Modelling of Organic Device Cathode Obtained by Ion Beam Assisted Deposition

Organic devices like solar cells or light emitting diodes (OLEDs) are intensively studied since the last years and are potentially able to reach the market. Nevertheless both polymer or small molecule based devices behave poor stability in open air conditions so that encapsulation process will by essential. A solution would be to use the top electrode (generally the cathode) as the encapsulating layer. In this case ion beam assisted deposition (IBAD) of the layer is an accurate process to obtain a dense layer which can act as a barrier to moisture and oxygen. First, a computer simulation, with the SRIM code based on the binary collision approximation, of a low energy argon ion beam interaction with an aluminium layer describes the densification effect of the IBAD process. It is found that the densification process is obtained by the aluminium recoil atom replacements which are preferentially located in a first domain near the surface, corresponding to the lacunas occurred by ion implantation, and a domain deeper than the mean free pass of the ions. Due to this latter replacement domain, a non assisted buffer layer is needed in the case of direct deposition of the metallic electrode on optically active organic layer, in order to avoid recoils atoms to act as traps. Then this process will be illustrated in the case of life time improvement of small molecule based OLEDs