Targeting the use of organic conjugated polymers in organic solar cells, this study looks at the electrochemical properties of poly(3-alkylthiophene) films: poly(3-methylthiophene), poly(3-hexylthiophene), poly(3-octylthiophene) and its copolymers electrochemically synthesized on a tin-doped indium oxide (ITO) substrate. Electrochemical impedance spectroscopy (EIS) was used to monitor the change in the electrochemical behavior of these films on the ITO and the charge transfer resistance (R CT ) values were determined in open circuit potential (OCP) and at different overpotentials. Together with the EIS, the ex situ and in situ Raman spectroscopy was used to characterize the influence of aromatic radical cation and dication species, present in the polymer matrix of homo and copolymers, in the management processes seen in the Nyquist and Bode-phase diagrams for different systems obtained on ITO. The EIS results in OCP showed an decrease in resistance demonstrating increased conductivity with the copolymerization, and through the Bode-phase diagram and the ex situ Raman spectra, these changes were related to the oscillation of the radical cation and dication along the polymer matrix. By studying Nyquist and Bodephase diagrams in the overpotentials, an increase in R CT values in higher potentials was seen that could be related to the bipolaronic process, which after the deconvolution of the in situ Raman spectra, was possible to relate these results to the stabilization of the dication species in the homo and copolymers matrix when subjected to high potential.

International audienceIn this study, we observed significant differences in the electrical and optical properties of polymer films electrochemically synthesized from two 3-alkylthiophene monomers on platinum wires in 0.100 mol L-1 LiClO4/acetonitrile (ACN) or Et4NBF4/ACN, when compared to the following homopolymer films: poly(3-methylthiophene) (P3MT), poly(3-hexylthiophene) (P3HT) and poly(3-octylthiophene) (P3OT), prepared under the same conditions. Electrical impedance spectroscopy was used to assess the resistive and capacitive properties of the polymer films [P3MT and P3HT-CP3(MT-HT); P3MT and P3OT-CP3(MT-OT); P3HT and P3OT-CP3(HT-OT)] at overpotentials determined beforehand by Cyclic Voltammetry. The films synthesized in LiClO4/ACN with the lowest charge transfer resistance values were CP3(MT-HT) and CP3(MT-OT), and synthesized in Et4NBF4/ACN, CP3(HT-OT). In terms of their optical properties, the films synthesized in LiClO4/ACN exhibited hypsochromic shift of E (g) values and a drop in electron affinity values by comparison with homopolymer films and those synthesized in Et4NBF4/ACN. Based on Photoluminescence (PL) Spectroscopy it was possible to identify the contributions of the quinone and aromatic segments characteristic of homopolymers in the films synthesized in Et4NBF4/ACN. For the films synthesized in LiClO4/ACN, it was not possible to perform the same comparison because there was a discrepancy between the bands observed in the PL images of these materials and those of the homopolymers, suggesting the formation of not only blend structures but also copolymer films. Using Raman Spectroscopy it was possible to identify aromatic, radical cation and dication segments and verify the higher stabilization of radical cation and dication segments in resistive films. It was also possible to observe changes in the morphological structures of the films by comparison with the homopolymers, in addition to alterations due to changes in electrolyte during synthesis using scanning electron microscopy

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International audienceThis study compares the electrical properties of two homopolymers, poly(3-methylthiophene) and poly(3-octylthiophene), and their copolymers with polydiphenylamine, previously synthesized electrochemically on a platinum wire electrode (average area 0.19 cm2) in 0.100 mol L−1 LiClO4 at 18 °C. Based on the cyclic voltammetry data from these systems, electrochemical impedance spectroscopy (EIS) was used to evaluate the resistive and capacitive properties of the homo- and copolymers using the open-circuit potential (OCP) and overvoltage potential methods. The copolymer of poly(3-methylthiophene) and polydiphenylamine showed lower resistivity between films obtained by OCP and overvoltage potential. For all EIS images obtained by overvoltage potential there was a drop in resistivity and lower variation among the capacitance values. Using a Bode plot, we observed two time constants related to the radical cation and dication species, as characterized by Raman spectroscopy. Using scanning electron microscopy, it was possible to observe the changes in the morphological structures of the copolymers by comparison with the homopolymers, confirming the influence of greater active area on the improved conductivity of the copolymers

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International audienceThis work examines the photodegradation of poly(3-octylthiophene) (P3OT) by UV-irradiation at 405 nm under vacuum and as a function of temperature (300 and 10 K). Two different P3OT films were studied. The first one was electrochemically synthesized on platinum plate and chemically reduced in a basic medium (P3OT-E) whereas the second one, chemically synthesized was spread out on glass by casting process from polymer previously dissolved in chloroform (P3OT-Q). After 200 s under UV illumination, the photoluminescence (PL) spectra observed on the P3OT-E samples showed an unexpected increase of some eight times in the emission intensity. In contrast, the PL spectra of P3OT-Q, subjected to the same temperature, pressure and photoirradiation time, showed a drop of to around half the initial signal intensity. Similarly experiments were performed at low temperature 10 K. In this temperature condition, PL spectra of P3OT-E and P3OT-Q obtained under photoirradiation, presented similar decreases of the intensity of their fluorescence. In order to explain these different results, Raman spectroscopy studies had been performed, and it was been possible to follow the formation of C=O group on the side alkyl chain after 200 min of irradiation. From the results obtained, we proposed a mechanism to explain the unexpected intensification of the PL emission signal for P3OT-E at 300 K. This mechanism was based on the destabilization of the charge transfer complex between the radical cations in P3OT-E and the residual dioxygen