Aligned photoelectrodes with large surface area prepared by pulsed laser deposition

Aligned photoelectrodes have been intensively investigated due to their prominent electron dynamics, but their device performance has been limited by their small surface area. Here, we synthesized vertically aligned TiO ₂ nanoarchitectures with large internal surface areas and open channels of pores via pulsed laser deposition (PLD) and investigated the effects of the deposition conditions and the postannealing on the formation and properties of nanoarchitecture photoelectrodes for dye-sensitized solar cells. Increasing the oxygen working pressure increases the porosity of the TiO ₂ film and decreases the amount of deposited materials resulting in an optimized oxygen working pressure of 100 mTorr. The as-deposited films were amorphous and crystallized to the pure anatase phase after annealing at 350 °C or higher. Annealing at higher temperatures resulted in larger grain sizes and larger electron diffusion coefficients. As a result of the compromise between the surface area and crystallinity (or diffusion coefficient), the TiO ₂ film that was annealed at 450 °C exhibited optimal solar cell performance. We showed that the optimized PLD-TiO ₂ photoelectrodes (i.e., deposited at 100 mTorr and annealed at 450 °C) exhibited higher solar conversion efficiencies than the conventional nanoparticle films owing to their larger short-circuit photocurrent density resulting from the larger surface area and slower charge recombination. Our results show that PLD is a promising technique for preparing various aligned functional nanomaterials with high surface area for the improved device performance.