Influence of flexible substrates on inverted organic solar cells using sputtered ZnO as cathode interfacial layer

Zinc oxide (ZnO) has recently shown to be of considerable interest for the development of interfacial buffer layers in inverted organic solar cells (OSCs). High quality ZnO thin films can indeed be prepared on large-area ITO-coated flexible substrates, using low temperature deposition techniques such as sputtering, a compatible technique with roll-to-roll process. However, further studies are still needed for a better understanding of the influence of the flexible substrate properties on the photovoltaic performances of those devices. In this work, ZnO films have been sputtered on ITO-coated flexible (PEN) substrates and annealed at different temperatures. The role of the surface morphology and the crystalline quality of ZnO films has been investigated. In the window of flexible compatible process, we found that moderate annealing temperatures of ZnO (?180 °C) lead to improved structural properties and performances. Interestingly, we achieve optimal performances for an annealing temperature of 160 °C, resulting in power conversion efficiency (PCE) equivalent to the highest performances usually achieved on rigid cells.