Deposition Simulation of Nanometer Sized Grains under High Electric Field with XFEM

The authors are working to develop a new method to fabricate an active layer of an organic photovoltaic (OPV) cell by electrospray deposition (ESD) of colloidal donor and acceptor materials. In this study, scanning electron microscope (SEM) observation of active layer formed by ESD method with colloidal materials shows unique aggregation patterns of deposited nanometer sized colloidal grains. The authors carried out simulations of electric charged colloidal grains deposition under high electric field environment, to make clear the cause of the aggregation patterns and to get hints for controlling it. The deposition simulation was constructed based on a ballistic aggregation (BA) model with the effect of electric field. The extended finite element (XFEM) method was applied for numerical computation of electric field around colloidal grains deposition, since XFEM is carried out numerical analysis for a model with very complex material interface of deposited grains without re-meshing as conventional FEM. The comparison between theoretical and numerical analysis around a dielectric sphere in uniform electric field, shows that the developed XFEM analysis software can compute an electric field analysis with sufficient accuracy. Next, an example of an electric field numerical analysis of the space around two dimensional deposited grains is shown. Finally, by comparing between the three dimensional simulation and the experimental results, the possibility that the deposited grains are aggregated by the effect of electric field, is shown.