Photoinduced Charge Separation in Organic-Organic Heterojunctions Based on Porphyrin Electropolymers

DURANTINI J, GALICIA M, SANTO M, OTERO L, DURANTINI E N, DITTRICH T, GERVALDO M

Cordoba

Congreso; NANOCORDOBA 2014; 2014

In the development of organic-based optoelectronic devices the understanding of the processes that take place in the heterogeneous junction regions are a crucial issue. Heterojunction regions are formed by boundaries created between electron donor and electron acceptor materials in close contact, but also the interface between the conductor substrate and the organic material plays a determinant role in the device operation.[1,2] Due to their optical and electronic properties, indium tin oxide (ITO) is often the chose contact for the translucent electrode.[ 3] Because of their spectral, magnetic and electronic properties, several studies on the development of organic optoelectronic devices incorporate porphyrins and related metallized and unmetallized tetrapyrrolic compounds.[4] Electropolymerization is a relevant alternative technique to produce organic-organic heterojunctions because it is a practical method that allows the synthesis of subsequent conducting films.[5]. In the present work two porphyrin polymers derivate were electrodeposited as thin films on ITO substrate and their surface photovoltage properties were investigated. The key role of the presence of the central metal in charge separation processes was established. Furthermore, the four photoactive organic films were successfully formed on the top of ITO electrodes modified with poly 3,4-ethylenedioxythiophene (PEDOT) layer generated by electropolymerization. The presence of this hole transport polymer dramatically alters the formation and di↵usion process of the photocarriers generated by excitation of the porphyrin films, demonstrating the crucial role of the organic-organic heterojunctions built by electropolymerization in the generation of photovoltaic e↵ects. On the other hand, when the external surface of the porphyrin electropolymers was modified with a layer of a strong electron acceptor (C60 buckminsterfullerene) the photovoltage signal obtained under similar experimental conditions rose up to near two hundred times, showing that devices formed by combining the here reported porphyrin conducting electropolymers (as light harvesting, electron donor and hole-transport layers) and fullerenes (as electron acceptor and electron-transport) could present high efficiency in the conversion of solar radiation into electrical energy,[6] and are promising to be used in the development of new solar energy technologies.