Synthesis and application of nanostructured titania thin films and their composites with barium titanate

Bohač, Mario (2023) Synthesis and application of nanostructured titania thin films and their composites with barium titanate. Doctoral thesis, Ruđer Bošković Institute.

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Abstract

This doctoral dissertation investigates the influences of different preparation conditions on structural and optoelectrical properties of vertically oriented titania nanotube thin films and their composites with barium titanate, and also the optimisation of the materials’ properties for uses in photocatalysis and as electron transport layers in perovskite solar cells. Transparent thin film titania nanotubes with optimal pore length and thickness were prepared by implementing optimised physical and chemical methods of synthesis. Using magnetron sputtering, titanium thin films were deposited onto conductive oxide glass substrates. The titanium thin films were converted into vertically oriented titania nanotube thin films through electrochemical anodization followed by thermal annealing. In the last step, the composite materials were prepared by hydrothermal reactions, by spin coating barium hydroxide solutions or sol-gel mixtures, and by magnetron sputtering of barium titanate targets. The preparation conditions (e.g. sputtering duration of titanium thin films, electrolyte composition, anodization voltage, barium titanate precursor concentration) have been varied in a wide range and their influence on the properties of the titania nanotube thin films has been thoroughly analysed. Sol-gel and magnetron sputtering methods used for depositing barium titanate films have been proven to be incompatible because of the necessary high temperature processing needed to prepare crystalline barium titanate which would be detrimental to the structural, optical and electrical properties of titanium dioxide and the substrate. In this doctoral dissertation it has been shown that pure, unmodified titania nanotube thin films have great potential in photocatalysis, especially in the case of diclofenac degradation. Photocatalytic degradation has been investigated by tracking the change in diclofenac concentration during photocatalysis experiments. Composite materials prepared by spin coating solutions of barium hydroxide resulted in an increase in photocatalysis rates by 28 % and with the degradation of ≈ 90 % diclofenac under 60 min. However, the composite materials prepared by hydrothermal reactions with barium hydroxide showed a decrease in photocatalytic capabilities due to negative effects on optical and electrical properties of the nanotubes and due to the decrease in the specific surface of the nanotubes with the growth of the barium titanate layer. Titania nanotube thin films were also successfully implemented as an electron transport layer in perovskite solar cells with a standard layer configuration. The highest obtained solar conversion efficiency was 13,5 % for the solar cells containing titania nanotube thin films. To further increase the efficiency of the perovskite solar cells it would require the optimization of other layers which is above the scope of this dissertation, and will be investigated in future research. However, implementing composite electron transport layers in the perovskite solar cells showed a decrease in solar energy conversion efficiencies and solar cell parameters due to the coverage of nanotube pores with barium titanate, increases in electrical resistance, and decreases in transmittances correlated with the growth of the barium titanate layer. Overall, this transparent thin film nanotube technology is a promising new material with great potential for future uses and technological improvements, especially in the field of solar energy conversion such as photocatalysis and solar cells. On the other hand, the barium titanate and vertically oriented titania nanotube composite material requires further detailed research and optimization to fine-tune its properties to be successfully implemented in different use cases.

Item Type:	Thesis (Doctoral thesis)
Uncontrolled Keywords:	titanium dioxide; nanotubes; thin films; composite materials; barium titanate; photocatalysis; perovskite solar cells
Subjects:	NATURAL SCIENCES > Chemistry > Inorganic Chemistry
Divisions:	Division of Materials Physics
Projects:	Project title Project leader Project code Project type Nanokompoziti s perovskitima za fotovoltaike, fotokatalizu i senzoriku-NanoPeroPhotoSens Andreja Gajović; Vilko Mandić; Milivoj Plodinec; Davor Gracin; Nikša Krstulović; Jelena Macan; Igor Lukačević; Maja Varga; Matko Mužević; Denis Stanić; Ivana Grčić; Marko Petric; Igor Petrović; Ivana Melnjak; Lucija Radetić; Andreja Žužić IP-2018-01-5246 HRZZ
Depositing User:	Mario Bohač
Date Deposited:	07 Jul 2023 11:44
URI:	http://fulir.irb.hr/id/eprint/8011

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