Luminescent Downshifting by Photo-Induced Sol-Gel Hybrid Coatings: Accessing Multifunctionality on Flexible Organic Photovoltaics via Ambient Temperature Material Processing

A novel high-durability multifunctional organic-inorganic hybrid coating material is presented in this work as luminescent down-shifting (LDS) host matrix system for flexible organic photovoltaic (OPV) devices. Such new LDS coating is obtained by incorporating a convenient fluorescent organic dye in an appropriately functionalized fluoropolymeric resin that can be readily crosslinked by means of a dual-cure mechanism with a single-step ambient-temperature photo-induced sol-gel process. Due to its peculiar characteristics, the newly proposed system may be readily implemented in heat-sensitive flexible devices. By carefully tuning the amount of organic fluorophore in the hybrid coating material, a maximum increase in power conversion efficiency exceeding 4% is achieved on devices incorporating the new LDS layer with respect to control systems. This represents the highest efficiency enhancement reported to date on flexible OPVs by means of a polymer-based LDS layer. In addition, long-term accelerated weathering tests (>550 h) highlight the excellent stability of LDS-coated OPV devices, which can retain 80% of their initial performance, as opposed to the dramatic efficiency decay experienced by control uncoated devices. The approach presented here opens the way to the straightforward incorporation of versatile multifunctional light-managing layers on flexible OPV systems for improved device efficiency and lifetime.