Nanostructured Electrodes for Organic Solar Cells: Analysis and Design Fundamentals

Nanostructured electrodes (NEs) improve optical absorption and charge collection in photovoltaic (PV) devices. Traditionally, the electrodes have been designed exclusively for higher optical absorption. Such an optical design of the electrodes does not necessarily ensure better charge collection. Since the efficiency of organic PV (OPV) devices is hindered by the low carrier mobility of the organic semiconductors, the charge collection property of the NEs provides an interesting design alternative. The goal of this paper is the formulation of the essential design rules for NEs to improve charge collection in the low-mobility organic materials. We use detailed optoelectronic device simulation to explore the physics of NEs embedded in the organic semiconductors and quantify its effect on the performance gain of organic solar cells. Our analysis suggests that an optimum codesign of electrodes and morphology is essential for significant performance improvement (mainly through fill factor) in OPV cells.