High-efficiency inverted dithienogermole-thienopyrrolodione-based polymer solar cells

Inverted polymer bulk heterojunction solar cells have received a great deal of attention because of their compatibility with large-scale roll-to-roll processing. The inverted cell geometry has the following structure: substrate (rigid or flexible)/indium tin oxide/electron-transporting layer/photoactive layer/hole-transporting layer/top anode. Solution-processed metal-oxide films, based on materials such as ZnO and TiO2, are typically used as the electron-transporting layers. Here, we demonstrate enhanced charge collection in inverted polymer solar cells using a surface-modified ZnO-polymer nanocomposite electron-transporting layer. Using this approach, we demonstrate inverted polymer solar cells based on a low-bandgap polymer with an alternating dithienogermole-thienopyrrolodione repeat unit (PDTG-TPD) with certified power conversion efficiencies of 7.4%. To our knowledge, this is the highest efficiency reported to date for polymer solar cells with a device architecture compatible with the roll-to-roll process.