Laser welding of nanoparticulate TiO₂ and transparent conducting oxide electrodes for highly efficient dye-sensitized solar cell

Poor interfacial contact is often encountered in nanoparticulate film-based devices. The dye-sensitized solar cell (DSSC) is a representative case in which a nanoporous TiO₂ electrode needs to be prepared on the transparent conducting oxide (TCO)-coated glass substrate. In this study, we demonstrate that the inter-electrode contact resistance accounts for a considerable portion of the total resistance of a DSSC and its efficiency can be greatly enhanced by welding the interface with a laser. TiO₂ films formed on the TCO-coated glass substrate were irradiated with a pulsed ultraviolet laser beam at 355 nm; this transmits through the TCO and glass but is strongly absorbed by TiO₂. Electron microscopy analysis and impedance measurements showed that a thin continuous TiO₂ layer is formed at the interface as a result of the local melting of TiO₂ nanoparticles and this layer completely bridges the gap between the two electrodes, improving the current flow with a reduced contact resistance. We were able to improve the efficiency by 35-65% with this process. DSSCs fabricated using a homemade TiO₂ paste revealed an efficiency improvement from η = 3.3% to 5.4%, and an increase from 8.2% to 11.2% was achieved with the TiO₂ electrodes made from a commercial paste.