Hyper flexible dye-sensitized solar cells: towards microfluidic stable devices

One of the possible applications of dye-sensitized solar cells (DSSCs) is the biasing of low-power portable devices. However some critical issues still have to be faced in view of obtaining flexible cells, readily adaptable to complex shapes. Until today the best performing DSSCs are based on a rigid housing with glass/FTO electrodes and the use of a liquid electrolyte is crytical for the possible durability of the device. Therefore, suitable flexible electrodes and polymeric electrolytes are needed. During recent years we deepened a promising approach for the fabrication of quasi-solid DSSCs with excellent long-term durability. We thoroughly studied and characterized the integration of self standing polymeric membranes prepared by free radical photopolymerization, investigating different polymeric formulations. Very recently, this electrolytic system was integrated with an innovative design for DSSC photoanode, based on the use of semitransparent metallic meshes as a support for the sensitized nanostructured semiconductor. For photoanode fabrication, both the use of TiO2 nanotubes directly grown on bendable Ti mesh by anodic oxidation and the deposition of mesoporous layers of TiO2 nanoparticles were investigated with excellent results. The main advantage of this solution is the possibility to perform the high temperature sintering process (which is mandatory for a well performing semiconductor layer with good electron transport) before the integration on the final polymeric housing. In this work, two flexible electrodes (a titanium mesh supporting N719-sensitized TiO2 nanotubes by anodic oxidation and a Pt-coated mesh) are embedded in flexible PDMS substrates obtained by partial crosslink reaction before bonding. PDMS is almost totally transparent to VIS radiation down to 220 nm, thus it represents a valuable substrate for flexible DSSCs. Moreover, the two PDMS substrates can be sealed by means of UV-cured siloxane methacrylates, thus avoiding the use of thermoplastic films that would require pressure and high temperatures. Furthermore, PDMS is well suited for the fabrication of microfluidic devices, so it is possible to create holes and channels for the introduction of liquid electrolytes or UV-curable monomers containing different redox couples. The photovoltaic behavior of the resulting solid DSSCs is exhaustively investigated by electrical measurements and impedance spectroscopy.