Surface oxide on thin films of yttrium hydride studied by neutron reflectometry

The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride films

Vertical bifacial PV systems: irradiance modeling and performance analysis of a lightweight system for flat roofs

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Vertical bifacial PV systems: irradiance modeling and performance analysis of a lightweight system for flat roofs

Vertical bifacial photovoltaic (PV) systems are gaining interest as they can enable deployment of PV in locations with grid or area limitations. Over Easy Solar has developed a lightweight design for vertical bifacial systems for flat roofs employing small modules with the height of one cell. To model the expected output of these type of systems can, however, be challenging, as it is uncertain if conventional models will give accurate results for vertical bifacial PV. The irradiance conditions are different, and there can be other loss or gain mechanisms that are prominent in these types of systems compared to more conventional PV systems. In this study we assess the use of regular transposition modeling for plane of array irradiance modeling for vertical bifacial PV, and we evaluate the performance of Over Easy Solar pilot installations in Norway to identify prominent loss mechanisms. The results are relevant for most vertical bifacial systems. With regular transposition modeling plane of array irradiance is overestimated by less than 1%, but we find that accuracy of albedo input and choice of sky diffuse model impact modeling accuracy. Irradiance losses such as shading are not considered in the modeling. We calculate a median heat transfer coefficient of 55 W/m2K, indicating high heat transfer and low thermal losses. High annual plane-of-array insolation, module bifaciality, interrow shading, reflection losses caused by high angle of incidence of the direct irradiance, and snow also have significant impact on the overall performance

A new thin film photochromic material: Oxygen-containing yttrium hydride

In this work we report on photochromism in transparent thin film samples of oxygen-containing yttrium hydride. Exposure to visible and ultraviolet (UV) light at moderate intensity triggers a decrease in the optical transmission of visible and infrared (IR) light. The photo-darkening is colour-neutral. We show that the optical transmission of samples of 500 nm thickness can be reduced by up to 50% after one hour of illumination with light of moderate intensity. The reaction is reversible and samples that are left in the dark return to the initial transparent state. The relaxation time in the dark depends on the temperature of the sample and the duration of the light exposure. The photochromic reaction takes place under ambient conditions in the as-deposited state of the thin-film samples.Comment: Accepted for publication in Solar Energy Materials and Solar Cell

Thin-film metal hydrides for solar energy applications

Thin-film metal hydrides may become important solar energy materials in the future. This thesis demonstrates interesting material properties of metal hydride films, relevant for applications as semiconducting materials for photovoltaic (PV) solar cells and for regulation of light using smart window technology

The electronic state of thin films of yttrium, yttrium hydrides and yttrium oxide

-Thin films of yttrium hydride have for almost 20 years been under investigation for optoelectronic and solar energy applications due to the hydrogen-induced switching in electronic state from the metallic elemental yttrium and yttrium dihydride to the transparent semiconductor material yttrium trihydride. In this study, we investigate the electronic structure of yttrium, yttrium hydride and yttrium oxide by using X-ray photoelectron spectroscopy and kelvin probe measurements. The investigated samples have been prepared by reactive sputtering deposition. We show that the electronic work function of transparent yttrium hydride is of 4.76 eV and that the recently discovered photochromic reaction lowers the electronic work function of the transparent hydride by 0.2 eV

Identification of higher order silanes during monosilane pyrolysis using gas chromatography-mass spectrometry

publishedVersio

The electronic state of thin films of yttrium, yttrium hydrides and yttrium oxide

-Thin films of yttrium hydride have for almost 20 years been under investigation for optoelectronic and solar energy applications due to the hydrogen-induced switching in electronic state from the metallic elemental yttrium and yttrium dihydride to the transparent semiconductor material yttrium trihydride. In this study, we investigate the electronic structure of yttrium, yttrium hydride and yttrium oxide by using X-ray photoelectron spectroscopy and kelvin probe measurements. The investigated samples have been prepared by reactive sputtering deposition. We show that the electronic work function of transparent yttrium hydride is of 4.76 eV and that the recently discovered photochromic reaction lowers the electronic work function of the transparent hydride by 0.2 eV