Effect of Interfacial SiO2 on Performance of Rutile TiO2/Si Photoanodes for Solar Fuel Production

Abstract

Photoelectrochemical cells have the potential to revolutionize clean hydrogen production by harnessing solar power and carrying out water-splitting reactions. This thesis considers a silicon photoanode with a titanium dioxide protective layer fabricated via atomic layer deposition using a first precursor tetrakis(dimethylamido)titanium(IV) and second precursor water at growth temperature 200 °C. A post-deposition heat treatment was performed during which an interfacial silicon dioxide layer forms to the detriment of the cell. Utilizing X-ray photoelectron spectroscopy and the Beer-Lambert law, the silicon dioxide interfacial layer can be analyzed. The heat treatment temperatures of 250, 300, and 500 °C resulted in a silicon dioxide layer of 1.3, 1.4, and 2.7 nm respectively while the sample that did not undergo a heat treatment had a silicon dioxide thickness of 0.3 nm. To investigate the impact of these results, stability and linear sweep voltammetry tests were carried out in an experimental photoelectrochemical cell with an alkaline aqueous solution (1 M NaOH, pH 13.6). From these tests, it is concluded that the silicon dioxide interfacial layer negatively impacts the performance of the cell but the higher heat treatment temperature results in an advantageous crystal structure. This was seen in the crystalline samples’ ability to produce higher current densities over time and with increasing voltage.