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Advanced Nanostructured Transition Metal Oxide Semiconductors for Solar Energy Applications
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. (Experimental Physics)ORCID iD: 0000-0002-7893-7405
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Avanceradenanostrukturerade halvledare av övergångsmetalloxid för solenergiapplikationer (Swedish)
Abstract [en]

Increasing energy consumption and its environmental impacts make it necessary to look for alternative energy sources. Solar energy as huge energy source that can cover the terms sustainability is considered as a favorable alternative. Optoelectronic devices like solar cells and photoelectrochemical cells are in very high interest to provide the energy that we need. They can convert solar energy, as a sustainable energy source, to electricity and fuel. Transition metal oxides (TMOs) due to high chemical stability, abundance, facile production and low cost are favorable materials to be used in these optoelectronic applications. In TMOs, d orbitals electrons contribute in forming bonds that gives special magnetic, electronic and geometric characteristics to these materials. They can be synthesized with different types of chemical and physical deposition methods.

The electronic properties of TMOs varies from metallic characteristics to electrical insulators. Transition metal oxide semiconductors (TMOSs) are mostly used in optoelectronic devices. Tuning the properties of TMOSs like, composition, morphology, dimensions, crystal structure, improves the performance of the optoelectronic devices. The light absorption, charge carrier mobility, the time scale between charge injection, regeneration and recombination processes are some of the properties critical to exploitation of TMOSs in solar cells and solar fuel technology.

In this thesis, we explore the use of nanostructured TMOSs in all-oxide solar cells, photodetectors and photoelectrochemical cells. 1-dimentional heterojunctions of n-type transparent semi-conductive metal oxides (ZnO and TiO2) in conjunction to p-type light absorbing semi-conductive metal oxides (Cu2O and Co3O4) have been tested in all-oxide photodetectors and solar cells.  It is shown that the 1-dimentional nanostructured geometry (nanowires, nanotubes) improves the charge separation and charge transport properties. Increasing the surface to volume aspect ratio in nanowires and nanotubes improves the light absorption compare to the thin film geometry. Our ZnO-Cu2O core-shell nanowire photodetector is the fastest visible light photodetector reported till now. Mesoporous NiO photocathode, sensitized with a biomimetic FeFe-catalyst and coumarin C343 dye, was tested in a photoelectrochemical cell for hydrogen production. This system is the first solar fuel device based on a biomimetic FeFe-catalyst and it shows a Faradic efficiency of 50% in hydrogen production. Cobalt catalysts have higher Faradic efficiency but their performance due to hydrolysis in low pH condition is limited. Nanostructured hematite/magnetite film as a photoanode was tested in a photoelectrochemical cell for water splitting. This hybrid electrode improved the photoactivity of the photoelectrochemical cell for water splitting. The main mechanism for the improvement of the functional properties relies with the role of the magnetite phase, which improves the charge carrier mobility of the composite system, compared to pure hematite, which acts as good light absorbing semiconductor.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
Metal Oxide, Photovoltaic, Semiconductors, Self-powered photodetectors, Photoelectrochemical cell, Solar fuel, Water splitting
National Category
Materials Engineering
Research subject
Experimental Physics
Identifiers
URN: urn:nbn:se:ltu:diva-73709ISBN: 978-91-7790-366-6 (print)ISBN: 978-91-7790-367-3 (electronic)OAI: oai:DiVA.org:ltu-73709DiVA, id: diva2:1305909
Public defence
2019-06-14, E632, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Funder
Vinnova, 224320Available from: 2019-04-23 Created: 2019-04-19 Last updated: 2019-05-22Bibliographically approved
List of papers
1. ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors
Open this publication in new window or tab >>ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors
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2018 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 51, p. 308-316Article in journal (Refereed) Published
Abstract [en]

In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-69838 (URN)10.1016/j.nanoen.2018.06.058 (DOI)000440682100034 ()2-s2.0-85049324019 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-02 (rokbeg)

Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2019-04-19Bibliographically approved
2. Dynamics and Photochemical H-2 Evolution of Dye-NiO Photocathodes with a Biomimetic FeFe-Catalyst
Open this publication in new window or tab >>Dynamics and Photochemical H-2 Evolution of Dye-NiO Photocathodes with a Biomimetic FeFe-Catalyst
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2016 (English)In: ACS Energy Letters, ISSN 2380-8195, Vol. 1, no 6, p. 1106-1111Article in journal (Refereed) Published
Abstract [en]

Mesoporous NiO films were cosensitized with a coumarin 343 dye and a proton reduction catalyst of the [Fe-2(CO)(6)(bdt)] (bdt = benzene-1,2-dithiolate) family. Femtosecond ultraviolet visible transient absorption experiments directly demonstrated subpicosecond hole injection into NiO from excited dyes followed by rapid (t(50%) similar to 6 ps) reduction of the catalyst on the surface with similar to 70% yield. The reduced catalyst was long-lived (2 mu s to 20 ms), which may allow protonation and a second reduction step of the catalyst to occur. A photo electrochemical device based on this photocathode produced H-2 with a Faradaic efficiency of similar to 50%. Fourier transform infrared spectroscopy and gas chromatography experiments demonstrated that the observed device deterioration with time was mainly due to catalyst degradation and desorption from the NiO surface. The insights gained from these mechanistic studies, regarding development of dye-catalyst cosensitized photocathodes, are discussed.

National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-61410 (URN)10.1021/acsenergylett.6b00506 (DOI)000390086400005 ()
Note

Validerad; 2017; Nivå 2; 2017-01-12 (andbra)

Available from: 2017-01-12 Created: 2017-01-12 Last updated: 2019-04-19Bibliographically approved
3. Electronically-Coupled Phase Boundaries in α‑Fe2O3/Fe3O4 Nanocomposite Photoanodes for Enhanced Water Oxidation
Open this publication in new window or tab >>Electronically-Coupled Phase Boundaries in α‑Fe2O3/Fe3O4 Nanocomposite Photoanodes for Enhanced Water Oxidation
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2019 (English)In: ACS APPLIED NANO MATERIALS, E-ISSN 2574-0970, Vol. 2, no 1, p. 334-342Article in journal (Refereed) Published
Abstract [en]

Photoelectrochemical (PEC) water splittingreactions are promising for sustainable hydrogen productionfrom renewable sources. We report here, the preparation of α-Fe2O3/Fe3O4 composite films via a single-step chemical vapordeposition of [Fe(OtBu)3]2 and their use as efficient photoanode materials in PEC setups. Film thickness and phase segregation was controlled by varying the deposition time and corroborated through cross-section Raman spectroscopy and scanning electron microscopy. The highest water oxidationactivity (0.48 mA/cm2 at 1.23 V vs RHE) using intermittent AM 1.5 G (100 mW/cm2) standard illumination was found forhybrid films with a thickness of 11 μm. This phenomenon is attributed to an improved electron transport resulting from ahigher magnetite content toward the substrate interface and an increased light absorption due to the hematite layer mainly located at the top surface of the film. The observed high efficiency of α-Fe2O3/Fe3O4 nanocomposite photoanodes is attributed to the close proximity and establishment of 3D interfaces between the weakly ferro- (Fe2O3) and ferrimagnetic (Fe3O4) oxides, which in view of their differential chemical constitution andvalence states of Fe ions (Fe2+/Fe3+) can enhance the charge separation and thus the overall electrical conductivity of the layer.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
solar water splitting, valence dynamics, magnetite, Raman, single-source CVD, heterostructures
National Category
Composite Science and Engineering Chemical Process Engineering
Research subject
Experimental Physics; Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-73139 (URN)10.1021/acsanm.8b01936 (DOI)000464491500036 ()
Note

Validerad;2019;Nivå 2;2019-03-13 (oliekm)

Available from: 2019-03-08 Created: 2019-03-08 Last updated: 2019-08-23Bibliographically approved

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Ghamgosar, Pedram

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