Toward flexible dye-sensitized solar cells: exploring sintering conditions on thermally stable polymer substrates

Dye-Sensitized Solar Cells (DSSCs) have emerged as a promising alternative to conventional photovoltaic technologies due to their low production costs, simple fabrication process, and potential compatibility with flexible substrates. However, the requirement for high-temperature treatment, typically in the range of 450–500°C, significantly reduces the materials that could be used as substrate for the electrodes. In fact the materials that are flexible and transparent are usually polymers, characterized by a low thermal resistance, around 100°C. Above this, colorless polymide emerges as higly flexible and transparent material that can resist temperatures up to 330°C, being suitable to be tested as a possible alternative to conventional rigid materials. In this thesis, it was investigated the effect of different sintering techniques and conditions on the performance of DSSCs, with the goal to create flexible DSSC on polyimide substrate, focusing on conventional oven sintering and laser sintering techniques. DSSCs were fabricated using TiO2 photoanodes processed at various temperatures (300°C–475°C) and times, revealing that low-temperature sintering at 325°C produced results that are a good compromise with the ones sintered as traditionally at 475°C, suggesting potential compatibility with alternative substrates such as polyimide and prolonged sintering improved their performances. Despite its high thermal stability, polyimide is an insulating material, so it needs a conductive coating to become a valid substrate alternative for DSSC. To achieve a conductive substrate we speculate to use metal microgrids realised directly on the polyimide substrate. Polyimide exhibited adhesion Issues and thermal insulation for the correct TiO2 calcination. The probelm of Thermal insulation was solved increasing the sintering time while the issue of the adhesion needs to be proven on the conductive coating. Additionally, laser sintering was explored as a rapid, localized sintering method, screening all the process parameters. Apparently we succeded to remove the binder, however the obtained results from the closed cells are not comparable to the oven fired ones and still needs a further development in the future. To conclude, flexible DSSCs on polyimide substrate seems a good alternative to current flexible solar cells but further studies on the conductive coating and the laser sintering have to be done.