Quantitative analysis of electroluminescence images from polymer solar cells

We introduce the micro-diode-model (MDM) based on a discrete network of interconnected diodes, which allows for quantitative description of lateral electroluminescence emission images obtained from organic bulk heterojunction solar cells. Besides the distributed solar cell description, the equivalent circuit, respectively, network model considers interface and bulk resistances as well as the sheet resistance of the semitransparent electrode. The application of this model allows direct calculation of the lateral current and voltage distribution within the solar cell and thus accounts well for effects known as current crowding. In addition, network parameters such as internal resistances and the sheet-resistance of the higher resistive electrode can be determined. Furthermore, upon introduction of current sources the micro-diode-model also is able to describe and predict current-voltage characteristics for solar cell devices under illumination. The local nature of this description yields important conclusions concerning the geometry dependent performance and the validity of classical models and equivalent circuits describing thin film solar cells.