New dielectric/metal/dielectric electrode for organic photovoltaic cells using Cu:Al alloy as metal

Abstract Given the rapidly increasing demand for flexible and inexpensive optoelectronic devices, it is necessary to find a substitute for ITO (Indium Tin Oxide). Among the considered alternatives, we have chosen in the present work Dielectric/Metal/Dielectric (D/M/D) trilayer structures deposited under vacuum. In these D/M/D structures, when Ag is the metal, highly performing and stable Transparent Conductive Electrodes (TCEs) are obtained. When Ag is replaced by Cu, which is far less expensive, results are not similar due to the tendency of Cu to diffuse into the transition metal oxides. Therefore we improve the stability of the new TCEs by using the Cu alloy Cu:Ag in ZnS/M/WO3 structures. The best results were obtained when M = Cu:Ag (16 nm)/Ag (1 nm). Flexible and quite stable TCEs were obtained. These new TCEs are conductive and transparent with a figure of merit of 6.5 x 10−3Ω−1 and a quite small Root Mean Squared Roughnessis (RMS = 1.1 nm). Therefore, they were introduced as anode in organic photovoltaic cells (OPVs). In the same time, ZnS/Ag/TiO2 TCE were probed. These ZnS/Ag/TiO2 structures were transparent and conductive with optical and electrical performances similar to those of ITO, but, when used as anode, the OPVs performances were limited by the presence of Ag at the surface of the structures. In the other hand, the results obtained with ZnS/M/WO3 structures were very promising with an open circuit voltage, Voc, and a short circuit current, Jsc, whose values are slightly higher than those obtained with ITO. Nevertheless the fill factor FF is sensibly smaller, which is attributed to the presence of some Cu at the surface of the electrode.