Multifunctional down-shifting polymeric coatings for highly stable and efficient organic dye-sensitized solar cells

A new multifunctional polymeric coating for photovoltaic cells is presented in this work, incorporating light-management, UV-protection and easy-cleaning capabilities. Such coating consists of a new photocrosslinkable fluorinated polymer doped with a luminescent Europium complex that acts as luminescent down-shifting (LDS) material to convert UV photons into visible light. By applying this coating onto Ruthenium-free organic dye-sensitized solar cells (DSSCs), a 70% relative increase in power conversion efficiency could be achieved compared with control uncoated devices. To evaluate the photostabilizing effect of the new fluoropolymeric coating, long-term (> 2000 h) weathering tests in real outdoor conditions were conducted on these systems. DSSC devices incorporating the new multifunctional coating exhibited excellent outdoor stability and fully preserved their initial device performance. This behavior was 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 general approach presented in this study to simultaneously improve performance and outdoor stability of organic DSSC devices may be readily extended to a large variety of sensitizer/luminophore combinations with appropriate spectral match, thus ultimately enabling the fabrication of highly efficient and stable organic DSSCs in an easy and versatile fashion.