Molecular doping of organic semiconductors is critical for optimizing a range of optoelectronic devices such as field‐effect transistors, solar cells, and thermoelectric generators. However, many dopant:polymer pairs suffer from poor solubility in common organic solvents, which leads to a suboptimal solid‐state nanostructure and hence low electrical conductivity. A further drawback is the poor thermal stability through sublimation of the dopant. The use of oligo ethylene glycol side chains is demonstrated to significantly improve the processability of the conjugated polymer p(g42T‐T)—a polythiophene—in polar aprotic solvents, which facilitates coprocessing of dopant:polymer pairs from the same solution at room temperature. The use of common molecular dopants such as 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) is explored. Doping of p(g42T‐T) with F4TCNQ results in an electrical conductivity of up to 100 S cm−1. Moreover, the increased compatibility of the polar dopant F4TCNQ with the oligo ethylene glycol functionalized polythiophene results in a high degree of thermal stability at up to 150 °C.

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The photophysical properties and solar cell performance of the classical donor–acceptor copolymer PCDTBT(poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt ‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole))) in relation to unintentionally formed main chain defects are investigated. Carbazole–carbazole homocouplings (Cbz hc) are found to significant extent in PCDTBT made with a variety of Suzuki polycondensation conditions. Cbz hc vary between 0 and 8 mol% depending on the synthetic protocol used, and are quantified by detailed nuclear magnetic resonance spectroscopy including model compounds, which allows to establish a calibration curve from optical spectroscopy. The results are corroborated by extended time‐dependent density functional theory investigations on the structural, electronic, and optical properties of regularly alternating and homocoupled chains. The photovoltaic properties of PCDTBT:fullerene blend solar cells significantly depend on the Cbz hc content for constant molecular weight, whereby an increasing amount of Cbz hc leads to strongly decreased short circuit currents JSC. With increasing Cbz hc content, JSC decreases more strongly than the intensity of the low energy absorption band, suggesting that small losses in absorption cannot explain the decrease in JSC alone, rather than combined effects of a more localized LUMO level on the TBT unit and lower hole mobilities found in highly defective samples. Homocoupling‐free PCDTBT with optimized molecular weight yields the highest efficiency up to 7.2% without extensive optimization.

The synthesis of a naphthalene diimide bithiophene copolymer P­(EO-NDIT2) with branched, base-stable, and purely ether-based side chains is presented. Stille polycondensation leads to high molecular weights that are limited by methyl transfer and eventually T2 homocouplings. While extensive solution aggregation hampers molecular weight determination by conventional methods, NMR spectroscopy allows identification of both T2- (H and methyl) and NDI-related (methyl) end groups, enabling the determination of absolute number average molecular weights larger than M n,NMR ∼100 kg/mol. Solvent- and temperature-dependent aggregation in solution is investigated by NMR and UV–vis spectroscopy. These results are used for solution doping of P­(EO-NDIT2) with N-benzimidazole-based n-dopants. Spin coating from heated chlorobenzene solutions and using 4-(2,3-dihydro-1,3-dimethyl-1H-benzoimidazol-2-yl)-N,N-diisopropylaniline (N-DiPrBI) as the dopant leads to homogeneous films with highest conductivities up to 10–2 S/cm. Generally, N-DiPrBI concentrations as low as ∼5 wt % are sufficient to increase conductivity by orders of magnitude. Strikingly, maximum power factors up to 0.11 μW/mK2, although limited by conductivity, are achieved for the highest molar mass sample at a low dopant concentration of 2 wt % N-DiPrBI only.

Acceptor copolymers with low lowest unoccupied molecular orbital (LUMO) energy levels are key materials for organic electronics. In the present work, quaternization of pyridine-flanked diketopyrrolopyrrole (PyDPPPy) is used to lower the LUMO energy level of the resulting monomer (MePyDPPPy) by as much as 0.7 eV. The drastically changed electronic properties of MePyDPPPy hinder a second methylation step even in an excess of trimethyloxonium tetrafluoroborate and thereby give access to the asymmetric functionalization of N-heterocycle-flanked DPP building blocks. The corresponding n-type polymeric ionene PMePyDPPPyT2 with bithiophene as comonomer forms thixotropic organogels with the p-type polythiophene P(g 4 2T-TT), indicative of specific crossinteractions between this couple of copolymers. Gelation of polymer blend solutions, which is absent for other couples of p-type/ ntype polymers, is of general interest for (co)processing and orientation of different electronic polymers simultaneously into films or filaments. Detailed optical and electronic characterization reveals that films processed from organogels exhibit ground-state electron transfer (GSET) enabled by suitably positioned highest occupied molecular orbital (HOMO) and LUMO energy levels of P(g 4 2T-TT) (−4.07 eV) and PMePyDPPPyT2 (−4.20 eV), respectively. Furthermore, molecular interactions related to gelation and GSET do not appear to significantly influence the morphology of the polymer blend films.

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