Influence of indium tin oxide treatment using UV-ozone and argon plasma on the photovoltaic parameters of devices based on organic discotic materials

Recently, we reported that the open circuit voltage, V-0C, in two-layer organic solar cells depends on the indium tin oxide (ITO) treatment. However, the V-0C variation details were not clearly understood. The study of the electronic structure at the ITO/organic interface was carried out by using the Kelvin probe method. The results obtained show a strong dependence of the organic vacuum level on the ITO work function, which, in turn, depends on the anode treatment. An abrupt variation of the vacuum level was observed after deposition of a few organic monolayers, which could be attributed to the presence of dipoles at the interface. We demonstrate that the shift magnitude depends on the nature and duration of the ITO treatment. To this end, two different ITO treatments were used. The first one, based on UV-ozone exposure, is known to increase the ITO work function, W-ITO. The second of these uses a microwave argon plasma generated by a repartee cyclotron excitation. This was adapted for decreasing the W-ITO value. An investigation on the origin of these variations ('up and down') is presented in this study. (c) 2005 Society of Chemical Industry.