Solar energy converted by flexible devices: photocured polymer electrolytes and bendable nanotubes membranes

One of the possible applications of dye-sensitized solar cells (DSSCs) is the biasing of low-power portable devices. In this framework, the cells should be flexible and adaptable to complex shapes. Therefore, it is necessary to prepare suitable electrodic and electrolytic materials. As regards electrolytes, we have recently proposed polymer electrolyte membranes (PEMs), as a good alterna-tive to the traditionally used viscous gels. PEMs are prepared through a green, low-cost and fast process of photoinitiated polymerization, which allows obtaining a fast transformation of a liquid monomer or oligomer into a solid membrane with tailored physico-chemical and mechanical properties. We present here several acrylic/methacrylic PEMs, with emphasis also on unconventional fillers and redox couples. As regards photoanodes, one the most critical aspect in the development of flexible DSSCs lies in the fabrica-tion of a nanostructured TiO2 film with good adhesion to the conductive substrate, high surface area, excellent dye loading capabilities and good electronic transport properties. The employment of mesoporous TiO2 nanoparticles, treated with low-temperature procedures, has been recently explored, but it did not guarantee the desired results. A possible alternative way is based on the use of TiO2 nanotubes (NTs) grown by anodic oxidation. We have recently reported that TiO2 NTs show a good adhesion to the starting substrate of growth and can provide performances competitive with those of TiO2 nanoparticles, showing higher electron transport thanks to the quasi-one dimen-sional arrangement and high surface area for dye anchoring. The as grown and thermally treated samples were deeply investigated in order to gain a whole understanding of their structural, physical and chemical properties. Here we report for the first time the combination of a methacrylic crosslinked PEM (whose polymeric network has been deeply characterized by charge-transfer measurements and dynamo-mechanical analysis) and vertically oriented TiO2 nanotubes grown by anodic oxidation of flexible Ti mesh in order to fabricate a flexible and trans-parent DSSC. The photovoltaic behavior was exhaustively investigated by electrical measurements and impedance spectroscopy. To the state-of-the-art, the appropriate selection and optimization of all the materials allowed us to obtain the most efficient quasi-solid flexible DSSC ever produced.