Fabrication of Double Layered TiO2 Photoelectrodes Using Electrostatic Inkjet Printing

Dye-sensitized solar cells (DSSCs) are one of the most attractive electrochemical devices capable of converting light energy into electrical energy because they can be fabricated at low cost in an eco-friendly manner. Photo-electrode film of TiO₂ nanoparticles in DSSC plays a major role in the light absorption and charge carrier separation and collection process. Popular fabrication methods of the photo-electrode film are screen-printing, spray-coating, spin-coating, and blade-coating. Inkjet printing of functional materials has been attracting significant attention in the light of recent attempts to manufacture various electronics such as light-emitting diodes, thin film transistors, solar cells, memory devices, sensors, biological devices, passive circuit elements, etc. However, it is well known that current inkjet printers such as thermal and piezoelectric printers cannot eject a droplet of high-viscous liquid. TiO₂ paste consists of aqueous solution of TiO₂ nano-particles, surfactant and polyethylene glycol, and is very high viscosity. Recently, we developed new inkjet technology, electrostatically-injected spray method. When the strong electric field was applied to a nozzle, small droplets were ejected by the electrostatic force. In this study, we apply this inkjet printing technique to develop double layered TiO₂ photo-electrodes.

   The TiO₂ paste was printed by electric field-induced inkjet printing on fluorine-doped SnO₂-coated (FTO) glass electrodes and sintered at 450 °C for 30 min. DSSCs were prepared by a conventional procedure. Photovoltaic properties of each solar cell were characterized using simulated AM 1.5 sunlight illumination with an output power of 100 mW/cm².

   We have successfully fabricated double layered TiO₂ photo-anodes using an electrostatic inkjet printing technique. The structures and morphologies of the TiO₂ film, which ultimately influence the cell performance, were controlled by changing the distance between the capillary nozzle and the FTO substrate (spraying distance). The TiO₂ film formed by longer spraying distance yielded a large surface area and a highly porous structure.