Direct Visualization of Charge-Extraction in Metal-Mesh Based OPV Cells by Light-Biased LBIC

Metal-mesh based electrode systems are a highly conductive, versatile, and inexpensive alternative to ITO-electrodes for organic photovoltaic (OPV) cells. However, they do not offer full surface conductivity and are, therefore, usually combined with an additional conductive layer (e.g. PEDOT:PSS), which enables lateral charge-transport in the area in between the metal tracks. The sheet conductivity of this additional lateral conductive layer (LCL) needs to be carefully tuned with respect to the distance of the metal tracks to reduce short circuit current (Jsc) losses and additional series resistance due to resistive losses in the LCL material. Usually, this is done via electrical simulation or via analysis of IV-measurements of a large number of devices with different LCL sheet conductivities. Here, we present the light-biased light-beam-induced-current (LB-LBIC) measurement technique as a direct way to visualize current collection losses due to PEDOT:PSS sheet resistance in metal mesh/bus bar based OPV cells. We demonstrate that with LB-LBIC we are not only able to visualize and optimize lateral charge extraction under real-device operation conditions in OPV cells based on a high-resolution metal mesh but can measure the PEDOT:PSS sheet resistance in operating OPV devices as well.