Search

Hybrid solar cells of semiconductor oxides and conductive polymers have been broadly studied. Poly(3-octylthiophene) (P3OT), is an organic polymer formed by conjugated structures with conductive properties, photoluminescence, a relatively high charge mobility and stability. Zinc oxide (ZnO) has been used as an electron acceptor in this cell type because it offers great electron transport properties, simple manufacturing techniques, non-toxicity, variation and morphologic control. Different ZnO morphologies allow distinct properties in terms of electronic transport in solar cell interfaces. The objective of this paper was to evaluate whether ZnO with its different morphologies can improve the anchorage of P3OT and influence the conductive properties of hybrid solar cells of ZnO/P3OT. ZnO particles were synthetized by co-precipitation with Zn(NO3)2·6H2O in concentrations of 0.05, 0.10 and 0.15 mol L−1. The morphology was evaluated by scanning electron microscopy (SEM), and the suspension was evaluated by thermogravimetric analysis and differential scanning calorimetry and X-ray diffraction. Cells containing the working electrode (ZnO/P3OT) were evaluated by open circuit potential (Voc) and electrochemical impedance spectroscopy (EIS). The SEM images showed three morphologies: spherical ZnO (ZnOE), hexagonal ZnO (ZnOH) and ZnO without defined morphology (ZnOM) due to the variation of the precursor salt concentration. Cells with different morphologies presented medium values of Voc = −0.438 ± 0.027 V. The EIS indicated that ZnOM/P3OT cells have lower values of charge transfer resistance and higher values of capacitance at intermediate frequencies. ZnOM/P3OT solar cells presented the best results in relation to the electron transfer processes.

In 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.

International audience; This 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.