Multifunctional Luminescent Down-Shifting Fluoropolymer Coatings: A Straightforward Strategy to Improve the UV-Light Harvesting Ability and Long-Term Outdoor Stability of Organic Dye-Sensitized Solar Cells

A new multifunctional coating for photovoltaic cells incorporating light-management, UV-protection, and easy-cleaning capabilities is presented. Such coating consists of a new photocurable fluorinated polymer embedding a luminescent europium complex that acts as luminescent down-shifting (LDS) material converting UV photons into visible light. The combination of this system with ruthenium-free organic dye-sensitized solar cells (DSSCs) gives a 70% relative increase in power conversion efficiency as compared with control uncoated devices, which is the highest efficiency enhancement reported to date on organic DSSC systems by means of a polymeric LDS layer. Long-term (>2000 h) weathering tests in real outdoor conditions reveal the excellent stabilizing effect of the new coating on DSSC devices, which fully preserve their initial performance. This excellent outdoor stability is attributed to the combined action of the luminescent material that acts as UV-screen and the highly photostable, hydrophobic fluoropolymeric carrier that further prevents photochemical and physical degradation of the solar cell components. The straightforward approach presented to simultaneously improve performance and outdoor stability of DSSC devices may be readily extended to a large variety of sensitizer/luminophore combinations, thus enabling the fabrication of highly efficient and extremely stable DSSCs in an easy and versatile fashion.