Plastic dye-sensitized solar cells (DSCs) are a promising photochemical solar technology owing to their light weight, flexibility, and suitability for low-cost roll-to-roll production. In order to improve cell efficiency, a light scattering layer was prepared on the surface of nanocrystalline (NC) TiO 2 by vacuum cold spraying (VCS) at room temperature using submicron-sized TiO 2 particles. The influence of the scattering layer and its connection with the underlying TiO 2 was investigated to understand the improvement in cell efficiency. For comparison, two scattering layers were prepared by spray deposition using ethanol-based suspensions with either submicron Al 2 O 3 or TiO 2 particles. All three layers exhibited a higher light-reflecting capacity than the TiO 2 nanocrystalline layer, although dark current test results showed that the biggest efficiency improvement was achieved in the NC-VCS-TiO 2 cells.

Submicro-sized anatase TiO 2 powder was used to prepare light scattering layers by vacuum cold spraying at room temperature. The microstructure of the TiO 2 coatings was characterized to be correlated with optical property and adhesion/cohesion of the coatings. Results show that the light-reflecting ability of the coatings decreased with the increase of accelerating gas flow rate from 3.5 to 7.5 L/min and increased with the increase of coating thickness from 2 to 10 µm. Both the cohesion and adhesion of the coatings increased with the increase of the accelerating gas flow rate, due to the improvement of the particle-particle contact and the particle-substrate contact by the high velocity impact resulting from the increased powder particle velocity.

The pore structure in nano-porous TiO 2 coating influences the ion diffusion property and photovoltaic performance of dye-sensitized solar cells (DSC). In this paper, TiO 2 coatings were deposited by vacuum cold spray (VCS) using a strengthened nanostructured powder. The pore structure, ion diffusion and dye infiltration properties were examined to understand the deposition mechanism of the coating and the suitability of cold sprayed TiO 2 coating for DSC. It was interestingly found that the pores in the VCS TiO 2 coating presented a bimodal size distribution with two peaks at ~15 nm and ~50 nm, which contributed to a much higher ion diffusion coefficient comparing to that of the conventional unimodal-sized nano-porous coating. The dye infiltration and loading are beneficial from the bimodal size distribution of the pores. Based on the impact behavior of the spray powder, a deposition model was proposed to explain the deposition mechanism of the strengthened nanostructured powder during vacuum cold spray.

This study investigates the effect of powder size on the porosity and diffusion properties of vacuum cold sprayed TiO 2 coatings. In the experiments, coating samples are produced using powders with different primary particle sizes. Porosity and pore size in the TiO 2 coatings are assessed via nitrogen adsorption and desorption and correlated with the diffusion coefficient of I 3 ֿ in acetonitrile. The results show that pore size is significantly influenced by primary particle size, but porosity is the same regardless of the particle size of the powder. The I 3 ֿ ion diffusion coefficient is shown to increase with increasing pore size and can thus be adjusted through proper selection of the powder feedstock.

Composite powder in sub-micrometer size was prepared using a primary nano-TiO 2 powder and polyethylene glycol (PEG). The nano-TiO 2 coating was deposited through vacuum cold spray using both the composite powder and primary nano- TiO 2 powder. The influence of annealing treatment on coating adhesion and photocatalytic activity was investigated. The coating adhesion was estimated through erosion test by water jet. The photocatalytic performance of the TiO 2 coatings was evaluated through photodegradation of phenol in water. The results showed that annealing of the coating at a temperature from 450 to 500 °C yielded both higher activity and better adhesion. The adhesion of the coating deposited using the composite powder was better than that using primary nano- TiO 2 powder. It was found that TiO 2 coating resulting from the composite powder presented much higher activity than that deposited with primary nano-particles. The better activity is attributed to the existence of large pores resulting from the stacking of composite powder, which benefits the reactants transportation through the porous coating.

Deposition of nanocrystalline TiO 2 coatings at low temperatures is becoming more attractive due to the possibility for continuous roll production of coatings for assembly lines of dye-sensitized solar cell at a low cost. In this study, porous nano-TiO 2 coatings were deposited by vacuum cold spraying at room temperature on a conducting glass substrate using commercial P25 nanocrystalline TiO 2 powder. The microstructure of TiO 2 coatings was characterized by field emission scanning electron microscopy and N 2 adsorption test. A commercial dye (N719) was adsorbed on the surface of TiO 2 particles within the coating to assemble a dye-sensitized solar cell. The cell performance was evaluated employing simulated solar light at an intensity of 100 mW/cm 2 . The results showed that TiO 2 coatings were deposited by the agglomerates of nano-TiO 2 powders. The BET test of the as-sprayed TiO 2 coatings yielded a porosity of 49% and an average pore size of 17 nm. The assembled solar cell yielded a short-circuit current density of 7.3 mA/cm 2 and an energy conversion efficiency of 2.4%. The test result indicates that vacuum cold spraying was a promising method to deposit nanocrystalline TiO 2 coating at low temperature applied to the dye-sensitized solar cell.

The control of microstructure of TiO 2 coating through preparation methods influences significantly the performance of the coating. In this study, vacuum cold spray process as a new coating technology is employed to deposit nanocrystalline TiO 2 coatings on glass and stainless steel substrates. TiO 2 deposits were formed using two types of nanocrystalline TiO 2 powders having mean particle diameters of 200 nm and 25 nm. The microstructure of the coating was characterized by scanning electron microscopy, x-ray diffraction analysis. The results demonstrate that a thick nanocrystalline TiO 2 coating can be deposited by vacuum cold spray process. The coating was stacked of particles in agglomerate of several hundred nanometers. The coating presents a mesoporous microstructure which would be effective for applications in photocatalytic degradation, dye-sensitized solar cell and so on.