Electrochemical deposition of poly[ethylene-dioxythiophene] (PEDOT) films on ITO electrodes for organic photovoltaic cells: control of morphology, thickness, and electronic properties

Abstract

In this article, controlled changes on morphology, thickness, and band gap of poly[ethylenedioxythiophene] (PEDOT) polymer films fabricated by electrochemical polymerization (potentiostatically) are analyzed. Electropolymerization of the monomer ethylenedioxythiophene (EDOT) was carried out on indium tin oxide (ITO) electrodes, in different dry organic electrolytic media, such as acetonitrile, acetonitrile–dichloromethane, and toluene–acetonitrile mixtures. It was found that electropolymerization kinetics can be controlled by changing the polarity of the electrolytic media, and kinetics is slower for those with low polarity. This fact combined with an accurate control of EDOT monomer concentration and electropolymerization at Epeak/2 potential, allows to control the morphology and thickness of the electropolymerized PEDOT films (E-PEDOT:ClO4); toluene/ACN (4:1, v/v) and [EDOT] = 0.3 mM gave the best films for application in organic photovoltaic (OPV) cells. The performance of the E-PEDOT:ClO4 films was tested on ITO electrodes as anode buffer layer in OPV cells with the configuration ITO/E-PEDOT:ClO4/P3HT:PC61BM/Field’s metal, where Field’s metal (cathode) is a eutectic alloy that lets to fabricate OPV devices easily and in a fast and economical way at free vacuum conditions. The performance of these devices was compared with an OPV device constructed with a buffer layer anode, prepared using the classical spin coating of PEDOT:PSS on ITO. Results showed that OPV cells fabricated with E-PEDOT:ClO4 have a slightly increased PV performance.