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We have prepared thiophene/phenylene/thiophene (TPT)-based low bandgap conjugated polymers exhibiting tunable energy levels and investigated their application in solar cells. By incorporating various electron-withdrawing comonomers through Stille coupling reactions, we obtained TPT-based donor/acceptor copolymers having bandgaps ranging from 1.0 to 1.8 eV. We compared the absorption spectra, electrochemistry, field effect hole mobility, and photovoltaic properties of these low bandgap TPT derivatives with those of poly(3-hexylthiophene) (P3HT). The absorption coefficients of the thin films fell in the range from 0.77 Â 10 5 to 1.4 Â 10 5 cm -1 . These materials displayed sufficiently high hole mobilities (>10 -3 cm 2 V -1 s -1 ) for efficient charge extraction and good fill-factors for organic photovoltaic applications. Electrochemical studies indicated desirable HOMO/LUMO levels, with a good correlation between the HOMO energy levels and the open circuit voltage (V oc ) when the polymers were blended with fullerene derivative as an electron acceptor. Power conversion efficiencies of up to 4.3% were achieved under AM 1.5G simulated solar light (100 mW cm -2 ). Our findings suggest that TPT derivatives presenting suitable electron-withdrawing groups are promising photovoltaic materials.

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Self-doped sulfonic acid ring-substituted polyaniline (SPAN) reported so far is only slightly soluble in water. This work reports the synthesis route of SPAN in water with a solid content at least 50% by weight, which is stable (without precipitation) for more than 1 year and can be cast into free-standing films. The protons on the bound sulfonic acid groups can dope the imine nitrogens both in its aqueous form and as a solid film as evidenced by the presence of polaron absorption bands in its UV−vis spectra and of free spins from the ESR measurement. Titration analysis and spectroscopic data of the polymer in aqueous solution and as solid film, respectively, show that, surprisingly, the fractions of −SO3H groups that protonate (dope) the imine nitrogens to give semiquinone radical cations are equal in both cases, about 0.60 (equivalent to the doping level, 0.30). However, the free spins in the aqueous solution are more localized than those in the solid film. The thermostability of SPAN is also investigated. The conductivity of SPAN film (at 25 °C, 0.01 S/cm) increases with temperature from −10 (0.002 S/cm) to 190 °C (0.09 S/cm) and decreases with temperature from 190 to 225 °C (0.06 S/cm) due to thermal undoping accompanying a loss of some polarons as confirmed by the UV−vis, IR, and TGA analyses. After the heating scan, the conductivity at room temperature drops by a factor of 103.

This paper describes the influence of the solvent on the morphological evolution and performance of polymer solar cells (PSCs) based on blended films of poly(thiophene-phenylene-thiophene) and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM). The blends are spin-coated with solvents exhibiting various evaporation rates, including o-dichlorobenzene (DCB), chlorobenzene (CB), chloroform (CF), and tetralin. The changing morphologies of these blended films are monitored using atomic force microscopy (AFM) and transmission electron microscopy (TEM). A solvent having a higher boiling point [1,8octanedithiol (OT)] is also introduced as an additive to further fine-tune the morphology of the bulk heterojunction (BHJ). We demonstrate herein that the morphology of a blend;and, hence, the performance of a BHJ device;can be manipulated by controlling the rate of solvent evaporation during film formation. The resulted fine-scale phase separation leads to enhanced performance of such organic photovoltaic devices. The highest power efficiency for our PSCs (5.8%, AM 1.5G irradiation (100 mW/cm 2 )) resulted when we use DCB as the solvent with OT as a processing additive.