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Mesoporous photoelectrodes for dye-sensitized solar cells (DSSCs) in a ZnO/TiO core-shell structure have been fabricated at low temperature by combination of screen printing of ZnO nanoparticles and room temperature atomic layer deposition (ALD) of TiO. ALD nicely achieved a uniform coating of the individual ZnO particles with a thin skin of TiO of uniform thickness. The overall mesoporous structure was unchanged, so that a high surface area for dye adsorption and pores for penetration of the electrolyte solution were preserved. DSSCs employing the core-shell electrode sensitized with D149 indoline dye achieved a higher open circuit voltage ( V ) than that with ZnO, but accompanied with a decrease of short circuit photocurrent density ( J ) due to decreased efficiency of electron injection. Increase of the recombination resistance to extend the electron lifetime by the TiO shell has been confirmed by electrochemical impedance spectroscopy (EIS). X-ray diffraction analysis has revealed that the ALD TiO is amorphous and can only be converted to crystalline anatase TiO by annealing at 450 °C. The crystallization recovered current but lost the advantage of the voltage increase. EIS has indicated a high trap density introduced by the amorphous ALD TiO, which could be reduced by crystallization, but accompanied with an increased rate of recombination. [ABSTRACT FROM AUTHOR]

The authors developed a room temperature atomic layer deposition (ALD) system that can deposit TiO2 on gold nanoparticles by using tetrakis(dimethylamino)titanium and plasma-excited humidified argon. The growth per cycle of TiO2 was measured to be 0.25 nm/cycle on a monitored Si sample. For applying the nanoparticle coating, the source material, i.e., gold particles, is electrostatically attached to the susceptor in the ALD system to avoid their gas transport. These particles are then mixed by a rotating scraper during the ALD process. This system allows a conformal deposition of TiO2 without the aggregation of nanoparticles. The thickness of TiO2 for shell coating is controlled by counting the number of ALD cycles. The deposition of TiO2 coating with a nanometer scale thickness on the gold nanoparticle is demonstrated in this paper. [ABSTRACT FROM AUTHOR]