Low-Temperature Solution-Processed Electron Transport Layers for Inverted Polymer Solar Cells

Processing temperature is highlighted as a convenient means of controlling the optical and charge transport properties of solution processed electron transport layers (ETLs) in inverted polymer solar cells. Using the well-studied active layer-poly(3-hexylthiophene-2,5-diyl):indene-C-60 bisadduct - the influence of ETL processing temperatures from 25 to 450 degrees C is shown, reporting the role of crystallinity, structure, charge transport, and Fermi level (E-F) on numerous device performance characteristics. It has been determined that an exceptionally low temperature processed ETL (110 degrees C) increases device power conversion efficiency by a factor greater than 50% compared with a high temperature (450 degrees C) processed ETL. Modulations in device series and shunt resistance, induced by changes in the ETL transport properties, are observed in parallel to significant changes in device open circuit voltage attributed to changes on the E-F of the ETLs. This work highlights the importance of interlayer control in multilayer photovoltaic devices and presents a convenient material compatible with future flexible and roll-to-roll processes.