a hole mobility of 2.30 cm2 V‐1 s‐1, which is record high for green solvent‐processable semiconducting polymers via spin‐coating, together with commendable operational and storage stability. The hybrid building block emerges as a pioneering electroactive unit, shedding light on future design strategies in high‐performance semiconducting polymers compatible with green processing and marking a significant stride towards ecofriendly organic electronics.


Fabrication and characterization of field effect transistors (OFETs)
Polymer thin film field effect transistors were fabricated in a typical bottom gate, top contact architecture.Transistors were fabricated with highly doped Si as the gated electrode, gold (Au) as both source and drain electrodes.Substrates were cleaned by successive sonication with soap water, deionized water, acetone and absolute ethanol.Then the substrate gate dielectric layers were modified by n-octadecyltrichlorosilane (OTS) by submersion in a solution of OTS in toluene.The four polymer films for comparison were all prepared from pplymer solution (CB, 5.0 mg/mL) by spin-coating (3000 rpm, 30 s) onto the OTS treated substrates.Besides, PTQBT-T in anisole (2 mg/ml) was spin-coated (2000 rpm, 35 s) onto the OTS treated substrates to form polymer thin films.When thermal treatment was noted, the polymer films were annealed at 200 °C or 150°C for 15 minutes on a hotplate in a nitrogen glovebox.Gold contacts (40 nm) were evaporated on the polymer film layer through a metal mask to define channels of 80 µm in length and 1400 µm in width.The film thickness of the devices ranges from 60 to 100 nm.
Field effect mobility was calculated from the standard equation for saturation region in metaldioxide-semiconductor field effect transistors: 2 , where Ids is drainsource current, µ is field effect mobility, W and L are the channel width and length, Ci is the capacitance per unit area of the gate insulator (Ci = 10 nF/cm 2 ), Vg is the gate voltage and Vt is the threshold voltage.

Theoretical calculations
For simplicity, the alkyl chains were all replaced by methyl groups.Density functional theory (DFT) calculations of building block, monomer and trimer of polymers were performed using Gaussian 09 [5] at the B3LYP [6] /6-311G (d, p) [7] level with the D3 (BJ) empirical dispersion correction. [8]The calculation of band structures and density of states of the polymers were performed using Vienna ab initio simulation package (VASP) [9] with the Perdew-Burke-Ernzerhof (PBE) functional instead of B3LYP functional due to its mild demands of computational resources and the importance of being consistent with previous related studies. [10]iform 21 × 1 × 1 Monkhorst-Pack k-point mesh was used for structural optimization.The energy cut off for the plane-wave expansion was set to 400 eV and the force criteria was less than 0.05 eV/Å.41 k-points were calculated between the gamma point and the edge of the first BZ to afford band structure and density of states.The hole effective mass (mh*) [11] for 1D crystal is calculated based on band structure by the equation: Where E is the band energy and k is the electron wave vector along backbone direction.

Solubility Limit Measurement
The solubility of PTQBT-based polymers were measured by a standard calibration curve method. [12]Firstly, to construct standard calibration curves, the absorbance of different concentrations of PTQBT, PTQBT-V, PTQBT-T and PTQBT-2T polymer (0.01−0.05 mg/mL) in CB and PTQBT-T polymer (0.01−0.07 mg/mL) in anisole solutions were measured.Then, the polymer was gradually added to the solution until saturation was achieved, the CB and anisole solution were stirred at 70°C for four hours.The solution was then cooled to room temperature and centrifuged (e.g., 10000 rpm for 30 min).Finally, the top clear solution in each centrifuge tube was selected, and the solubility of each material was determined by measuring its absorbance after dilution with a saturated solution and using individual standard curves.

Figure S1 .
Figure S1.Calculated dipole memonts of D-A building block and their corresponding D-Q-A building block.

Figure S3 .
Figure S3.Optimized geometries and dipole moments for the three possible segments of the dimeric units of four TQBT-based polymers.

Figure S4 .
Figure S4.Optimized geometries and dipole moments for the four possible trimers with different TQBT orientations in the copolymer PTQBT-T.

Figure S5 .
Figure S5.Calculated diople moments of the corresponding building block, monomer and trimer of previouly reported polymer PBNT-TzTz and FDPP-F.

Figure S7 .
Figure S7.Calculated dipole moments, optimized geometries, orbital distributions and energy levels of the trimers of TQT-based polymers.

Figure S8 .
Figure S8.(a) Theoretical model for the calculation of torsional potential energy.Calculated torsional energy barrier as a function of b) dihedral angel (θ1) and c) dihedral angel (θ2).

Figure S9 .
Figure S9.Optimized packing geometries and calculated binding energies of PTQBT-T and PTQT-T dimers.

Figure S10 .
Figure S10.a) Curve fitting based on band structure to obtain the effective hole masses of four polymers.b) Plots of carbon−carbon bond length for each respective bond number in benzothiadiazole and oligothiophene segments in PTQBT, PTQBT-T and PTQBT-2T.

Figure S12 .
Figure S12.X-ray structures of a) TQBT and b) TQT building block.

Figure S13 .
Figure S13.Photographs of five polymers in chlorobenzene.

Figure S15 .
Figure S15.Absorption spectra for determining the solubility of four polymers in 70 °C chlorobenzene and anisole: a) absorption spectra of standard solution four polymers.b) plot of absorbance at a certain wavelength (as indicated in the figures) versus concentration.The unknown PTQBT, PTQBT-V, PTQBT-T, PTQBT-2T and PTQBT-T-Anisole based samples were prepared by dilution of 600, 600, 600, 600, 300 times from saturated solution.

Figure S17 .
Figure S17.Absorption spectra of PTQBT-T solution in a) chlorobenzene and b) anisole in the filtration experiments.[13]c) Size distributions of solution aggregates of PTQBT-T in chlorobenzene and anisole at room temperature.

Figure S18 .
Figure S18.Cyclic voltammetry curves of polymers at a scan rate of 100 mV/s.

Figure S20 .
Figure S20.Typical a) transfer and b) output characteristics of OFETs without thermal annealing.

Figure S21 .
Figure S21.The mobility statistic graphs for OFETs based on annealed TQBT-based polymer films.

Figure S22 .
Figure S22.Mobility versus gate voltage plots of annealed OFETs based on four TQBT-based polymers spuncast from chlorobenzene or anisole.

Figure S23 .
Figure S23.Chemical structures from the literature of green solvent-processed polymers by spin-coating deposition method in recent 10 years.

Figure
Figure S24 a) On-off cyclic tests (9000 cycles) by applying VG of −80 and 0 V at VD of −80 V, b) Repeatability of transfer curves (30 cycles) by applying VD of −80 V, c) Bias stress tests by applying continuous bias voltage of −80 V for up to 2000 s and d) Transfer curves before and after storing in ambient air for 30 days of OFET devices based on PTQBT, PTQBT-V and PTQBT-2T.

Figure
Figure S25.a) GIWAXS patterns and b) AFM images of as-cast polymer films.

Table S2 .
OFET performances and reliability factor of the polymers.