Interface States Controls Energy Level Alignment in Cathode Contacts of Organic Bulk-Heterojunction Solar Cells

n organic photovoltaic devices, outer interface structures play a significant role in establishing optimal contact condi-tions for efficient extraction (or blocking) of charge carriers. Buffer layers of different nature are currently employed to enhance both power conversion efficiency (PCE) and cell stability by improving contact perfor-mance. Several materials have been ex-plored to enhance the electron selectivity of the cathode contact: alkali metal com-pounds (LiF, etc.), metal oxides (TiOx, ZnO, etc.), and low molecular weight organic compounds have been reported to contri-bute to the overall PCE and solar cell lifetime