Applications of ytterbium in inverted organic photovoltaic cells as high-performance and stable electron transport layers

The electron transport layer (ETL) increases the power conversion efficiency (PCE) in organic photovoltaic cells (OPVs) by promoting the formation of ohmic contact between the active layer and the cathode metal. Here, we introduce ytterbium (Yb) as the electron transport layer into inverted OPVs where Yb is evaporated directly onto indium tin oxide (ITO). The inverted OPVs composed of ITO/Yb/P3HT:PCBM/MoO3/Ag recorded PCEs of up to 4.3%, achieving 71% of the fill factor (FF) in one sun irradiation. Over 80% of its original PCE was retained after 30 days. The results indicate that Yb in inverted OPVs is vastly superior to other ETLs as it improves the majority of the parameters including the short circuit current, FE and PCE. In this report, we will discuss the physical and optical functions of Yb in inverted OPVs which make Yb a promising candidate for simultaneously achieving high PCE and good air stability.