ENGINEERING OF GOLD SURFACE WORK FUNCTION BY ELECTRODEPOSITION OF SPIROBIFLUORENE-BASED DONOR-ACCEPTOR BIPOLAR SYSTEMS

L FERNANDEZ, PHILIPP ZABEL, THOMAS DITTRICH, YUAN-LI LIAO, CHI-YEN LIN, KEN-TSUNG WONG, FERNANDO FUNGO AND LUIS OTERO

La Plata

Jornada; Cuarto Encuentro de Física y Química de Superficies; 2009

Interfaces between metals and organic materials are crucial for electronic properties andcharge separation in devices such as organic light emitting diodes; organic field effecttransistors; electrochromic systems and organic solar cells. The efficiency of theseheterojunction devices strongly depends on the charge injection process (of holes or electrons)between the metal electrodes and the active organic layers. Metal/organic material interface isone of the device parameters that more attention has attracted in the search of improvementdevices performance, because the formation of the metal/organic junction leads tomodification in important properties, such as metal work function and orbital energy of theorganic layer.In this work, charge separation in gold/spirobifluorene-based donor (triphenylamine)-acceptor(cyano) bipolar systems has been investigated by contact potential difference and surfacephotovoltage spectroscopy. Organic films were formed on gold electrode by electrochemicalpolymerization and by dipping in dye solution. The gold surface work function has beenchanged over more than 0.4 V depending on the numbers of electrochemical depositioncycles. Photovoltage effects were analyzed in terms of internal photoemission from Au intoorganic film, and organic layer light absorption. The energetic differences between the Fermilevelof Au and HOMO levels of organic systems were obtained. The results showed that theelectrodeposition is a versatile tool for electrode surface work function tuning.