Synthesis of 3',4'-disubstituted terthiophenes--Characterization and electropolymerization. II. 3'-bromo-4'-thienyl-2,2':5',2'-terthiophene and 3',4'-diphenyl-2,2':5',2'-terthiophene in photovoltaic displays

In a previous work 3',4'-dibromo substituted polythiophene film was used to produce an electronic device with photovoltaic characteristic but only 0.006% yield was achieved. In an effort to understand the reason of this low-yield, we intend to elucidate the effect of substituents of terthiophene compounds on the morphological characteristics and conductivity of the electrochemical deposit. Thus, in this article we describe the electrochemical properties of thin films of poly(3',4'-diphenyl-2,2':5',2"-terthiophene), and poly(3'-bromo-4'-thienyl-2,2':5',2"-terthiophene), the studies of electropolymerization using cyclic voltammetry, the determination of nucleation and growth mechanism using potential steps, and the morphology. Furthermore, a ZnO/Polymer/PTCDA/Li/Al photovoltaic cells have been devised and their I-V characteristics studied in the presence and in the absence of light. Incorporation of 3,4-9,10-tetracarboxylic dianhydride, PTCDA, as acceptor, induces a wider absorption spectrum in the visible region. Study of the photovoltaic efficiency, that increased with a decrease of the polymeric coating thickness, which in turn, is related to the number of voltammetric cycles, was also accomplished, but the desired thickness was never obtained without missing the electronic properties. Thus, even if the polymeric layer had the appropriate structure, this study corroborates that, to prepare the deposit, the electrochemical parameters must be previously controlled so as to obtain the thickness and morphology that render the best response.