Photoelectrochemical studies of dye-sensitized polycrystalline titanium oxide thin films prepared by sputtering
Introduction
Titanium oxide is a semiconductor that holds much promise for photoelectrochemical applications related to energy conversion [1], [2], [3]. The material is of large interest for solar cells [4], [5] and for photocatalytic destruction of organic pollutants in wastewater [6], [7], [8]. Other potential applications concern optical devices [9], [10] and electrical batteries [11], and the hardness of Ti oxide makes this material of importance for protective uses.
The purpose of the present work is to explore the possibilities to employ sputter-deposited Ti oxide films in solar cells. Sputtering as a thin film preparation technique is of particular significance owing to its well documented upscaling capability and its industrial viability [12]. Some previous work on sputter-deposited Ti-oxide-based solar cells has been reported by Sheng et al. [13].
Section snippets
Film preparation and characterization
Oxide films were deposited using reactive DC magnetron sputtering in a system based on a Balzers UTT 400 vacuum chamber [14]. The targets were 5-cm-diameter metallic plates of Ti (99.9%). The chamber was evacuated to ∼10−7 Torr by turbo molecular pumping. Prior to sputter deposition, Ar (99.998%) and O2 (99.998%) gas were introduced via separate mass-flow-controlled inlets. The O2/Ar gas flow ratio was kept constant at a value Γ. The pressure in the sputter plasma was 12 mTorr. The films were
Incident photon-to-current efficiency
Incident photon-to-current efficiency (IPCE) was determined from experiments using three- and two-electrode cells. Spectral data were registered point by point, taking random values of the wavelength to avoid systematic errors during the measurement. The IPCE was then calculated fromwhere iph (in μA/cm2) and P (in μW/cm2) are photocurrent and power of the incident radiation per unit area, respectively, and λ (in nm) is the wavelength of the light. No corrections were made for
Conclusions
Polycrystalline sputter deposited Ti oxide thin film electrodes having mixed anatase–rutile structure had higher incident photon-to-current efficiency than amorphous and fine-grained anatase phase electrodes. Thick dye-sensitized semiconductor films showed a photoresponse as high as 30% at a wavelength of 530 nm. The incident photon-to-current efficiency depends strongly on the morphological and structural properties of the electrodes, and optimization appears possible by properly tuning the
Acknowledgements
We appreciate very valuable assistance by Nils-Olov Ersson for the XRD data, Richard Karmhag, and Eva Olsson for the SEM measurements. José Solís is thanked for providing AFM images. M.G. and J.R. want to thank the International Science Programs at Uppsala University for scholarships.
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