Surface modelling of organic solar cells

Modelling of physical phenomena in optoelectronic devices enables to define new strategies to optimize organic components (organic photovoltaic cells (OPVs), organic light emitting diodes (OLEDs), etc ....). The organic photovoltaic technology allows producing more attractive and lighter weight photovoltaic devices than silicon solar technology. Both organic small molecule based and polymer based devices are studied. These devices needs the use of two different materials in the active layer (one electron acceptor and one electron donor) in order to separate the photogenerated electron-hole pairs due to their excitonic behaviour in organic compounds. However, the power efficiencies of the organic solar cells are lower than those obtained with silicon solar cells. In our laboratory, the efforts in order to enhance the power efficiency of OPV devices are in progress. One way consists to minimise the power dissipated by the photogenerated current in the electrodes, particularly in the case of the anode which is constituted of a low conductive transparent thin layer (indium tin oxide ITO). In this communication, electromagnetic field modelling in this anode (mapping of current density obtained by numerical modelling), explains the decrease of the power conversion efficiency in the device due to its surface enhancement. To optimise the photovoltaic cell performance, we have modelized by using two powerful tools (GSMH and Shell) the electromagnetic fields and the dissipated power in different cells characterized by their electrode design: rectangle with different surface (varying length with constant width). The simulated results are then compared with photovoltaic characterizations under light illumination of organic small molecule based solar cells built with these geometries, where the device structure is ITO/PEDOT-PSS (30 nm) / CUPC (25 nm) / C60 (40 nm) / BCP (2.5 nm) / Al (100 nm). A perfect correlation between power dissipation in the electrodes and measured serial - resistance of the devices is found.