Abstract

Electron extraction contact in organic photovoltaic cells (OPVs) is very important to extract electrons from the active layer efficiently, improve the open-circuit voltage, and thus improve the power conversion efficiency. This paper reviews the various approaches to form an electron extraction contact for better power conversion efficiency and device lifetime, especially in organic bulk heterojunction photovoltaic cells based on conjugated polymer: fullerene blends. We discuss the roles of thin metal fluorides, a thin polymeric layer, and a solution processed metal oxide layer at the interface between the photoactive layer and the negative electrode for efficient and stable electron extraction contact in OPVs. In addition, we discuss the effects of various metallic negative electrodes in OPVs in terms of device efficiency and stability. Since these approaches are well established in organic light-emitting diodes, they can be exploited to accelerate research in device engineering to improve device performance.