Current-Voltage Characteristics Simulations of Organic Solar Cells Using Discontinuous Galerkin Method

The steady state drift-diffusion model (DDM) of organic solar cells that considers the surface recombination processes for majority and minority carriers, as well as their thermionic emission on both electrodes, is presented in this paper. When the full Robin boundary conditions (BCs) and the popular finite difference method with Schaffeter-Gummel discretization (FDSG) were applied, significant instabilities were observed when surface recombination velocities (SRVs) for majority carriers on one or both electrodes were reduced. To analyze this problem and perceive the independent impacts of electron and hole contact processes, the model was simplified by assuming a constant electric field in the device and by solving the electron and hole continuity equations separately. The stability of numerical DDM solutions obtained by the FDSG and Discontinuous Galerkin (DG) methods for three different types of BCs (Dirichlet and two mixed BCs) was examined. The DG method showed a better stability when majority carriers SRVs were reduced. The current density versus voltage (J-V) characteristic calculated by the DDM with Dirichlet BCs using the DG method was compared to the measured ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell J-V curve for the model validation.