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 TiO2 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 TiO2 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 TiO2 film that was annealed at 450 °C exhibited optimal solar cell performance. We showed that the optimized PLD-TiO2 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.

Among ternary oxides, Zn2 SnO4 (ZSO) is considered for dye-sensitized solar cells (DSSCs) because of its wide bandgap, high optical transmittance, and high electrical conductivity. However, ZSO-based DSSCs have a poor performance record owing largely to the absence of systematic efforts to enhance their performance. Herein, general strategies are proposed to improve the performance of ZSO-based DSSCs involving interfacial engineering/modification of the photoanode. A conformal ZSO thin film (blocking layer) deposited at the fluorine-doped tin oxide-electrolyte interface by pulsed laser deposition suppressed the back-electron transfer effectively while maintaining a high optical transmittance, which resulted in a 22 % improvement in the short-circuit photocurrent density. Surface modification of ZSO nanoparticles (NPs) resulted in an ultrathin ZnO shell layer, a 9 % improvement in the open-circuit voltage, and a 4 % improvement in the fill factor because of the reduced electron recombination at the ZSO NPs-electrolyte interface. The ZSO-based DSSCs exhibited a faster charge injection and electron transport than their TiO2 -based counterparts, and their superior properties were not inhibited by the ZnO shell layer, which indicates their feasibility for highly efficient DSSCs. Each interfacial engineering strategy could be applied to the ZSO-based DSSC independently to lead to an improved conversion efficiency of 6 %, a very high conversion efficiency for a non-TiO2 based DSSC.

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Water content in an anodic electrolyte affects the crystallization route of anodic TiO2 nanotube arrays during annealing, which determines the crystallographic orientation of the nanotubes.

A facile approach to fabricate dye-sensitized solar cells (DSSCs) is demonstrated by depositing (001) oriented zinc oxide (ZnO) nanostructures on both glass and flexible substrates at room temperature using pulsed laser deposition. Unique crystallographic characteristics of ZnO combined with highly non-equilibrium state of pulsed laser-induced ablated species enabled highly crystalline ZnO nanostructures without aid of any chemically induced additives or organic/inorganic impurities at room temperature. Film morphology as well as internal surface area is tailored by varying ambient oxygen pressure and deposition time. It is revealed that the optimization of these two experimental factors was essential for achieving structure providing large surface area as well as efficient charge collection. The DSSCs with optimized ZnO photoanodes showed overall efficiencies of 3.89 and 3.4 % on glass and polyethylene naphthalate substrates, respectively, under AM 1.5G light illumination. The high conversion efficiencies are attributed to elongated electron lifetime and enhanced electrolyte diffusion in the high crystalline ZnO nanostructures, verified by intensity-modulated voltage spectroscopy and electrochemical impedance measurements.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1437-2) contains supplementary material, which is available to authorized users.