Abstract
The present work describes an electrochemical method to produce the copolymer poly(2-methoxy-5-bromo-p-phenylenevinylene)/(2,5-dicyano-p-phenylenevinylene) (cop-MB-PPV/DCN-PPV). This copolymer was proposed due to its D-A characteristic produced by the presence of the electron-donating methoxy moiety and the electron-withdrawing dicyano moiety. The copolymer was electrochemically synthetized by cathodic reduction of the convenient starting materials dissolved in a DMF/LiClO4 using a mercury pool acting as working electrode. The copolymer was characterized by infrared (IR), UV-Vis and fluorescence (FL) spectroscopy and cyclic voltammetry (CV). All the results were compared to the MB-PPV homopolymer. The analysis of electrochemical measurements and IR indicated that the cop-MB-PPV/DCN-PPV was obtained through the formation of blocks containing DCN-PPV units linked by blocks containing MB-PPV units. The electronic structure, performed by CV, UV-Vis and FL showed that the conduction band is more stabilized in the copolymer than in homopolymer. Furthermore, the FL spectra indicated that the light emission of the cop-MB-PPV/DCN-PPV in chloroform solution occurs by means of excimer formation.
Highlights
During the last two decades, bulk heterojunction polymer solar cells (PSCs) have been widely studied regarding the possibility of developing efficient and renewable energy sources through the low cost devices production.[1,2,3] Due to massive research efforts there has been significant progress in the field of organic solar cells and within about 25 years higher efficiencies and lifetimes were achieved and power conversion efficiencies (PCEs) higher than 10% have been reported.[4]
For this reason the preparation of copolymer MB-PPV/DCN-PPV was held through the application of a more negative potential value in order to increase the amount of MB-PPV units in the copolymeric chain since the formation of DCN-PPV would be predominant in less negative potentials
It can be observed that the reduction to cop‐MB‐PPV/DCN-PPV begins to flow through the system in less negative potentials compared to MB-PPV. These results indicate that the copolymer presents a more stable conduction band than MB-PPV, which is consistent with the presence of DCN-PPV blocks formed during electropolymerization process, as already shown by IR results
Summary
During the last two decades, bulk heterojunction polymer solar cells (PSCs) have been widely studied regarding the possibility of developing efficient and renewable energy sources through the low cost devices production.[1,2,3] Due to massive research efforts there has been significant progress in the field of organic solar cells and within about 25 years higher efficiencies and lifetimes were achieved and power conversion efficiencies (PCEs) higher than 10% have been reported.[4]. In the case of the preparation of cop-MB-DCN-PPV (Figure 1b) the current profile as a function of time shows that the current value is greater at the beginning of the process and decreases with increasing time.
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